Method for adjusting current tuning sensitivity of DFB semiconductor laser

Abstract

The invention discloses a method for adjusting the current tuning sensitivity of a DFB semiconductor laser, and the method comprises the steps: obtaining a beat frequency signal with a high signal-to-noise ratio through a photoelectric detector in a signal obtaining module, and averagely distributing the power of the beat frequency signal to a digital frequency pre-control module and a feedforward control module through a power divider; the beat frequency signal is filtered, amplified, divided and shaped, the frequency value of the shaped signal is measured in real time by the digital frequency measurement unit, and the digital frequency stabilization control module compares the frequency value with a target set frequency. According to the method, the frequency measurement precision is improved through the multi-period synchronous frequency measurement technology, accurate feedback control over the frequency is achieved through a PID control algorithm, rapid control over the laser frequency is achieved in combination with feed-forward control over the acousto-optic frequency shifter, the current tuning sensitivity of the DFB semiconductor laser is effectively improved, and the frequency tuning precision of the DFB semiconductor laser is improved. The problems that in the prior art, the adjusting direction is not clear, errors are large, and the anti-interference capacity is weak are solved.

Description

Technical Field

[0001] The invention relates to the technical field of laser adjustment, and in particular to a method for adjusting the current tuning sensitivity of a DFB semiconductor laser. Background Art

[0002] Semiconductor lasers, especially distributed feedback semiconductor lasers, are core components of modern optical communications and optical sensing systems. In optical communications, they are key components of optical transmitters and are used to convert electrical signals into optical signals for high-speed, long-distance information transmission. Current tuning sensitivity is a key performance indicator of DFB semiconductor lasers. DFB semiconductor lasers determine the efficiency of adjusting the laser output wavelength by changing the injected current. In the wavelength division multiplexing system of optical communications, the wavelength of the laser needs to be precisely adjusted to achieve efficient transmission of optical signals of different wavelengths in the same optical fiber. Higher current tuning sensitivity can control the wavelength more finely, which helps to increase the number of channels and improve spectrum utilization. In optical sensing applications, precise wavelength tuning can improve the resolution of the sensor and more accurately measure small changes in physical quantities.

[0003] In the prior art, for example, Chinese patent CN102931584A discloses a "wavelength tunable laser system and control method thereof", which uses a temperature control device to adjust the operating temperature to affect the output wavelength of the laser, but this method has a slow response speed and is difficult to achieve fast and accurate wavelength adjustment. In addition, as described in the academic document "Experimental Study on Tuning Characteristics of Semiconductor Fiber Ring Cavity Lasers" (Laser Technology, Vol. 25, No. 6, December 2001), the traditional DFB laser structure does not fully consider how to optimize the current tuning sensitivity in design. When controlling the working conditions of the DFB laser, the prior art has obvious limitations. Although there are some cooling devices for temperature control, in actual applications, the accuracy of temperature control is not high enough, or the response speed of temperature control is slow, and it is impossible to compensate for the impact of temperature changes on current tuning sensitivity in time. From the perspective of existing technology, common laser current tuning is simply to measure the optical frequency comb emitted by the semiconductor laser, compare the measurement results with the set values, and then manually calculate and adjust the current output value to make the measured value of the semiconductor laser close to the set value to achieve laser adjustment. The adjustment sensitivity is not high, and it needs to react after deviation occurs. The adjustment direction is unclear, the error is large, and it is easy to be affected by external interference.

[0004] Therefore, a method for adjusting the current tuning sensitivity of a DFB semiconductor laser is proposed. Summary of the invention

[0005] In order to overcome the problems of low current tuning sensitivity, unclear adjustment direction, large error and weak anti-interference ability of DFB semiconductor laser in the prior art, the present invention provides a method for adjusting the current tuning sensitivity of DFB semiconductor laser.

[0006] To achieve the above object, the present invention provides the following technical solutions: A method for adjusting the current tuning sensitivity of a DFB semiconductor laser comprises the following steps: Step S1: The photoelectric detector in the signal acquisition module acquires a beat frequency signal with a high signal-to-noise ratio, and the power of the beat frequency signal is evenly distributed to the digital frequency pre-control module and the feedforward control module through a power divider; Step S2: In the digital frequency pre-control module, the beat frequency signal is filtered, amplified, divided and shaped; Step S3: In the digital frequency pre-control module, the digital frequency measuring unit measures the frequency value of the beat frequency signal in real time for the signal after shaping; Step S4: The digital frequency stabilization control module compares the frequency value with the target set frequency and obtains the feedback control amount in real time through the PID control algorithm; Step S5: the feedback control amount is converted into a digital-to-analog converter to output a control voltage to a voltage modulation port of a semiconductor laser driver, thereby changing the injection current of the semiconductor laser to achieve a rough control of the output laser frequency; Step S6: In the feedforward control module, the other branch of the power divider is subjected to bandpass filtering to extract the controlled beat frequency signal; Step S7: The beat frequency signal is frequency-shifted to the vicinity of the AOFS center frequency through a mixer and a high-pass filter, and the AOFS is directly driven after power amplification through an RF power amplifier to achieve rapid control of the laser frequency. In this step, the feedforward time delay and frequency offset are closely related to the phase noise suppression index; Step S8: using phase-locked loop technology to phase-lock the beat frequency to the reference frequency, achieving the same frequency stability as the reference frequency, and reaching the frequency stability limit.

[0007] In a preferred embodiment, in step S1, the signal acquisition module includes a photodetector and a power divider. The photodetector receives the optical signal and generates an electrical pulse signal corresponding to the optical signal. The photodetector outputs the electrical signal and transmits it to the power divider. The power divider uses an impedance matching network to evenly distribute the electrical pulse signal to the digital frequency pre-control module and the feedforward control module.

[0008] In a preferred embodiment, in step S2, the digital frequency pre-control module filters the beat frequency signal. is the output voltage after filtering, is the transimpedance gain, is the proportional factor, and the filtering formula is: .

[0009] In a preferred embodiment, in step S2, the digital frequency pre-control module amplifies, divides and shapes the filtered beat frequency signal, and the filtered beat frequency signal is amplified in two stages by the transistor in the amplifier circuit. is the magnification, is the current amplification factor of the transistor, is the collector resistance, is the input resistance of the transistor, and the amplification formula is: ;set up To output the beat frequency signal, is the input beat signal frequency, is the frequency division coefficient, and the frequency division formula of the beat frequency signal is: ; Assume the input beat frequency signal is , after passing through the comparator, the output signal is The square wave and beat frequency signal shaping formula is: .

[0010] In a preferred embodiment, in step S3, the digital frequency measurement unit adopts a multi-cycle synchronous frequency measurement method. First, the crystal oscillator generates a preset gate signal with a duty cycle of 50% through frequency division processing. Then, when the preset gate is at a high level, if the synchronization circuit receives the rising edge of the measured signal, it will immediately generate a synchronous gate signal. At this time, the rising edge of the synchronous gate signal is synchronized with the rising edge of the measured signal. When the synchronous gate is at a high level, counters A and B are turned on to perform edge-triggered counting on the measured signal and the time base signal respectively; when the preset gate signal becomes a low level, the synchronization circuit sets the synchronous gate signal to a low level while receiving the rising edge of the measured signal, so that counters A and B stop counting and latch the count value. Finally, the operator collects the latched results of counters A and B to obtain the frequency value of the measured signal, and a complete measurement is completed. The relative uncertainty of the frequency measurement of this method is related to the length of the high level time of the synchronous gate and the size of the time base frequency. The relative uncertainty of the frequency measurement result of the periodic synchronous frequency measurement method is: .

[0011] In a preferred embodiment, in step S4, the digital frequency stabilization control unit is composed of a microcontroller and a digital-to-analog converter. The microcontroller reads the frequency discrimination result of the digital frequency measurement unit through the data transmission line, and then obtains a digital control signal according to the frequency value. Finally, the digital-to-analog converter is used to provide an analog control voltage to the current tuning port of the laser driver, thereby achieving control of the frequency of the semiconductor laser.

[0012] In a preferred embodiment, in step S4, the digital frequency stabilization control module uses a PID control algorithm to calculate the real-time feedback control quantity. Assuming that KP, KI, and KD in the PID control algorithm are proportional, integral, and differential parameters, the PID algorithm is: .

[0013] In a preferred embodiment, in step S7, the output signal of the feedforward control module is , after mixing, two frequency components are obtained, which are and , after high-pass filtering, the low-frequency components are filtered out, so that the driving frequency of AOFS is obtained as ,set up is the frequency of the nearest tooth of the optical frequency comb, is the laser frequency output by the semiconductor laser, and the frequency of the first-order diffraction light diffracted by AOFS is: .

[0014] In a preferred embodiment, in step S7, the feedforward time delay and frequency offset are associated with the phase noise suppression index. The longer the delay time and the larger the frequency offset, the larger the corresponding phase noise suppression index and the worse the frequency feedforward control effect. The delay time of the feedforward control system mainly includes the photoelectric conversion time, the RF device and transmission line delay time, and the AOFS frequency rise time. This part of the content echoes the newly added related content in step S7, further emphasizing this feature.

[0015] In a preferred embodiment, in step S8, the beat frequency is phase-locked to the reference frequency through a phase-locked loop technology, entering a locked state, and the frequency fluctuation is lower than 1 Hz, that is, the same frequency stability as the reference frequency is achieved, reaching the frequency stability limit.

[0016] The method for adjusting the current tuning sensitivity of a DFB semiconductor laser provided by the present invention has the following significant technical effects: 1. It has the advantage of high-precision frequency measurement: it adopts multi-cycle synchronous frequency measurement technology. This method ensures the complete periodicity of the measured signal by setting a synchronous gate, effectively eliminates the ±1 quantization error in the traditional method, realizes equal-precision measurement of measured signals of different frequencies, and significantly improves the frequency measurement accuracy.

[0017] 2. Advantages of adaptive control and anti-interference ability: The PID control algorithm realizes precise control of the DFB laser under different working environments. By dynamically adjusting the three parameters of proportion, integration and differentiation, the system can flexibly adapt to the changes in the characteristics of various controlled objects, effectively resist external interference such as temperature fluctuations and power supply fluctuations, and improve system stability.

[0018] 3. It has the advantage of fast feedforward control: the innovative introduction of the acousto-optic frequency shifter (AOFS) feedforward control mechanism realizes real-time monitoring and rapid compensation of interference, without having to wait for the output deviation to occur before making adjustments. It greatly reduces the system response delay, improves the dynamic tracking capability, and effectively reduces or even eliminates the system error under steady-state conditions.

[0019] Through the synergistic effect of the above three key technologies, the present invention realizes the precise adjustment of the current tuning sensitivity of the DFB semiconductor laser, solves the core problems of unclear adjustment direction, large error and weak anti-interference ability in the prior art, and provides reliable technical support for high-performance optical communication and precision optical sensing systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for describing the embodiments are briefly introduced below.

[0021] Figure 1 It is a system flow diagram of a method for adjusting the current tuning sensitivity of a DFB semiconductor laser proposed by the present invention, which shows a signal acquisition module, a digital frequency pre-control module, a feedforward control module and the signal flow relationship between the modules. DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the statement "include..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0024] Example 1, reference Figure 1, a method for adjusting the current tuning sensitivity of a DFB semiconductor laser is provided in the present invention, comprising the following steps: Step S1: The photoelectric detector in the signal acquisition module acquires a beat frequency signal with a high signal-to-noise ratio, and the power of the beat frequency signal is evenly distributed to the digital frequency pre-control module and the feedforward control module by a power divider. The signal acquisition module includes a photoelectric detector and a power divider. The photoelectric detector receives an optical signal and generates an electrical pulse signal corresponding to the optical signal. The photoelectric detector outputs an electrical signal and transmits it to the power divider. The power divider uses an impedance matching network to evenly distribute the electrical pulse signal to the digital frequency pre-control module and the feedforward control module. Step S2: In the digital frequency pre-control module, the beat frequency signal is filtered, amplified, divided and shaped; Step S3: In the digital frequency pre-control module, the digital frequency measuring unit measures the frequency value of the beat frequency signal in real time for the signal after shaping; Step S4: comparing the measured frequency value with the target set frequency; Step S5: outputting a control voltage to a voltage modulation port of a semiconductor laser driver by comparing the difference, thereby changing the injection current of the semiconductor laser to achieve coarse control of the output laser frequency.

[0025] Among them, the digital frequency pre-control module filters the beat frequency signal. is the output voltage after filtering, is the transimpedance gain, is the proportional factor, and the filtering formula is: .

[0026] The digital frequency pre-control module amplifies, divides and shapes the filtered beat frequency signal. The filtered beat frequency signal is amplified in two stages by the transistor in the amplifier circuit. is the magnification, is the current amplification factor of the transistor, is the collector resistance, is the input resistance of the transistor, and the amplification formula is: ;set up To output the beat frequency signal, is the input beat signal frequency, is the frequency division coefficient, and the frequency division formula of the beat frequency signal is: ; Assume the input beat frequency signal is , after passing through the comparator, the output signal is The square wave and beat frequency signal shaping formula is: .

[0027] Embodiment 2 provides a method for adjusting the current tuning sensitivity of a DFB semiconductor laser according to the present invention, comprising the following steps: Step S1: The photoelectric detector in the signal acquisition module acquires a beat frequency signal with a high signal-to-noise ratio, and the power of the beat frequency signal is evenly distributed to the digital frequency pre-control module and the feedforward control module by a power divider; Step S2: In the digital frequency pre-control module, the beat frequency signal is filtered, amplified, divided and shaped; Step S3: In the digital frequency pre-control module, the digital frequency measuring unit measures the frequency value of the beat frequency signal in real time for the signal after shaping; Step S4: comparing the measured frequency value with the target set frequency; Step S5: After digital-to-analog conversion, the feedback control quantity outputs a control voltage to the voltage modulation port of the semiconductor laser driver, thereby changing the injection current of the semiconductor laser to achieve coarse control of the output laser frequency.

[0028] On the basis of Example 1, a multi-cycle synchronous frequency measurement method is added. The digital frequency measurement unit in the digital frequency pre-control module adopts a multi-cycle synchronous frequency measurement method. First, the crystal oscillator generates a preset gate signal with a duty cycle of 50% through frequency division processing. Then, when the preset gate is at a high level, if the synchronization circuit receives the rising edge of the measured signal, it will immediately generate a synchronous gate signal. At this time, the rising edge of the synchronous gate signal is synchronized with the rising edge of the measured signal. When the synchronous gate is at a high level, counters A and B are turned on to perform edge-triggered counting on the measured signal and the time base signal respectively; when the preset gate signal becomes a low level, the synchronization circuit sets the synchronous gate signal to a low level while receiving the rising edge of the measured signal, so that counters A and B stop counting and latch the count value. Finally, the operator collects the latched results of counters A and B to obtain the frequency value of the measured signal, and a complete measurement is completed. The relative uncertainty of the frequency measurement of this method is related to the length of the high level time of the synchronous gate and the size of the time base frequency. The relative uncertainty of the frequency measurement result of the periodic synchronous frequency measurement method is: .

[0029] By selecting the multi-cycle synchronous frequency measurement method, compared with the direct frequency measurement method, this method ensures the complete periodicity of the measured signal by setting the synchronous gate, thereby eliminating the quantization error of ±1 and achieving equal-precision measurement of measured signals of different frequencies.

[0030] Example 3, reference Figure 1 The present invention provides a method for adjusting the current tuning sensitivity of a DFB semiconductor laser, comprising the following steps: Step S1: The photoelectric detector in the signal acquisition module acquires a beat frequency signal with a high signal-to-noise ratio, and the power of the beat frequency signal is evenly distributed to the digital frequency pre-control module and the feedforward control module by a power divider; Step S2: In the digital frequency pre-control module, the beat frequency signal is filtered, amplified, divided and shaped; Step S3: In the digital frequency pre-control module, the digital frequency measuring unit measures the frequency value of the beat frequency signal in real time for the signal after shaping; Step S4: The digital frequency stabilization control module compares the frequency value with the target set frequency and obtains the feedback control amount in real time through the PID control algorithm; Step S5: After digital-to-analog conversion, the feedback control quantity outputs a control voltage to the voltage modulation port of the semiconductor laser driver, thereby changing the injection current of the semiconductor laser to achieve coarse control of the output laser frequency.

[0031] A digital frequency stabilization control unit is added on the basis of Example 1 and Example 2. The digital frequency stabilization control unit is composed of a microcontroller and a digital-to-analog converter. The microcontroller reads the frequency discrimination result of the digital frequency measurement unit through the data transmission line, and then the microcontroller obtains a digital control signal according to the frequency value. Finally, the digital-to-analog converter is used to provide an analog control voltage to the current tuning port of the laser driver, thereby realizing the control of the semiconductor laser frequency. The digital frequency stabilization control module uses a PID control algorithm to calculate the real-time feedback control quantity. Assuming that KP, KI, and KD in the PID control algorithm are proportional, integral, and differential parameters, the PID algorithm is: .

[0032] In the digital frequency stabilization system, the dynamic characteristics of the controlled object may vary due to factors such as model and working environment. The PID algorithm is used to flexibly adapt to the characteristics of various controlled objects by adjusting the three parameters of proportion, integration and differentiation. The actual digital frequency stabilization system will be subject to various external interferences, such as temperature changes, power supply fluctuations, etc. These interferences may cause frequency changes. The PID algorithm can adjust the control signal in time according to the frequency deviation and its changes, and effectively resist these interferences.

[0033] Embodiment 4 provides a method for adjusting the current tuning sensitivity of a DFB semiconductor laser according to the present invention, comprising the following steps: Step S1: The photoelectric detector in the signal acquisition module acquires a beat frequency signal with a high signal-to-noise ratio, and the power of the beat frequency signal is evenly distributed to the digital frequency pre-control module and the feedforward control module by a power divider; Step S2: In the digital frequency pre-control module, the beat frequency signal is filtered, amplified, divided and shaped; Step S3: In the digital frequency pre-control module, the digital frequency measuring unit measures the frequency value of the beat frequency signal in real time for the signal after shaping; Step S4: The digital frequency stabilization control module compares the frequency value with the target set frequency and obtains the feedback control amount in real time through the PID control algorithm; Step S5: the feedback control amount is converted into a digital-to-analog converter to output a control voltage to a voltage modulation port of a semiconductor laser driver, thereby changing the injection current of the semiconductor laser to achieve a rough control of the output laser frequency; Step S6: In the feedforward control module, the other branch of the power divider is subjected to bandpass filtering to extract the controlled beat frequency signal; Step S7: The beat frequency signal is frequency-shifted to the vicinity of the AOFS center frequency through a mixer and a high-pass filter, and the AOFS is directly driven after power amplification through an RF power amplifier to achieve rapid control of the laser frequency. In this step, the feedforward time delay and frequency offset are closely related to the phase noise suppression index. Specifically, the longer the delay time, the greater the frequency offset, and the corresponding phase noise suppression index, which will result in worse frequency feedforward control effect. The delay time of the feedforward control system mainly includes the photoelectric conversion time, the RF device and transmission line delay time, and the AOFS frequency rise time; Step S8: using phase-locked loop technology to phase-lock the beat frequency to the reference frequency, achieving the same frequency stability as the reference frequency, and reaching the frequency stability limit.

[0034] A feedforward control module is added on the basis of embodiment 1-3, and the output signal of the feedforward control module is , after mixing, two frequency components are obtained, which are and , after high-pass filtering, the low-frequency components are filtered out, so that the driving frequency of AOFS is obtained as ,set up is the frequency of the nearest tooth of the optical frequency comb, is the laser frequency output by the semiconductor laser, and the frequency of the first-order diffraction light diffracted by AOFS is: .

[0035] Among them, the feedforward time delay and frequency offset are related to the phase noise suppression index. The longer the delay time and the larger the frequency offset, the larger the corresponding phase noise suppression index and the worse the frequency feedforward control effect. The delay time of the feedforward control system mainly includes the photoelectric conversion time, the delay time of the RF device and the transmission line, and the AOFS frequency rise time. The beat frequency is phase-locked to the reference frequency using the phase-locked loop technology to achieve the same frequency stability as the reference frequency and reach the frequency stability limit. The AOFS in the feedforward control module can monitor the interference factors in the system in real time. Once interference is detected, there is no need to wait for the system output to deviate before making adjustments. Instead, the corresponding control action is made directly according to the interference situation to compensate for the impact of the interference on the system in time, thereby effectively reducing the response delay of the system. When the set value of the system changes, AOFS quickly calculates the required control adjustment based on the pre-established model or algorithm, so that the system output can quickly keep up with the change of the set value, and realizes fast dynamic tracking. By compensating for known system changes in advance, the error of the system in steady state can be effectively reduced or even eliminated.

[0036] The above embodiments may be implemented in whole or in part by software, hardware, firmware or any other combination. When implemented by software, the above embodiments may be implemented in whole or in part in the form of a computer program product.

[0037] Those of ordinary skill in the art will appreciate that the modules and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0038] In addition, each functional module in each embodiment of the present application may be integrated into one processing module, or each module may exist physically separately, or two or more modules may be integrated into one module.

[0039] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

[0040] Finally: The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for adjusting the current tuning sensitivity of a DFB semiconductor laser, characterized in that: The following steps are involved: Step S1: acquiring a beat frequency signal with a high signal-to-noise ratio through a photoelectric detector in a signal acquisition module, and evenly distributing the power of the beat frequency signal to a digital frequency pre-control module and a feedforward control module through a power divider; Step S2: In the digital frequency pre-control module, the acquired beat frequency signal is filtered, amplified, divided and shaped; Step S3: using a digital frequency measuring unit to perform real-time measurement of the beat signal frequency value of the signal shaped in step S2; Step S4: Compare the frequency value measured in step S3 with the target set frequency through the digital frequency stabilization control module, and calculate the feedback control amount in real time through the PID control algorithm; Step S5: after the feedback control amount in step S4 is converted into digital-to-analog, a control voltage is output to the voltage modulation port of the semiconductor laser driver, thereby changing the injection current of the semiconductor laser to achieve coarse control of the output laser frequency; Step S6: In the feedforward control module, the other branch signal of the power divider is processed by bandpass filtering to extract the controlled beat frequency signal; Step S7: The beat frequency signal in step S6 is frequency-shifted to the vicinity of the AOFS center frequency through a mixer and a high-pass filter, and the AOFS is directly driven after power amplification through a radio frequency power amplifier to achieve rapid control of the laser frequency; Step S8: using a phase-locked loop technology to phase-lock the beat frequency to the reference frequency, so as to achieve the same frequency stability as the reference frequency.

2. A method for adjusting the current tuning sensitivity of a DFB semiconductor laser according to claim 1, characterized in that: The signal acquisition module in step S1 includes a photoelectric detector and a power divider, wherein: The photodetector receives the light signal and generates an electrical pulse signal corresponding to the light signal; The electrical signal output by the photodetector is transmitted to the power divider; The power divider uses an impedance matching network to evenly distribute the electrical pulse signal to the digital frequency pre-control module and the feedforward control module.

3. The method for adjusting the current tuning sensitivity of a DFB semiconductor laser according to claim 1, characterized in that: The digital frequency pre-control module in step S2 filters the beat frequency signal. is the output voltage after filtering, is the transimpedance gain, is the proportional factor, and the filtering formula is: .

4. The method for adjusting the current tuning sensitivity of a DFB semiconductor laser according to claim 1, characterized in that: The digital frequency pre-control module in step S2 processes the filtered beat frequency signal, specifically including: Amplification: The filtered beat frequency signal is amplified in two stages by the transistors in the amplifier circuit. is the magnification, is the current amplification factor of the transistor, is the collector resistance, is the input resistance of the transistor, and the amplification formula is: ; Frequency division: set To output the beat frequency signal, is the input beat signal frequency, is the frequency division coefficient, and the frequency division formula of the beat frequency signal is: ; Shaping: Assume the input beat frequency signal is , after passing through the comparator, the output signal is The square wave and beat frequency signal shaping formula is: .

5. The method for adjusting the current tuning sensitivity of a DFB semiconductor laser according to claim 1, characterized in that: The digital frequency measurement unit in step S3 adopts a multi-cycle synchronous frequency measurement method, which includes: The crystal oscillator generates a preset gate signal with a duty cycle of 50% through frequency division processing; When the preset gate is at a high level, the synchronization circuit generates a synchronization gate signal immediately after receiving the rising edge of the measured signal, so that the rising edge of the synchronization gate signal is synchronized with the rising edge of the measured signal; When the synchronization gate is at a high level, counters A and B are turned on to perform edge-triggered counting on the measured signal and the time base signal respectively; When the preset gate signal becomes low level, the synchronization circuit sets the synchronization gate signal to low level when receiving the rising edge of the measured signal, so that counters A and B stop counting and latch the count value; The operator collects the latch results of counters A and B to obtain the frequency value of the measured signal; The relative uncertainty of the frequency measurement of this method is related to the length of the high level time of the synchronous gate and the size of the time base frequency. The relative uncertainty of the frequency measurement result of the periodic synchronous frequency measurement method is: .

6. The method for adjusting the current tuning sensitivity of a DFB semiconductor laser according to claim 1, characterized in that: The digital frequency stabilization control unit in step S4 is composed of a microcontroller and a digital-to-analog converter, and its working process includes: The microcontroller reads the discrimination result of the digital frequency measuring unit through the data transmission line; The microcontroller calculates the digital control signal according to the frequency value; The digital control signal is converted into an analog control voltage through a digital-to-analog converter and output to the current tuning port of the laser driver, thereby achieving control of the semiconductor laser frequency.

7. The method for adjusting the current tuning sensitivity of a DFB semiconductor laser according to claim 1, characterized in that: The digital frequency stabilization control module in step S4 uses the PID control algorithm to calculate the real-time feedback control quantity. Assuming that KP, KI, and KD in the PID control algorithm are proportional, integral, and differential parameters, the PID algorithm is: .

8. The method for adjusting the current tuning sensitivity of a DFB semiconductor laser according to claim 1, characterized in that: In step S7, the signal processing of the feedforward control module is specifically as follows: The output signal of the feedforward control module is ; After mixing, two frequency components are obtained, namely and ; After filtering out the low-frequency components through a high-pass filter, the driving frequency of AOFS is obtained as follows: ; set up is the frequency of the nearest tooth of the optical frequency comb, is the laser frequency output by the semiconductor laser, and the frequency of the first-order diffraction light diffracted by AOFS is: ; The feedforward time delay and frequency offset magnitude are closely related to the phase noise suppression index.

9. The method for adjusting the current tuning sensitivity of a DFB semiconductor laser according to claim 8, characterized in that: The relationship between the feedforward time delay and frequency offset and the phase noise suppression index is: The longer the delay time and the larger the frequency offset, the larger the corresponding phase noise suppression index and the worse the frequency feedforward control effect; The delay time of the feedforward control system mainly includes the photoelectric conversion time, the RF device and transmission line delay time, and the AOFS frequency rise time.

10. The method for adjusting the current tuning sensitivity of a DFB semiconductor laser according to claim 1, characterized in that: In step S8, the beat frequency is phase-locked to the reference frequency through the phase-locked loop technology, so that the system enters a locked state, the frequency fluctuation is lower than 1 Hz, and the frequency stability is the same as the reference frequency reference, reaching the frequency stability limit.

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