阅读说明：本技术 光调制控制装置及马赫曾德干涉装置 (Optical modulation control device and Mach-Zehnder interference device ) 是由 三浦浩志 铃木巨生 于 2019-04-18 设计创作，主要内容包括：光调制控制装置(5)构成为,具备：光检测器(21)或光检测器(29),其检测从马赫曾德干涉仪(4)出射的光,输出表示光的强度的强度信号；以及相位偏置搜索部(22),其调整向马赫曾德干涉仪(4)的内部的光路注入的相位偏置,并搜索从光检测器(21)输出的强度信号成为极小值时的相位偏置、或者从光检测器(29)输出的强度信号成为极大值时的相位偏置,记录搜索到的相位偏置和光的波长的组。(The optical modulation control device (5) is configured to include: a photodetector (21) or a photodetector (29) that detects the light emitted from the Mach-Zehnder interferometer (4) and outputs an intensity signal indicating the intensity of the light; and a phase offset search unit (22) which adjusts the phase offset injected into the optical path inside the Mach-Zehnder interferometer (4), searches for a phase offset when the intensity signal output from the optical detector (21) becomes a minimum value, or a phase offset when the intensity signal output from the optical detector (29) becomes a maximum value, and records the searched phase offset and the set of the wavelength of the light.)

1. An optical modulation control apparatus, wherein,

the light modulation control device includes:

a photodetector that detects light emitted from the Mach-Zehnder interferometer and outputs an intensity signal indicating intensity of the light; and

and a phase offset search unit that adjusts a phase offset injected into an optical path inside the mach-zehnder interferometer, searches for a phase offset when an intensity signal output from the photodetector has a minimum value or a phase offset when the intensity signal has a maximum value, and records a set of the searched phase offset and a wavelength of the light.

2. The light modulation control apparatus according to claim 1,

the Mach-Zehnder interferometer has a 1 st output port for emitting light and a 2 nd output port for emitting light in reverse phase to the light emitted from the 1 st output port,

the phase offset search unit searches for a phase offset when an intensity signal output from the photodetector has a minimum value if the light detected by the photodetector is light emitted from the 1 st output port,

the phase offset search unit searches for a phase offset when the intensity signal output from the photodetector has a maximum value if the light detected by the photodetector is the light emitted from the 2 nd output port.

3. The light modulation control apparatus according to claim 1,

the phase offset search unit includes:

a phase offset adjustment unit that adjusts a phase offset to be injected into an optical path inside the Mach-Zehnder interferometer;

a delay unit that holds the intensity signal output from the photodetector for a delay time and outputs the intensity signal;

an amplifier that amplifies the intensity signal output from the photodetector and outputs the amplified intensity signal;

a comparator that outputs a differential signal representing a difference between the intensity signal output from the delay and the intensity signal output from the amplifier; and

and a phase offset recording unit that searches for 1 or more phase offsets when the absolute value of the differential signal output from the comparator is smaller than a threshold value from among the phase offsets injected into the optical path, searches for a minimum intensity signal or a maximum intensity signal from among intensity signals output from the photodetector, the intensity signals corresponding to the searched 1 or more phase offsets, and records a set of the phase offset corresponding to the searched minimum intensity signal and the wavelength of the light, or a set of the phase offset corresponding to the searched maximum intensity signal and the wavelength of the light.

4. The light modulation control device of claim 3,

the phase offset adjustment unit adjusts the amplification factor of the intensity signal in the amplifier in accordance with the differential signal output from the comparator.

5. The light modulation control device of claim 3,

the Mach-Zehnder interferometer distributes incident light into 2 pieces of light, emits the combined light of the distributed 2 pieces of light to the photodetector,

the mach-zehnder interferometer has 2 optical paths that transmit the 2 lights respectively as the optical paths inside,

the phase offset adjustment unit adjusts the phase offset injected into one of the 2 optical paths in accordance with the differential signal output from the comparator.

6. The light modulation control device of claim 3,

the Mach-Zehnder interferometer distributes incident light into 2 pieces of light, emits the combined light of the distributed 2 pieces of light to the photodetector,

the mach-zehnder interferometer has 2 optical paths that transmit the 2 lights respectively as the optical paths inside,

the phase offset adjustment unit adjusts the phase offsets to be injected into the 2 optical paths, respectively, in accordance with the differential signal output from the comparator.

7. The light modulation control apparatus according to claim 1,

the phase offset search unit adjusts a phase offset injected into an optical path inside the mach-zehnder interferometer, searches for a phase offset when an intensity signal output from the photodetector has an minimum value and a phase offset when the intensity signal has a maximum value, and records a set of the phase offset when the intensity signal has the minimum value, the phase offset when the intensity signal has the maximum value, and the wavelength of the light.

8. The light modulation control apparatus according to claim 1,

the Mach-Zehnder interferometer includes:

a 1 st mach-zehnder interferometer that divides incident light into 2 lights and has 2 optical paths that respectively transmit the 2 lights after division;

a 2 nd Mach-Zehnder interferometer inserted into one of 2 optical paths of the 1 st Mach-Zehnder interferometer; and

a 3 rd Mach-Zehnder interferometer inserted into the other of the 2 optical paths of the 1 st Mach-Zehnder interferometer,

the photodetector detects light emitted from each of the 1 st Mach-Zehnder interferometer, the 2 nd Mach-Zehnder interferometer, and the 3 rd Mach-Zehnder interferometer,

the phase offset search unit adjusts a phase offset injected into an optical path inside the Mach-Zehnder interferometer, searches for a phase offset when a 2 nd intensity signal indicating an intensity of light emitted from the Mach-Zehnder interferometer among intensity signals output from the photodetector is at an extremely small value or a phase offset when the 2 nd intensity signal is at a maximum value, and records a set of the phase offset when the 2 nd intensity signal is at an extremely small value or a maximum value and a wavelength of the light,

the phase offset search unit adjusts a phase offset injected into an optical path inside the 3 rd Mach-Zehnder interferometer, searches for a phase offset when a 3 rd intensity signal indicating an intensity of light emitted from the 3 rd Mach-Zehnder interferometer among intensity signals output from the photodetector is at an extremely small value or a phase offset when the 3 rd intensity signal is at a maximum value, and records a combination of the phase offset when the 3 rd intensity signal is at an extremely small value or a maximum value and a wavelength of the light,

the phase offset search unit adjusts a phase offset injected into an optical path inside the 1 st mach-zehnder interferometer, and searches for a phase offset at 1/2 of a sum of a phase offset at which a 1 st intensity signal indicating an intensity of light emitted from the 1 st mach-zehnder interferometer among intensity signals output from the photodetector is at an extremely small value and a phase offset at which the 1 st intensity signal is at a maximum value, and records a combination of the phase offset at 1/2 and a wavelength of the light.

9. The light modulation control apparatus according to claim 1,

the Mach-Zehnder interferometer includes:

a 1 st mach-zehnder interferometer that divides a 1 st polarized wave in incident light into 2 lights and has 2 optical paths that respectively transmit the 21 st polarized waves after division;

a 2 nd Mach-Zehnder interferometer inserted into one of 2 optical paths of the 1 st Mach-Zehnder interferometer;

a 3 rd Mach-Zehnder interferometer inserted into the other of the 2 optical paths of the 1 st Mach-Zehnder interferometer;

a 4 th mach-zehnder interferometer that divides the 2 nd polarized wave of the incident light into 2 pieces of light and has 2 optical paths that respectively transmit the 2 nd polarized waves after division;

a 5 th Mach-Zehnder interferometer inserted into one of the 2 optical paths of the 4 th Mach-Zehnder interferometer; and

a 6 th Mach-Zehnder interferometer inserted into the other of the 2 optical paths of the 4 th Mach-Zehnder interferometer,

the photodetector detects light emitted from each of the 1 st Mach-Zehnder interferometer, the 2 nd Mach-Zehnder interferometer, the 3 rd Mach-Zehnder interferometer, the 4 th Mach-Zehnder interferometer, the 5 th Mach-Zehnder interferometer, and the 6 th Mach-Zehnder interferometer,

the phase offset search unit adjusts a phase offset injected into an optical path inside the Mach-Zehnder interferometer, searches for a phase offset when a 2 nd intensity signal indicating an intensity of light emitted from the Mach-Zehnder interferometer among intensity signals output from the photodetector is at an extremely small value or a phase offset when the 2 nd intensity signal is at a maximum value, and records a combination of the phase offset when the 2 nd intensity signal is at an extremely small value or a maximum value and a wavelength of the light,

the phase offset search unit adjusts a phase offset injected into an optical path inside the 3 rd Mach-Zehnder interferometer, searches for a phase offset when a 3 rd intensity signal indicating an intensity of light emitted from the 3 rd Mach-Zehnder interferometer among intensity signals output from the photodetector is at an extremely small value or a phase offset when the 3 rd intensity signal is at a maximum value, and records a combination of the phase offset when the 3 rd intensity signal is at an extremely small value or a maximum value and a wavelength of the light,

the phase offset search unit adjusts a phase offset injected into an optical path inside the 1 st Mach-Zehnder interferometer, and searches for a phase offset at a time of 1/2 of a sum of a phase offset at which a 1 st intensity signal indicating an intensity of light emitted from the 1 st Mach-Zehnder interferometer among intensity signals output from the photodetector becomes an extremely small value and a phase offset at which the 1 st intensity signal becomes a maximum value, the phase offset search unit recording a combination of the phase offset at the time of 1/2 and a wavelength of the light,

the phase offset search unit adjusts a phase offset injected into an optical path inside the 5 th Mach-Zehnder interferometer, searches for a phase offset when a 5 th intensity signal indicating an intensity of light emitted from the 5 th Mach-Zehnder interferometer among intensity signals output from the photodetector is at an extremely small value or a phase offset when the 5 th intensity signal is at a maximum value, and records a combination of the phase offset when the 5 th intensity signal is at an extremely small value or a maximum value and a wavelength of the light,

the phase offset search unit adjusts a phase offset injected into an optical path inside the 6 th Mach-Zehnder interferometer, searches for a phase offset when a 6 th intensity signal indicating an intensity of light emitted from the 6 th Mach-Zehnder interferometer among intensity signals output from the photodetector is at an extremely small value or a phase offset when the 6 th intensity signal is at a maximum value, and records a set of the phase offset when the 6 th intensity signal is at an extremely small value or a maximum value and a wavelength of the light,

the phase offset search unit adjusts a phase offset injected into an optical path inside the 4-th mach-zehnder interferometer, and searches for a phase offset when a sum of a phase offset obtained when a 4-th intensity signal indicating an intensity of light emitted from the 4-th mach-zehnder interferometer among intensity signals output from the photodetector becomes a minimum value and a phase offset obtained when the 4-th intensity signal becomes a maximum value, and the phase offset search unit records a combination of the phase offset when the sum of the phase offset obtained when the sum of the phase offset becomes 1 out of 2 and the wavelength of the light.

10. A Mach-Zehnder interference device, wherein,

the Mach-Zehnder interference device includes:

a mach-zehnder interferometer that divides incident light into 2 lights and has an optical path that transmits the divided 2 lights;

a photodetector that detects light emitted from the mach-zehnder interferometer and outputs an intensity signal indicating intensity of the light; and

and a phase offset search unit that adjusts a phase offset injected into an optical path of the mach-zehnder interferometer, searches for a phase offset when an intensity signal output from the photodetector has a minimum value or a phase offset when the intensity signal has a maximum value, and records a set of the searched phase offset and a wavelength of the light.

Technical Field

The present invention relates to an optical modulation control device and a mach-zehnder interferometer for searching for a phase offset.

Background

In the field of optical fiber communication, a modulator using a Modulation scheme such as QAM (Quadrature Amplitude Modulation) is sometimes used in order to increase the transmission capacity per 1 channel.

Non-patent document 1 below discloses a mach-zehnder modulator for modulating light emitted from a light source.

In the mach-zehnder modulator disclosed in non-patent document 1 below, a semiconductor material such as indium phosphide (InP) is used.

By using a semiconductor material such as InP, the mach-zehnder modulator and the light source can be integrated, and therefore, the entire device including the mach-zehnder modulator and the light source can be downsized.

Documents of the prior art

Patent document

Non-patent document 1: "ultrahigh-speed and large-capacity optical YUN delivery を," する high-speed and high-precision optical refrigeration, "academic society of optics/application physics, japan optical society, volume 38, No. 5, pp.246-252, and may.2009.

Disclosure of Invention

Problems to be solved by the invention

The mach-zehnder modulator is a modulator that divides light emitted from a light source into 2 light beams and outputs a combined light beam of the 2 divided light beams, and modulated signals are superimposed on the 2 divided light beams, respectively. In the mach-zehnder modulator, the phase difference of the 2 lights on which the modulation signals are superimposed needs to be maintained at 180 degrees. In order to keep the phase difference of the 2 lights at 180 degrees, an appropriate bias may be applied to the 2 lights, but the appropriate bias differs depending on the wavelength of the light emitted from the light source.

In the mach-zehnder modulator disclosed in non-patent document 1, when the wavelength of light emitted from the light source changes, an offset corresponding to the changed wavelength cannot be generated, and thus there is a problem that the modulation characteristics may deteriorate.

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an optical modulation control device and a mach-zehnder interference device capable of superimposing a phase offset corresponding to the wavelength of incident light on light even if the wavelength of the incident light changes.

Means for solving the problems

An optical modulation control device according to the present invention includes: a photodetector that detects light emitted from the Mach-Zehnder interferometer and outputs an intensity signal indicating intensity of the light; and a phase offset recording unit that adjusts a phase offset injected into an optical path inside the Mach-Zehnder interferometer, searches for a phase offset when an intensity signal output from the photodetector has a minimum value or a phase offset when the intensity signal has a maximum value, and records a set of the searched phase offset and a wavelength of light.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, the optical modulation control device is configured to include a phase offset recording unit that adjusts a phase offset injected into an optical path inside the mach-zehnder interferometer, searches for a phase offset when an intensity signal output from the photodetector becomes a minimum value or a phase offset when the intensity signal becomes a maximum value, and records a set of the searched phase offset and a wavelength of light. Therefore, even if the wavelength of the incident light changes, the optical modulation control device of the present invention can superimpose the phase offset corresponding to the wavelength of the incident light on the light.

Drawings

Fig. 1 is a configuration diagram showing a mach-zehnder interference device 2 including an optical modulation control device 5 according to embodiment 1.

Fig. 2 is a hardware configuration diagram showing hardware of each of the phase offset adjustment unit 26, the phase offset recording unit 27, and the control unit 28 included in the optical modulation control device 5.

Fig. 3 is a hardware configuration diagram of a computer in a case where a part of the optical modulation control apparatus 5 is implemented by software, firmware, or the like.

Fig. 4 is a flowchart showing the processing procedure of the optical modulation control device 5 at the initial setting of the mach-zehnder interferometer 4.

FIG. 5 shows the phase offset I outputted from the phase offset adjustment unit 26 to the phase adjustment electrode 15_φ(t) and the intensity signal I output from the photodetector 21_PD(t) an explanatory view of an example of the relationship between the two.

FIG. 6 shows the phase offset I outputted from the phase offset adjustment unit 26 to the phase adjustment electrode 15_φ(t) is an explanatory view of a temporal change.

FIG. 7 is a graph showing the intensity signal β (t). I output from the amplifier 24_PD(t) is an explanatory view of a temporal change.

Fig. 8 is a configuration diagram showing a mach-zehnder interference device 2 including another optical modulation control device 5 according to embodiment 1.

FIG. 9 shows the phase offset I outputted from the phase offset adjustment unit 26 to the phase adjustment electrode 15_φ(t) and the intensity signal I output from the photodetector 29_PD(t) an explanatory view of an example of the relationship between the two.

Fig. 10 is a configuration diagram showing a mach-zehnder interference device 2 including the optical modulation control device 5 of embodiment 2.

Fig. 11 is a configuration diagram showing a mach-zehnder interference device 2 including the optical modulation control device 5 according to embodiment 3.

Fig. 12 is a configuration diagram showing a mach-zehnder interference device 2 including the optical modulation control device 5 of embodiment 4.

Detailed Description

Hereinafter, in order to explain the present invention in more detail, embodiments for carrying out the present invention will be described with reference to the accompanying drawings.

Embodiment 1.

Fig. 1 is a configuration diagram showing a mach-zehnder interference device 2 including an optical modulation control device 5 according to embodiment 1.

Fig. 2 is a hardware configuration diagram showing hardware of each of the phase offset adjustment unit 26, the phase offset recording unit 27, and the control unit 28 included in the optical modulation control device 5.

In fig. 1, the light source 1 is realized, for example, by an LD (Laser Diode).

The light source 1 is connected to a mach-zehnder interferometer 4 via an optical fiber 3.

The light source 1 emits the continuous light to the optical fiber 3 as incident light of the mach-zehnder interferometer 4.

The mach-zehnder interferometer 2 includes an optical fiber 3, a mach-zehnder interferometer 4, and an optical modulation control device 5.

The mach-zehnder interferometer 2 is a device that performs Binary Phase Shift Keying (BPSK).

One end of the optical fiber 3 is connected to the light source 1, and the other end of the optical fiber 3 is connected to a branch point 10 of the mach-zehnder interferometer 4.

The optical fiber 3 transmits the continuous light emitted from the light source 1 to the branch point 10 of the mach-zehnder interferometer 4.

The mach-zehnder interferometer 4 includes a 1 st optical path 11, a 2 nd optical path 12, a normal phase signal electrode 13, a reverse phase signal electrode 14, a phase adjustment electrode 15, a 1 st output port 17, and a 2 nd output port 18.

The mach-zehnder interferometer 4 has a branch point 10 that divides incident light into 2 pieces of light, and a combining point 16 that combines the 2 pieces of light that have been divided.

The mach-zehnder interferometer 4 distributes incident light into 2 light beams at the branch point 10, combines the distributed 2 light beams at the combining point 16, and outputs the combined light beam of the 2 light beams to the photodetector 21.

The 1 st optical path 11 is an optical path inside the mach-zehnder interferometer 4, and is implemented by, for example, an optical fiber.

One end of the 1 st optical path 11 is connected to the branch point 10, and the other end of the 1 st optical path 11 is connected to the combining point 16.

The 1 st optical path 11 transmits one of the 2 lights distributed at the branch point 10 to the combining point 16.

The 2 nd optical path 12 is an optical path inside the mach-zehnder interferometer 4, and is implemented by, for example, an optical fiber.

One end of the 2 nd optical path 12 is connected to the branch point 10, and the other end of the 2 nd optical path 12 is connected to the combining point 16.

The 2 nd optical path 12 transmits the other of the 2 lights distributed at the branch point 10 to the combining point 16.

The positive phase signal electrode 13 is inserted into the 1 st optical path 11.

The normal phase signal electrode 13 superimposes a DC bias corresponding to the wavelength of the incident light on the light transmitted through the 1 st optical path 11. The DC bias may be a direct current or a direct voltage.

In the initial setting of the mach-zehnder interferometer 4, the normal phase signal electrode 13 superimposes only the DC bias on the light, and does not superimpose the modulation signal on the light.

In actual operation of the mach-zehnder interferometer 4 after the initial setting is completed, the normal-phase signal electrode 13 superimposes both the DC bias and the modulation signal on the light.

An inverted signal electrode 14 is inserted into the 2 nd optical path 12.

The inverted signal electrode 14 superimposes a DC bias corresponding to the wavelength of the incident light on the light transmitted through the 2 nd optical path 12.

In the initial setting of the mach-zehnder interferometer 4, the inverted signal electrode 14 superimposes only the DC bias on the light, and does not superimpose the modulation signal on the light.

In actual use after the initial setting of the mach-zehnder interferometer 4 is completed, the inverted signal electrode 14 superimposes both the DC bias and the modulation signal on the light.

The phase adjustment electrode 15 is inserted into the 1 st optical path 11.

The phase adjustment electrode 15 offsets the phase I outputted from the phase offset adjustment unit 26_φ(t) overlaps with the light transmitted through the 1 st optical path 11.

In the Mach-Zehnder interference device 2 shown in FIG. 1, the phase offset I_φ(t) is current, but phase offset I_φ(t) may be a voltage.

The 1 st output port 17 is a port for emitting the combined light to the photodetector 21.

The 2 nd output port 18 is a port for emitting light in opposite phase to the combined light. When the intensity of the light emitted from the 1 st output port 17 is a maximum value, the intensity of the light emitted from the 2 nd output port 18 is a minimum value. When the intensity of the light emitted from the 1 st output port 17 is a minimum value, the intensity of the light emitted from the 2 nd output port 18 is a maximum value.

In the mach-zehnder interference device 2 shown in fig. 1, the light emitted from the 2 nd output port 18 is not used.

The optical modulation control device 5 includes a photodetector 21, a phase offset search unit 22, and a control unit 28.

The light detector 21 is implemented by a photodiode, for example.

The optical detector 21 is connected to the 1 st output port 17 of the mach-zehnder interferometer 4.

The photodetector 21 detects the synthesized light emitted from the 1 st output port 17, and outputs an intensity signal I indicating the intensity of the detected synthesized light_PD(t) is output to the delay unit 23, the amplifier 24, and the phase offset recording unit 27.

The photodetector 21 outputs the detected combined light to the outside as output light.

In the Mach-Zehnder interference device 2 shown in FIG. 1, the intensity signal I_PD(t) is the current, but the intensity signal I_PD(t) may be a voltage.

The phase offset search unit 22 includes a delay unit 23, an amplifier 24, a comparator 25, a phase offset adjustment unit 26, and a phase offset recording unit 27.

The phase offset search unit 22 adjusts the phase offset I injected into the 1 st optical path 11 of the Mach-Zehnder interferometer 4_φ(t) searching for the intensity signal I outputted from the photodetector 21_PD(t) phase offset I at minimum value_φ(t)_min。

The phase offset search unit 22 causes the control unit 28 to record the searched phase offset I_φ(t)_minAnd the wavelength of the incident light.

The delay unit 23 outputs the intensity signal I outputted from the photodetector 21_PD(t) holding the delay time Deltat, the intensity signal I_PD(t- Δ t) is output to the input terminal 25a of the comparator 25.

The amplifier 24 has its amplification factor β (t) adjusted by the phase offset adjustment unit 26.

The amplifier 24 amplifies the intensity signal I output from the photodetector 21 at an amplification rate β (t)_PD(t) amplifying the intensity signal β (t) I_PD(t) is output to the inverting input terminal 25b of the comparator 25.

The comparator 25 compares the intensity signal I outputted from the delay 23 with the intensity signal I_PD(t- Δ t) and the intensity signal β (t) · I output from the amplifier 24_PDDifference between (t)(I_PD(t-Δt)-β(t)·I_PD(t)) the proportional differential signal e (t) is output to the phase offset adjustment unit 26 and the phase offset recording unit 27, respectively.

The phase offset adjustment unit 26 is realized by, for example, a phase offset adjustment circuit 31 shown in fig. 2.

The phase offset adjustment unit 26 adjusts the phase offset I to be output to the phase adjustment electrode 15 in accordance with the differential signal e (t) output from the comparator 25 at the time of initial setting of the mach-zehnder interferometer 4_φ(t)。

The phase offset adjustment unit 26 adjusts the phase offset I outputted from the control unit 28 during actual use of the mach-zehnder interferometer 4_φ(t)_minAnd outputs the signal to the phase adjustment electrode 15.

The phase offset recording section 27 is realized by, for example, a phase offset recording circuit 32 shown in fig. 2.

The phase offset recording section 27 records the phase offset I from the phase injected into the 1 st optical path 11_φIn (t), 1 or more phase offsets are searched for when the absolute values of the differential signals e (t) output from the comparator 25 are smaller than the threshold Th.

The phase offset recording part 27 is at least 1 phase offset I with the searched phase offset_φ(t) corresponding intensity signal I_PD(t) searching for the minimum intensity signal I_PD(t)_min。

The phase offset recording section 27 causes the control section 28 to record the intensity signal I corresponding to the minimum intensity_PD(t)_minPhase offset of_φ(t)_minAnd the wavelength of the incident light.

The threshold Th is, for example, a few [ mu A ]]The threshold Th may be stored in an internal memory of the phase offset recording unit 27 or may be given from the outside of the mach-zehnder interferometer 2. In addition, the intensity signal I_PD(t) is a few [ mA]The current of (2).

In the optical modulation control device 5 shown in fig. 1, the comparator 25 outputs the differential signal e (t) to the phase offset adjustment unit 26 and the phase offset recording unit 27, respectively. However, this is merely an example, and the optical modulation control device 5 may include an analog-to-digital converter (hereinafter referred to as "a/D converter") that converts the differential signal e (t) output from the comparator 25 from an analog signal to a digital signal, and the a/D converter may output the digital signal to the phase offset adjustment unit 26 and the phase offset recording unit 27, respectively.

By providing the optical modulation control device 5 shown in fig. 1 with an a/D converter, the calculation process of the phase offset adjustment unit 26, the determination process of the phase offset recording unit 27, and the like can be handled digitally.

In the case where the optical modulation control device 5 shown in fig. 1 includes an a/D converter, the phase offset I output from the phase offset adjustment unit 26_φ(t) becomes a digital signal. Therefore, the optical modulation control device 5 includes the phase offset I to be output from the phase offset adjustment unit 26_φ(t) a digital-to-analog converter (hereinafter referred to as "D/a converter") for converting the analog signal, and the D/a converter outputs the analog signal to the phase adjustment electrode 15.

The control unit 28 is realized by, for example, a control circuit 33 shown in fig. 2.

The control unit 28 records the wavelength and phase offset I of the incident light at the initial setting of the Mach-Zehnder interferometer 4_φ(t)_minThe group (2).

The control unit 28 offsets the phase I corresponding to the wavelength when the Mach-Zehnder interferometer 4 is actually used_φ(t)_minAnd outputs the signal to the phase offset adjustment unit 26.

In fig. 1, it is assumed that the phase offset adjustment unit 26, the phase offset recording unit 27, and the control unit 28, which are part of the components of the optical modulation control device 5, are each implemented by dedicated hardware as shown in fig. 2. That is, it is assumed that a part of the optical modulation control device 5 is realized by the phase offset adjustment circuit 31, the phase offset recording circuit 32, and the control circuit 33.

Here, the phase offset adjustment Circuit 31, the phase offset recording Circuit 32, and the control Circuit 33 correspond to, for example, a single Circuit, a composite Circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a combination thereof.

A part of the components of the optical modulation control device 5 is not limited to being implemented by dedicated hardware, and a part of the optical modulation control device 5 may be implemented by software, firmware, or a combination of software and firmware.

The software or firmware is stored in the form of a program in the memory of the computer. The computer is hardware that executes a program, and corresponds to, for example, a CPU (Central Processing Unit), a Central Processing Unit, a Processing device, an arithmetic device, a microprocessor, a microcomputer, a Processor, or a DSP (Digital Signal Processor).

Fig. 3 is a hardware configuration diagram of a computer in a case where a part of the optical modulation control apparatus 5 is implemented by software, firmware, or the like.

When a part of the optical modulation control device 5 is implemented by software, firmware, or the like, a program for causing a computer to execute the processing steps of the phase offset adjustment unit 26, the phase offset recording unit 27, and the control unit 28 is stored in the memory 41. Then, the processor 42 of the computer executes the program stored in the memory 41.

Fig. 2 shows an example in which a part of the components of the optical modulation control device 5 is realized by dedicated hardware, and fig. 3 shows an example in which a part of the optical modulation control device 5 is realized by software, firmware, or the like. However, this is merely an example, and some of the components of the light modulation control device 5 may be implemented by dedicated hardware, and the remaining components may be implemented by software, firmware, or the like.

Next, the operation of the mach-zehnder interference device 2 shown in fig. 1 will be described.

First, the operation of the mach-zehnder interferometer 4 at the time of initial setting will be described.

When the modulation signal is not superimposed on the optical path inside the mach-zehnder interferometer 4, it is desirable that the combined light emitted from the 1 st output port 17 of the mach-zehnder interferometer 4 be close to 0 in modulation characteristics. Therefore, at the initial setting of the mach-zehnder interferometer 4, the phase offset I in which the combined light emitted from the 1 st output port 17 is in a state close to 0 is searched for_φ(t)。

Fig. 4 is a flowchart showing the processing procedure of the optical modulation control device 5 at the initial setting of the mach-zehnder interferometer 4.

In the mach-zehnder interferometer 2 shown in fig. 1, the wavelength that can be used as the wavelength of the incident light of the mach-zehnder interferometer 4 is λ₁、…、λ_NN of (a). N is an integer of 2 or more.

In the Mach-Zehnder interference device 2 shown in FIG. 1, the interference with the wavelength λ_nThe DC offset for (N-1, …, N) is a known value.

In the mach-zehnder interferometer 2 shown in fig. 1, the variable indicating the time is T, and T is 0, 1, 2, …, T. T is a positive integer.

In the mach-zehnder interference device 2 shown in fig. 1, a signal indicating N wavelengths λ is supplied from the outside to the light source 1 and the control unit 28₁、…、λ_NWavelength λ used at initial setting in (1)_nWavelength information of (2).

Wavelength lambda indicated by wavelength information_nThe phase offset recording section 27, which will be described later, records the phase offset I in the control section 28 every time_φ(t)_minWith the wavelength lambda of the incident light_nThe group of (a) is changed.

The light source 1 displays the wavelength λ indicated by the wavelength information_nThe continuous light (a) is emitted to the optical fiber 3 as incident light of the mach-zehnder interferometer 4.

In the mach-zehnder interference device 2 shown in fig. 1, wavelength information is given to the light source 1 and the control unit 28 from the outside. However, this is merely an example, and the wavelength λ may be selected by the user operating the light source 1_n。

The optical fiber 3 transmits the continuous light emitted from the light source 1 to the branch point 10 of the mach-zehnder interferometer 4.

The mach-zehnder interferometer 4 divides incident light, which is continuous light emitted from the light source 1, into 2 light beams at the branch point 10.

The 1 st optical path 11 of the mach-zehnder interferometer 4 transmits one of the 2 lights distributed at the branching point 10 to the combining point 16.

The 2 nd optical path 12 of the mach-zehnder interferometer 4 transmits the other of the 2 lights distributed at the branching point 10 to the combining point 16.

The wavelength λ of the continuous light emitted from the light source 1 is given to the positive phase signal electrode 13 and the negative phase signal electrode 14, respectively_nA corresponding DC bias.

When a DC bias is applied to the positive-phase signal electrode 13, the DC bias is superimposed on the light transmitted through the 1 st optical path 11.

When a DC bias is applied to the inverted signal electrode 14, the DC bias is superimposed on the light transmitted through the 2 nd optical path 12.

In the mach-zehnder interference device 2 shown in fig. 1, a DC bias is applied to each of the normal-phase signal electrode 13 and the reverse-phase signal electrode 14 from the outside. However, this is merely an example, and the control unit 28 may apply the wavelength λ to each of the normal-phase signal electrode 13 and the reverse-phase signal electrode 14_nA corresponding DC bias.

In the initial setting of the mach-zehnder interferometer 4, the positive-phase signal electrode 13 and the negative-phase signal electrode 14 respectively superimpose only the DC bias on the light and do not superimpose the modulation signal on the light.

The control unit 28 initializes the time t to "1" (step ST1 of fig. 4).

The phase offset adjustment unit 26 offsets the phase at time t by I_φ(t) are output to the phase adjustment electrode 15 and the phase offset recording unit 27, respectively (step ST2 in fig. 4).

The phase offset adjustment unit 26 outputs the amplification factor β (t) at time t to the phase offset recording unit 27.

Phase offset I when t is 0_φ(0) The initial value is stored in the internal memory of the phase offset adjustment unit 26. I is_φ(0) For example, 0[ mA ]]。

For example, according to the following formula (2) described later, the phase offset I_φ(0) To calculate the phase offset I at the time t equal to 1_φ(1)。

the amplification factor β (0) when t is 0 is stored as an initial value in the internal memory of the phase offset adjustment unit 26. The amplification factor β (0) is, for example, 1.

For example, the amplification factor β (1) at time t of 1 is calculated from the amplification factor β (0) according to the following expression (3) described later.

The phase adjustment electrode 15 offsets the phase I outputted from the phase offset adjustment unit 26_φ(t) overlaps with the light transmitted through the 1 st optical path 11.

The mach-zehnder interferometer 4 combines one light traveling through the 1 st optical path 11 and the other light traveling through the 2 nd optical path 12 at a combining point 16.

The mach-zehnder interferometer 4 outputs the combined light of 2 lights combined at the combining point 16 from the 1 st output port 17 to the photodetector 21.

The photodetector 21 detects the combined light emitted from the 1 ST output port 17 (step ST3 in fig. 4).

The light detector 21 converts an intensity signal I representing the intensity of the detected combined light_PD(t) is output to the delayer 2, the amplifier 244, and the phase offset recording unit 27.

FIG. 5 shows the phase offset I outputted from the phase offset adjustment unit 26 to the phase adjustment electrode 15_φ(t) and the intensity signal I output from the photodetector 21_PD(t) an explanatory view of an example of the relationship between the two.

In the example of fig. 5, T is 31, and at T, the phase offset I of 6_φ(6) Time, intensity signal I_PD(t) has a maximum value, and a phase offset I of 22 at t_φ(22) Time, intensity signal I_PD(t) becomes a minimum value.

FIG. 6 shows the phase offset I outputted from the phase offset adjustment unit 26 to the phase adjustment electrode 15_φ(t) is an explanatory view of a temporal change.

The delay device 23 receives the intensity signal I from the optical detector 21_PD(t) after, the intensity signal I_PD(t) holding the delay time Δ t. The delay time Δ t is a time equal to the time difference between the time t and the time t-1.

The delay 23 will maintain the intensity signal I of the delay time deltat_PD(t) as intensity signal I_PD(t- Δ t) is output to the input terminal 25a of the comparator 25.

The amplifier 24 obtains the amplification factor β (t) output from the phase offset adjustment unit 26.

The amplifier 24 receives the intensity signal I from the photodetector 21_PD(t) thereafter, amplifying the intensity signal I with an amplification factor β (t)_PD(t) amplifying the intensity signal β (t) I_PD(t) is output to the inverting input terminal 25b of the comparator 25.

FIG. 7 is a graph showing the intensity signal β (t). I output from the amplifier 24_PD(t) is an explanatory view of a temporal change.

Intensity signal β (t). I output from amplifier 24_PD(t) changes with the passage of time as shown in FIG. 7.

The comparator 25 takes the intensity signal I from the delay 23_PD(t- Δ t), the intensity signal β (t). I is obtained from the amplifier 24_PD(t)。

The comparator 25 calculates the intensity signal I as shown in the following equation (1)_PD(t- Δ t) and intensity signal β (t). I_PDDifference (I) of (t)_PD(t-Δt)-β(t)·I_PD(t)) the proportional differential signal e (t) (step ST4 of fig. 4).

e(t)＝α(I_PD(t-Δt)-β(t)·I_PD(t)) (1)

In formula (1), α is a normal number.

The comparator 25 outputs the calculated differential signal e (t) to the phase offset adjustment unit 26 and the phase offset recording unit 27, respectively.

After receiving the differential signal e (t) from the comparator 25, the phase offset adjustment unit 26 calculates the differential signal e (t) and the phase offset I as shown in the following equation (2)_φ(t) adding to thereby calculate the phase offset I at time t +1_φ(t +1) (step ST5 of fig. 4).

The phase offset adjusting unit 26 adjusts the calculated phase offset I_φ(t +1) is output to the phase adjustment electrode 15.

I_φ(t+1)＝e(t)+I_φ(t) (2)

Phase offset I adjusted by phase offset adjusting section 26_φ(t) changes as shown in fig. 6 with the elapse of time t.

Further, the phase offset adjustment unit 26 calculates the amplification factor β (t +1) at time t +1 based on the differential signal e (t) as shown in the following expression (3) (step ST6 in fig. 4).

When the differential signal e (t) is positive, the amplification factor β (t +1) is decreased as compared with the amplification factor β (t), and when the differential signal e (t) is negative, the amplification factor β (t +1) is increased as compared with the amplification factor β (t).

The phase offset adjustment unit 26 outputs the calculated amplification factor β (t +1) to the amplifier 24 and the phase offset recording unit 27, respectively.

Upon receiving the differential signal e (t) from the comparator 25, the phase offset recording unit 27 determines whether or not the absolute value of the differential signal e (t) is smaller than the threshold Th as shown in the following expression (4) (step ST7 in fig. 4).

|e(t)|＜Th (4)

At phase offset I_φ(t) intensity signal I_PDWhen the relation of (t) is shown in fig. 5, if the absolute value of the differential signal e (t) is smaller than the threshold Th, the intensity signal I output from the photodetector 21 is output_PDThe probability that (t) is a maximum value or a minimum value is high.

If the intensity signal I_PD(t) is an extreme value, then, as shown in FIG. 5, compared to the intensity signal I_PD(t) is a value other than the extreme value, I_PD(t-1) and I_PDThe difference in (t) is small.

If the absolute value of the differential signal e (t) is smaller than the threshold Th (step ST 7: "YES" of FIG. 4), the intensity signal I is_PDSince (t) is highly likely to be a maximum value or a minimum value, the phase offset recording section 27 records the intensity signal I_PD(t) and phase offset I_φ(t) are stored in the internal memories, respectively (step ST9 in fig. 4).

In the example of fig. 5, the intensity signal I_PD(6) And phase offset I_φ(6) And the intensity signal I_PD(22) And phase offset I_φ(22) The group (2) is stored in the internal memory of the phase offset recording unit 27.

As shown in FIG. 7, the intensity signal β (t). I output from the amplifier 24_PD(t) becomes a minimum value in the vicinity of t4, and therefore, the intensity signal I_PD(4) And phase offset I_φ(4) May be stored in the internal memory of the phase offset recording section 27. However, as shown in fig. 5, the intensity signal I output from the photodetector 21_PD(4) Is not a minimum value, and therefore, the intensity signal I_PD(4) And phase offset I_φ(4) The group of (1) is saved by mistake.

The control unit 28 determines whether or not the time T is T (step ST10 in fig. 4).

If the time T is smaller than T (in the case of step ST 10: "YES" of FIG. 4), the control unit 28 increments the time T by 1 (step ST8 of FIG. 4).

When the absolute value of the differential signal e (t) is equal to or greater than the threshold Th (in the case of no at step ST7 in fig. 4), the control unit 28 also adds 1 to the time t (step ST8 in fig. 4).

Thereafter, the processing of steps ST2 to ST10 is repeated until time T becomes T (step ST10 of FIG. 4, in the case of "NO").

When the time T is T, the phase offset recording unit 27 stores 1 or more intensity signals I stored in the internal memory_PD(t) comparing them with each other, searching for the signal I of minimum intensity_PD(t)_min。

For example, storing the intensity signal I_PD(4) Intensity signal I_PD(6) And intensity signal I_PD(22) In the case of (2), as shown in FIG. 5, due to the intensity signal I_PD(22) Minimum, therefore, the intensity signal I is searched for_PD(22) As the minimum intensity signal I_PD(t)_min。

The phase offset recording section 27 searches for the minimum intensity signal I_PD(t)_minThen, the control unit 28 records the intensity signal I_PD(t)_minPhase offset of_φ(t)_minWith the wavelength lambda of the incident light_nGroup (step ST11 of fig. 4).

If the intensity signal I is searched_PD(22) As intensity signals I_PD(t)_minThen the phase is biased to I_φ(22) And wavelength lambda_nThe group (2) is recorded in the control unit 28.

Here, the phase offset recording section 27 causes the control section 28 to record a phaseBit offset I_φ(t)_minAnd wavelength lambda_nThe group (2). However, this is merely an example, and the phase offset recording section 27 may cause the control section 28 to record the phase offset I_φ(t)_minWavelength lambda of_nAnd a set of DC biases.

The control unit 28 records the phase offset I_φ(t)_minWavelength lambda of_nAnd DC offset, the control unit 28 can adjust the wavelength λ corresponding to the actual operation of the Mach-Zehnder interferometer 4_nThe DC bias of (1) is outputted to the positive phase signal electrode 13 and the negative phase signal electrode 14, respectively.

The phase offset search unit 22 determines the wavelength λ for all of the N wavelengths_nPhase offset of_φ(t)_minIs completed (step ST12 of fig. 4).

If for all N wavelengths lambda_nPhase offset of_φ(t)_minWhen the recording of (2) is completed (step ST12 of fig. 4: yes), the operation at the time of initial setting of the mach-zehnder interferometer 4 is ended.

If N wavelengths λ_nWith a residual phase offset I_φ(t)_minWavelength λ at which recording is not completed_n(in the case of step ST 12: "NO" of FIG. 4), the processing of steps ST1 to ST12 is repeated.

Next, the operation of the mach-zehnder interferometer 4 in actual use will be described.

In the mach-zehnder interference device 2 shown in fig. 1, the light source 1 and the control unit 28 are supplied with a signal indicating N wavelengths λ₁、…、λ_NWavelength λ used in practical use in (1)_nWavelength information of (2).

The light source 1 displays the wavelength λ indicated by the wavelength information_nThe continuous light (a) is emitted to the optical fiber 3 as incident light of the mach-zehnder interferometer 4.

The wavelength λ of the continuous light emitted from the light source 1 is given to the positive phase signal electrode 13 and the negative phase signal electrode 14, respectively_nA corresponding DC bias.

When a DC bias is applied to the positive-phase signal electrode 13, both the DC bias and the modulation signal are superimposed on the light transmitted through the 1 st optical path 11.

When a DC bias is applied to the inverted signal electrode 14, both the DC bias and the modulation signal are superimposed on the light transmitted through the 2 nd optical path 12.

The control unit 28 controls the wavelength of the light emitted from the light source based on the N wavelengths λ recorded at the initial setting₁、…、λ_NCorresponding phase offset I_φ(t)_minTo obtain the wavelength lambda shown by the wavelength information_nCorresponding phase offset I_φ(t)_min。

The control unit 28 offsets the acquired phase by I_φ(t)_minAnd outputs the signal to the phase offset adjustment unit 26.

The phase offset adjustment unit 26 adjusts the phase offset I output from the control unit 28_φ(t)_minAnd outputs the signal to the phase adjustment electrode 15.

The phase adjustment electrode 15 offsets the phase I outputted from the phase offset adjustment unit 26_φ(t)_minOverlapping the light transmitted through the 1 st optical path 11.

The photodetector 21 detects the synthesized light emitted from the 1 st output port 17, and outputs the detected synthesized light to the outside as output light.

The mach-zehnder interferometer 2 shown in fig. 1 includes a photodetector 21, and the photodetector 21 detects the combined light emitted from the 1 st output port 17 of the mach-zehnder interferometer 4.

However, this is merely an example, and as shown in fig. 8, the mach-zehnder interferometer 2 may be provided with an optical detector 29, and the optical detector 29 may detect the combined light emitted from the 2 nd output port 18 of the mach-zehnder interferometer 4.

Fig. 8 is a configuration diagram showing a mach-zehnder interference device 2 including another optical modulation control device 5 according to embodiment 1. In fig. 8, the same reference numerals as in fig. 1 denote the same or corresponding parts, and thus, the description thereof will be omitted.

The light detector 29 is implemented by, for example, a photodiode.

The optical detector 29 is connected to the 2 nd output port 18 of the mach-zehnder interferometer 4.

The photodetector 29 pair outputs from the 2 nd outputThe combined light emitted from the port 18 is detected, and an intensity signal I representing the intensity of the detected combined light is generated_PD(t) is output to the delay unit 23, the amplifier 24, and the phase offset recording unit 27.

The 2 nd output port 18 is a port for emitting light in reverse phase to the synthesized light emitted from the 1 st output port 17.

Therefore, the phase offset I outputted from the phase offset adjustment unit 26 to the phase adjustment electrode 15_φ(t) and the intensity signal I output from the photodetector 29_PDThe relationship between (t) is shown in fig. 9.

FIG. 9 shows the phase offset I outputted from the phase offset adjustment unit 26 to the phase adjustment electrode 15_φ(t) and the intensity signal I output from the photodetector 29_PD(t) an explanatory view of an example of the relationship between the two.

When the waveform shown in fig. 9 is compared with the waveform shown in fig. 5, the intensity signal I starts at the beginning of the waveform shown in fig. 5_PD(t) has a maximum value and then has a minimum value, but in the waveform shown in FIG. 9, the intensity signal I is initially present_PD(t) becomes a minimum value and then becomes a maximum value.

In the example of fig. 9, T is 31, and at T, the phase offset I of 6_φ(6) Time, intensity signal I_PD(t) is a minimum value, and at t, 22, the phase offset I is_φ(22) Time, intensity signal I_PD(t) becomes a maximum value.

The phase offset search unit 22 shown in fig. 8 differs from the phase offset search unit 22 shown in fig. 1 in the phase offset I injected into the 1 st optical path 11_φ(t) searching for the intensity signal I output from the photodetector 29_PD(t) phase offset I at maximum_φ(t)_max。

The phase offset search unit 22 causes the control unit 28 to record the searched phase offset I_φ(t)_maxWith the wavelength lambda of the incident light_nThe group (2).

Specifically, the phase offset recording unit 27 shown in fig. 8, like the phase offset recording unit 27 shown in fig. 1, sets the intensity signal I if the absolute value of the difference signal e (t) is smaller than the threshold Th_PD(t) and phase offset I_φ(t) are stored in the internal memories, respectively.

Unlike the phase offset recording unit 27 shown in fig. 1, the phase offset recording unit 27 shown in fig. 8 stores 1 or more intensity signals I stored in the internal memory when the time T is T_PD(t) comparing them with each other, searching for the maximum intensity signal I_PD(t)_max。

For example, storing the intensity signal I_PD(4) Intensity signal I_PD(6) And intensity signal I_PD(22) In the case of (2), as shown in FIG. 9, due to the intensity signal I_PD(22) Maximum, and therefore, the intensity signal I is searched for_PD(22) As the maximum intensity signal I_PD(t)_max。

The phase offset recording section 27 searches for the maximum intensity signal I_PD(t)_maxThen, the control unit 28 records the intensity signal I_PD(t)_maxPhase offset of_φ(t)_maxWith the wavelength lambda of the incident light_nThe group (2).

If it is taken as the intensity signal I_PD(t)_maxWhile searching for an intensity signal I_PD(22) Then the phase is biased to I_φ(22) And wavelength lambda_nThe group (2) is recorded in the control unit 28.

The phase offset I recorded by the phase offset recording section 27 shown in FIG. 8_φ(t)_maxAnd the phase offset I recorded by the phase offset recording section 27 shown in FIG. 1_φ(t)_minIs the same phase offset I_φ(22)。

Thus, the Mach-Zehnder interference device 2 shown in FIG. 1 achieves the same results as the Mach-Zehnder interference device 2 shown in FIG. 8.

In embodiment 1 described above, the light modulation control device 5 includes: a photodetector 21 or a photodetector 29 that detects light emitted from the mach-zehnder interferometer 4 and outputs an intensity signal indicating the intensity of the light; and a phase offset search unit 22 for adjusting a phase offset injected into the optical path inside the mach-zehnder interferometer 4, searching for a phase offset when the intensity signal output from the optical detector 21 becomes a minimum value or a phase offset when the intensity signal output from the optical detector 29 becomes a maximum value, and recording a set of the searched phase offset and the wavelength of the light. Therefore, even if the wavelength of the incident light changes, the optical modulation control device 5 can superimpose the phase offset corresponding to the wavelength of the incident light on the light.

In the optical modulation control device 5 shown in fig. 1, the control unit 28 records the intensity signal I output from the photodetector 21_PD(t) phase offset I at minimum value_φ(t)_minWith the wavelength lambda of the incident light_nThe group (2).

In the optical modulation control device 5 shown in fig. 8, the control unit 28 records the intensity signal I output from the optical detector 29_PD(t) phase offset I at maximum_φ(t)_maxWith the wavelength lambda of the incident light_nThe group (2).

However, this is merely an example, and in the light modulation control device 5 shown in fig. 1, the control unit 28 records the intensity signal I output from the photodetector 21_PD(t) phase offset I at minimum value_φ(t)_minWith the wavelength lambda of the incident light_nIn addition to the group (2), the control unit 28 may record the intensity signal I_PD(t) phase offset I at maximum_φ(t)_maxWith the wavelength lambda of the incident light_nThe group (2).

In the light modulation control device 5 shown in fig. 8, the intensity signal I output from the photodetector 29 is recorded in the control unit 28_PD(t) phase offset I at maximum_φ(t)_maxWith the wavelength lambda of the incident light_nIn addition to the group (2), the control unit 28 may record the intensity signal I_PD(t) phase offset I at minimum value_φ(t)_minWith the wavelength lambda of the incident light_nThe group (2).

In the light modulation control device 5 shown in fig. 1 and 8, if the absolute value of the differential signal e (t) is smaller than the threshold Th, the phase offset recording section 27 records the intensity signal I_PD(t) and phase offset I_φ(t) are stored in the internal memories, respectively. However, this is merely an example,the phase offset recording unit 27 may also record the intensity signal I at all times t (t is 1, …, N)_PD(t) and phase offset I_φ(t) are stored in the internal memories, respectively.

The phase offset recording section 27 stores the intensity signals I at all times t_PD(t) and phase offset I_φ(t) and (f) storing the intensity signal I when the absolute value of the differential signal e (t) is smaller than the threshold Th_PD(t) and phase offset I_φIn the case of (t), an internal memory having a larger capacity is required. However, the phase offset recording section 27 stores the intensity signals I at all times t_PD(t) and phase offset I_φIn the case of (t), each of the delay device 23, the amplifier 24, and the comparator 25 is not necessary, and the structure of the optical modulation control device 5 can be simplified.

Embodiment 2.

In the optical modulation control apparatus 5 shown in fig. 1, the phase offset adjustment unit 26 adjusts the phase offset I injected into the 1 st optical path 11_φ(t)。

In embodiment 2, the phase offset adjustment unit 26 adjusts the phase offset injected into the 1 st optical path 11 And phase offset of injection into the 2 nd optical path 12Both the light modulation control devices 5 will be explained.

Fig. 10 is a configuration diagram showing a mach-zehnder interference device 2 including the optical modulation control device 5 of embodiment 2. In fig. 10, the same reference numerals as in fig. 1 denote the same or corresponding parts.

In the optical modulation control device 5 shown in fig. 10, the optical detector 21 detects the combined light emitted from the 1 st output port 17 of the mach-zehnder interferometer 4. Instead of providing the photodetector 21, the optical modulation control device 5 may include a photodetector 29, and the photodetector 29 may detect the combined light emitted from the 2 nd output port 18 of the mach-zehnder interferometer 4.

The phase adjustment electrode 15a is inserted into the 1 st optical path 11 in the same manner as the phase adjustment electrode 15 shown in fig. 1.

The phase adjustment electrode 15a offsets the phase outputted from the phase offset adjustment unit 26Overlapping the light transmitted through the 1 st optical path 11.

The phase is biased by the phase adjusting electrode 15aThe phase of the light transmitted through the 1 st optical path 11 is rotated to the positive side by overlapping the light transmitted through the 1 st optical path 11.

The phase adjustment electrode 15b is inserted into the 2 nd optical path 12.

The phase adjustment electrode 15b offsets the phase outputted from the phase offset adjustment unit 26Overlapping the light transmitted through the 2 nd optical path 12.

The phase is biased by the phase adjusting electrode 15bThe light transmitted through the 2 nd optical path 12 is superimposed on the light, and thereby the phase of the light transmitted through the 2 nd optical path 12 is rotated to the negative side.

The direction of rotation of the phase of the light transmitted through the 1 st optical path 11 is opposite to the direction of rotation of the phase of the light transmitted through the 2 nd optical path 12. However, due to phase offsetAbsolute value and phase offset ofAre the same, and thus, the phase of the light transmitted through the 1 st optical path 11The amount of rotation of the bits is the same as the amount of rotation of the phase of the light transmitted through the 2 nd optical path 12.

However, the same is not limited to strict agreement, and may be shifted within a range that is practically unproblematic.

The operation of the phase offset search unit 22 shown in fig. 10 is substantially the same as the operation of the phase offset search unit 22 shown in fig. 1. However, the phase offset adjustment unit 26 shown in fig. 10 differs from the phase offset adjustment unit 26 shown in fig. 1 in that the phase offset is adjustedOutputs the phase of the signal to the phase adjusting electrode 15aAnd outputs the signal to the phase adjustment electrode 15 b.

In addition, the phase offset adjustment unit 26 shown in fig. 10 shifts the phasePhase offsetAnd the amplification factor β (t) are outputted to the phase offset recording section 27.

The phase offset adjustment unit 26 shown in fig. 10 adjusts the differential signal e (t) and the phase offset I as shown in the following equation (5)_φ(t) adding to calculate the phase offset I at time t +1_φ(t+1)。

The phase offset adjustment unit 26 shown in fig. 10 calculates the phase offset at time t +1 as shown in the following equation (6)

The phase offset adjustment unit 26 shown in fig. 10 adjusts the phase offset by adjusting the phase offsetOutputs to the phase adjusting electrode 15a and biases the phaseOutput to the phase adjusting electrode 15b, if so Even when the phase offset I is outputted to the phase adjustment electrode 15 as shown in fig. 1_φIn the case of (t), the phase rotation amount is also 2 times.

By multiplying the amount of phase rotation by 2, the dynamic range in the phase control can be expanded to output the phase offset I to the phase adjustment electrode 15_φ(t) 2 times in the case of (t).

Since the phase rotation amount is 2 times, the phase offset adjustment unit 26 may calculate the amplification factor β (t +1) at time t +1 as shown in the following equation (7).

In the denominator of the right-hand 2 nd term of expression (7), the constant multiplied by | e (t) | becomes 20, and becomes 2 times the constant "10" multiplied by | e (t) | in expression (3).

Therefore, the phase offset I is outputted to the phase adjustment electrode 15 as compared with that shown in fig. 1_φIn the case of (t), the increase and decrease of the amplification factor β (t +1) at the time t +1 become small.

Embodiment 3.

BPSK is performed in the mach-zehnder interference devices 2 according to embodiments 1 and 2.

In embodiment 3, a mach-zehnder interferometer 2 that performs Quadrature Phase Shift modulation (QPSK: Quadrature Phase Shift Keying) will be described.

Fig. 11 is a configuration diagram showing a mach-zehnder interference device 2 including the optical modulation control device 5 according to embodiment 3. In fig. 11, the same reference numerals as in fig. 1 denote the same or corresponding parts, and thus, the description thereof will be omitted.

The 1 st Mach-Zehnder interferometer 4-1 includes a 2 nd Mach-Zehnder interferometer 4-2 and a 3 rd Mach-Zehnder interferometer 4-3.

The 1 st Mach-Zehnder interferometer 4-1 includes a 1 st optical path 11-1, a 2 nd optical path 12-1, photodetectors 21-2, 21-3, a phase adjustment electrode 15-1, a 1 st output port 17-1, and a 2 nd output port 18-1.

The 1 st Mach-Zehnder interferometer 4-1 has a branch point 10-1 for dividing incident light into 2 light beams and a combining point 16-1 for combining the 2 divided light beams.

The 1 st mach-zehnder interferometer 4-1 distributes incident light into 2 pieces of light at a branch point 10-1, combines the distributed 2 pieces of light at a combining point 16-1, and emits a combined light-1 of the 2 pieces of light to a photodetector 21-1.

The 1 st optical path 11-1 is realized by an optical fiber, for example.

One end of the 1 st optical path 11-1 is connected to the branch point 10-1, and the other end of the 1 st optical path 11-1 is connected to the combining point 16-1.

The 1 st optical path 11-1 transmits one of the 2 lights distributed at the branch point 10-1 to the combining point 16-1 via the 2 nd Mach-Zehnder interferometer 4-2.

The 2 nd optical path 12-1 is realized by an optical fiber, for example.

One end of the 2 nd optical path 12-1 is connected to the branch point 10-1, and the other end of the 2 nd optical path 12-1 is connected to the combining point 16-1.

The 2 nd optical path 12-1 transmits the other light of the 2 lights distributed at the branch point 10-1 to the combining point 16-1 via the 3 rd Mach-Zehnder interferometer 4-3.

The phase adjustment electrode 15-1 is inserted into the 2 nd optical path 12-1.

The phase adjustment electrode 15-1 makes the phase outputted from the phase offset search section 50BiasingOverlapping the light transmitted through the 2 nd optical path 12-1.

The 1 st output port 17-1 is a port for emitting the combined light to the photodetector 21-1.

The 2 nd output port 18-1 is a port for emitting light in the opposite phase to the combined light.

In the mach-zehnder interference device 2 shown in fig. 11, the light emitted from the 2 nd output port 18-1 is not used.

The 2 nd Mach-Zehnder interferometer 4-2 includes a 1 st optical path 11-2, a 2 nd optical path 12-2, a normal phase signal electrode 13-2, a reverse phase signal electrode 14-2, a phase adjustment electrode 15-2, a 1 st output port 17-2, and a 2 nd output port 18-2.

The 2 nd mach-zehnder interferometer 4-2 has a branch point 10-2 for dividing incident light into 2 pieces of light, and a combining point 16-2 for combining the 2 pieces of light after division.

The 2 nd mach-zehnder interferometer 4-2 distributes incident light into 2 pieces of light at the branch point 10-2, combines the distributed 2 pieces of light at the combining point 16-2, and emits the combined light of the 2 pieces of light to the photodetector 21-2.

The positive phase signal electrode 13-2 is inserted into the 1 st optical path 11-2.

The positive-phase signal electrode 13-2 superimposes a DC bias corresponding to the wavelength of incident light on the light transmitted through the 1 st optical path 11-2.

In the initial setting of the 2 nd mach-zehnder interferometer 4-2, the normal-phase signal electrode 13-2 superimposes only the DC bias on the light, and does not superimpose the modulation signal on the light.

In actual operation after the initial setting of the 2 nd mach-zehnder interferometer 4-2 is completed, the normal phase signal electrode 13-2 superimposes both the DC bias and the modulation signal on the light.

Inverted signal electrode 14-2 is inserted into optical path 2 12-2.

The inverted signal electrode 14-2 superimposes a DC bias corresponding to the wavelength of the incident light on the light transmitted through the 2 nd optical path 12-2.

In the initial setting of the 2 nd mach-zehnder interferometer 4-2, the inverted signal electrode 14-2 superimposes only the DC bias on the light and does not superimpose the modulation signal on the light.

In actual use after the initial setting of the 2 nd mach-zehnder interferometer 4-2 is completed, the inverted signal electrode 14-2 superimposes both the DC bias and the modulation signal on the light.

The phase adjustment electrode 15-2 is inserted into the 1 st optical path 11-2.

The phase adjustment electrode 15-2 offsets the phase outputted from the phase offset search unit 50Overlapping the light transmitted through the 1 st optical path 11-2.

The 1 st output port 17-2 is a port for emitting the combined light to the photodetector 21-2.

The 2 nd output port 18-2 is a port for emitting light in the opposite phase to the synthesized light.

In the mach-zehnder interference device 2 shown in fig. 11, the light emitted from the 2 nd output port 18-2 is not used.

The 3 rd Mach-Zehnder interferometer 4-3 includes a 1 st optical path 11-3, a 2 nd optical path 12-3, a normal phase signal electrode 13-3, a reverse phase signal electrode 14-3, a phase adjustment electrode 15-3, a 1 st output port 17-3, and a 2 nd output port 18-3.

The 3 rd mach-zehnder interferometer 4-3 has a branch point 10-3 for dividing incident light into 2 pieces of light, and a combining point 16-3 for combining the 2 pieces of light after division.

The 3 rd mach-zehnder interferometer 4-3 distributes incident light into 2 pieces of light at the branch point 10-3, combines the distributed 2 pieces of light at the combining point 16-3, and emits the combined light of the 2 pieces of light to the photodetector 21-3.

The positive phase signal electrode 13-3 is inserted into the 1 st optical path 11-3.

The positive-phase signal electrode 13-3 superimposes a DC bias corresponding to the wavelength of incident light on the light transmitted through the 1 st optical path 11-3.

In the initial setting of the 3 rd mach-zehnder interferometer 4-3, the normal-phase signal electrode 13-3 superimposes only the DC bias on the light, and does not superimpose the modulation signal on the light.

In actual operation after the initial setting of the 3 rd mach-zehnder interferometer 4-3 is completed, the normal phase signal electrode 13-3 superimposes both the DC bias and the modulation signal on the light.

The inverted signal electrode 14-3 is inserted into the 2 nd optical path 12-3.

The inverted signal electrode 14-3 superimposes a DC bias corresponding to the wavelength of the incident light on the light transmitted through the 2 nd optical path 12-3.

In the initial setting of the 3 rd mach-zehnder interferometer 4-3, the inverted signal electrode 14-3 superimposes only the DC bias on the light and does not superimpose the modulation signal on the light.

In actual use after the initial setting of the 3 rd mach-zehnder interferometer 4-3 is completed, the inverted signal electrode 14-3 superimposes both the DC bias and the modulation signal on the light.

The phase adjustment electrode 15-3 is inserted into the 1 st optical path 11-3.

The phase adjustment electrode 15-3 offsets the phase outputted from the phase offset search section 50Overlapping the light transmitted through the 1 st optical path 11-3.

The 1 st output port 17-3 is a port for emitting the combined light to the photodetector 21-3.

The 2 nd output port 18-3 is a port for emitting light in the opposite phase to the combined light.

In the mach-zehnder interference device 2 shown in fig. 11, the light emitted from the 2 nd output port 18-3 is not used.

The light detector 21-2 is realized by a photodiode, for example.

The optical detector 21-2 is connected to the 1 st output port 17-2 of the 2 nd mach-zehnder interferometer 4-2.

The photodetector 21-2 detects the synthesized light emitted from the 1 st output port 17-2, and outputs a 2 nd intensity signal I indicating the intensity of the detected synthesized light_PD2(t) is output to the phase offset search unit 50.

The photodetector 21-2 outputs the detected combined light to the 1 st optical path 11-1.

The light detector 21-3 is realized by a photodiode, for example.

The optical detector 21-3 is connected to the 1 st output port 17-3 of the 3 rd mach-zehnder interferometer 4-3.

The photodetector 21-3 detects the combined light emitted from the 1 st output port 17-3, and outputs a 3 rd intensity signal I indicating the intensity of the detected combined light_PD3(t) is output to the phase offset search unit 50.

The photodetector 21-3 outputs the detected combined light to the phase adjustment electrode 15-1.

The light detector 21-1 is realized by a photodiode, for example.

The optical detector 21-1 is connected to the 1 st output port 17-1 of the 1 st mach-zehnder interferometer 4-1.

The photodetector 21-1 detects the combined light emitted from the 1 st output port 17-1, and outputs a 1 st intensity signal I indicating the intensity of the detected combined light_PD1(t) is output to the phase offset search unit 50.

The photodetector 21-1 outputs the detected combined light to the outside as outgoing light.

The phase offset search unit 50 adjusts the phase offset injected into the 1 st optical path 11-2 of the 2 nd Mach-Zehnder interferometer 4-2And searches for the 2 nd intensity signal I output from the photodetector 21-2_PD2(t) phase offset at minimum value

The phase offset search unit 50 causes the control unit 51 to record the searched phase offsetWith the wavelength lambda of the incident light_nThe group (2).

The phase offset search section 50 adjusts the phase offset injected into the 1 st optical path 11-3 of the 3 rd Mach-Zehnder interferometer 4-3And searches for the 3 rd intensity signal I output from the photodetector 21-3_PD3(t) phase offset at minimum value

The phase offset search unit 50 causes the control unit 51 to record the searched phase offsetWith the wavelength lambda of the incident light_nThe group (2).

The phase offset search unit 50 adjusts the phase offset injected into the 2 nd optical path 12-1 of the 1 st Mach-Zehnder interferometer 4-1And searching for a phase offset which becomes 1/2 of the sum of the following two phase offsetsThe two phase offsets are the 1 st intensity signal I output from the photodetector 21-1_PD1(t) phase offset at minimum valueAnd 1 st intensity signal I_PD1(t) phase offset at the time of maximum value

The phase offset search unit 50 causes the control unit 51 to record the searched phase offsetWith the wavelength lambda of the incident light_nThe group (2).

The control section 51 records the wavelength λ of the incident light_nPhase offsetPhase offsetAnd phase offsetThe group (2).

The control unit 51 controls the wavelength λ of the Mach-Zehnder interferometer 4-1 during actual use_nCorresponding phase offsetAnd outputs the result to the phase offset search unit 50.

The control unit 51 controls the wavelength λ of the Mach-Zehnder interferometer 4-2 during actual use_nCorresponding phase offsetAnd outputs the result to the phase offset search unit 50.

The control unit 51 controls the wavelength λ of the 3 rd Mach-Zehnder interferometer 4-3 during actual use_nCorresponding phase offsetAnd outputs the result to the phase offset search unit 50.

Next, the operation of the mach-zehnder interference device 2 shown in fig. 11 will be described.

First, the operation of the 1 st Mach-Zehnder interferometer 4-1, the 2 nd Mach-Zehnder interferometer 4-2, and the 3 rd Mach-Zehnder interferometer 4-3 at the time of initial setting will be described.

In the mach-zehnder interference device 2 shown in fig. 11, a signal indicating N wavelengths λ is supplied from the outside to the light source 1 and the control unit 28₁、…、λ_NWavelength λ used at initial setting in (1)_nWavelength information of (2).

Wavelength lambda indicated by wavelength information_nThe control unit 51 records the wavelength λ of the incident light every time in the phase offset search unit 50 described later_nPhase offsetPhase offsetAnd phase offsetThe group of (a) is changed.

The light source 1 displays the wavelength λ indicated by the wavelength information_nThe continuous light (a) is emitted to the optical fiber 3 as the incident light of the 1 st mach-zehnder interferometer 4-1.

The optical fiber 3 transmits the continuous light emitted from the light source 1 to the branch point 10-1 of the 1 st Mach-Zehnder interferometer 4-1.

The 1 st Mach-Zehnder interferometer 4-1 splits incident light, which is continuous light emitted from the light source 1, into 2 light at a branch point 10-1.

The 1 st optical path 11-1 of the 1 st Mach-Zehnder interferometer 4-1 transmits one of the 2 lights distributed at the branch point 10-1 to the branch point 10-2 of the 2 nd Mach-Zehnder interferometer 4-2.

The 2 nd optical path 12-1 of the 1 st Mach-Zehnder interferometer 4-1 transmits the other of the 2 lights distributed at the branch point 10-1 to the branch point 10-3 of the 3 rd Mach-Zehnder interferometer 4-3.

The 2 nd mach-zehnder interferometer 4-2 divides the light transmitted through the 1 st optical path 11-1 into 2 lights at the branch point 10-2.

The 1 st optical path 11-2 of the 2 nd mach-zehnder interferometer 4-2 transmits one of the 2 lights distributed at the branch point 10-2 to the combining point 16-2.

The 2 nd optical path 12-2 of the 2 nd mach-zehnder interferometer 4-2 transmits the other of the 2 lights distributed at the branch point 10-2 to the combining point 16-2.

The forward phase signal electrode 13-2 and the reverse phase signal electrode 14-2 are each provided with a wavelength λ corresponding to the continuous light emitted from the light source 1_nA corresponding DC bias.

When a DC bias is applied to the positive-phase signal electrode 13-2, the DC bias is superimposed on the light transmitted through the 1 st optical path 11-2.

The inverted signal electrode 14-2, when given a DC bias, causes the DC bias to overlap with the light transmitted through the 2 nd optical path 12-2.

The phase adjustment electrode 15-2 offsets the phase outputted from the phase offset search unit 50Overlapping the light transmitted through the 1 st optical path 11-2.

The 3 rd mach-zehnder interferometer 4-3 splits the light transmitted by the 2 nd optical path 12-1 into 2 lights at the branch point 10-3.

The 1 st optical path 11-3 of the 3 rd Mach-Zehnder interferometer 4-3 transmits one of the 2 lights distributed at the branch point 10-3 to the combining point 16-3.

The 2 nd optical path 12-3 of the 3 rd mach-zehnder interferometer 4-3 transmits the other of the 2 lights distributed at the branch point 10-3 to the combining point 16-3.

The forward phase signal electrode 13-3 and the reverse phase signal electrode 14-3 are each provided with a wavelength λ corresponding to the continuous light emitted from the light source 1_nA corresponding DC bias.

When a DC bias is applied to the positive-phase signal electrode 13-3, the DC bias is superimposed on the light transmitted through the 1 st optical path 11-3.

The inverted signal electrode 14-3, when given a DC bias, causes the DC bias to overlap with the light transmitted through the 2 nd optical path 12-3.

The phase adjustment electrode 15-3 offsets the phase outputted from the phase offset search section 50Overlapping the light transmitted through the 1 st optical path 11-3.

The photodetector 21-2 detects the combined light emitted from the 1 st output port 17-2 of the 2 nd mach-zehnder interferometer 4-2.

The photodetector 21-2 converts a 2 nd intensity signal I indicating the intensity of the detected combined light_PD2(t) is output to the phase offset search unit 50.

The optical detector 21-3 detects the combined light emitted from the 1 st output port 17-3 of the 3 rd mach-zehnder interferometer 4-3.

The photodetector 21-3 converts a 3 rd intensity signal I representing the intensity of the detected combined light_PD3(t) is output to the phase offset search unit 50.

The phase offset search unit 50 adjusts the phase offset injected into the 1 st optical path 11-2 of the 2 nd Mach-Zehnder interferometer 4-2And searches for the 2 nd intensity signal I output from the photodetector 21-2_PD2(t) phase offset at minimum value

2 nd intensity signal I_PD2(t) phase offset at minimum valueThe search method of (2) is the same as the phase offset search unit 22 shown in fig. 1, and thus detailed description thereof is omitted.

The phase offset search unit 50 causes the control unit 51 to record the searched phase offsetWith the wavelength lambda of the incident light_nThe group (2).

The phase offset search section 50 adjusts the phase offset injected into the 1 st optical path 11-3 of the 3 rd Mach-Zehnder interferometer 4-3And searches for the 3 rd intensity signal I output from the photodetector 21-3_PD3(t) phase offset at minimum value

3 rd intensity signal I_PD3(t) phase offset at minimum valueThe search method of (2) is the same as the phase offset search unit 22 shown in fig. 1, and thus detailed description thereof is omitted.

The phase offset search unit 50 causes the control unit 51 to record the searched phase offsetWith the wavelength lambda of the incident light_nThe group (2).

The phase offset search unit 50 adjusts the phase offset injected into the 2 nd optical path 12-1 of the 1 st Mach-Zehnder interferometer 4-1And searches for the 1 st intensity signal I output from the photodetector 21-1_PD1(t) phase offset at minimum value

The phase offset search section 50 temporarily stores the 1 st intensity signal I_PD1(t) phase offset at minimum value

The phase offset search unit 50 adjusts the phase offset injected into the 2 nd optical path 12-1 of the 1 st Mach-Zehnder interferometer 4-1And searches for the 1 st intensity signal I output from the photodetector 21-1_PD1(t) phase offset at the time of maximum value

The phase offset search section 50 temporarily stores the 1 st intensity signal I_PD1(t) phase offset at the time of maximum value

The phase offset search unit 50 is calculated as shown in the following equation (8)Calculating temporarily saved phase offsetsPhase offset from temporary holdPhase offset of 1/2 of the sum

The phase offset search unit 50 causes the control unit 51 to record the calculated phase offsetWith the wavelength lambda of the incident light_nThe group (2).

Next, the operation of the 1 st Mach-Zehnder interferometer 4-1, the 2 nd Mach-Zehnder interferometer 4-2, and the 3 rd Mach-Zehnder interferometer 4-3 in actual use will be described.

In the mach-zehnder interference device 2 shown in fig. 11, the light source 1 and the control unit 51 are supplied with a signal indicating N wavelengths λ₁、…、λ_NWavelength λ used in practical use in (1)_nWavelength information of (2).

The light source 1 displays the wavelength λ indicated by the wavelength information_nThe continuous light (a) is emitted to the optical fiber 3 as the incident light of the 1 st mach-zehnder interferometer 4-1.

The forward phase signal electrodes 13-2 and 13-3 and the reverse phase signal electrodes 14-2 and 14-3 are each provided with a wavelength λ corresponding to the continuous light emitted from the light source 1_nA corresponding DC bias.

When a DC bias is applied to the positive-phase signal electrode 13-2, both the DC bias and the modulation signal are superimposed on the light transmitted through the 1 st optical path 11-2.

When a DC bias is applied to the positive-phase signal electrode 13-3, both the DC bias and the modulation signal are superimposed on the light transmitted through the 1 st optical path 11-3.

When a DC bias is applied to the inverted signal electrode 14-2, both the DC bias and the modulation signal are superimposed on the light transmitted through the 2 nd optical path 12-2.

When a DC bias is applied to the inverted signal electrode 14-3, both the DC bias and the modulation signal are superimposed on the light transmitted through the 2 nd optical path 12-3.

The control section 51 controls the wavelength of the light emitted from the light source based on the N wavelengths λ recorded at the initial setting₁、…、λ_NObtaining the wavelength lambda shown by the wavelength information in the corresponding phase offset_nCorresponding phase offsetAnd wavelength lambda_nCorresponding phase offset And with the wavelength lambda_nCorresponding phase offset

The control section 51 biases the phasePhase offsetAnd phase offsetAnd outputs the result to the phase offset search unit 50.

The phase offset search unit 50 outputs the phase offset from the control unit 51Outputs the phase offset to the phase adjustment electrode 15-2, and offsets the phase output from the control unit 51And outputs the signal to the phase adjustment electrode 15-3.

Further, the phase offset search unit 50 outputs the phase offset from the control unit 51And outputs the signal to the phase adjustment electrode 15-1.

The phase adjustment electrode 15-2 offsets the phase outputted from the phase offset search unit 50Overlapping the light transmitted through the 1 st optical path 11-2.

The photodetector 21-2 detects the combined light emitted from the 1 st output port 17-2 of the 2 nd mach-zehnder interferometer 4-2, and outputs the detected combined light to the combining point 16-1.

The phase adjustment electrode 15-3 offsets the phase outputted from the phase offset search section 50Overlapping the light transmitted through the 1 st optical path 11-3.

The photodetector 21-3 detects the combined light emitted from the 1 st output port 17-3 of the 3 rd Mach-Zehnder interferometer 4-3, and outputs the detected combined light to the phase adjustment electrode 15-1.

The phase adjustment electrode 15-1 offsets the phase outputted from the phase offset search section 50Overlapping the light output from the photodetector 21-3.

The photodetector 21-1 detects the synthesized light emitted from the 1 st output port 17-1 of the 1 st Mach-Zehnder interferometer 4-1, and outputs the detected synthesized light to the outside as output light.

As described above, in the mach-zehnder interference device 2 that performs QPSK, even when the wavelength of incident light changes, a phase offset corresponding to the wavelength of the incident light can be superimposed on the light, as in the case of the mach-zehnder interference device 2 shown in fig. 1.

In the mach-zehnder interferometer 2 shown in fig. 11, the optical detector 21-2 detects the combined light emitted from the 1 st output port 17-2 of the 2 nd mach-zehnder interferometer 4-2, and the optical detector 21-3 detects the combined light emitted from the 1 st output port 17-3 of the 3 rd mach-zehnder interferometer 4-3. The photodetector 21-1 detects the combined light emitted from the 1 st output port 17-1 of the 1 st Mach-Zehnder interferometer 4-1.

However, this is merely an example, and the photodetector 21-2 may detect the combined light emitted from the 2 nd output port 18-2 of the 2 nd Mach-Zehnder interferometer 4-2, and the photodetector 21-3 may detect the combined light emitted from the 2 nd output port 18-3 of the 3 rd Mach-Zehnder interferometer 4-3. The photodetector 21-1 may detect the combined light emitted from the 2 nd output port 18-1 of the 1 st Mach-Zehnder interferometer 4-1. In this case, the phase offset search unit 50 adjusts the phase offset injected into the 1 st optical path 11-2 of the 2 nd Mach-Zehnder interferometer 4-2And searches for the 2 nd intensity signal I output from the photodetector 21-2_PD2(t) phase offset at the time of maximum value In addition, the phase offset search section 50 adjusts the phase offset injected into the 1 st optical path 11-3 of the 3 rd Mach-Zehnder interferometer 4-3And searches for the 3 rd intensity signal I output from the photodetector 21-3_PD3(t) phase offset at the time of maximum value

The phase offset search unit 50 adjusts the phase offset injected into the 2 nd optical path 12-1 of the 1 st Mach-Zehnder interferometer 4-1And searching for a phase offset which becomes 1/2 of the sum of the following two phase offsetsThe two phase offsets are the 1 st intensity signal I output from the photodetector 21-1_PD1(t) phase offset at minimum valueAnd 1 st intensity signal I_PD1(t) phase offset at the time of maximum value

Embodiment 4.

In embodiment 4, a mach-zehnder interferometer 2 that performs dual polarization QPSK (hereinafter referred to as "DP-QPSK") will be described.

Fig. 12 is a configuration diagram showing a mach-zehnder interference device 2 including the optical modulation control device 5 of embodiment 4. In fig. 12, the same reference numerals as those in fig. 1 and 11 denote the same or corresponding parts, and thus, the description thereof will be omitted.

The demultiplexer 61 demultiplexes the continuous light emitted from the light source 1 into an X-polarized wave (1 st polarized wave) and a Y-polarized wave (2 nd polarized wave), outputs the X-polarized wave to the 1 st mach-zehnder interferometer 4-1 via the optical fiber 3a, and outputs the Y-polarized wave to the 4 th mach-zehnder interferometer 4-4 via the optical fiber 3 b.

One end of the optical fiber 3a is connected to the demultiplexer 61, and the other end of the optical fiber 3a is connected to the branch point 10-1 of the 1 st Mach-Zehnder interferometer 4-1.

One end of the optical fiber 3b is connected to the demultiplexer 61, and the other end of the optical fiber 3b is connected to the branch point 10-4 of the 4 th Mach-Zehnder interferometer 4-4.

The 4 th mach-zehnder interferometer 4-4 includes a 5 th mach-zehnder interferometer 4-5 and a 6 th mach-zehnder interferometer 4-6.

The 4 th Mach-Zehnder interferometer 4-4 includes a 1 st optical path 11-4, a 2 nd optical path 12-4, photodetectors 21-5, 21-6, a phase adjustment electrode 15-4, a 1 st output port 17-4, and a 2 nd output port 18-4.

The 4 th mach-zehnder interferometer 4-4 has a branch point 10-4 for dividing incident light into 2 pieces of light, and a combining point 16-4 for combining the 2 pieces of light after division.

The 4 th mach-zehnder interferometer 4-4 distributes incident light into 2 light at the branch point 10-4, combines the distributed 2 light at the combining point 16-4, and emits the combined light of the 2 light to the photodetector 21-4.

The 1 st optical path 11-4 is realized by an optical fiber, for example.

One end of the 1 st optical path 11-4 is connected to the branch point 10-4, and the other end of the 1 st optical path 11-4 is connected to the combining point 16-4.

The 1 st optical path 11-4 transmits one of the 2 lights distributed at the branch point 10-4 to the combining point 16-4 via the 5 th Mach-Zehnder interferometer 4-5.

The 2 nd optical path 12-4 is realized by an optical fiber, for example.

One end of the 2 nd optical path 12-4 is connected to the branch point 10-4, and the other end of the 2 nd optical path 12-4 is connected to the combining point 16-4.

The 2 nd optical path 12-4 transmits the other light of the 2 lights distributed at the branch point 10-4 to the combining point 16-4 via the 6 th Mach-Zehnder interferometer 4-6.

The phase adjusting electrode 15-4 is inserted into the 2 nd optical path 12-4.

The phase adjustment electrode 15-4 offsets the phase outputted from the phase offset search section 62Overlapping the light transmitted through the 2 nd optical path 12-4.

The 1 st output port 17-4 is a port for emitting the combined light to the photodetector 21-4.

The 2 nd output port 18-4 is a port for emitting light in the opposite phase to the combined light.

In the mach-zehnder interference device 2 shown in fig. 12, the light emitted from the 2 nd output port 18-4 is not used.

The 5 th Mach-Zehnder interferometer 4-5 includes a 1 st optical path 11-5, a 2 nd optical path 12-5, a normal phase signal electrode 13-5, a reverse phase signal electrode 14-5, a phase adjustment electrode 15-5, a 1 st output port 17-5, and a 2 nd output port 18-5.

The 5 th Mach-Zehnder interferometer 4-5 has a branch point 10-5 for dividing incident light into 2 light beams and a combining point 16-5 for combining the 2 divided light beams.

The 5 th mach-zehnder interferometer 4-5 distributes incident light into 2 pieces of light at a branch point 10-5, combines the distributed 2 pieces of light at a combining point 16-5, and emits the combined light of the 2 pieces of light to a photodetector 21-5.

The positive phase signal electrode 13-5 is inserted into the 1 st optical path 11-5.

The positive-phase signal electrode 13-5 superimposes a DC bias corresponding to the wavelength of incident light on the light transmitted through the 1 st optical path 11-5.

In the initial setting of the 5 th mach-zehnder interferometer 4-5, the normal-phase signal electrode 13-5 superimposes only the DC bias on the light, and does not superimpose the modulation signal on the light.

In actual operation of the 5 th mach-zehnder interferometer 4-5 after the initial setting is completed, the normal-phase signal electrode 13-5 superimposes both the DC bias and the modulation signal on the light.

Inverted signal electrode 14-5 is inserted into optical path 2 12-5.

The inverted signal electrode 14-5 superimposes a DC bias corresponding to the wavelength of the incident light on the light transmitted through the 2 nd optical path 12-5.

In the initial setting of the 5 th mach-zehnder interferometer 4-5, the inverted signal electrode 14-5 superimposes only the DC bias on the light and does not superimpose the modulation signal on the light.

In actual use after the initial setting of the 5 th mach-zehnder interferometer 4-5 is completed, the inverted signal electrode 14-5 superimposes both the DC bias and the modulation signal on the light.

The phase adjusting electrode 15-5 is inserted into the 1 st optical path 11-5.

The phase adjustment electrode 15-5 offsets the phase outputted from the phase offset search section 62Superimposed on the light transmitted through the 1 st optical path 11-5。

The 1 st output port 17-5 is a port for emitting the combined light to the photodetector 21-5.

The 2 nd output port 18-5 is a port for emitting light in the opposite phase to the combined light.

In the mach-zehnder interference device 2 shown in fig. 12, the light emitted from the 2 nd output port 18-5 is not used.

The 6 th Mach-Zehnder interferometer 4-6 includes a 1 st optical path 11-6, a 2 nd optical path 12-6, a normal phase signal electrode 13-6, a reverse phase signal electrode 14-6, a phase adjustment electrode 15-6, a 1 st output port 17-6, and a 2 nd output port 18-6.

The 6 th Mach-Zehnder interferometer 4-6 has a branch point 10-6 for dividing incident light into 2 light beams and a combining point 16-6 for combining the 2 divided light beams.

The 6 th mach-zehnder interferometer 4-6 distributes incident light into 2 light at the branch point 10-6, combines the distributed 2 light at the combining point 16-6, and emits the combined light of the 2 light to the photodetector 21-6.

The positive phase signal electrode 13-6 is inserted into the 1 st optical path 11-6.

The positive phase signal electrode 13-6 superimposes a DC bias corresponding to the wavelength of the incident light on the light transmitted through the 1 st optical path 11-6.

In the initial setting of the 6 th mach-zehnder interferometer 4-6, the normal-phase signal electrode 13-6 superimposes only the DC bias on the light, and does not superimpose the modulation signal on the light.

In actual operation after the initial setting of the 6 th mach-zehnder interferometer 4-6 is completed, the normal phase signal electrode 13-6 superimposes both the DC bias and the modulation signal on the light.

Inverted signal electrode 14-6 is inserted into optical path 2 12-6.

The inverted signal electrode 14-6 superimposes a DC bias corresponding to the wavelength of the incident light on the light transmitted through the 2 nd optical path 12-6.

In the initial setting of the 6 th Mach-Zehnder interferometer 4-6, the inverted signal electrode 14-6 superimposes only the DC bias on the light and does not superimpose the modulation signal on the light.

In actual use after the initial setting of the 6 th Mach-Zehnder interferometer 4-6 is completed, the inverted signal electrode 14-6 superimposes both the DC bias and the modulation signal on the light.

The phase adjusting electrode 15-6 is inserted into the 1 st optical path 11-6.

The phase adjustment electrode 15-6 offsets the phase outputted from the phase offset search section 50Overlapping the light transmitted through the 1 st optical path 11-6.

The 1 st output port 17-6 is a port for emitting the combined light to the photodetector 21-6.

The 2 nd output port 18-6 is a port for emitting light in the opposite phase to the combined light.

In the mach-zehnder interference device 2 shown in fig. 12, the light emitted from the 2 nd output port 18-6 is not used.

The light detector 21-5 is realized by a photodiode, for example.

The optical detector 21-5 is connected to the 1 st output port 17-5 of the 5 th mach-zehnder interferometer 4-5.

The photodetector 21-5 detects the combined light emitted from the 1 st output port 17-5, and outputs a 5 th intensity signal I representing the intensity of the detected combined light_PD5(t) is output to the phase offset search unit 62.

Further, the photodetector 21-5 outputs the detected combined light to the 1 st optical path 11-4.

The light detector 21-6 is realized by a photodiode, for example.

The optical detector 21-6 is connected to the 1 st output port 17-6 of the 6 th mach-zehnder interferometer 4-6.

The photodetector 21-6 detects the combined light emitted from the 1 st output port 17-6, and outputs a 6 th intensity signal I representing the intensity of the detected combined light_PD6(t) is output to the phase offset search unit 62.

The photodetector 21-6 outputs the detected combined light to the phase adjustment electrode 15-4.

The light detector 21-4 is realized by a photodiode, for example.

The optical detector 21-4 is connected to the 1 st output port 17-4 of the 4 th mach-zehnder interferometer 4-4.

The photodetector 21-4 detects the combined light emitted from the 1 st output port 17-4, and outputs a 4 th intensity signal I indicating the intensity of the detected combined light_PD4(t) is output to the phase offset search unit 62.

The photodetector 21-4 outputs the detected combined light to the outside as outgoing light.

The phase offset search unit 62 adjusts the phase offset injected into the 1 st optical path 11-2 of the 2 nd Mach-Zehnder interferometer 4-2And searches for the 2 nd intensity signal I output from the photodetector 21-2_PD2(t) phase offset at minimum value

The phase offset search unit 62 causes the control unit 63 to record the searched phase offsetWith the wavelength lambda of the incident light_nThe group (2).

The phase offset search unit 62 adjusts the phase offset injected into the 1 st optical path 11-3 of the 3 rd Mach-Zehnder interferometer 4-3And searches for the 3 rd intensity signal I output from the photodetector 21-3_PD3(t) phase offset at minimum value

The phase offset search unit 62 causes the control unit 63 to record the searched phase offsetWith the wavelength lambda of the incident light_nThe group (2).

The phase offset search unit 62 adjusts the phase offset injected into the 2 nd optical path 12-1 of the 1 st Mach-Zehnder interferometer 4-1Device for placingAnd searching for a phase offset which becomes 1/2 of the sum of the following two phase offsetsThe two phase offsets are the 1 st intensity signal I output from the photodetector 21-1_PD1(t) phase offset at minimum valueAnd 1 st intensity signal I_PD1(t) phase offset at the time of maximum value

The phase offset search unit 62 causes the control unit 63 to record the searched phase offsetWith the wavelength lambda of the incident light_nThe group (2).

The phase offset search unit 62 adjusts the phase offset injected into the 1 st optical path 11-5 of the 5 th Mach-Zehnder interferometer 4-5And searches for the 5 th intensity signal I output from the photodetector 21-5_PD5(t) phase offset at minimum value

The phase offset search unit 62 causes the control unit 63 to record the searched phase offsetWith the wavelength lambda of the incident light_nThe group (2).

The phase offset search unit 62 adjusts the phase offset injected into the 1 st optical path 11-6 of the 6 th Mach-Zehnder interferometer 4-6And searches for the 6 th intensity signal I output from the photodetector 21-6_PD6(t) phase offset at minimum value

The phase offset search unit 62 causes the control unit 63 to record the searched phase offsetWith the wavelength lambda of the incident light_nThe group (2).

The phase offset search unit 62 adjusts the phase offset injected into the 2 nd optical path 12-4 of the 4 th Mach-Zehnder interferometer 4-4And searching for a phase offset which becomes 1/2 of the sum of the following two phase offsetsThe two phase offsets are the 4 th intensity signal I output from the photodetector 21-4_PD4(t) phase offset at minimum valueAnd 4 th intensity signal I_PD4(t) phase offset at the time of maximum value

The phase offset search unit 62 causes the control unit 63 to record the searched phase offsetWith the wavelength lambda of the incident light_nThe group (2).

The control section 63 determines the wavelength λ of the incident light_nPhase offsetPhase offsetPhase offsetPhase offsetPhase offsetAnd phase offset The group (2).

The control unit 63 controls the wavelength λ of the Mach-Zehnder interferometer 4-1 during actual use_nCorresponding phase offsetAnd outputs the result to the phase offset search unit 62.

The control unit 63 controls the wavelength λ of the Mach-Zehnder interferometer 4-2 during actual use_nCorresponding phase offsetAnd outputs the result to the phase offset search unit 62.

The control unit 63 controls the wavelength λ of the 3 rd Mach-Zehnder interferometer 4-3 during actual use_nCorresponding phase offsetAnd outputs the result to the phase offset search unit 62.

The control unit 63 controls the wavelength λ of the Mach-Zehnder interferometer 4-4 during actual use_nCorresponding phase offsetAnd outputs the result to the phase offset search unit 62.

The control unit 63 controls the wavelength λ of the Mach-Zehnder interferometer 4-5 during actual use_nCorresponding phase offsetAnd outputs the result to the phase offset search unit 62.

The control unit 63 controls the wavelength λ of the Mach-Zehnder interferometer 4-6 during actual use_nCorresponding phase offsetAnd outputs the result to the phase offset search unit 62.

Next, the operation of the mach-zehnder interference device 2 shown in fig. 12 will be described.

First, the operation at the time of initial setting will be described.

The operation of the 4 th Mach-Zehnder interferometer 4-4 is similar to the operation of the 1 st Mach-Zehnder interferometer 4-1, and the operation of the 5 th Mach-Zehnder interferometer 4-5 is similar to the operation of the 2 nd Mach-Zehnder interferometer 4-2.

The operation of the 6 th Mach-Zehnder interferometer 4-6 is the same as that of the 3 rd Mach-Zehnder interferometer 4-3.

Therefore, the detailed operations of the 4 th Mach-Zehnder interferometer 4-4, the 5 th Mach-Zehnder interferometer 4-5, and the 6 th Mach-Zehnder interferometer 4-6 are omitted.

The phase offset search unit 62 adjusts the phase offset injected into the 1 st optical path 11-2 of the 2 nd Mach-Zehnder interferometer 4-2, similarly to the phase offset search unit 50 shown in FIG. 11And searches for the 2 nd intensity signal I output from the photodetector 21-2_PD2(t) phase offset at minimum value

The phase offset search unit 62 records the searched phase offset in the control unit 63Device for placingWith the wavelength lambda of the incident light_nThe group (2).

The phase offset search unit 62 adjusts the phase offset injected into the 1 st optical path 11-3 of the 3 rd Mach-Zehnder interferometer 4-3, similarly to the phase offset search unit 50 shown in FIG. 11And searches for the 3 rd intensity signal I output from the photodetector 21-3_PD3(t) phase offset at minimum value

The phase offset search unit 62 causes the control unit 63 to record the searched phase offsetWith the wavelength lambda of the incident light_nThe group (2).

The phase offset search unit 62 adjusts the phase offset injected into the 2 nd optical path 12-1 of the 1 st Mach-Zehnder interferometer 4-1 in the same manner as the phase offset search unit 50 shown in FIG. 11And searches for the 1 st intensity signal I output from the photodetector 21-1_PD1(t) phase offset at minimum value

The phase offset search unit 62 temporarily stores the 1 st intensity signal I_PD1(t) phase offset at minimum value

The phase offset search unit 62 adjusts injection into the 2 nd optical path 12-1Phase offset ofAnd searches for the 1 st intensity signal I output from the photodetector 21-1_PD1(t) phase offset at the time of maximum value

The phase offset search unit 62 temporarily stores the 1 st intensity signal I_PD1(t) phase offset at the time of maximum value

The phase offset search unit 62 calculates the phase offset temporarily stored as shown in equation (8)Phase offset from temporary holdPhase offset of 1/2 of the sum

The phase offset search unit 62 causes the control unit 63 to record the calculated phase offsetWith the wavelength lambda of the incident light_nThe group (2).

The phase offset search unit 62 adjusts the phase offset injected into the 1 st optical path 11-5 of the 5 th Mach-Zehnder interferometer 4-5And searches for the 5 th intensity signal I output from the photodetector 21-5_PD5(t) phase offset at minimum value

The phase offset search unit 62 causes the control unit 63 to record the searched phase offsetWith the wavelength lambda of the incident light_nThe group (2).

The phase offset search unit 62 adjusts the phase offset injected into the 1 st optical path 11-6 of the 6 th Mach-Zehnder interferometer 4-6And searches for the 6 th intensity signal I output from the photodetector 21-6_PD6(t) phase offset at minimum value

The phase offset search unit 62 causes the control unit 63 to record the searched phase offsetWith the wavelength lambda of the incident light_nThe group (2).

The phase offset search unit 62 adjusts the phase offset injected into the 2 nd optical path 12-4 of the 4 th Mach-Zehnder interferometer 4-4And searches for the 4 th intensity signal I output from the photodetector 21-4_PD4(t) phase offset at minimum value

The phase offset search unit 62 temporarily stores the 4 th intensity signal I_PD4(t) phase offset at minimum value

The phase offset search unit 62 adjusts the phase offset injected into the 2 nd optical path 12-4And searches for the 4 th intensity signal I output from the photodetector 21-4_PD4(t) phase offset at the time of maximum value

The phase offset search unit 62 temporarily stores the 4 th intensity signal I_PD4(t) phase offset at the time of maximum value

The phase offset search unit 62 calculates the phase offset temporarily stored as shown in the following expression (9)Phase offset from temporary holdPhase offset of 1/2 of the sum

The phase offset search unit 62 causes the control unit 63 to record the calculated phase offsetWith the wavelength lambda of the incident light_nThe group (2).

Next, the operation in actual use will be described.

In the mach-zehnder interference device 2 shown in fig. 12, the light source 1 and the control unit 63 are supplied with a signal indicating N wavelengths λ₁、…、λ_NWavelength λ used in practical use in (1)_nWavelength information of (2).

The light source 1 displays the wavelength λ indicated by the wavelength information_nThe continuous light is emitted toward the optical fiber 3.

The forward phase signal electrodes 13-2 and 13-3 and the reverse phase signal electrodes 14-2 and 14-3 are each provided with a wavelength λ corresponding to the continuous light emitted from the light source 1_nA corresponding DC bias.

When a DC bias is applied to the positive-phase signal electrode 13-2, both the DC bias and the modulation signal are superimposed on the light transmitted through the 1 st optical path 11-2.

When a DC bias is applied to the positive-phase signal electrode 13-3, both the DC bias and the modulation signal are superimposed on the light transmitted through the 1 st optical path 11-3.

When a DC bias is applied to the inverted signal electrode 14-2, both the DC bias and the modulation signal are superimposed on the light transmitted through the 2 nd optical path 12-2.

When a DC bias is applied to the inverted signal electrode 14-3, both the DC bias and the modulation signal are superimposed on the light transmitted through the 2 nd optical path 12-3.

The forward phase signal electrodes 13-5 and 13-6 and the reverse phase signal electrodes 14-5 and 14-6 are each provided with a wavelength λ corresponding to the continuous light emitted from the light source 1_nA corresponding DC bias.

When a DC bias is applied to the positive-phase signal electrode 13-5, both the DC bias and the modulation signal are superimposed on the light transmitted through the 1 st optical path 11-5.

When a DC bias is applied to the positive-phase signal electrode 13-6, both the DC bias and the modulation signal are superimposed on the light transmitted through the 1 st optical path 11-6.

When a DC bias is applied to the inverted signal electrode 14-5, both the DC bias and the modulation signal are superimposed on the light transmitted through the 2 nd optical path 12-5.

When a DC bias is applied to the inverted signal electrode 14-6, both the DC bias and the modulation signal are superimposed on the light transmitted through the 2 nd optical path 12-6.

The control section 63 performs the initial settingTime-recorded with N wavelengths lambda₁、…、λ_NObtaining the wavelength lambda shown by the wavelength information in the corresponding phase offset_nCorresponding phase offsetAnd wavelength lambda_nCorresponding phase offset And with the wavelength lambda_nCorresponding phase offset

The control section 63 biases the phasePhase offsetAnd phase offsetAnd outputs the result to the phase offset search unit 62.

The phase offset search unit 62 outputs the phase offset from the control unit 63Outputs the phase of the signal to the phase adjustment electrode 15-2, and biases the phase output from the control unit 63And outputs the signal to the phase adjustment electrode 15-3.

Further, the phase offset search unit 62 outputs the phase offset from the control unit 63And outputs the signal to the phase adjustment electrode 15-1.

The control section 63 records the data from the N wavelengths λ recorded at the initial setting₁、…、λ_NObtaining the wavelength lambda shown by the wavelength information in the corresponding phase offset_nCorresponding phase offsetAnd wavelength lambda_nCorresponding phase offset And with the wavelength lambda_nCorresponding phase offset

The control section 63 biases the phasePhase offsetAnd phase offsetAnd outputs the result to the phase offset search unit 62.

The phase offset search unit 62 outputs the phase offset from the control unit 63Outputs the phase of the signal to the phase adjusting electrode 15-5, and biases the phase output from the control unit 63And outputs to the phase adjusting electrode 15-6.

Further, the phase offset search unit 62 outputs the phase offset from the control unit 63And outputs to the phase adjustment electrode 15-4.

The phase adjustment electrode 15-2 offsets the phase outputted from the phase offset search unit 62Overlapping the light transmitted through the 1 st optical path 11-2.

The photodetector 21-2 detects the combined light emitted from the 1 st output port 17-2 of the 2 nd mach-zehnder interferometer 4-2, and outputs the detected combined light to the combining point 16-1.

The phase adjustment electrode 15-3 offsets the phase outputted from the phase offset search section 62Overlapping the light transmitted through the 1 st optical path 11-3.

The photodetector 21-3 detects the combined light emitted from the 1 st output port 17-3 of the 3 rd Mach-Zehnder interferometer 4-3, and outputs the detected combined light to the phase adjustment electrode 15-1.

The phase adjustment electrode 15-1 offsets the phase outputted from the phase offset search unit 62Overlapping the light output from the photodetector 21-3.

The photodetector 21-1 detects the synthesized light emitted from the 1 st output port 17-1 of the 1 st Mach-Zehnder interferometer 4-1, and outputs the detected synthesized light to the outside as output light.

The phase adjustment electrode 15-5 offsets the phase outputted from the phase offset search section 62Overlapping the light transmitted through the 1 st optical path 11-5.

The photodetector 21-5 detects the combined light emitted from the 1 st output port 17-5 of the 5 th mach-zehnder interferometer 4-5, and outputs the detected combined light to the combining point 16-4.

The phase adjustment electrode 15-6 offsets the phase outputted from the phase offset search section 62Overlapping the light transmitted through the 1 st optical path 11-6.

The photodetector 21-6 detects the combined light emitted from the 1 st output port 17-6 of the 6 th mach-zehnder interferometer 4-6, and outputs the detected combined light to the phase adjustment electrode 15-4.

The phase adjustment electrode 15-4 offsets the phase outputted from the phase offset search section 62Overlapping the light output from the light detector 21-6.

The photodetector 21-4 detects the combined light emitted from the 1 st output port 17-4 of the 4 th mach-zehnder interferometer 4-4, and outputs the detected combined light to the outside as output light.

In the mach-zehnder interferometer 2 shown in fig. 12, the optical detector 21-2 detects the combined light emitted from the 1 st output port 17-2 of the 2 nd mach-zehnder interferometer 4-2, the optical detector 21-3 detects the combined light emitted from the 1 st output port 17-3 of the 3 rd mach-zehnder interferometer 4-3, and the optical detector 21-1 detects the combined light emitted from the 1 st output port 17-1 of the 1 st mach-zehnder interferometer 4-1.

The optical detector 21-5 detects the combined light emitted from the 1 st output port 17-5 of the 5 th Mach-Zehnder interferometer 4-5, the optical detector 21-6 detects the combined light emitted from the 1 st output port 17-6 of the 6 th Mach-Zehnder interferometer 4-6, and the optical detector 21-4 detects the combined light emitted from the 1 st output port 17-4 of the 4 th Mach-Zehnder interferometer 4-4.

However, this is merely an example, and the photodetector 21-2 may detect the combined light emitted from the 2 nd output port 18-2 of the 2 nd Mach-Zehnder interferometer 4-2, the photodetector 21-3 may detect the combined light emitted from the 2 nd output port 18-3 of the 3 rd Mach-Zehnder interferometer 4-3, and the photodetector 21-1 may detect the combined light emitted from the 2 nd output port 18-1 of the 1 st Mach-Zehnder interferometer 4-1.

Further, the optical detector 21-5 may detect the combined light emitted from the 2 nd output port 18-5 of the 5 th Mach-Zehnder interferometer 4-5, the optical detector 21-6 may detect the combined light emitted from the 2 nd output port 18-6 of the 6 th Mach-Zehnder interferometer 4-6, and the optical detector 21-4 may detect the combined light emitted from the 2 nd output port 18-4 of the 4 th Mach-Zehnder interferometer 4-4.

In this case, the phase offset search section 62 searches for the 2 nd intensity signal I output from the photodetector 21-2_PD2(t) phase offset at the time of maximum valueIn addition, the phase offset search section 62 searches for the 3 rd intensity signal I output from the photodetector 21-3_PD3(t) phase offset at the time of maximum valueThe phase offset search unit 62 searches for a phase offset that is 1/2 of the sum of the following two phase offsets The two phase offsets are the 1 st intensity signal I output from the photodetector 21-1_PD1(t) phase offset at minimum valueAnd 1 st intensity signal I_PD1(t) phase offset at the time of maximum value

In addition, the phase offset search section 62 searches for the 5 th intensity signal I output from the photodetector 21-5_PD5(t) phase offset at the time of maximum valueIn addition, the phase offset search section 62 searches for the 6 th intensity signal I output from the photodetector 21-6_PD6(t) phase offset at the time of maximum valueThe phase offset search unit 62 searches for a phase offset that is 1/2 of the sum of the following two phase offsetsThe two phase offsets are the 4 th intensity signal I output from the photodetector 21-4_PD4(t) phase offset at minimum valueAnd 4 th intensity signal I_PD4(t) phase offset at the time of maximum value

As described above, in the mach-zehnder interference device 2 that performs DP-QPSK, as in the mach-zehnder interference device 2 shown in fig. 1, even if the wavelength of incident light changes, a phase offset corresponding to the wavelength of the incident light can be superimposed on the light.

In the present invention, the optional combinations of the respective embodiments, modifications of arbitrary components of the respective embodiments, or omission of arbitrary components in the respective embodiments can be made within the scope of the present invention.

Industrial applicability

The present invention is suitable for an optical modulation control device and a Mach-Zehnder interferometer for searching for a phase offset.

Description of the reference symbols

1 light source, 2 Mach-Zehnder interferometer, 3 optical fiber, 4 Mach-Zehnder interferometer, 4-1 st Mach-Zehnder interferometer, 4-2 nd Mach-Zehnder interferometer, 4-3 rd Mach-Zehnder interferometer, 4-4 th Mach-Zehnder interferometer, 4-5 th Mach-Zehnder interferometer, 4-6 th Mach-Zehnder interferometer, 5 optical modulation control device, 10-1, 10-2, 10-3, 10-4, 10-5, 10-6 branch point, 11-1, 11-2, 11-3, 11-4, 11-5, 11-6 1 st optical path, 12-1, 12-2, 12-3, 12-4, 12-5, 12-6 nd 2 nd optical path, 13-1, 13, 13-2, 13-3, 13-4, 13-5, 13-6 positive phase signal electrodes, 14-1, 14-2, 14-3, 14-4, 14-5, 14-6 negative phase signal electrodes, 15a, 15b, 15-1, 15-2, 15-3, 15-4, 15-5, 15-6 phase adjusting electrodes, 16-1, 16-2, 16-3, 16-4, 16-5, 16-6 synthetic points, 17-1, 17-2, 17-3, 17-4, 17-5, 17-6 1 st output port, 18-1, 18-2, 18-3, 18-4, 18-5, 18-6 nd output port, 21. 21-1, 21-2, 21-3, 21-4, 21-5, 21-6 photo detectors, 22 phase offset search section, 23 delay, 24 amplifier, 25 comparator, 25a input terminal, 25b inverting input terminal, 26 phase offset adjustment section, 27 phase offset recording section, 28 control section, 29 photo detectors, 31 phase offset adjustment circuit, 32 phase offset recording circuit, 33 control circuit, 41 memory, 42 processor, 50 phase offset search section, 51 control section, 61 demultiplexer, 62 phase offset search section, 63 control section.