A method and device for calibrating bottom noise of photoelectric converter

Abstract

The present application discloses a method for calibrating the bottom noise of a photoelectric converter, comprising the following steps: a low phase noise optical frequency comb is locked to a high stability light source by optical frequency locking; a high frequency harmonic sequence of the low phase noise optical frequency comb is extracted, and a microwave carrier frequency signal is generated by photoelectric frequency conversion; the intensity of the high stability light source is modulated by the low phase noise microwave frequency signal to generate a modulated output light; the modulated output light is photoelectrically converted by the photoelectric converter to be tested to restore the microwave carrier frequency signal; the phase noise of the restored carrier frequency signal is measured to obtain the bottom noise of the photoelectric converter to be tested. The present application also includes a photoelectric converter bottom noise calibration device for implementing the method. The present application overcomes the problems of low sensitivity and large blind spots existing in traditional calibration devices.

Description

Technical Field

[0001] This application relates to the field of optoelectronic technologies, and particularly to a bottom noise device for an optoelectronic converter based on an ultra-low phase noise optoelectronic frequency synthesis technology. Background Art

[0002] In microwave photon radar technology, the bottom noise of the optoelectronic converter at the receiving end directly affects the target capture performance of the radar and is an important parameter. However, the technical indicators of optoelectronic converters usually only include bandwidth, dark current, responsivity, etc. In practical applications in the fields of radar and communication, it is necessary to calibrate the bottom noise of optoelectronic converters.

[0003] Currently, the traditional delay line method is adopted for the bottom noise calibration device of optoelectronic converters. The device components include a low phase noise reference source, a laser, an electro-optic modulator, a delay line, a phase detector, and a digital acquisition processor. The disadvantages of this device are as follows: The phase noise of the low phase noise reference source generated by the traditional frequency synthesis technology is larger than the bottom noise of the optoelectronic converter. Even in the quadrature phase detection state, the influence of the phase noise of the low phase noise reference source cannot be completely eliminated; the calibration method of the traditional electrical delay line has low measurement sensitivity and there is a Fourier analysis frequency deviation blind area; when using a narrow linewidth laser, the near-carrier phase noise is poor, resulting in poor bottom noise of the overall calibration device near the carrier frequency; due to the imbalance of the electrical delays of the two arms of the phase detection in the traditional delay line calibration device, the calibration uncertainty of the phase detection sensitivity is relatively large.

[0004] Due to the above limitations of the current bottom noise calibration device for optoelectronic converters, problems such as a decrease in measurement sensitivity, a Fourier analysis frequency deviation blind area, and a large calibration uncertainty occur. Therefore, it is necessary to propose a bottom noise device for an optoelectronic converter based on an ultra-low phase noise optoelectronic frequency synthesis technology to overcome the disadvantages of the above calibration device. Summary of the Invention

[0005] This application proposes a calibration method and device for the bottom noise of an optoelectronic converter, which is particularly suitable for calibrating the bottom noise of high-sensitivity optoelectronic converters. The application of this device can avoid problems such as a decrease in measurement sensitivity and a Fourier analysis frequency deviation blind area brought by the existing calibration device.

[0006] On the one hand, an embodiment of this application proposes a calibration method for the bottom noise of an optoelectronic converter, including the following steps:

[0007] The low phase noise optical frequency comb is locked on the high-stability light source through an optical frequency locking method;

[0008] The high-frequency harmonic sequence of the low phase noise optical frequency comb is extracted and converted into a microwave carrier frequency signal through optoelectronic frequency conversion;

[0009] The high-stability light source is intensity-modulated with the low phase noise microwave frequency signal to generate a modulated output light;

[0010] The photoelectric converter to be measured performs photoelectric conversion on the modulated output light to recover the microwave carrier frequency signal;

[0011] Measure the phase noise of the recovered carrier frequency signal to obtain the bottom noise of the photoelectric converter to be measured.

[0012] Preferably, the high-stability light source has a linewidth less than a first set threshold; the low-phase-noise optical frequency comb introduces a bottom noise less than a second set threshold; the photoelectric frequency conversion introduces a bottom noise less than a third set threshold.

[0013] Preferably, the optical frequency locking method includes beat frequency locking, and the first beat frequency generated by mixing the output light of the low-phase-noise optical frequency comb and the output light of the high-stability light source is locked by using the PID technology.

[0014] Preferably, the optical frequency locking method includes repetition frequency locking, and the second beat frequency generated by mixing the repetition frequency of the optical frequency comb output and the bias signal is locked by using the PID technology.

[0015] Preferably, the optical frequency locking method includes bias frequency locking, and the third beat frequency obtained by performing photoelectric conversion on the output light of the optical frequency comb is locked by using the PID technology.

[0016] On the other hand, an embodiment of the present application proposes a device for calibrating the bottom noise of a photoelectric converter, which is used to implement the method described in any embodiment of the present application, and includes a high-stability light source, an optical fiber beat frequency locking loop, a low-phase-noise optical frequency comb, a photoelectric frequency conversion link, an electro-optic modulator, a test input end, a test output end, an amplifier, and a signal source analyzer.

[0017] The optical output end of the high-stability light source is connected to the optical input end of the optical fiber beat frequency locking loop by a single-mode optical fiber. The output signal of the optical fiber beat frequency locking loop is connected to the voltage-controlled end of the low-phase-noise optical frequency comb by a radio frequency cable. The output light of the low-phase-noise optical frequency comb outputs a microwave carrier frequency signal through the photoelectric frequency conversion link. The microwave frequency signal is input into the electro-optic modulator to intensity-modulate another output light of the high-stability light source to generate a modulated output light, which is output to the test input end. The signal at the test output end is amplified by the amplifier and then input into the signal source analyzer.

[0018] Preferably, the optical fiber beat frequency locking loop includes a high-stability light source beat frequency locking loop. The high-stability light source beat frequency locking loop includes: the output light of the low-phase-noise optical frequency comb and the output light of the high-stability light source generate a first beat frequency through an optical mixer; the first beat frequency signal and the first output signal of the DDS generate a first error signal through a first radio frequency mixer, and pass through a first PID loop to generate a first feedback signal, which is input to the voltage-controlled input end of the low-phase-noise optical frequency comb.

[0019] Preferably, the fiber optic beat frequency locking loop includes a repetition frequency locking loop. The repetition frequency locking loop includes: the repetition frequency signal output by the low-phase-noise optical frequency comb is multiplied in frequency, and then mixed with the bias signal by a second radio frequency mixer to generate a second beat frequency. The second beat frequency signal and the second output signal of the DDS are mixed by a third radio frequency mixer to generate a second error signal, which is then generated into a second feedback signal through a second PID loop and input to the voltage-controlled input end of the low-phase-noise optical frequency comb.

[0020] Preferably, the fiber optic beat frequency locking loop includes a bias frequency locking loop. The bias frequency locking loop includes: the light output by the low-phase-noise optical frequency comb is converted by a photoelectric converter to obtain a third beat frequency. The third beat frequency signal and the third output signal of the DDS are mixed by a fourth radio frequency mixer to generate a third error signal, which is then generated into a third feedback signal through a third PID loop and input to the modulation end of the low-phase-noise optical frequency comb.

[0021] Preferably, the photoelectric frequency conversion link includes a photoelectric converter, a band-pass filter, and a microwave amplifier. The light output by the low-phase-noise optical frequency comb is converted by the photoelectric converter to generate a microwave harmonic sequence; the target frequency component is extracted by the band-pass filter, and the microwave carrier frequency signal is output by the microwave amplifier.

[0022] The above at least one technical solution adopted in the embodiments of the present application can achieve the following beneficial effects:

[0023] For the device and method of the present application, the phase noise of the low-phase-noise carrier signal generated by the ultra-low phase noise optoelectronic frequency synthesis technology is much better than the bottom noise of the photoelectric converter; there is no problem of analyzing the Fourier frequency deviation blind area in the calibration result; the near-carrier frequency phase noise of the high-stability light source is quite excellent, greatly optimizing the near-carrier frequency bottom noise of the overall calibration device; reducing the uncertainty of calibration. Description of the Drawings

[0024] The drawings described herein are used to provide a further understanding of the present application and form a part of the present application. The illustrative embodiments and descriptions thereof of the present application are used to explain the present application and do not constitute an improper limitation to the present application. In the drawings:

[0025] Figure 1 It is a flowchart of an embodiment of the method of the present application;

[0026] Figure 2 It is an embodiment of the device of the present application;

[0027] Figure 3 It is an embodiment of the fiber optic beat frequency locking loop;

[0028] Figure 4 It is an embodiment of the photoelectric frequency conversion link. Detailed Embodiments

[0029] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments of this application and the corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in this application without creative efforts shall fall within the scope of protection of this application.

[0030] The following will, in conjunction with the drawings, elaborate on the technical solutions provided by each embodiment of this application.

[0031] Figure 1 It is a flowchart of an embodiment of the method of this application.

[0032] On the one hand, an embodiment of this application proposes a method for calibrating the bottom noise of an optical-electric converter, including the following steps:

[0033] Step 101: Lock the low-phase-noise optical frequency comb on the high-stability light source through optical frequency locking.

[0034] Preferably, the optical frequency locking method includes beat frequency locking. The first beat frequency generated by mixing the output light of the low-phase-noise optical frequency comb and the output light of the high-stability light source is locked using PID technology.

[0035] Preferably, the optical frequency locking method includes repetition frequency locking. The second beat frequency generated by mixing the repetition frequency of the optical frequency comb output and the bias signal is locked using PID technology.

[0036] Preferably, the optical frequency locking method includes bias frequency locking. The third beat frequency obtained by photoelectric conversion of the output light of the optical frequency comb is locked using PID technology.

[0037] Preferably, for the high-stability light source, the line width is less than the first set threshold; for the low-phase-noise optical frequency comb, the introduced bottom noise is less than the second set threshold. In the embodiments of this application, the line width of the high-stability light source is less than 1 Hz, the wavelength is 1550 nm ± 20 nm, and the output optical power is +11 dBm; the repetition frequency of the low-phase-noise optical frequency comb is 1 GHz, the output optical pulse power is +11 dBm, and the bottom noise is less than -160 dBc / Hz @ 100 kHz.

[0038] Step 102: Extract the high-frequency harmonic sequence of the low-phase-noise optical frequency comb and generate a microwave carrier frequency signal through photoelectric frequency conversion.

[0039] The introduced bottom noise of the optoelectronic frequency conversion is less than the third set threshold. In an embodiment of the present application, the input optical power of the optoelectronic frequency conversion link is > +5 dBm, the bottom noise is less than -170 dBc / Hz @ 100 kHz, the output electrical signal frequency range is 1 GHz to 40 GHz, and the electrical signal output power is > +8 dBm.

[0040] Step 103: Intensity-modulate the high-stability light source with the low-phase-noise microwave frequency signal to generate a modulated output light.

[0041] Step 104: Perform optoelectronic conversion on the modulated output light with the optoelectronic converter to be measured to recover the microwave carrier frequency signal.

[0042] Step 105: Measure the phase noise of the recovered carrier frequency signal to obtain the bottom noise of the optoelectronic converter to be measured.

[0043] Figure 2 This is an embodiment of the device of the present application.

[0044] On the other hand, an embodiment of the present application proposes a bottom noise calibration device for an optoelectronic converter, which is used to implement the method described in any embodiment of the present application, including a high-stability light source 21, a fiber optic beat frequency locking loop 22, a low-phase-noise optical frequency comb 23, an optoelectronic frequency conversion link 24, an electro-optic modulator 25, a test input terminal TI, a test output terminal TO, an amplifier 26, and a signal source analyzer 27.

[0045] The optical output terminal of the high-stability light source is connected to the optical input terminal of the fiber optic beat frequency locking loop with a single-mode optical fiber. The output signal of the fiber optic beat frequency locking loop is connected to the voltage-controlled terminal of the low-phase-noise optical frequency comb with a radio frequency cable. The output light of the low-phase-noise optical frequency comb outputs a microwave carrier frequency signal through the optoelectronic frequency conversion link.

[0046] Specifically, as Figure 2 , the optical frequency output terminal of the low-phase-noise optical frequency comb is connected to the optical comb terminal (i.e., the optical comb pulse input port) of the fiber optic beat frequency locking loop with a single-mode optical fiber, the loop output terminal of the fiber optic beat frequency locking loop is connected to the voltage-controlled terminal of the low-phase-noise optical frequency comb with a radio frequency cable, the optical pulse output terminal of the low-phase-noise optical frequency comb is connected to the input terminal of the optoelectronic frequency conversion link with a single-mode optical fiber, and the output terminal of the optoelectronic frequency conversion link is connected to the radio frequency input terminal of the electro-optic modulator with a radio frequency cable.

[0047] In an embodiment of the present application, the input power of the reference light source of the fiber optic beat frequency locking loop is > +5 dBm, the input power of the optical frequency comb is > +5 dBm, and the loop bandwidth is less than 1 Hz.

[0048] The microwave frequency signal is input into the electro-optic modulator to intensity-modulate another output light of the high-stability light source, generating a modulated output light, which is output to the test input terminal. Between the test input terminal and the test output terminal, a photoelectric converter 28 to be measured is connected. The signal at the test output terminal is amplified by an amplifier and then input into a signal source analyzer.

[0049] Specifically, the optical input terminal of the electro-optic modulator is connected to the modulation terminal of the high-stability light source by a single-mode optical fiber. The output terminal of the electro-optic modulator is connected to the test input terminal of the photoelectric converter to be measured by a single-mode optical fiber. The test output terminal of the photoelectric converter to be measured is connected to the input terminal of the amplifier by a radio frequency cable. The output terminal of the amplifier is connected to the input terminal of the signal source analyzer by a radio frequency cable.

[0050] In the embodiment of the present application, the input optical wavelength of the electro-optic modulator is 1550 nm ± 20 nm, the optical input power is > +5 dBm, the frequency range of the electrical modulation signal is 1 GHz to 40 GHz, the input electrical signal power is > +0 dBm, and the optical insertion loss is 8 dB.

[0051] Figure 3 It is an embodiment of the fiber optic beat frequency locking loop.

[0052] The low-phase-noise optical frequency comb is locked to the high-stability light source by using a fiber optic beat frequency locking loop. The composition of the fiber optic beat frequency locking loop is as Figure 3 shown, realizing three functions. One is the beat frequency locking loop between the low-phase-noise optical frequency comb and the high-stability light source. One is the repetition frequency locking loop of the optical frequency comb. One is the offset frequency locking loop of the optical frequency comb.

[0053] Preferably, the fiber optic beat frequency locking loop includes a high-stability light source beat frequency locking loop. The high-stability light source beat frequency locking loop includes: the output light of the low-phase-noise optical frequency comb 23 and the output light of the high-stability light source 21 generate a first beat frequency through an optical mixer 311; the first beat frequency signal and the first output signal of the DDS 313 generate a first error signal through a first radio frequency mixer 312, and generate a first feedback signal through a first PID loop 314, which is input to the voltage-controlled input terminal PZT of the low-phase-noise optical frequency comb. For example, the beat frequency locking loop between the low-phase-noise optical frequency comb and the high-stability light source is as Figure 3 shown. The output optical pulse of the low-phase-noise optical frequency comb is optically mixed with the high-stability light source. The first beat frequency obtained by mixing is a beat signal of 0 to 125 MHz. This beat signal is phase-detected with the first output signal of the DDS with a frequency of 35 MHz. The phase-detection error is integrated through the PID loop, and the integral output is given to the piezoelectric ceramic of the low-phase-noise optical frequency comb to form a beat frequency locking loop.

[0054] Preferably, the fiber optic beat frequency locking loop includes a repetition frequency locking loop. The repetition frequency locking loop includes: the repetition frequency signal output by the low-phase-noise optical frequency comb 23 is frequency-doubled, and then mixed with the bias signal 322 by the second radio frequency mixer 323 to generate a second beat frequency. The second beat frequency signal and the second output signal of the DDS 325 are mixed by the third radio frequency mixer 324 to generate a second error signal, which is then passed through the second PID loop 326 to generate a second feedback signal and input to the voltage-controlled input terminal of the low-phase-noise optical frequency comb. Specifically, for example, the repetition frequency locking loop of the optical frequency comb is the output optical pulse of the low-phase-noise optical frequency comb with a repetition frequency of 250 MHz. Through the optical quadrupler 321, the repetition frequency is frequency-doubled to 1 GHz. This 1 GHz signal is mixed with the bias signal of 780 MHz to obtain a beat signal, which is a beat signal with a second beat frequency of 20 MHz. It is phase-detected with the signal output by the DDS. The phase detection error passes through the second PID loop, and the second feedback signal is output. It is then jointly input to the piezoelectric ceramic control port of the low-phase-noise optical frequency comb through the adder 327 and the first feedback signal.

[0055] Preferably, the fiber optic beat frequency locking loop includes a bias frequency locking loop. The bias frequency locking loop includes: the output light of the low-phase-noise optical frequency comb 23 is amplified by the photoelectric converter 331 to obtain a third beat frequency. The third beat frequency signal and the third output signal of the DDS 333 are mixed by the fourth radio frequency mixer 332 to generate a third error signal, which is then passed through the third PID loop 334 to generate a third feedback signal and input to the modulation terminal of the low-phase-noise optical frequency comb. Specifically, for example, in the bias frequency locking loop of the optical frequency comb, after the low-phase-noise optical frequency comb passes through the photoelectric converter, a beat signal with a third beat frequency of 0 - 125 MHz is obtained. This beat signal is phase-detected with the output frequency of 35 MHz of the DDS in the radio frequency domain. The phase detection error is integrated through the PID loop, and the loop integration output is given to the EOM terminal of the low-phase-noise optical frequency comb to form a bias frequency locking loop.

[0056] Figure 4 This is an embodiment of the optoelectronic frequency conversion link.

[0057] Preferably, the optoelectronic frequency conversion link includes a photoelectric converter, a band-pass filter, and a microwave amplifier. The output light of the low-phase-noise optical frequency comb is converted by the photoelectric converter to generate a microwave harmonic sequence; the target frequency components are extracted by the band-pass filter, and the microwave carrier frequency signal is output by the microwave amplifier.

[0058] For example, the output optical pulse of the optical frequency comb is subjected to optoelectronic conversion by the photoelectric converter. The dark current of the photoelectric converter is less than 5 nA, the responsivity is greater than 0.8 A / W, and the frequency range covers the frequency points to be calibrated. The microwave harmonic sequence obtained by the optoelectronic conversion is used to extract the carrier frequency by the band-pass filter, and the extracted carrier frequency signal is amplified by the microwave amplifier.

[0059] The bottom noise calibration device of the optoelectronic converter based on the ultra-low phase noise optoelectronic frequency synthesis technology can calibrate the bottom noise of the optoelectronic converter, which is mainly determined by the superiority of the phase noise of the microwave signal generated based on the ultra-low phase noise optoelectronic frequency synthesis technology. The reason why the phase noise of the microwave signal generated by this technology is superior is that the high-stability light source has superior noise characteristics in the optical domain, and the low-phase noise optical frequency comb is the medium for converting the optical domain to the electrical domain, which plays the role of frequency division of the optical frequency. The optical frequency of 1550nm is frequency-divided to the microwave frequency, and the frequency division coefficient reaches 1E6. When the phase noise reaches the microwave frequency, it can be optimized by more than 120dB. Theoretically, the phase noise of the microwave signal obtained in this way can reach -200dBc / Hz.

[0060] When the device of the present application works, the low-phase noise optical frequency comb is locked on the high-stability light source through the fiber optic beat frequency locking loop, and the optoelectronic frequency conversion link extracts the harmonic sequence of the low-phase noise optical frequency comb. Since the low-phase noise optical frequency comb plays the role of high-order frequency division for the high-stability light source, the phase noise of the carrier obtained by the optoelectronic frequency conversion link is very superior, being more than 40dB better than the reference source of the traditional frequency synthesis near the carrier frequency and more than 20dB better than that in the far carrier frequency. After obtaining the low-phase noise carrier frequency, the high-stability light source is intensity-modulated through the electro-optic modulator, and the modulated optical output is subjected to optoelectronic conversion through the optoelectronic converter to be measured. After optoelectronic conversion, a low-phase noise carrier frequency is obtained. The amplitude of the carrier frequency signal is compensated through the amplifier. After the carrier frequency obtains sufficient gain, the phase noise characteristics of it are analyzed through the signal source analyzer. Since the phase noise of the low-phase noise carrier signal generated by using the ultra-low phase noise optoelectronic frequency synthesis technology is far superior to the bottom noise of the optoelectronic converter to be measured, the calibration result obtained by the signal source analyzer can characterize the bottom noise of the optoelectronic converter to be measured.

[0061] It should also be noted that the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements not only includes those elements but also includes other elements not expressly listed, or also includes elements inherent to such process, method, commodity or device. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of another identical element in the process, method, commodity or device including the said element.

[0062] The above are only the embodiments of the present application and are not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the scope of the claims of the present application.

Claims

1. A method for calibrating the bottom noise of a photoelectric converter, characterized in that: The following steps are involved: The low phase noise optical frequency comb is locked to a highly stable light source by optical frequency locking; Extract the high-frequency harmonic sequence of the low-phase-noise optical frequency comb and generate a microwave carrier signal through optoelectronic frequency conversion; Using the low phase noise microwave frequency signal to modulate the intensity of a high stability light source to generate modulated output light; Performing photoelectric conversion on the modulated output light using a photoelectric converter to be tested to restore the microwave carrier frequency signal; The phase noise of the recovered carrier frequency signal is measured to obtain the bottom noise of the photoelectric converter to be tested; The optical frequency locking method includes beat frequency locking, mixing the output light of the low phase noise optical frequency comb and the output light of the high stability light source to generate a first beat frequency, and locking the first beat frequency using PID technology; The optical frequency locking method includes repetition frequency locking, mixing the repetition frequency output by the optical frequency comb with the bias signal to generate a second beat frequency, and locking the second beat frequency using PID technology; The optical frequency locking method includes bias frequency locking, performing photoelectric conversion on the output light of the optical frequency comb to obtain a third beat frequency, and locking the third beat frequency using PID technology.

2. The photoelectric converter bottom noise calibration method according to claim 1, characterized in that: The high-stability light source has a line width less than a first set threshold; the low phase noise optical frequency comb introduces a bottom noise less than a second set threshold; the photoelectric frequency conversion introduces a bottom noise less than a third set threshold.

3. A photoelectric converter bottom noise calibration device, used to implement the method described in claim 1 or 2, characterized in that: It includes high-stability light source, fiber beat frequency locked loop, low phase noise optical frequency comb, optoelectronic frequency conversion link, electro-optic modulator, test input, test output, amplifier, and signal source analyzer; The optical output end of the high-stability light source and the optical input end of the optical fiber beat frequency locked loop are connected by a single-mode optical fiber; the output signal of the optical fiber beat frequency locked loop is connected to the voltage control end of the low phase noise optical frequency comb by a radio frequency cable; the output light of the low phase noise optical frequency comb is output as a microwave carrier signal via an optoelectronic frequency conversion link; The microwave frequency signal is input into the electro-optic modulator to modulate the intensity of another output light of the high-stability light source to generate modulated output light, which is output to the test input end; the signal at the test output end is amplified by the amplifier and then input into the signal source analyzer.

4. The photoelectric converter bottom noise calibration device according to claim 3, characterized in that: The optical fiber beat frequency locking loop includes a high-stability light source beat frequency locking loop; the high-stability light source beat frequency locking loop includes: the low phase noise optical frequency comb output light and the high-stability light source output light are used to generate a first difference beat frequency through an optical mixer; the first difference beat frequency signal and the DDS first output signal are used to generate a first error signal through a first radio frequency mixer, and a first feedback signal is generated through a first PID loop and input into the voltage-controlled input end of the low phase noise optical frequency comb.

5. The photoelectric converter bottom noise calibration device according to claim 3, characterized in that: The optical fiber beat frequency locking loop includes a repetition frequency locking loop; the repetition frequency locking loop includes: the repetition frequency signal output by the low phase noise optical frequency comb is frequency-multiplied, and the second difference beat frequency is generated by the second radio frequency mixer with the bias signal, the second difference beat frequency signal and the second output signal of the DDS are generated by the third radio frequency mixer. The second error signal is generated by the second PID loop, and the second feedback signal is input to the voltage-controlled input end of the low phase noise optical frequency comb.

6. The photoelectric converter bottom noise calibration device according to claim 3, characterized in that: The optical fiber beat frequency locking loop includes a bias frequency locking loop; the bias frequency locking loop includes: the output light of the low phase noise optical frequency comb is passed through a photoelectric converter to obtain a third beat frequency, the third beat frequency signal and the third output signal of the DDS are passed through a fourth RF mixer to generate a third error signal, and a third feedback signal is generated through a third PID loop and input to the modulation end of the low phase noise optical frequency comb.

7. The photoelectric converter bottom noise calibration device according to claim 3, characterized in that: The photoelectric frequency conversion link includes a photoelectric converter, a bandpass filter, and a microwave amplifier; The output light of the low phase noise optical frequency comb is converted into a microwave harmonic sequence through a photoelectric converter; The target frequency component is extracted through a bandpass filter and the microwave carrier frequency signal is output through a microwave amplifier.

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