阅读说明：本技术 一种基于微波光子下变频的光器件光谱响应测试装置及方法 (Optical device spectral response testing device and method based on microwave photon down-conversion ) 是由 恽斌峰 徐雪朦 胡国华 崔一平 于 2019-09-02 设计创作，主要内容包括：本发明公布了一种基于微波光子下变频的光器件光谱响应测试装置及方法,所述装置包括激光器,相位调制器,光学带通滤波器,待测器件,强度调制器,低速光电探测器,电压源,第一射频源,第二射频源,频谱仪。所述方法如下：激光进入相位调制器,由第一射频源输出的微波信号调制后,经带通滤波器产生光学单边带信号,通过待测器件后进入强度调制器,同时第二射频源输出与第一射频源频率相近的微波信号进入强度调制器,进一步调制后经低速光电探测器拍频产生两个同幅同相的低频信号,叠加后由频谱仪探测。本方法可通过检测固定低频处的响应来测试待测器件在一个频率范围内的器件响应；本发明具有测试系统复杂度低,损耗小,无需考虑信号干涉等优点。(The invention discloses a device and a method for testing spectral response of an optical device based on microwave photon down-conversion. The method comprises the following steps: laser enters a phase modulator, an optical single-side signal is generated through a band-pass filter after being modulated by a microwave signal output by a first radio frequency source, the optical single-side signal enters an intensity modulator after passing through a device to be detected, meanwhile, a microwave signal with the frequency similar to that of the first radio frequency source is output by a second radio frequency source, the optical single-side signal enters the intensity modulator, the optical single-side signal is further modulated and then is subjected to beat frequency by a low-speed photoelectric detector to generate two low-frequency signals with the same amplitude and the same phase, and the two low-frequency signals are. The method can test the device response of the device to be tested in a frequency range by detecting the response at a fixed low frequency; the invention has the advantages of low complexity of the test system, low loss, no need of considering signal interference and the like.)

1. A kind of optical device spectral response testing arrangement based on microwave photon frequency conversion, characterized by including: the system comprises a laser (1), a phase modulator (2), a first radio frequency source (3), a tunable band-pass filter (4), an intensity modulator (6), a second radio frequency source (7), a photoelectric detector (8) and a frequency spectrograph (9); the optical input end of the phase modulator (2) is connected with the output end of the laser (1), and the radio frequency input end of the phase modulator (2) is connected with the output end of the first radio frequency source (3); the input end of the tunable band-pass filter (4) is connected with the output end of the phase modulator (2), and the output end of the tunable band-pass filter (4) is connected with the input end of the device to be tested (5); the optical input end of the intensity modulator (6) is connected with the output end of the device to be tested (5), the radio frequency input end of the intensity modulator (6) is connected with the output end of the second radio frequency source (7), and the optical output end of the intensity modulator (6) is connected with the input end of the photoelectric detector (8); the input end of the frequency spectrograph (9) is connected with the output end of the photoelectric detector (8).

2. The method for testing the optical device spectral response testing device based on microwave photon down-conversion according to claim 1, characterized by comprising the following steps:

the method comprises the following steps: a laser (1) is adopted to output continuous waves, the continuous waves enter a phase modulator (2) through an optical input end of the phase modulator (2), and microwave signals output by a first radio frequency source (3) enter the phase modulator (2) through a radio frequency input end of the phase modulator (2); the signal modulated by the phase modulator (2) generates an optical single sideband signal only containing 0 order and +1 order sidebands through a tunable band-pass filter (4);

step two: the optical single-sideband signal enters the optical input end of the intensity modulator (6) after passing through the device to be tested (5); the second radio frequency source (7) outputs a microwave signal with the frequency similar to that of the first radio frequency source (3) and enters the radio frequency input end of the intensity modulator (6); after further modulation by the intensity modulator (6), two groups of optical sidebands which have similar frequencies and carry the transmission characteristics of the device to be tested are generated;

step three: after the two groups of optical sidebands are subjected to beat frequency by a low-speed photoelectric detector (8), two low-frequency signals with the same amplitude and the same phase are generated, and the superposed signals are detected by a frequency spectrograph (9);

step four: the output frequencies of the first radio frequency source (3) and the second radio frequency source (7) are changed, the frequency difference of the output signals of the first radio frequency source (3) and the second radio frequency source (7) is kept fixed, and the spectral response of the optical device to be tested in the frequency range can be obtained by detecting the device response at the fixed low frequency.

3. The testing method of the optical device spectral response testing device based on microwave photon down-conversion as claimed in claim 2, characterized in that: in the first step, the signal modulated by the phase modulator (2) passes through the tunable band-pass filter (4) to filter the negative order sideband and the sideband above +2 order, and an optical single sideband signal only containing the sideband of 0 order and +1 order is obtained.

4. The testing method of the optical device spectral response testing device based on microwave photon down-conversion as claimed in claim 2, characterized in that: in the third step, the optical single-side band signal enters the intensity modulator (6) after passing through the device to be tested (5), the intensity modulator (6) works at an orthogonal bias point through direct current bias, and after the signal with the frequency similar to that of the first radio frequency source (3) is output by the second radio frequency source (7) and is further modulated, two groups of optical side bands with the similar frequencies and carrying the transmission characteristics of the device to be tested are generated.

Technical Field

The invention relates to a passive optical device frequency spectrum response testing device and method based on a microwave photon down-conversion technology, and belongs to the technical field of microwave photonics, down-conversion technology and low-frequency detection.

Background

Optical passive devices, such as micro-ring resonators, tunable optical delay lines, waveguide bragg gratings, etc., have been widely used in the fields of information storage, biomedicine, military radar, etc. In order to put the optical passive device into practice, the transmission characteristics of the optical passive device need to be tested. Considering that the wavelength scanning has higher requirements on the precision and stability of the laser and low testing precision, the frequency scanning test is more suitable for testing high-Q-value devices because the frequency scanning test has higher precision and higher speed. When the test range is large, a wide bandwidth photodetector is required to respond. In order to reduce the requirements on the bandwidth and response speed of the photoelectric detector, the problem can be effectively solved by combining the down-conversion technology with the microwave photon test.

Currently, there are two main schemes for implementing down conversion: a series link, a parallel link. Wherein the serial link may be implemented by cascaded modulators; the parallel link can be realized by modulator parallel connection, a double-drive intensity modulator and a frequency shifter. The research combining the down-conversion technology and the microwave photon test is less at present, the reported schemes are realized by parallel links, the structure needs an optical coupler to divide signals into two paths, one path of the signals passes through a device, meanwhile, the two paths of the signals are modulated by radio frequency with similar frequency, then are combined by the optical coupler, and finally, a photoelectric detector beats frequency to generate low-frequency signals; the structure is complex, the link loss is large, and the problem of unstable detection signals caused by residual optical carrier interference needs to be considered during beam combination. In order to simplify the test system and reduce the insertion loss, the down-conversion technology and the device test are skillfully combined in a mode of cascading modulator-device-modulator, so that the device can be tested in a frequency sweeping mode, low-frequency detection can be realized, and the requirements of the bandwidth and the response speed of the photoelectric detector are reduced.

Disclosure of Invention

The invention aims to enable the complexity of the traditional test system based on microwave photon down-conversion to be lower, the insertion loss to be lower and the test system to be free from the influence of residual optical carriers, and provides a passive optical device frequency spectrum response test device and a method based on the microwave photon down-conversion technology.

In order to achieve the purpose, the method adopted by the invention is as follows: a spectral response testing device of an optical device based on microwave photon down-conversion comprises a laser, a phase modulator, a first radio frequency source, a tunable band-pass filter, an intensity modulator, a second radio frequency source, a photoelectric detector and a frequency spectrograph; the optical input end of the phase modulator is connected with the output end of the laser, and the radio frequency input end of the phase modulator is connected with the output end of the first radio frequency source; the input end of the tunable band-pass filter is connected with the output end of the phase modulator, and the output end of the tunable band-pass filter is connected with the input end of the device to be tested; the optical input end of the intensity modulator is connected with the output end of the device to be tested, the radio frequency input end of the intensity modulator is connected with the output end of the second radio frequency source, and the optical output end of the intensity modulator is connected with the input end of the photoelectric detector; and the input end of the frequency spectrograph is connected with the output end of the photoelectric detector.

The invention also discloses a testing method of the optical device spectral response testing device based on the microwave photon down-conversion, which comprises the following steps:

the method comprises the following steps: a laser is adopted to output continuous waves, the continuous waves enter a phase modulator through an optical input end of the phase modulator, and microwave signals output by a first radio frequency source enter the phase modulator through a radio frequency input end of the phase modulator; the signal modulated by the phase modulator is passed through a tunable band-pass filter to produce an optical single sideband signal containing only the 0 th order and +1 st order sidebands,

step two: the optical single sideband signal enters the optical input end of the intensity modulator after passing through the device to be tested; the second radio frequency source outputs a microwave signal with the frequency similar to that of the first radio frequency source, and the microwave signal enters the radio frequency input end of the intensity modulator; after further modulation by the intensity modulator, two groups of optical sidebands which have similar frequencies and carry the transmission characteristics of the device to be tested are generated;

step three: after the two groups of optical sidebands are subjected to beat frequency by a low-speed photoelectric detector, two low-frequency signals with the same amplitude and the same phase are generated, and the superposed signals are detected by a frequency spectrograph;

step four: the output frequencies of the first radio frequency source and the second radio frequency source are changed, the frequency difference of the output signals of the first radio frequency source and the second radio frequency source is kept fixed, and the frequency spectrum response of the optical device to be tested in the frequency range can be obtained by detecting the device response at the fixed low frequency.

As an improvement of the present invention, in the step one, the signal modulated by the phase modulator is filtered by the tunable band-pass filter to remove the negative order sideband and the sideband above +2 order, so as to obtain the optical single sideband signal containing only the sideband of 0 order and +1 order.

In the third step, the optical single-sideband signal enters the intensity modulator after passing through the device to be tested, the intensity modulator works at the orthogonal bias point through direct current bias voltage, and after being further modulated by a signal with the frequency similar to that of the first radio frequency source output by the second radio frequency source, two groups of optical sidebands with the similar frequencies and carrying the transmission characteristics of the device to be tested are generated.

Has the advantages that:

(1) compared with the prior art, the method effectively combines the down-conversion technology with the microwave photon test by cascading the phase modulator-the device to be tested-the intensity modulator;

(2) compared with the low-frequency detection of the device realized through the parallel structure, the use of the coupler is avoided, so that the test system is simpler, the loss is lower, and the problem of unstable detection signals caused by the combination of residual optical carriers is not required to be considered.

Drawings

Fig. 1 is a schematic structural diagram of a device for testing spectral response of an optical device based on microwave photon down-conversion provided by the present invention.

Fig. 2 is a schematic sideband diagram of a method for testing spectral response of an optical device based on microwave photon down-conversion provided by the invention.

Fig. 3 is a comparison graph of the results of testing a narrow bandwidth device (microdisk) by using the microwave photon down-conversion based optical device spectral response testing apparatus and method provided by the present invention.

Fig. 4 is a comparison graph of the result of testing a wide bandwidth device (micro-ring) by using the device and method for testing the spectral response of an optical device based on microwave photon down-conversion provided by the invention.

Detailed Description

In order that the objects, technical solutions and advantages of the present invention will be more clearly understood, the present invention will be further described in detail with reference to the accompanying drawings in conjunction with the following specific embodiments.

Fig. 1 is a schematic structural diagram of an optical device spectral response testing apparatus based on microwave photon down-conversion provided by the present invention, which includes a laser 1, a phase modulator 2, a first radio frequency source 3, a tunable band-pass filter 4, an intensity modulator 6, a second radio frequency source 7, a photodetector 8, and a spectrometer 9; the optical input end of the phase modulator 2 is connected with the output end of the laser 1, and the radio frequency input end of the phase modulator 2 is connected with the output end of the first radio frequency source 3; the input end of the tunable band-pass filter 4 is connected with the output end of the phase modulator 2, and the output end of the tunable band-pass filter 4 is connected with the input end of the device to be tested 5; the optical input end of the intensity modulator 6 is connected with the output end of the device to be tested 5, the radio frequency input end of the intensity modulator 6 is connected with the output end of the second radio frequency source 7, and the optical output end of the intensity modulator 6 is connected with the input end of the photoelectric detector 8; the input end of the frequency spectrograph 9 is connected with the output end of the photoelectric detector 8.

The testing method of the optical device spectral response testing device based on microwave photon down-conversion comprises the following steps:

the continuous wave output by the laser 1 enters the phase modulator 2, is modulated by the radio frequency signal output by the first radio frequency source 3 to generate an optical double sideband signal, filters a negative order sideband and a sideband above +2 order by the tunable band-pass filter 4 to obtain an optical single sideband signal only with a 0 order sideband and a +1 order sideband,

the optical single-sideband signal enters an intensity modulator 6 after passing through a device to be detected 5, the intensity modulator works at a quadrature bias point through direct current bias voltage, a signal with a frequency similar to that of a first radio frequency source 3 is output through a second radio frequency source 7 and is further modulated to generate two groups of optical sidebands with similar frequencies and carrying transmission characteristics of the device to be detected, two low-frequency signals with the same amplitude and the same phase are generated after beat frequency of a low-speed photoelectric detector 8, the superposed signals are detected by a frequency spectrograph 9, the frequency difference of the output signals of the two frequency sources is kept constant by changing the output frequencies of the first radio frequency source 3 and the second radio frequency source 7, and the frequency spectrum response of the optical device to be detected in the frequency range can be obtained by detecting the frequency spectrum response at the fixed low frequency.

According to the schematic structural diagram of the testing device shown in FIG. 1, the output power of the laser is P_cFrequency of ω_cThe signal of (c):

the first radio frequency source has an output frequency of omega₀Modulates the optical signal entering the PM1, the modulated signal being:

wherein eta₁Insertion loss of PM1, m₁For a modulation factor of PM1, u is_A(t) when Bessel expansion and small signal modulation are carried out, only 0 order and +/-1 order sidebands are considered and are respectively recorded as u_A(0)(t)、u_A(-1)(t)、u_A(+1)(t) the expression is as follows:

after filtering the-1 order sidebands by the band pass filter, only the 0 order +1 order sidebands remain, as shown by point B in FIG. 2, which is denoted as u_B(0)(t) and u_B(+1)(t), the expression is as follows:

wherein eta₂For the insertion loss of the tunable band-pass filter, the device transfer function is set as follows:

the 0 th order sideband u after passing through the device_C(0)(t) and +1 order sidebands u_C(+1)(t) the signal expression is:

the output frequency of the second radio frequency source is omega through the intensity modulator (arranged at a quadrature bias point)₁After further modulation, the frequency of the radio frequency signal is omega in consideration of the small signal condition_c、ω_c+ω₀、ω_c+ω₁、ω_c+ω₀-ω₁、ω_c-ω₁The sideband signals (shown as point D in fig. 2) are:

wherein eta₃For the insertion loss of the intensity modulator, when detected by the low-speed photodetector, it can only respond to the signal picked up by the sideband with small frequency difference, i.e. the sideband with frequency "omega" as shown by point D in FIG. 2_cAnd omega_c+ω₁-ω₀'and' omega_c+ω₀And omega_c+ω₁"component of; frequency is recorded as_cAnd omega_c+ω₁-ω₀"the photocurrent of the low-frequency signal generated after the sideband beat frequency of the optical fiber is i₁(t) frequency of "ω_c+ω₀And omega_c+ω₁"the photocurrent of the low-frequency signal generated after the sideband beat frequency of the optical fiber is i₂(t), the expression is as follows:

is obtained from the formula (8) i₁(t) and i₂(t) the amplitude and phase are the same, so the total current (denoted as i (t)) generated after PD beat frequency is:

considering the amplitude term of the photocurrent, denoted as a (i), it can be obtained from equation (9):

A(i)∝T(ω_c)T(ω_c+ω₀) (10)

a (i) to ω₀Taking the derivative, we can get:

the electrical amplitude response measured by the optical device spectral response test method (11) based on the microwave photon down-conversion of the cascade of "phase modulator-band pass filter-device under test-intensity modulator" is consistent with the optical amplitude response of the device under test, i.e. the method can be used to measure the amplitude response of the optical device.

Based on the device and the method for testing the spectral response of the optical device based on the microwave photon down-conversion of the cascade phase modulator-to-device-to-be-tested-intensity modulator, provided by the invention, the amplitude responses of a narrow-bandwidth device (microdisk) and a wide-bandwidth device (microring) are tested, and the test result is compared with the amplitude response measured by a light wave test system, so that the test system disclosed by the invention is higher in test precision, as shown in fig. 3 and 4. And theoretically, the test of ultrahigh resolution can be realized by changing the step of frequency scanning.

The above-described embodiments of the present invention will be described in further detail with respect to the objects, technical solutions and advantageous effects thereof. It should be understood that the above-mentioned embodiments are merely exemplary of the present invention, and are not intended to limit the present invention, and any modification, equivalent replacement, or improvement made without departing from the spirit and principle of the present invention should be included in the protection scope of the present invention.