阅读说明：本技术 光学发送设备、光学接收设备和光学通信方法 (Optical transmission apparatus, optical reception apparatus, and optical communication method ) 是由 村木弘法 于 2019-02-05 设计创作，主要内容包括：[问题]为了提供一种能够用来在接收侧执行稳定的相干检测并且能够用来维持接收信号质量的光学发送设备。[解决方案]一种光学发送设备被配置为包括：光输出装置(1)；光调制装置(2)；接收信息获取装置(3)；和频率调整装置(4)。光输出装置(1)输出分配给光学发送设备的频率的光。光调制装置(2)将由光输出装置(1)输出的光分离成相互正交的偏振波,对每个偏振波的同相分量和正交分量执行调制,并且输出通过对调制的分量波进行偏振波合成而获得的光学信号。接收信息获取装置(3)在用作光学信号的发送目的地的光学接收设备中获取光学信号的接收状态的信息。频率调整装置(4)基于接收状态信息来控制由光输出装置(1)输出的光的频率,并且调整作为当光学接收设备执行光学信号的相干检测时使用的本地发射光的频率与由光输出装置(1)输出的光的频率之间的差的频率偏移。([ problem ] to provide an optical transmission device that can be used to perform stable coherent detection on the reception side and that can be used to maintain the quality of a received signal. [ solution ] an optical transmission device is configured to include: a light output device (1); a light modulation device (2); a reception information acquisition device (3); and a frequency adjusting device (4). The optical output device (1) outputs light of a frequency assigned to the optical transmission apparatus. The optical modulation device (2) separates light output by the optical output device (1) into mutually orthogonal polarized waves, performs modulation on an in-phase component and an orthogonal component of each polarized wave, and outputs an optical signal obtained by polarization-wave-combining the modulated component waves. A reception information acquisition means (3) acquires information of the reception state of an optical signal in an optical reception device serving as the transmission destination of the optical signal. The frequency adjusting means (4) controls the frequency of the light output by the light output means (1) based on the reception state information, and adjusts a frequency offset that is a difference between the frequency of the locally emitted light used when the optical receiving apparatus performs coherent detection of the optical signal and the frequency of the light output by the light output means (1).)

1. An optical transmission apparatus comprising:

a light output device for outputting light of a frequency assigned to the optical transmission apparatus;

an optical modulation device for separating the light output by the optical output device into mutually orthogonal polarized waves, modulating an in-phase component and an orthogonal component in each of the polarized waves, and outputting an optical signal obtained by polarization-combining the modulated component waves;

reception information acquisition means for acquiring information on a reception state of the optical signal in an optical reception apparatus as a transmission destination of the optical signal; and

frequency adjustment means for controlling a frequency of light to be output by the optical output means based on the information on the reception state, and adjusting a frequency offset that is a difference between the frequency of the light output by the optical output means and a frequency of local oscillation light used in coherent detection of the optical signal by the optical reception apparatus.

2. The optical transmitting apparatus of claim 1, wherein

The reception information acquisition means acquires information on the number of errors in the optical signal as the information on the reception state, and

the frequency adjusting means controls the frequency of the light to be output by the light output means in such a manner as to minimize the number of errors.

3. The optical transmitting apparatus of claim 1, further comprising

A frequency measuring device for measuring a frequency of the optical signal output from the optical modulating device, wherein

The reception information acquisition means acquires information on the frequency of the local oscillation light from the optical reception device, and

the frequency adjusting means controls the frequency of the light to be output by the light output means based on the frequency of the optical signal measured by the frequency measuring means and the frequency of the local oscillation light acquired by the reception information acquiring means in such a manner that the frequency offset becomes a preset value.

4. The optical transmitting apparatus of claim 1, wherein

The reception information acquisition means acquires information indicating a difference between the frequency of the optical signal received from the optical reception device and the frequency of the local oscillation light, and

the frequency adjusting means controls the frequency of the light to be output by the light output means based on the difference between the frequency of the optical signal received from the optical receiving device acquired by the reception information acquiring means and the frequency of the local oscillation light in such a manner that the frequency offset becomes a preset value.

5. An optical receiving apparatus comprising:

a local oscillation optical output device for outputting local oscillation light whose frequency is set based on a frequency of an optical signal obtained by modulating an in-phase component and a quadrature component in each of the quadrature polarized waves by the optical transmission apparatus;

optical signal receiving means for combining the optical signal with the local oscillation light and converting the combined signal into an electrical signal;

demodulation means for performing demodulation processing based on the electrical signal converted by the optical signal reception means; and

a local oscillation light adjustment means for controlling a frequency of light to be output by the local oscillation light output means based on information on a reception state of the optical signal, and adjusting a frequency offset that is a difference between the frequency of the optical signal and the frequency of the local oscillation light output by the local oscillation light output means.

6. The optical receiving device of claim 5, wherein

The local oscillation light adjustment means controls the frequency of the local oscillation light to be output by the local oscillation light output means in such a manner as to minimize the number of errors detected by the demodulation means.

7. The optical receiving device of claim 5, further comprising:

a local oscillation light measuring device for measuring a frequency of the local oscillation light output from the local oscillation light output device; and

transmission information acquisition means for acquiring information on the frequency of the optical signal from the optical transmission device, wherein

The local oscillation light adjustment device controls the frequency of the local oscillation light to be output by the local oscillation light output device based on the frequency of the local oscillation light measured by the local oscillation light measurement device and the frequency of the optical signal acquired by the transmission information acquisition device so that the frequency offset becomes a preset value.

8. The optical receiving device of claim 5, wherein

The local oscillation light adjustment means controls the frequency of the light to be output by the local oscillation light output means based on a difference between the frequency of the optical signal detected by the demodulation means and the frequency of the local oscillation light in such a manner that the frequency offset becomes a value set in advance.

9. An optical communication system comprising:

the optical transmission device according to any one of claims 1 to 4; and

the optical receiving device of claim 5, wherein

The frequency adjusting means of the optical transmission apparatus adjusts a frequency offset, which is a difference from the frequency of the light output by the light output means, based on the information on the reception state of the optical signal acquired from the optical reception apparatus.

10. An optical communication method, comprising:

outputting light of a frequency assigned to the own device;

separating the output light into polarized waves orthogonal to each other, modulating an in-phase component and an orthogonal component in each of the polarized waves, and outputting an optical signal obtained by polarization-synthesizing the modulated component waves;

acquiring information on a reception state of the optical signal in an optical receiving apparatus as a transmission destination of the optical signal; and

controlling a frequency of the light to be output based on the information on the reception state, and adjusting a frequency offset, which is a difference between the frequency of the light to be output and a frequency of local oscillation light used in coherent detection of the optical signal by the optical reception apparatus.

11. The optical communication method of claim 10, wherein:

acquiring information on the number of errors in the optical signal as the information on the reception state when acquiring the information on the reception state; and

when controlling the frequency of the light to be output, the frequency of the light to be output is controlled in such a manner that the number of errors is minimized.

12. The optical communication method of claim 10, further comprising:

measuring a frequency of the output optical signal, wherein:

acquiring information on a frequency of the local oscillation light from the optical reception device when acquiring the information on the reception state; and

when controlling the frequency of the light to be output, the frequency of the light to be output is controlled so that the frequency offset becomes a preset value, based on the measured frequency of the optical signal and the acquired frequency of the local oscillation light.

13. The optical communication method of claim 10, wherein:

acquiring information indicating a difference between a sum of a frequency of the optical signal received from the optical reception device and a frequency of the local oscillation light when the information on the reception state is acquired; and

when controlling the frequency of the light to be output, the frequency of the light to be output is controlled in such a manner that the frequency offset becomes a value set in advance, based on the acquired difference between the frequency of the optical signal received from the optical receiving device and the frequency of the local oscillation light.

14. The optical communication method according to any one of claims 10 to 13, further comprising:

outputting the local oscillation light, a frequency of which is set based on a frequency of an optical signal obtained by modulating an in-phase component and a quadrature component in each of the quadrature polarized waves by the optical transmission apparatus;

combining the received optical signal with the local oscillating light and converting the combined signal into an electrical signal;

performing demodulation processing based on the converted electric signal;

controlling a frequency of the local oscillation light to be output based on information on a reception state of the optical signal; and

adjusting a frequency offset that is a difference between a frequency of the optical signal and a frequency of the local oscillation light.

Technical Field

The present invention relates to an optical communication technique of a digital coherent scheme, and more particularly to a technique for maintaining reception quality.

Background

A digital coherent optical communication scheme is used as an optical communication technology capable of high-speed and large-capacity transmission. For the digital coherent optical communication scheme, various modulation schemes such as a polarization multiplexing scheme and a multi-stage modulation scheme have been proposed. As the multi-level modulation scheme, for example, Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), 8 quadrature amplitude modulation (8QAM), or the like is used.

In the digital coherent scheme, a baseband signal is generated by multiplying a received optical signal by output light (local oscillation light) from a local oscillator. The original transmission signal is reproduced by analog-to-digital converting a baseband signal and performing digital signal processing. Therefore, in order to maintain the reception quality, it is necessary to stably perform coherent detection of the optical signal. As such a technique for stably performing coherent detection of an optical signal and maintaining signal quality, for example, a technique as in patent document 1 is disclosed.

Patent document 1 relates to an optical transmission apparatus of a digital coherent scheme. The optical transmission device in patent document 1 adjusts the wavelength and power of the local oscillation light in such a manner as to improve the signal quality of the received signal, and controls the wavelength of the local oscillation light in such a manner that no wavelength difference is generated between the optical signal and the local oscillation light. Patent document 1 having such a configuration can realize high-precision optical signal reception performance. Similarly, patent documents 2 and 3 also disclose a technique related to an optical transmission device of a digital coherent scheme.

[ list of references ]

[ patent document ]

[ patent document 1] Japanese unexamined patent application publication No.2015-

[ patent document 2] International publication WO 2012/132374

[ patent document 3] Japanese unexamined patent application publication No.2015-

Disclosure of Invention

[ problem ] to

However, the technique in patent document 1 is insufficient in the following points. In the case where coherent detection is performed on the reception side, when the frequency of the optical signal coincides with the frequency of the local oscillation light, the symbol may be fixed to the in-phase (I) axis or the quadrature (Q) axis. In such a case, when the gain is automatically controlled in such a manner that the output amplitude becomes constant in the optical signal detection element, since the input signal is not present in the 0 component of the component in a state of being fixed to the shaft, the gain may be set large so as to increase the output amplitude. When the gain is set large, noise in the signal increases, and degradation in the quality of the signal occurs. Similarly, the techniques in patent documents 2 and 3 are also insufficient as a technique for preventing quality degradation of a signal. Therefore, the techniques in patent documents 1, 2, and 3 are insufficient as techniques for maintaining reception quality with which stable reception processing can be performed in an optical communication system of a digital coherent scheme.

In order to solve the above-described problems, an object of the present invention is to provide an optical transmission apparatus capable of maintaining reception quality with which stable reception processing can be performed.

[ solution of problem ]

In order to solve the above problem, an optical transmission apparatus according to the present invention includes a light output device, a light modulation device, a reception information acquisition device, and a frequency adjustment device. The light output means outputs light of a frequency assigned to the optical transmission device. The optical modulation device separates light output by the optical output device into mutually orthogonal polarized waves, modulates an in-phase component and an orthogonal component in each of the polarized waves, and outputs an optical signal obtained by polarization-combining the modulated component waves. The reception information acquisition means acquires information on a reception state of an optical signal in an optical reception device as a transmission destination of the optical signal. The frequency adjusting means controls the frequency of the light to be output by the optical output means based on the information on the reception state, and adjusts a frequency offset, which is a difference between the frequency of the local oscillation light used in coherent detection of the optical signal by the optical receiving apparatus and the frequency of the light output by the optical output means.

The optical communication method according to the present exemplary embodiment includes: outputting light of a frequency assigned to the own device; separating the output light into polarized waves orthogonal to each other; modulating an in-phase component and a quadrature component in each of the polarized waves; and outputting an optical signal obtained by polarization-synthesizing the modulated component waves. The optical communication method according to the present exemplary embodiment includes: information on a reception state of an optical signal in an optical receiving apparatus as a transmission destination of the optical signal is acquired. The optical communication method according to the present exemplary embodiment includes: controlling a frequency of light to be output based on the information on the reception state; and adjusting a frequency offset that is a difference between a frequency of the local oscillation light used in coherent detection of the optical signal by the optical receiving apparatus and a frequency of the light to be output.

[ advantageous effects of the invention ]

The present invention enables stable coherent detection on the receiving side and can maintain the quality of the received signal.

Drawings

Fig. 1 is a diagram illustrating an outline of a configuration according to a first exemplary embodiment of the present invention.

Fig. 2 is a diagram illustrating an outline of a configuration according to a second exemplary embodiment of the present invention.

Fig. 3 is a diagram illustrating a configuration of an optical transmission apparatus according to a second exemplary embodiment of the present invention.

Fig. 4 is a diagram illustrating a configuration of an optical receiving apparatus according to a second exemplary embodiment of the present invention.

Fig. 5 is a diagram illustrating an operation flow of an optical communication system according to a second exemplary embodiment of the present invention.

Fig. 6 is a diagram illustrating an example of a result of measuring the number of errors per frequency offset according to the second exemplary embodiment of the present invention.

Fig. 7 is a diagram illustrating an example of a frame transmitted in an example of another configuration according to a second exemplary embodiment of the present invention.

Fig. 8 is a diagram illustrating an example of a constellation in a multi-level modulation scheme.

Fig. 9 is a diagram illustrating an example of shifting of constellations in a multi-level modulation scheme.

Fig. 10 is a diagram illustrating an outline of a configuration according to a third exemplary embodiment of the present invention.

Fig. 11 is a diagram illustrating a configuration of an optical transmission apparatus according to a third exemplary embodiment of the present invention.

Fig. 12 is a diagram illustrating a configuration of an optical receiving apparatus according to a third exemplary embodiment of the present invention.

Fig. 13 is a diagram illustrating an outline of a configuration according to a fourth exemplary embodiment of the present invention.

Fig. 14 is a diagram illustrating a configuration of an optical transmission apparatus according to a fourth exemplary embodiment of the present invention.

Fig. 15 is a diagram illustrating a configuration of an optical receiving apparatus according to a fourth exemplary embodiment of the present invention.

Fig. 16 is a diagram illustrating an operation flow of an optical communication system according to a fourth exemplary embodiment of the present invention.

Fig. 17 is a diagram illustrating an outline of a configuration according to a fifth exemplary embodiment of the present invention.

Fig. 18 is a diagram illustrating a configuration of an optical transmission apparatus according to a fifth exemplary embodiment of the present invention.

Fig. 19 is a diagram illustrating a configuration of an optical receiving apparatus according to a fifth exemplary embodiment of the present invention.

Fig. 20 is a diagram illustrating an outline of a configuration according to a sixth exemplary embodiment of the present invention.

Fig. 21 is a diagram illustrating a configuration of an optical transmission apparatus according to a sixth exemplary embodiment of the present invention.

Fig. 22 is a diagram illustrating a configuration of an optical receiving apparatus according to a sixth exemplary embodiment of the present invention.

Fig. 23 is a diagram illustrating an operation flow of an optical communication system according to a sixth exemplary embodiment of the present invention.

Fig. 24 is a diagram illustrating an outline of a configuration according to a seventh exemplary embodiment of the present invention.

Fig. 25 is a diagram illustrating a configuration of an optical transmission device according to a seventh exemplary embodiment of the present invention.

Fig. 26 is a diagram illustrating a configuration of an optical receiving apparatus according to a seventh exemplary embodiment of the present invention.

Detailed Description

(first exemplary embodiment)

A first exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings. Fig. 1 illustrates an outline of a configuration of an optical transmission apparatus according to the present exemplary embodiment. The optical transmission apparatus according to the present exemplary embodiment includes: an optical output device 1, an optical modulation device 2, a reception information acquisition device 3, and a frequency adjustment device 4. The light output device 1 outputs light of a frequency assigned to its own apparatus. The optical modulation device 2 separates light output by the optical output device 1 into mutually orthogonal polarized waves, modulates an in-phase component and an orthogonal component in each of the polarized waves, and outputs an optical signal obtained by polarization-combining the modulated component waves. The reception information acquiring means 3 acquires information on the reception state of the optical signal in the optical receiving apparatus as the transmission destination of the optical signal. The frequency adjusting means 4 controls the frequency of the light output by the optical output apparatus 1 based on the information on the reception state, and adjusts a frequency offset which is a difference between the frequency of the local oscillation light used in coherent detection of the optical signal by the optical receiving device and the frequency of the light output by the optical output apparatus 1.

In the optical transmission apparatus according to the present exemplary embodiment, the reception information acquiring means 3 acquires information on the reception state of the optical reception apparatus, and the frequency adjusting means 4 adjusts the frequency offset which is the difference between the frequency of the light output by the light output means 1 and the frequency of the local oscillation light of the optical reception apparatus. In the optical transmission apparatus according to the present exemplary embodiment, by adding an offset to the frequency of the light output by the optical output device 1 and the frequency of the local oscillation light, a component whose output amplitude is 0 is not generated in the signal detection element of the optical reception apparatus. This can prevent a state where noise is generated in the signal in order to increase the gain in the optical receiving apparatus, and therefore, the reception quality can be maintained. Therefore, the use of the optical transmission device according to the present exemplary embodiment enables stable coherent detection on the reception side and can maintain the quality of the reception signal.

(second example embodiment)

A second exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings. Fig. 2 is a diagram illustrating an outline of the configuration of an optical communication system according to the present exemplary embodiment. The optical communication system according to the present exemplary embodiment includes an optical transmission device 10 and an optical reception device 20. The optical transmission apparatus 10 and the optical reception apparatus 20 are connected to each other via a communication channel 201 and a communication channel 202. The optical communication system according to the present exemplary embodiment is a network system that performs optical communication of a digital coherent scheme between the optical transmission apparatus 10 and the optical reception apparatus 20 via the communication channel 201.

The configuration of the optical transmission device 10 will be described. Fig. 3 illustrates the configuration of the optical transmission device 10 according to the present exemplary embodiment. The optical transmission device 10 includes a client signal input unit 11, a signal processing unit 12, a signal modulation unit 13, a light source unit 14, and a frequency adjustment unit 15.

The client signal input unit 11 is an input port for a client signal transmitted via the communication channel 201. The client signal input to the client signal input unit 11 is sent to the signal processing unit 12.

The signal processing unit 12 performs processing such as redundancy processing on the input client signal, and maps the client signal on a frame for transmission through the communication channel 201.

The signal modulation unit 13 modulates the light input from the light source unit 14 based on the signal input from the signal processing unit 12, and generates an optical signal to be transmitted to the communication channel 201. The signal modulation unit 13 according to the present exemplary embodiment performs modulation by using, for example, a Binary Phase Shift Keying (BPSK) modulation scheme. The modulation scheme may be another multi-level modulation scheme other than BPSK, such as Quadrature Phase Shift Keying (QPSK) or 8 quadrature amplitude modulation (8 QAM). The signal modulation unit 13 according to the present exemplary embodiment functions as the light modulation device 2 according to the first exemplary embodiment.

The light source unit 14 outputs continuous light of a predetermined frequency to the signal modulation unit 13. The predetermined frequency is assigned based on the wavelength design of the optical communication network. By setting the predetermined frequency to the set value, the light source unit 14 outputs light having a frequency added to the offset of the set value. The frequency offset is controlled by the frequency adjustment unit 15. The light source unit 14 according to the present exemplary embodiment functions as the light output device 1 according to the first exemplary embodiment.

The frequency adjustment unit 15 controls the frequency shift amount of the light source unit 14. The frequency adjustment unit 15 controls the frequency offset amount based on the error information transmitted from the optical reception device 20. The frequency adjustment unit 15 controls the frequency offset so as to reduce the Bit Error Rate (BER) transmitted as error information. The frequency adjustment device 4 according to the present exemplary embodiment functions as the reception information acquisition device 3 and the frequency adjustment device 4 according to the first exemplary embodiment.

The configuration of the optical receiving apparatus 20 will be described. Fig. 4 illustrates the configuration of the optical receiving apparatus 20 according to the present exemplary embodiment. The optical receiving apparatus 20 includes a client signal output unit 21, a PBS22, a 90-degree mixer 23, and a light detection unit 24. The optical receiving device 20 further includes an analog-to-digital converter (ADC)25, a Digital Signal Processor (DSP)26, a local oscillation optical output unit 27, and an error detection unit 28.

The client signal output unit 21 is an output port for outputting the demodulated client signal.

A Polarization Beam Splitter (PBS)22 polarization-separates an input optical signal and outputs it. PBS22 includes PBS 22-1 that polarization-separates the optical signal and PBS 22-2 that polarization-separates the local oscillator light. The PBS 22-1 performs polarization separation on the optical signal input from the communication channel 201, outputs an X-polarized wave to the 90-degree mixer 23-1, and transmits a Y-polarized wave to the 90-degree mixer 23-2. The PBS 22-2 performs polarization separation on the light input from the local oscillation light output unit 27, outputs an X-polarized wave to the 90-degree mixer 23-1, and transmits a Y-polarized wave to the 90-degree mixer 23-2.

The 90-degree mixer 23 combines the input optical signal with the local oscillation light through two paths having phases different by 90 degrees. The 90-degree mixer 23-1 combines the X-polarized wave component of the optical signal input from the PBS 22-1 with the X-polarized wave component of the local oscillation light input from the PBS 22-2 through two paths that are 90 degrees out of phase with each other.

The 90-degree mixer 23-1 transmits signals of an in-phase (I) component and a quadrature (Q) component generated by combining an optical signal with local oscillation light via paths whose phases are different by 90 degrees to the light detection unit 24-1. The 90-degree hybrid 23-2 combines the Y-polarized wave component of the optical signal input from the PBS 22-1 and the Y-polarized wave component of the local oscillation light input from the PBS 22-2 through two paths that are 90 degrees out of phase with each other. The 90-degree mixer 23-2 transmits signals of I and Q components generated by combining the optical signal with the local oscillation light via paths different in phase by 90 degrees to the light detection unit 24-2.

The light detection unit 24 converts the input optical signal into an electrical signal, and outputs the electrical signal. The light detection unit 24 is configured by using a photodiode. The light detection unit 24-1 converts the optical signals of the X-polarized I and Q components input from the 90-degree mixer 23-1 into electrical signals, and transmits the electrical signals to the ADC 25-1. The light detection unit 24-2 converts the optical signals of the Y-polarized I and Q components input from the 90-degree mixer 23-2 into electrical signals, and sends the electrical signals to the ADC 25-2.

The ADC25 converts the input analog signal into a digital signal. The ADC 25-1 converts an analog signal input from the light detection unit 24-1 into a digital signal and transmits the digital signal to the DSP 26. The ADC25-2 converts an analog signal input from the light detection unit 24-2 into a digital signal and transmits the digital signal to the DSP 26.

The DSP26 demodulates the client signal by performing reception processing of the output signal such as distortion correction, decoding, and error correction. The DSP26 is configured by a semiconductor device. The receive processing functions of the DSP26 may be configured by using a Field Programmable Gate Array (FPGA). The reception processing function of the DSP26 may be performed by executing a computer program by a general-purpose processor such as a Central Processing Unit (CPU). The DSP26 sends the demodulated client signal to the client signal output unit 21.

The local oscillation light output unit 27 generates local oscillation light which is combined with the optical signal transmitted via the communication channel 201 and used when generating an optical signal of an intermediate frequency. The local oscillation light output unit 27 includes a semiconductor laser, and outputs light of a frequency set based on the frequency of the optical signal transmitted via the communication channel 201.

The error detection unit 28 monitors the error correction processing performed by the DSP26, and measures the number of errors. The error detection unit 28 according to the present exemplary embodiment calculates a BER based on the measured number of errors, and transmits information about the calculated BER as error information to the optical transmission apparatus 10 via the communication channel 202. The error detection unit 28 may be integrated with the DSP26 as part of the DSP 26.

The communication channel 201 is configured as an optical communication network using optical fibers. The communication channel 201 transmits an optical signal in a direction from the optical transmission apparatus 10 to the optical reception apparatus 20. The communication channel 202 is a communication network through which control signals and the like are transmitted from the optical reception apparatus 20 to the optical reception apparatus. The communication channel 202 is included as a line for controlling the device by a communication management system, for example.

The operation of the optical communication system according to the present exemplary embodiment will be described. First, a client signal to be transmitted through the communication channel 201 is input to the client signal input unit 11. As the client signal, for example, a signal of a Synchronous Optical Network (SONET), an ethernet (registered trademark), a Fiber Channel (FC), an Optical Transport Network (OTN), or the like is used. The client signal input to the client signal input unit 11 is sent to the signal processing unit 12.

Upon input of the client signal, the signal processing unit 12 maps the client signal on a frame for transmission through the communication channel 201. When mapping is performed, the signal processing unit 12 sends the mapped signal to the signal modulation unit 13.

When inputting a signal based on the data of the frame on which the mapping is performed, the signal modulation unit 13 modulates the light output from the light source unit 14 based on the data of the frame input from the signal processing unit 12. The signal modulation unit 13 performs conversion from an electric signal into an optical signal by using the BPSK scheme. The signal modulation unit 13 transmits an optical signal generated by modulation to the communication channel 201.

The optical signal transmitted to the communication channel 201 is transmitted through the communication channel 201, and is transmitted to the optical reception device 20. The optical signal received by the optical receiving device 20 is input to the PBS 22-1. Upon input of the optical signal, PBS22 polarization-separates the input optical signal, sends an X-polarized optical signal to 90-degree hybrid 23-1, and sends a Y-polarized optical signal to 90-degree hybrid 23-2.

When an optical signal is input from PBS 22-1, 90-degree mixers 23-1 and 23-2 combine the optical signal input from PBS 22-1 with local oscillation light input from PBS 22-2, and generate signals of intermediate frequencies associated with I and Q components. The 90-degree mixers 23-1 and 23-2 transmit the generated optical signals of the intermediate frequency to the light detection units 24-1 and 24-2.

When an optical signal is input, the light detection unit 24-1 and the light detection unit 24-2 convert the input optical signal into an electrical signal and transmit the electrical signal to the ADC 25-1 and the ADC 25-2. When the electric signal converted from the optical signal is input, the ADC 25-1 and the ADC25-2 convert the input signal into a digital signal and transmit the digital signal to the DSP 26.

When a signal is input to the DSP26, the DSP26 demodulates the client signal by performing reception processing on the input signal, and sends the demodulated client signal to the client signal output unit 21. The client signal output unit 21 outputs the input client signal to the communication network and the communication device.

When the reception processing is performed by the DSP26, the error detection unit 28 monitors the error correction processing performed by the DSP26, and measures the number of errors in the received signal. The error detection unit 28 according to the present exemplary embodiment calculates the number of errors as BER. When the BER is calculated, the error detection unit 28 transmits information about the calculated BER to the optical transmission apparatus 10 as error information via the communication channel 202.

The error information received by the optical transmission apparatus 10 via the communication channel 202 is transmitted to the frequency adjustment unit 15. Upon receiving the error information, the frequency adjustment unit 15 adjusts the frequency offset of the light source unit 14 in such a manner as to reduce the BER value. The frequency adjustment unit 15 changes the frequency offset based on the change in BER and controls the frequency offset in such a manner as to minimize the BER. The light source unit 14 outputs light of a frequency having the corrected offset amount to the signal modulation unit 13.

The operation when the frequency of the light output by the light source unit 14 is adjusted by the optical transmission device 10 will be described in more detail. Fig. 5 illustrates an operation flow when the frequency of light output by the light source unit 14 is adjusted.

First, the frequency adjustment unit 15 sets a search range of the frequency offset, that is, a range for changing the amount of frequency offset in the case of finding the frequency to be output by the light source unit 14 when the number of errors is minimum (step S11). The search range of the frequency offset may be stored in the frequency adjusting unit 15 in advance, or the set value of the search range may be input by an operator or the like.

When the search range of the frequency offset is set, the frequency adjustment unit 15 sets the frequency offset ofs (i.e., the amount of deviation from the set value of the frequency of the light output from the light source unit 14) to 0 (step S12). When ofs is 0, the light source unit 14 outputs a set value, that is, light of a frequency assigned to its own apparatus.

The frequency adjustment unit 15 extracts information on the error number from the error information received from the optical reception apparatus 20, and substitutes the error number in the case where ofs is 0 into the minimum value ofs _ err _ best of the error (step S13). The frequency adjustment unit 15 substitutes the value of the set frequency offset ofs into ofs _ best indicating information on the frequency offset associated with the data substituted into the minimum value ofs _ err _ best (step S14). When the error number in the case where ofs is 0 is substituted into ofs _ err _ best, then ofs _ best is established as 0.

When storing the error number in the case where the frequency offset is 0, the frequency adjustment unit 15 sets the set value of the frequency offset ofs to min, that is, the minimum value min of the search range of the frequency offset (step S15).

When the value of the frequency offset ofs is set, the frequency adjusting unit 15 compares the set value of the frequency offset ofs with the maximum value ofs _ max of the search range of the frequency offset. When the frequency offset ofs is equal to or smaller than the maximum value ofs _ max (no in step S16), the frequency adjustment unit 15 corrects the frequency of the light source based on the frequency offset ofs. The frequency adjustment unit 15 calculates the frequency to be output by the light source unit 14 and sets the frequency to be output by the light source unit 14 as the frequency of the light source + ofs (step S17).

When the frequency of the light source unit 14 is set based on the frequency offset ofs, light having a frequency offset from the set value by a certain amount is output from the light source unit 14. When light having an offset frequency is output to the communication channel 201, information on the number of errors is transmitted from the optical reception device 20 as a transmission destination.

Upon receiving the information on the error number, the frequency adjustment unit 15 substitutes the error number into ofs _ err (step S18), and compares the received error number ofs _ err with ofs _ err _ best stored as the minimum value so far. When the number of newly received errors is small (yes in step S19), the frequency adjustment unit 15 updates the number of errors ofs _ err _ best with the value of the newly received error number ofs _ err (step S20). When the ofs _ err _ best is updated, the frequency adjustment unit 15 substitutes the value of the frequency offset ofs into the ofs _ best indicating information on the frequency offset associated with the minimum value ofs _ err _ best (step S21).

When the information on the frequency offset associated with the minimum value ofs _ err _ best is updated, the frequency adjustment unit 15 changes the frequency offset ofs to ofs + Δ f (step S22), and performs an operation from step S16 onward. Δ f, which is an amount for changing the frequency offset, is set in advance. Δ f may be set by dividing the search range of the frequency offset by a preset number.

When the newly received error number is equal to or larger than the hitherto minimum value (no in step S19), the frequency adjustment unit 15 changes the frequency offset ofs to ofs + Δ f (step S22), and performs an operation from step S16.

In step S16, when the frequency offset ofs is larger than the maximum value ofs _ max of the search range (yes in step S16), the frequency adjustment unit 15 sets the frequency of the light source unit 14 to the frequency associated with the minimum value ofs _ err _ best. The frequency adjustment unit 15 calculates the frequency of the light source as the frequency of the light source + ofs _ best, and controls the frequency of the signal to be output by the light source unit 14 so that the frequency becomes the calculated frequency (step S23).

Fig. 6 is a diagram illustrating an example of the relationship between the frequency offset amount and the error number. In the example in fig. 6, the error number is measured by changing the frequency offset for Δ f. In the example in fig. 6, minus 3 Δ f having the smallest number of errors is set as the amount of shift with respect to the frequency of light output by the light source unit 14.

In the optical communication system according to the present exemplary embodiment, error information is transmitted from the optical reception apparatus 20 to the optical transmission apparatus 10 via the communication channel 202. However, when bidirectional optical communication is performed, error information may be added to a frame to be transmitted as a main signal from the optical reception apparatus 20 to the optical transmission apparatus 10. Fig. 7 illustrates a configuration of an OTN frame. For example, when data communication using an OTN frame as in fig. 7 is performed, error information can be transmitted from the optical reception apparatus 20 to the optical transmission apparatus 10 by adding the error information to the reserved bits in the overhead. Such a configuration eliminates the need to communicate using the communication channel 202, thereby simplifying the configuration.

Fig. 8 is a diagram illustrating a constellation when a BPSK modulation scheme and a QPSK modulation scheme are used. In the constellation in fig. 8, the sign of the signal is plotted on a plane, where the I-axis represents the phase component in phase with the carrier and the Q-axis represents the phase component in quadrature with the carrier. In the case of a BPSK modulation scheme, symbols are mapped on the I axis. Therefore, when the frequency offset of the optical signal and the local oscillation light is small from (it produces a state on the left side in fig. 8), the Q component of the optical signal becomes 0. In this state, when the gain is automatically controlled so as to reach a constant output amplitude of the light detection unit 24, no signal is input to Q-ch to which the signal having the Q component is input, and therefore, the output amplitude does not increase when the Q-ch signal is amplified. Therefore, in order to increase the output amplitude of the Q-ch signal, the gain is set large, a noise component is added to Q-ch, and degradation in signal quality occurs.

On the other hand, when a frequency offset is generated between the light source of the optical signal and the light source of the local oscillation light, the constellation rotates as illustrated in fig. 9. In the BPSK scheme illustrated in fig. 8, only the I-axis component is given. However, by intentionally generating the frequency offset, not only the I-axis component but also the Q-axis component can have a value. By giving the Q-axis component, an appropriate gain is set, so that noise in the signal is prevented from becoming too large, and degradation of the signal quality can be prevented.

In the optical communication system according to the present exemplary embodiment, the frequency adjustment unit 15 in the optical transmission device 10 adjusts the frequency of light to be output from the light source unit 14 based on the error information detected by the error detection unit 28 in the optical reception device 20. By adjusting the frequency in such a manner as to reduce the number of errors, an appropriate offset can be added to the frequency of the optical signal transmitted from the optical transmission device 10 and the frequency of the local oscillation light used in the detection of the received signal performed by the optical reception device 20. Therefore, the optical communication system according to the present exemplary embodiment can suppress the influence of noise generated in the reception signal and can maintain the reception quality.

(third exemplary embodiment)

An optical communication system according to a third exemplary embodiment of the present invention will be described. Fig. 10 illustrates an outline of the configuration of an optical communication system according to the present exemplary embodiment. The optical communication system according to the present exemplary embodiment includes an optical transmission device 30 and an optical reception device 40. The optical transmission apparatus 30 and the optical reception apparatus 40 are connected to each other via a communication channel 201.

The optical communication system according to the present exemplary embodiment is a network system that performs optical communication of a digital coherent scheme via the communication channel 201 similarly to the second exemplary embodiment. In the optical communication network according to the second exemplary embodiment, the offset amount of the frequency of the light source of the optical transmission apparatus is adjusted. In contrast, the optical communication network according to the present exemplary embodiment is characterized in that the offset amount of the frequency of the local oscillation light of the optical reception device is adjusted.

The configuration of the optical transmission device 30 will be described. Fig. 11 illustrates a configuration of the optical transmission device 30 according to the present exemplary embodiment. The optical transmission device 30 includes a client signal input unit 11, a signal processing unit 12, a signal modulation unit 13, and a light source unit 31. The configurations and functions of the client signal input unit 11, the signal processing unit 12, and the signal modulation unit 13 according to the present exemplary embodiment are similar to those of the same-name units according to the second exemplary embodiment.

The light source unit 31 has a function similar to that of the light source unit 14 according to the second exemplary embodiment, in addition to the function of shifting the frequency of light to be output. In other words, the light source unit 31 includes a semiconductor laser, and outputs continuous light of a predetermined frequency to the signal modulation unit 13. The predetermined frequency is assigned based on a wavelength design of the optical communication network.

The configuration of the optical receiving apparatus 40 will be described. Fig. 12 illustrates the configuration of the optical receiving apparatus 40 according to the present exemplary embodiment. The optical receiving device 40 includes a client signal output unit 21, a PBS22, a 90-degree mixer 23, a light detection unit 24, an ADC25, a DSP26, a local oscillation light output unit 41, an error detection unit 42, and a frequency adjustment unit 43.

The configurations and functions of the client signal output unit 21, PBS22, 90-degree mixer 23, light detection unit 24, ADC25, and DSP26 according to the present exemplary embodiment are similar to those of the same-name unit according to the second exemplary embodiment. In other words, as the PBS22, a PBS 22-1 that polarization-separates an optical signal input via the communication channel 201 and a PBS 22-2 that polarization-separates local oscillation light are included. Including a 90-degree mixer 23-1, a photodetection unit 24-1, and an ADC 25-1 that process signals of X-polarized waves, and including a 90-degree mixer 23-2, a photodetection unit 24-2, and an ADC25-2 that process signals of Y-polarized waves.

The local oscillation light output unit 41 generates local oscillation light of a predetermined frequency, which is combined with the optical signal transmitted via the communication channel 201 and used in generating an optical signal of an intermediate frequency. The local oscillation light output unit 41 is configured by using a semiconductor laser. The predetermined frequency is set based on the frequency of the optical signal transmitted via the communication channel 201. The local oscillation light output unit 41 outputs light having a frequency added to the offset of the predetermined frequency. The frequency offset is controlled by the frequency adjustment unit 43.

The error detection unit 42 has a function similar to that of the error detection unit 28 according to the second exemplary embodiment. The error detection unit 42 according to the present exemplary embodiment monitors the signal reception processing performed by the DSP26, and measures the error number based on the error number correction. The error detection unit 42 transmits error information calculated based on the result of the measurement error to the frequency adjustment unit 43 in its own device. The error detection unit 42 according to the present exemplary embodiment transmits the BER to the frequency adjustment unit 43 as error information. The error detection unit 42 may be integrated with the DSP26 as part of the DSP 26.

The frequency adjustment unit 43 controls the offset amount of the frequency of the local oscillation light output unit 41. The frequency adjusting unit 43 controls the frequency offset amount based on the error information transmitted from the error detecting unit 42. The frequency adjustment unit 43 controls the frequency offset so as to reduce the BER transmitted as error information.

The operation of the optical communication system according to the present exemplary embodiment will be described. The optical communication system according to the present exemplary embodiment operates similarly to the optical communication system according to the second exemplary embodiment with respect to operations other than adjusting the frequency offset of the optical signal and the local oscillation light. In the optical communication system according to the present exemplary embodiment, the frequency offset of the optical signal and the local oscillation light is adjusted based on the detection result of the number of errors performed by the optical receiving apparatus 40. In other words, in the optical communication system according to the present exemplary embodiment, the frequency adjusting unit 43 in the optical receiving apparatus 40 changes the offset amount according to the set value of the frequency of the local oscillation light output from the local oscillation light output unit 41, and controls the frequency of the local oscillation light based on the offset amount when the number of errors is smallest.

The optical communication system according to the present exemplary embodiment has similar advantageous effects to the optical communication system according to the second exemplary embodiment. Since the frequency of the local oscillation light is adjusted on the optical receiving apparatus 40 side based on the error number, it is not necessary to transmit the error number to the optical transmitting apparatus 30, and therefore, the configuration of the system can be further simplified.

(fourth example embodiment)

A fourth exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings. Fig. 13 illustrates an outline of the configuration of an optical communication system according to the present exemplary embodiment. The optical communication system according to the present exemplary embodiment includes an optical transmission device 50 and an optical reception device 60. The optical transmission apparatus 50 and the optical reception apparatus 60 are connected via a communication channel 201 and a communication channel 202.

The optical communication system according to the present exemplary embodiment is a network system that performs optical communication of a digital coherent scheme via the communication channel 201 similarly to the second exemplary embodiment. In the optical communication system according to the second exemplary embodiment, the frequency offset of the optical signal and the local oscillation light is adjusted by adjusting the optical signal in such a manner that the number of errors is minimized. The optical communication system according to the present exemplary embodiment is characterized in that, instead of such a configuration, the frequency of the optical signal is monitored, and the frequency of the light output from the light source unit is adjusted in such a manner that the frequency offset of the optical signal and the local oscillation light becomes a set value.

The configuration of the optical transmission device 50 will be described. Fig. 14 illustrates the configuration of the optical transmission device 50 according to the present exemplary embodiment. The optical transmission device 50 includes a client signal input unit 11, a signal processing unit 12, a signal modulation unit 13, a light source unit 14, a frequency monitoring unit 51, and a frequency adjustment unit 52.

The configurations and functions of the client signal input unit 11, the signal processing unit 12, the signal modulation unit 13, and the light source unit 14 according to the present exemplary embodiment are similar to those of the same-name unit according to the second exemplary embodiment.

The frequency monitoring unit 51 has a function of measuring the frequency of the output signal of the signal modulation unit 13. For example, the output signal of the signal modulation unit 13 is input to the frequency monitoring unit 51 by being branched by an optical coupler. The frequency monitoring unit 51 transmits information on the frequency of the output signal of the signal modulation unit 13 to the frequency adjustment unit 52.

The frequency adjustment unit 52 controls the offset value of the frequency of the light output by the light source unit 14 based on the frequency of the output signal transmitted from the frequency monitoring unit 51 and the frequency of the local oscillation light transmitted from the optical reception device 60 via the communication channel 202. The frequency adjustment unit 52 monitors the difference between the frequency of the output signal transmitted from the frequency monitoring unit 51 and the frequency of the local oscillation light transmitted from the optical receiving device 60. The frequency adjustment unit 52 controls the amount of shift in the frequency of the light to be output by the light source unit 14 based on the set value of the frequency shift set in such a manner that the frequency shift does not become 0.

The configuration of the optical receiving apparatus 60 will be described. Fig. 15 illustrates a configuration of an optical receiving apparatus 60 according to the present exemplary embodiment. The optical reception device 60 includes a client signal output unit 21, PBS22, 90-degree mixer 23, light detection unit 24, ADC25, DSP26, local oscillation light output unit 27, and frequency monitoring unit 61.

The client signal output unit 21, the PBS22, the 90-degree mixer 23, the light detection unit 24, the ADC25, the DSP26, and the local oscillation light output unit 27 according to the present exemplary embodiment are similar in configuration and function to the same-named units according to the second exemplary embodiment. In other words, as the PBS22, a PBS 22-1 that polarization-separates an optical signal input via the communication channel 201 and a PBS 22-2 that polarization-separates local oscillation light are included. Including a 90-degree mixer 23-1, a light detection unit 24-1, and an ADC 25-1 that process X-polarized waves, and including a 90-degree mixer 23-2, a light detection unit 24-2, and an ADC25-2 that process Y-polarized waves.

The frequency monitoring unit 61 has a function of measuring the frequency of the output light of the local oscillation light output unit 27. The output light of the local oscillation light output unit 27 is input to the frequency monitoring unit 61 by being branched by, for example, an optical coupler. The frequency monitoring unit 61 transmits information on the frequency of the output light of the local oscillation light output unit 27 to the frequency adjusting unit 52 in the optical transmission apparatus 50 via the communication channel 202.

The operation of the optical communication system according to the present exemplary embodiment will be described. The optical communication system according to the present exemplary embodiment operates similarly to the optical communication system according to the second exemplary embodiment with respect to operations other than adjusting the frequency offset of the optical signal and the local oscillation light.

An operation of adjusting the frequency to be output by the light source unit 14 by the optical transmission device 50 according to the present exemplary embodiment will be described. Fig. 16 illustrates an operation flow of adjusting the frequency of light to be output by the light source unit 14.

First, the frequency adjustment unit 52 sets the frequency offset target ofs _ target (step S31). The frequency offset target ofs _ target indicates a target of a difference between the frequency of the light output by the light source unit 14 and the frequency of the light output by the local oscillation light output unit 41. The frequency offset target ofs _ target is stored in advance in the frequency adjustment unit 52. The set value of the frequency offset target ofs _ target may be input by an operator or the like.

When the frequency offset target ofs _ target is set, the frequency adjustment unit 52 calculates the frequency offset sig _ ofs of the optical signal, that is, the difference between the frequency of the optical signal actually output and the frequency setting value of the optical signal (step S32). The frequency adjusting unit 52 calculates the frequency offset sig _ ofs of the optical signal based on the result of monitoring the frequency of the optical signal transmitted from the frequency monitoring unit 51. The frequency adjustment unit 52 calculates the frequency offset of the optical signal as a frequency offset sig _ ofs, which is a monitored value of the frequency of the optical signal — a frequency set value of the optical signal.

When the frequency offset of the optical signal is calculated, the frequency adjustment unit 52 calculates the frequency offset lo _ ofs of the local oscillation light, that is, the difference between the frequency of the local oscillation light actually output by the optical receiving apparatus 60 and the frequency setting value of the local oscillation light (step S33). The frequency adjusting unit 52 calculates the frequency offset lo _ ofs of the local oscillation light based on the result of monitoring the frequency of the local oscillation light transmitted from the frequency monitoring unit 61 via the communication channel 202. The frequency adjusting unit 52 calculates the frequency offset of the local oscillation light as a frequency offset lo _ ofs, which is a frequency set value of the local oscillation light as a result of monitoring the frequency of the local oscillation light.

When the frequency offsets of the optical signal and the local oscillation light are calculated, the frequency adjustment unit 52 calculates the frequency offsets total _ ofs of the optical signal and the local oscillation light (step S34). The frequency adjusting unit 52 calculates the frequency offset of the optical signal and the local oscillation light by using the frequency offset total _ ofs — the frequency offset of the optical signal sig _ ofs — the frequency offset of the local oscillation light lo _ ofs.

When the frequency difference of the optical signal and the local oscillation light, that is, the frequency offset is calculated, the frequency adjustment unit 52 checks the plus/minus of the frequency offset target ofs _ target, and determines the coefficient SIGN for use in calculating the correction amount diff of the frequency of the light output by the light source unit 14.

When the value of the frequency offset target ofs _ target is equal to or greater than 0 (yes in step S35), the frequency adjusting unit 52 sets the coefficient SIGN to +1 (step S36). When the value of the frequency offset target ofs _ target is less than 0 (no in step S35), the frequency adjusting unit 52 sets the coefficient SIGN to-1 (step S39).

When the coefficient SIGN for use in calculating the correction amount diff of the frequency of the light output by the light source unit 14 is determined, the frequency adjustment unit 52 calculates the correction amount diff of the frequency shift (step S37). The frequency adjustment unit 52 calculates the correction amount diff as diff ═ SIGN × ofs _ target-SIGN × total _ ofs.

When the correction amount diff of the frequency is calculated, the frequency adjustment unit 52 calculates the frequency of the light to be output by the light source unit 14 as the frequency set value + SIGN × diff (step S37). When the frequency of light to be output by the light source unit 14 is calculated, the frequency adjustment unit 52 controls the light source unit 14 in such a manner as to output light of the calculated frequency.

In the optical communication system according to the present exemplary embodiment, the frequencies of the optical signal and the local oscillation light are monitored, and the frequency adjustment unit 52 controls the frequency of the light to be output from the light source unit 14 in such a manner that the frequency offset, which is the frequency difference between the optical signal and the local oscillation light, becomes a set value. By keeping the frequencies of the optical signal and the local oscillation light at set values other than 0 and giving a frequency offset between the optical signal and the local oscillation light in such a manner, noise generated in the Q-ch signal can be prevented. Therefore, the optical communication system according to the present exemplary embodiment can suppress the influence of noise generated in the reception signal and can maintain the reception quality.

(fifth exemplary embodiment)

A fifth exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings. Fig. 17 illustrates an outline of the configuration of an optical communication system according to the present exemplary embodiment. The optical communication system according to the present exemplary embodiment includes an optical transmission device 70 and an optical reception device 80. The optical transmission device 70 and the optical reception device 80 are connected via a communication channel 201 and a communication channel 203. The communication channel 203 is a communication network through which a control signal or the like is transmitted from the optical transmission apparatus 70 to the optical reception apparatus 80.

The optical communication system according to the present exemplary embodiment is a network system that performs optical communication of a digital coherent scheme via the communication channel 201 similarly to the second exemplary embodiment. The optical communication system according to the present exemplary embodiment is characterized in that the frequency of the local oscillation light of the optical reception device 80 is controlled based on the result of measuring the frequencies of the optical signal and the local oscillation light so that the frequency offset of the optical signal and the local oscillation light becomes a set value.

The configuration of the optical transmission device 70 will be described. Fig. 18 illustrates a configuration of an optical transmission device 70 according to the present exemplary embodiment. The optical transmission device 70 includes a client signal input unit 11, a signal processing unit 12, a signal modulation unit 13, a light source unit 71, and a frequency monitoring unit 72. The configurations and functions of the client signal input unit 11, the signal processing unit 12, and the signal modulation unit 13 according to the present exemplary embodiment are similar to those of the same-name units according to the second exemplary embodiment.

The light source unit 71 has a function similar to that of the light source unit 14 according to the second exemplary embodiment, in addition to the function of shifting the frequency of light to be output. In other words, the light source unit 71 includes a semiconductor laser, and outputs continuous light of a predetermined frequency to the signal modulation unit 13. The predetermined frequency is assigned based on a wavelength design of the optical communication network.

The frequency monitoring unit 72 has a function of measuring the frequency of the output signal of the signal processing unit 12. For example, the output signal of the signal modulation unit 13 is input to the frequency monitoring unit 72 by being branched by the optical coupler. The frequency monitoring unit 72 transmits information on the frequency of the output signal of the signal modulation unit 13 to the frequency adjustment unit 82 in the optical reception device 80 via the communication channel 203.

The configuration of the optical receiving apparatus 80 will be described. Fig. 19 illustrates a configuration of an optical receiving apparatus 80 according to the present exemplary embodiment. The optical receiving device 80 includes a client signal output unit 21, PBS22, 90-degree mixer 23, light detection unit 24, ADC25, DSP26, local oscillation light output unit 27, frequency monitoring unit 81, and frequency adjusting unit 82.

The configurations and functions of the client signal output unit 21, PBS22, 90-degree mixer 23, light detection unit 24, ADC25, and DSP26 according to the present exemplary embodiment are similar to those of the same-name unit according to the second exemplary embodiment. In other words, as the PBS22, a PBS 22-1 that polarization-separates an optical signal input via the communication channel 201 and a PBS 22-2 that polarization-separates local oscillation light are included. Including a 90-degree mixer 23-1, a photodetection unit 24-1, and an ADC 25-1 that process signals of X-polarized waves, and including a 90-degree mixer 23-2, a photodetection unit 24-2, and an ADC25-2 that process signals of Y-polarized waves.

The frequency monitoring unit 81 has a function of measuring the frequency of the output light of the local oscillation light output unit 27. The output light of the local oscillation light output unit 27 is input to the frequency monitoring unit 81 by being branched by, for example, an optical coupler. The frequency monitoring unit 81 transmits information on the frequency of the output light of the local oscillation light output unit 27 to the frequency adjusting unit 82 of the own device.

The frequency adjusting unit 82 controls the amount of shift of the frequency of the light output by the local oscillation light output unit 27 based on the frequency of the output signal transmitted from the frequency monitoring unit 72 in the optical transmission device 70 via the communication channel 203 and the frequency of the local oscillation light transmitted from the frequency monitoring unit 81 of the own device. The frequency adjusting unit 82 monitors the frequency of the optical signal transmitted from the optical transmission device 70 and the frequency of the local oscillation light, and controls the amount of shift of the frequency of the local oscillation light output by the local oscillation light output unit 27 based on the set value of the frequency shift set in such a manner that the total shift does not become 0.

The operation of the optical communication system according to the present exemplary embodiment will be described. The optical communication system according to the present exemplary embodiment operates similarly to the fourth exemplary embodiment, except that the frequency offset is adjusted by controlling the frequency of the local oscillation light on the optical receiving apparatus side. In the optical communication system according to the present exemplary embodiment, the frequency adjustment unit 82 in the optical reception device 80 calculates the frequency difference based on the frequency of the optical signal transmitted from the optical transmission device 70 and the frequency of the local oscillation light measured by the own device. The frequency adjusting unit 82 adjusts the frequency of the local oscillation light based on the frequency difference between the optical signal and the local oscillation light and the set value of the frequency offset. The frequency adjusting unit 82 adjusts the frequency of the local oscillation light to be output from the local oscillation light output unit 27 in such a manner that the calculated frequency difference between the optical signal and the local oscillation light coincides with the set value of the frequency offset.

The optical communication system according to the present exemplary embodiment has similar advantageous effects to the optical communication system according to the fourth exemplary embodiment. In other words, in the optical communication system according to the present exemplary embodiment, the frequencies of the optical signal and the local oscillation light are monitored, and the frequency adjustment unit 82 controls the frequency of the light to be output from the local oscillation light output unit 27 in such a manner that the frequency offset, which is the frequency difference between the optical signal and the local oscillation light, becomes a set value. By keeping the frequencies of the optical signal and the local oscillation light at set values other than 0 and giving a frequency offset between the optical signal and the local oscillation light in such a manner, noise generated in the Q-ch signal can be prevented. Therefore, the optical communication system according to the present exemplary embodiment can suppress the influence of noise generated in the reception signal and can maintain the reception quality.

(sixth example embodiment)

A sixth exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings. Fig. 20 illustrates an outline of the configuration of an optical communication system according to the present exemplary embodiment. The optical communication system according to the present exemplary embodiment includes an optical transmission apparatus 90 and an optical reception apparatus 100. The optical transmission apparatus 90 and the optical reception apparatus 100 are connected via a communication channel 201 and a communication channel 202.

The optical communication system according to the present exemplary embodiment is a network system that performs optical communication of a digital coherent scheme via the communication channel 201 similarly to the second exemplary embodiment. In the optical communication systems according to the fourth and fifth exemplary embodiments, the frequency difference is calculated by measuring the frequencies of the optical signal and the local oscillation light. In contrast, the optical communication system according to the present exemplary embodiment is characterized in that the information on the frequency difference between the optical signal and the local oscillation light is acquired by monitoring signal processing of the optical receiving apparatus.

The configuration of the optical transmission device 90 will be described. Fig. 21 illustrates a configuration of an optical transmission device 90 according to the present exemplary embodiment. The optical transmission device 90 includes a client signal input unit 11, a signal processing unit 12, a signal modulation unit 13, a light source unit 14, and a frequency adjustment unit 91.

The configurations and functions of the client signal input unit 11, the signal processing unit 12, the signal modulation unit 13, and the light source unit 14 according to the present exemplary embodiment are similar to those of the same name unit according to the second exemplary embodiment.

The frequency adjustment unit 91 controls the amount of shift of the frequency of the light output by the light source unit 14 based on the amount of shift of the frequency of the optical signal transmitted by the optical transmission apparatus 90 and the frequency of the local oscillation of the optical reception apparatus 100 transmitted from the frequency shift detection unit 101 in the optical reception apparatus 100 via the communication channel 202. The frequency adjustment unit 91 controls the amount of shift of the frequency of the light source unit 14 based on the amount of shift of the frequency of the optical signal and the local oscillation light transmitted from the optical reception device 100 in such a manner that the total shift does not become 0.

The configuration of the optical receiving apparatus 100 will be described. Fig. 22 illustrates the configuration of the optical receiving apparatus 100 according to the present exemplary embodiment. The optical receiving apparatus 100 includes a client signal output unit 21, a PBS22, a 90-degree mixer 23, a light detection unit 24, an ADC25, a DSP26, a local oscillation light output unit 27, and a frequency offset detection unit 101.

The client signal output unit 21, the PBS22, the 90-degree mixer 23, the light detection unit 24, the ADC25, the DSP26, and the local oscillation light output unit 27 according to the present exemplary embodiment are similar in configuration and function to the same-named units according to the second exemplary embodiment. In other words, as the PBS22, a PBS 22-1 that polarization-separates an optical signal input via the communication channel 201 and a PBS 22-2 that polarization-separates local oscillation light are included. Including a 90-degree mixer 23-1, a photodetection unit 24-1, and an ADC 25-1 that process signals of X-polarized waves, and including a 90-degree mixer 23-2, a photodetection unit 24-2, and an ADC25-2 that process signals of Y-polarized waves.

The frequency offset detection unit 101 monitors the reception processing performed by the DSP26, and detects a difference between the frequency of the optical signal transmitted by the optical transmission device 90 and the frequency of the local oscillation light output by the local oscillation light output unit 27 as a frequency offset. The frequency offset detection unit 101 transmits information on a frequency offset indicating a frequency difference between the detected optical signal and the local oscillation light to the frequency adjustment unit 91 in the optical transmission apparatus 90 via the communication channel 202. The frequency offset detection unit 101 may be integrated with the DSP26 as part of the DSP 26.

The operation of the optical communication system according to the present exemplary embodiment will be described. The optical communication system according to the present exemplary embodiment operates similarly to the optical communication system according to the second exemplary embodiment with respect to operations other than adjusting the frequency offset of the optical signal and the local oscillation light. An operation of adjusting the frequency output by the light source unit 14 by the optical transmission device 90 according to the present exemplary embodiment will be described. Fig. 23 illustrates an operation flow of adjusting the frequency of light output by the light source unit 14.

First, the frequency adjustment unit 91 sets the frequency offset target ofs _ target (step S41). The frequency offset target ofs _ target indicates a target of a difference between the frequency of the light output by the light source unit 14 and the frequency of the light output by the local oscillation light output unit 27. The frequency offset target ofs _ target may be stored in the frequency adjustment unit 91 in advance, or a set value may be input by an operator or the like.

When the frequency offset target ofs _ target is set, the frequency adjustment unit 91 acquires data on the frequency offset total _ ofs of the optical signal and the local oscillation light (step S42). Data on the frequency offset total _ ofs of the optical signal and the local oscillation light is received from the frequency offset detection unit 101 in the optical reception apparatus 100 via the communication channel 202.

Upon receiving data on the frequency offset of the optical signal and the local oscillation light, the frequency adjustment unit 91 checks the plus/minus of the frequency offset target ofs _ target, and determines the coefficient SIGN for use in calculating the correction amount diff of the frequency offset.

When the value of the frequency offset target ofs _ target is equal to or greater than 0 (yes in step S43), the frequency adjustment unit 91 sets the coefficient SIGN to +1 (step S44). When the value of the frequency offset target ofs _ target is less than 0 (no in step S43), the frequency adjustment unit 91 sets the coefficient SIGN to-1 (step S47).

When the coefficient SIGN for use in calculating the correction amount diff is determined, the frequency adjustment unit 91 calculates the correction amount diff of the frequency offset (step S45). The frequency adjustment unit 91 calculates the correction amount diff as diff ═ SIGN × ofs _ target-SIGN × total _ ofs.

When the correction amount diff of the frequency is calculated, the frequency adjustment unit 91 calculates the frequency of the light to be output by the light source unit 14 as the frequency set value + SIGN × diff (step S46). When the frequency of light to be output by the light source unit 14 is calculated, the frequency adjustment unit 91 controls the light source unit 14 in such a manner that light of the calculated frequency is output.

In the optical communication system according to the present exemplary embodiment, the frequencies of the optical signal and the local oscillation light are acquired from the frequency offset detection unit 101, and the frequency of the light to be output from the light source unit 14 is controlled in such a manner that the frequency offset indicating the frequency difference of the optical signal and the local oscillation light becomes a set value. By keeping the frequencies of the optical signal and the local oscillation light at set values other than 0 and giving a frequency offset between the optical signal and the local oscillation light in such a manner, noise generated in the Q-ch signal can be prevented. Therefore, the optical communication system according to the present exemplary embodiment can suppress the influence of noise generated in the reception signal and can maintain the reception quality.

(seventh exemplary embodiment)

A seventh exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings. Fig. 24 illustrates an outline of the configuration of an optical communication system according to the present exemplary embodiment. The optical communication system according to the present exemplary embodiment includes an optical transmission device 110 and an optical reception device 120. The optical transmission apparatus 110 and the optical reception apparatus 120 are connected via a communication channel 201.

The optical communication system according to the present exemplary embodiment is a network system that performs optical communication of a digital coherent scheme via the communication channel 201 similarly to the second exemplary embodiment. In the optical communication system according to the sixth exemplary embodiment, the processing performed on the received signal by the DSP26 is monitored by the frequency offset detection unit 101, information on the frequency difference of the optical signal and the local oscillation light is acquired, and the frequency of the optical signal is adjusted in the optical transmission apparatus. The optical communication system according to the present exemplary embodiment is characterized in that the processing performed on the received signal by the DSP26 is monitored by the frequency offset detection unit 101, and the frequency offset of the optical signal and the local oscillation light is adjusted by adjusting the frequency of the local oscillation light.

The configuration of the optical transmission device 110 will be described. Fig. 25 illustrates a configuration of the optical transmission device 110 according to the present exemplary embodiment. The optical transmission device 110 includes a client signal input unit 11, a signal processing unit 12, a signal modulation unit 13, and a light source unit 111. The configurations and functions of the client signal input unit 11, the signal processing unit 12, and the signal modulation unit 13 according to the present exemplary embodiment are similar to those of the same-name units according to the second exemplary embodiment.

The light source unit 111 has a function similar to that of the light source unit 14 according to the second exemplary embodiment, in addition to the function of shifting the frequency of light to be output. In other words, the light source unit 111 includes a semiconductor laser, and outputs continuous light of a predetermined frequency to the signal modulation unit 13. The predetermined frequency is assigned based on a wavelength design of the optical communication network.

The configuration of the optical receiving apparatus 120 will be described. Fig. 26 illustrates a configuration of the optical receiving apparatus 120 according to the present exemplary embodiment. The optical receiving device 120 includes a client signal output unit 21, a PBS22, a 90-degree mixer 23, a light detection unit 24, an ADC25, a DSP26, a local oscillation light output unit 121, a frequency offset detection unit 122, and a frequency adjustment unit 123.

The configurations and functions of the client signal output unit 21, PBS22, 90-degree mixer 23, light detection unit 24, ADC25, and DSP26 according to the present exemplary embodiment are similar to those of the same-name unit according to the second exemplary embodiment. In other words, as the PBS22, a PBS 22-1 that polarization-separates an optical signal input via the communication channel 201 and a PBS 22-2 that polarization-separates local oscillation light are included. Including a 90-degree mixer 23-1, a photodetection unit 24-1, and an ADC 25-1 that process signals of X-polarized waves, and including a 90-degree mixer 23-2, a photodetection unit 24-2, and an ADC25-2 that process signals of Y-polarized waves.

The local oscillation light output unit 121 generates local oscillation light of a predetermined frequency, which is combined with the optical signal transmitted via the communication channel 201 and used in generating an optical signal of an intermediate frequency. The local oscillation light output unit 121 includes a semiconductor laser, and outputs light of a frequency set based on the frequency of an optical signal transmitted via the communication channel 201. The local oscillation light output unit 121 outputs light having a certain frequency offset from a predetermined frequency as a center frequency. The frequency offset is controlled by the frequency adjustment unit 123.

The frequency offset detection unit 122 monitors the reception processing performed by the DSP26, and detects an offset amount of the frequency of the optical signal transmitted by the optical transmission device 110 and the frequency of the local oscillation light output by the local oscillation light output unit 121. The frequency offset detection unit 122 transmits information on the offset amount of the frequency to the frequency adjustment unit 123 of the own device. The frequency offset detection unit 122 may be integrated with the DSP26 as part of the DSP 26.

The frequency adjustment unit 123 controls the amount of shift of the frequency of the local oscillation light output by the local oscillation light output unit 121. The frequency adjustment unit 123 controls the amount of shift of the frequency of the local oscillation light output by the local oscillation light output unit 121 based on information on the frequency shift of the local oscillation light and the optical signal transmitted from the frequency shift detection unit 122.

The optical communication system according to the present exemplary embodiment operates similarly to the sixth exemplary embodiment except that the frequency offset is adjusted by controlling the frequency of the local oscillation light on the optical receiving apparatus side. In the optical communication system according to the present exemplary embodiment, the frequency adjustment unit 123 in the optical reception device 120 acquires information on the frequency difference of the optical signal and the local oscillation light detected by the frequency offset detection unit 122. The frequency adjusting unit 123 adjusts the frequency of the local oscillation light based on a set value of a frequency offset indicating a difference between the frequency of the optical signal and the frequency of the local oscillation light. The frequency adjusting unit 123 adjusts the frequency of the local oscillation light to be output from the local oscillation light output section 121 so that the calculated frequency difference between the optical signal and the local oscillation light coincides with the set value of the frequency offset.

In the optical communication system according to the present exemplary embodiment, the frequencies of the optical signal and the local oscillation light are acquired from the frequency offset detection unit 122, and the frequency of the light to be output from the local oscillation light output unit 121 is controlled in such a manner that the frequency offset indicating the frequency difference of the optical signal and the local oscillation light becomes a set value. By keeping the frequencies of the optical signal and the local oscillation light at the set values other than 0 and giving the frequency offset between the optical signal and the local oscillation light in such a manner, the optical communication system according to the present exemplary embodiment can prevent noise from being generated in the Q-ch signal. Therefore, the optical communication system according to the present exemplary embodiment can suppress the influence of noise generated in the reception signal and can maintain the reception quality.

The optical communication systems according to the second to seventh exemplary embodiments indicate a configuration of performing unidirectional communication of transmitting an optical signal from an optical transmission apparatus to an optical reception apparatus. Instead of such a configuration, the optical communication system according to the exemplary embodiment may perform bidirectional optical communication. When bidirectional optical communication is performed, control of a frequency offset, which is a frequency difference between an optical signal and local oscillation light, is performed in two directions. When performing bidirectional communication, the optical communication system according to example embodiments may be configured to transmit information, such as error information, information on the frequency of light, and information on the frequency difference between an optical signal and local oscillation light, by adding the information to a frame to be transmitted to an opposing apparatus.

All or part of the above disclosed example embodiments can be described as, but not limited to, the following supplementary notes.

[ supplementary notes 1]

An optical transmission apparatus comprising:

an optical output device for outputting light of a frequency assigned to the optical transmission apparatus;

an optical modulation device for separating light output by the optical output device into mutually orthogonal polarized waves, modulating an in-phase component and an orthogonal component in each of the polarized waves, and outputting an optical signal obtained by polarization-combining the modulated component waves;

reception information acquisition means for acquiring information on a reception state of an optical signal in an optical reception apparatus as a transmission destination of the optical signal; and

frequency adjusting means for controlling a frequency of light to be output by the optical output means based on the information on the reception state, and adjusting a frequency offset that is a difference between a frequency of local oscillation light used in coherent detection of an optical signal by the optical receiving apparatus and the frequency of light output by the optical output means.

[ supplementary notes 2]

The optical transmission device according to supplementary note 1, wherein

The reception information acquiring means acquires information on the number of errors in the optical signal as information on the reception state, and

the frequency adjustment means controls the frequency of the light to be output by the light output means in such a manner as to minimize the number of errors.

[ supplementary notes 3]

The optical transmission device according to supplementary note 1, further comprising

A frequency measuring device for measuring a frequency of the optical signal output from the optical modulating device, wherein

The reception information acquisition means acquires information on the frequency of the local oscillation light from the optical reception device, and

the frequency adjusting means controls the frequency of the light to be output by the light output means based on the frequency of the optical signal measured by the frequency measuring means and the frequency of the local oscillation light acquired by the reception information acquiring means so that the frequency offset becomes a value set in advance.

[ supplementary notes 4]

The optical transmission device according to supplementary note 1, wherein

The reception information acquisition means acquires information indicating a difference between a frequency of an optical signal received from the optical reception device and a frequency of the local oscillation light, and

the frequency adjusting means controls the frequency of the light to be output by the light output means based on the difference between the frequency of the optical signal received from the optical receiving apparatus acquired by the reception information acquiring means and the frequency of the local oscillation light in such a manner that the frequency offset becomes a value set in advance.

[ supplementary notes 5]

An optical receiving apparatus, comprising:

a local oscillation optical output device for outputting local oscillation light whose frequency is set based on a frequency of an optical signal obtained by modulating an in-phase component and a quadrature component in each of the quadrature polarized waves by the optical transmission apparatus;

optical signal receiving means for combining an optical signal with the local oscillation light and converting the combined signal into an electrical signal;

demodulation means for performing demodulation processing based on the electrical signal converted by the optical signal reception means; and

a local oscillation light adjustment means for controlling a frequency of light to be output by the local oscillation light output means based on information on a reception state of the optical signal, and adjusting a frequency offset that is a difference between the frequency of the optical signal and the frequency of the local oscillation light output by the local oscillation light output means.

[ supplementary notes 6]

The optical receiving device according to supplementary note 5, wherein

The local oscillation light adjusting means controls the frequency of the local oscillation light to be output by the local oscillation light output means in such a manner as to minimize the number of errors detected by the demodulating means.

[ supplementary notes 7]

The optical receiving apparatus according to supplementary note 5, further comprising:

a local oscillation light measuring device for measuring a frequency of the local oscillation light output from the local oscillation light output device; and

transmission information acquisition means for acquiring information on the frequency of the optical signal from the optical transmission apparatus, wherein

The local oscillation light adjusting device controls the frequency of the local oscillation light to be output by the local oscillation light outputting device based on the frequency of the local oscillation light measured by the local oscillation light measuring device and the frequency of the optical signal acquired by the transmission information acquiring device in such a manner that the frequency offset becomes a preset value.

[ supplementary notes 8]

The optical receiving device according to supplementary note 5, wherein

The local oscillation light adjustment means controls the frequency of light to be output by the local oscillation light output means based on a difference between the frequency of the optical signal detected by the demodulation means and the frequency of the local oscillation light in such a manner that the frequency offset becomes a value set in advance.

[ supplementary notes 9]

An optical communication system, the optical communication system comprising:

the optical transmission device according to any one of supplementary notes 1 to 4; and

the optical receiving device according to supplementary note 5, wherein

The frequency adjusting means of the optical transmission apparatus adjusts the frequency offset, which is a difference from the frequency of the light output by the light output means, based on the information on the reception state of the optical signal acquired from the optical reception apparatus.

[ supplementary notes 10]

An optical communication method, the optical communication method comprising:

outputting light of a frequency assigned to the own device;

separating the output light into mutually orthogonal polarized waves, modulating an in-phase component and an orthogonal component in each of the polarized waves, and outputting an optical signal obtained by polarization-synthesizing the modulated component waves;

acquiring information on a reception state of an optical signal in an optical receiving apparatus as a transmission destination of the optical signal; and

the frequency of light to be output is controlled based on the information on the reception state, and a frequency offset, which is a difference between the frequency of local oscillation light used in coherent detection of an optical signal by the optical reception device and the frequency of light to be output, is adjusted.

[ supplementary notes 11]

The optical communication method according to supplementary note 10, wherein:

acquiring information on the number of errors in the optical signal as information on the reception state when acquiring the information on the reception state; and

when controlling the frequency of light to be output, the frequency of light to be output is controlled in such a manner that the number of errors is minimized.

[ supplementary notes 12]

The optical communication method according to supplementary note 10, further comprising:

measuring a frequency of the output optical signal, wherein:

acquiring information on the frequency of the local oscillation light from the optical reception device when acquiring the information on the reception state; and

when controlling the frequency of light to be output, the frequency of light to be output is controlled based on the measured frequency of the optical signal and the acquired frequency of the local oscillation light in such a manner that the frequency offset becomes a value set in advance.

[ supplementary notes 13]

The optical communication method according to supplementary note 10, wherein:

acquiring information indicating a difference between a frequency of an optical signal received from the optical receiving apparatus and a frequency of local oscillation light when acquiring the information on the reception state; and

when controlling the frequency of the light to be output, the frequency of the light to be output is controlled in such a manner that the frequency offset becomes a value set in advance, based on the acquired difference between the frequency of the optical signal received from the optical receiving device and the frequency of the local oscillation light.

[ supplementary notes 14]

The optical communication method according to any one of supplementary notes 10 to 13, further comprising:

outputting local oscillation light of which a frequency is a frequency set based on a frequency of an optical signal obtained by modulating an in-phase component and a quadrature component in each of the quadrature polarized waves by the optical transmission apparatus;

combining the received optical signal with local oscillating light and converting the combined signal into an electrical signal;

performing demodulation processing based on the converted electric signal;

controlling a frequency of local oscillation light to be output based on information on a reception state of the optical signal; and

a frequency offset that is a difference between the frequency of the optical signal and the frequency of the local oscillation light is adjusted.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, the invention is not limited to these embodiments. It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.

This application is based on and claims priority from japanese patent application No.2018-20995 filed on 8.2.2018, the disclosure of which is incorporated herein by reference in its entirety.

[ list of reference numerals ]

1 light output device

2 light modulation device

3 received information acquiring apparatus

4 frequency adjusting device

10 optical transmission apparatus

11 client signal input unit

12 Signal processing unit

13 Signal modulation Unit

14 light source unit

15 frequency adjustment unit

20 optical receiving apparatus

21 client signal output unit

22 PBS

2390 degree mixer

24 light detection unit

25 ADC

26DSP

27 local oscillation light output unit

28 error detection unit

30 optical transmission device

31 light source unit

40 optical receiving apparatus

41 local oscillation light output unit

42 error detection unit

43 frequency adjusting unit

50 optical transmission device

51 frequency monitoring unit

52 frequency adjustment unit

60 optical receiving apparatus

61 frequency monitoring unit

70 optical transmission apparatus

71 light source unit

72 frequency monitoring unit

80 optical receiving apparatus

81 frequency monitoring unit

82 frequency adjustment unit

90 optical transmission apparatus

91 frequency adjustment unit

100 optical receiving apparatus

101 frequency offset detection unit

110 optical transmission device

111 light source unit

120 optical receiving apparatus

121 local oscillation light output unit

122 frequency offset detection unit

123 frequency adjustment unit

201 communication channel

202 communication channel

203 communication channel