A method for adjusting the current tuning sensitivity of a DFB semiconductor laser

Abstract

The present invention discloses a method for adjusting the current tuning sensitivity of a DFB semiconductor laser. A beat signal with high signal-to-noise ratio is obtained by a photodetector in a signal acquisition module, and the beat signal is equally divided in power by a power splitter and sent to a digital frequency pre-control module and a feedforward control module. The beat signal is filtered, amplified, frequency-divided and shaped. After shaping, the frequency value of the beat signal is measured in real time by a digital frequency measurement unit, and a digital frequency stabilization control module compares the frequency value with a target set frequency. This method improves the frequency measurement accuracy through multi-period synchronous frequency measurement technology, uses a PID control algorithm to achieve precise feedback control of the frequency, and combines feedforward control of an acousto-optic frequency shifter to achieve fast control of the laser frequency, effectively improving the current tuning sensitivity of the DFB semiconductor laser and solving the problems of unclear adjustment direction, large error and weak anti-interference ability in the prior art.

Description

Technical Field

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

[0002] Semiconductor lasers, especially distributed feedback semiconductor lasers, are the core components of modern optical communication and optical sensing systems. In optical communication, as a key component of an optical transmitter, it is used to convert electrical signals into optical signals for high-speed and long-distance information transmission. The current tuning sensitivity is a key performance index of DFB semiconductor lasers, which determines the efficiency of adjusting the output wavelength of the laser by changing the injection current. In the wavelength division multiplexing system of optical communication, it is necessary to accurately adjust the wavelength of the laser to achieve efficient transmission of optical signals with different wavelengths in the same optical fiber. A higher current tuning sensitivity can more finely control the wavelength, which helps to increase the number of channels and improve the spectral utilization rate. In optical sensing applications, accurate wavelength tuning can improve the resolution of the sensor and more accurately measure small changes in physical quantities.

[0003] In the prior art, as disclosed in Chinese Patent CN102931584A, "Wavelength Tunable Laser System and Its Control Method", it uses a temperature control device to affect the output wavelength of the laser by adjusting the operating temperature, but this method has a slow response speed and it is difficult to achieve fast and accurate wavelength adjustment. In addition, as described in the academic literature "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 its design. When controlling the operating conditions of DFB lasers, there are obvious limitations in the prior art. For temperature control, although there are some cooling devices, in practical applications, the accuracy of temperature control is not high enough, or the response speed of temperature control is relatively slow, and it cannot compensate for the influence of temperature changes on the current tuning sensitivity in a timely manner. From the prior art, the common current tuning of lasers is just a simple measurement of the optical frequency comb emitted by the semiconductor laser, comparing the measurement result with the set value, and after comparison, it is necessary to manually calculate and adjust the output value of the current so that the measurement value of the semiconductor laser is close to the set value to achieve the regulation of the laser. The regulation sensitivity is not high, and it can only respond after a deviation occurs. The regulation direction is not clear, the error is large, and it is easily affected by external interference.

[0004] Therefore, a method for regulating 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 lasers in the prior art, the present invention provides a method for adjusting the current tuning sensitivity of DFB semiconductor lasers.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for adjusting the current tuning sensitivity of a DFB semiconductor laser, comprising the following steps:

[0008] Step S1: The beat signal with high signal-to-noise ratio is obtained by the photodetector in the signal acquisition module, and the power of the beat signal is evenly distributed to the digital frequency pre-control module and the feed-forward control module through a power divider;

[0009] Step S2: In the digital frequency pre-control module, the beat signal is filtered, amplified, frequency-divided, and shaped;

[0010] Step S3: In the digital frequency pre-control module, the frequency value of the beat signal is measured in real time by the digital frequency measurement unit for the shaped signal;

[0011] Step S4: The digital frequency stabilization control module compares the frequency value with the target set frequency, and calculates the feedback control quantity in real time through the PID control algorithm;

[0012] Step S5: The above feedback control quantity is converted by digital-to-analog conversion and output as 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;

[0013] Step S6: In the feed-forward control module, the other branch of the power divider extracts the controlled beat signal through band-pass filtering;

[0014] Step S7: The beat signal is frequency-shifted to the vicinity of the AOFS center frequency through a mixer and a high-pass filter, and is directly driven by the AOFS after power amplification by a radio frequency power amplifier to achieve fast control of the laser frequency. In this step, the feed-forward time delay and the frequency offset size are closely related to the phase noise suppression index;

[0015] Step S8: The beat frequency is phase-locked to the reference frequency by using the phase-locked loop technology to achieve the same frequency stability as the reference frequency and reach the frequency stability limit.

[0016] 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 position of the power divider. The power divider uses an impedance matching network to equally divide the electrical pulse signal into the digital frequency pre-control module and the feed-forward control module.

[0017] In a preferred embodiment, in step S2, the digital frequency pre-control module filters the beat signal. Let be the output voltage after filtering, be the noise power of the beat signal, be the reference power of the continuous wave light source, be the transimpedance gain, be the scaling factor. The filtering formula is: .

[0018] In a preferred embodiment, in step S2, the digital frequency pre-control module amplifies, divides, and shapes the filtered beat signal. The filtered beat signal is amplified in two stages by the triode in the amplifier circuit. Let be the amplification factor, be the current amplification factor of the triode, be the collector resistance, be the input resistance of the triode. The amplification formula is: ; Let be the output beat signal, be the frequency of the input beat signal, be the division coefficient. The beat signal division formula is: ; Let the input beat signal be . After passing through the comparator, the output signal is square wave. The high-level signal is , and the low-level signal is . Among them, the high-level signal is , and the low-level signal is . The beat signal shaping formula is: .

[0019] In a preferred embodiment, in the step S3, the digital frequency measurement unit adopts a multi-period synchronous frequency measurement method. First, a preset gating signal with a duty cycle of 50% is generated by the crystal oscillator through frequency division processing. Then, when the preset gate is at a high level, if the synchronous circuit receives the rising edge of the signal to be measured, a synchronous gating signal is immediately generated. At this time, the rising edge of the synchronous gating signal is synchronized with the rising edge of the signal to be measured. When the synchronous gate is at a high level, counters A and B are enabled to perform edge-triggered counting on the signal to be measured and the time-base signal respectively. When the preset gating signal becomes low, the synchronous circuit sets the synchronous gating signal to low while receiving the rising edge of the signal to be measured, so that counters A and B stop counting and latch the count values. Finally, the arithmetic unit collects the latched results of counters A and B to obtain the frequency value of the signal to be measured, and a complete measurement is completed. The relative uncertainty of frequency measurement by this method is related to the length of the high-level time of the synchronous gate and the magnitude of the time-base frequency. Let be the frequency of the signal to be measured, the duration of the high level of the synchronous gate, be the time-base frequency, d be the small change amount of . The relative uncertainty of the frequency measurement result of the period synchronous frequency measurement method is:

[0020] In a preferred embodiment, in the 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 a data transmission line, and then the microcontroller obtains a digital control signal according to the frequency value, and finally gives an analog control voltage to the current tuning port of the laser driver through the digital-to-analog converter, so as to realize the control of the frequency of the semiconductor laser.

[0021] In a preferred embodiment, in the step S4, the digital frequency stabilization control module uses a PID control algorithm to calculate the real-time feedback control quantity. Let be the transfer function of the PID controller, be the proportional gain, be the integral gain, be the differential gain. The transfer function form of the PID algorithm is: , where s is the complex frequency variable in the Laplace transform,.

[0022] In a preferred embodiment, in the step S7, the output signal of the feedforward control module is , the frequency output by the local oscillator is , which is used to mix with the beat frequency signal. After mixing, two frequency components are obtained, which are and , after passing through a high-pass filter, the low-frequency components are filtered out, so that the driving frequency of AOFS is , let be the frequency of the closest comb teeth of the optical frequency comb, be the laser output frequency of the semiconductor laser, and the frequency of the positive first-order diffracted light diffracted by AOFS is: .

[0023] In a preferred embodiment, in step S7, the feedforward time delay and the frequency offset magnitude 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 feedforward control effect of the frequency. The delay time of the feedforward control system mainly includes the optoelectronic conversion time, the radio frequency device and transmission line delay time, and the AOFS frequency rise time. This part of the content echoes the newly added associated content in step S7, further emphasizing this characteristic.

[0024] In a preferred embodiment, in step S8, the beat frequency is phase-locked to the reference frequency through phase-locked loop technology and enters the locked state, and the frequency fluctuation is lower than 1 Hz, that is, the same frequency stability as the reference frequency reference is achieved, reaching the frequency stability limit.

[0025] The method for adjusting the current tuning sensitivity of a DFB semiconductor laser provided by the present invention has the following remarkable technical effects:

[0026] 1. It has the advantage of high-precision frequency measurement: The multi-period synchronous frequency measurement technology is adopted. 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 the equal-precision measurement of the measured signals with different frequencies, and significantly improves the frequency measurement accuracy.

[0027] 2. It has the advantages of adaptive control and anti-interference ability: The precise control of the DFB laser under different working environments is realized through the PID control algorithm. By dynamically adjusting the three parameters of proportional, integral and differential, the system can flexibly adapt to the changes in the characteristics of various controlled objects, effectively resist external interferences such as temperature fluctuations and power supply fluctuations, and improve the system stability.

[0028] 3. It has the advantage of fast feedforward control: The feedforward control mechanism of the acousto-optic frequency shifter (AOFS) is innovatively introduced, realizing the real-time monitoring and fast compensation of interference. There is no need to wait for the output deviation to occur before adjusting, greatly reducing the system response delay, improving the dynamic tracking ability, and effectively reducing or even eliminating the system error under steady-state conditions.

[0029] 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

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments.

[0031] Figure 1 It is a schematic system flow chart of a method for adjusting the current tuning sensitivity of a DFB semiconductor laser proposed by the present invention. The figure 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 OF THE EMBODIMENTS

[0032] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0033] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover a non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, the elements defined by the statement "including..." do not exclude the presence of additional identical elements in the process, method, article or device including the said elements.

[0034] Example 1, referring to Figure 1 A method for adjusting the current tuning sensitivity of a DFB semiconductor laser according to the present invention is given, including the following steps:

[0035] Step S1: The beat signal with high signal-to-noise ratio is obtained by the photodetector in the signal acquisition module, and the power of this beat signal is evenly distributed to the digital frequency pre-control module and the feedforward control module by a power splitter. The signal acquisition module includes a photodetector and a power splitter. The photodetector receives the optical signal and generates an electrical pulse signal corresponding to the optical signal. The photodetector outputs the electrical signal to the position of the power splitter, and the power splitter uses an impedance matching network to evenly distribute the electrical pulse signal to the digital frequency pre-control module and the feedforward control module;

[0036] Step S2: In the digital frequency pre-control module, the beat signal is filtered, amplified, frequency-divided, and shaped;

[0037] Step S3: In the digital frequency pre-control module, the frequency value of the shaped signal is measured in real time by the digital frequency measurement unit for the beat signal;

[0038] Step S4: The measured frequency value is compared with the target set frequency;

[0039] Step S5: A control voltage is output to the voltage modulation port of the semiconductor laser driver through the comparison difference, so as to change the injection current of the semiconductor laser to achieve coarse control of the output laser frequency.

[0040] Among them, the digital frequency pre-control module filters the beat signal. Let be the output voltage after filtering, be the noise power of the beat signal, be the reference power of the continuous wave light source, be the transimpedance gain, be the proportionality factor, and the filtering formula is: .

[0041] Among them, the digital frequency pre-control module amplifies, frequency-divides, and shapes the filtered beat signal. The filtered beat signal is amplified in two stages by the triode in the amplifier circuit. Let be the amplification factor, be the current amplification factor of the triode, be the collector resistance, be the input resistance of the triode, and the amplification formula is: ; Let be the output beat signal, be the input beat signal frequency, be the frequency division coefficient, and the beat signal frequency division formula is: ; Let the input beat signal be , after passing through the comparator, the output signal is square wave,, the high-level signal is , and the low-level signal is , where the high-level signal is , and the low-level signal is The shaping formula of the beat frequency signal is: .

[0042] Embodiment 2 provides a method for adjusting the current tuning sensitivity of a DFB semiconductor laser according to the present invention, including the following steps:

[0043] Step S1: The photodetector in the signal acquisition module acquires a beat frequency signal with high signal-to-noise ratio, and the power splitter evenly distributes the power of the beat frequency signal to the digital frequency pre-control module and the feedforward control module;

[0044] Step S2: In the digital frequency pre-control module, the beat frequency signal is filtered, amplified, frequency-divided and shaped;

[0045] Step S3: In the digital frequency pre-control module, the digital frequency measurement unit measures the frequency value of the beat frequency signal in real time for the shaped signal;

[0046] Step S4: Compare the measured frequency value with the target set frequency;

[0047] Step S5: The above feedback control quantity is converted by digital-to-analog conversion and then output as a control voltage to the voltage modulation port of the semiconductor laser driver, so as to change the injection current of the semiconductor laser to achieve coarse control of the output laser frequency.

[0048] On the basis of Embodiment 1, a multi-period synchronous frequency measurement method is added. The digital frequency measurement unit in the digital frequency pre-control module adopts the multi-period 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 synchronous circuit receives the rising edge of the signal to be measured, it immediately generates a synchronous gate signal. At this time, the rising edge of the synchronous gate signal is synchronized with the rising edge of the signal to be measured. When the synchronous gate is at a high level, counters A and B are started to perform edge-triggered counting on the signal to be measured and the time-base signal respectively; when the preset gate signal becomes low level, the synchronous circuit, while receiving the rising edge of the signal to be measured, sets the synchronous gate signal to low level, so that counters A and B stop counting and latch the count values. Finally, the arithmetic unit collects the latched results of counters A and B to obtain the frequency value of the signal to be measured, and a complete measurement is completed. The relative uncertainty of the frequency measurement by this method is related to the length of the high-level time of the synchronous gate and the magnitude of the time-base frequency. Let be the frequency of the signal to be measured, the duration of the high level of the synchronous gate, be the time-base frequency, d is the small change amount of , used to measure the uncertainty of the frequency measurement. The relative uncertainty of the frequency measurement result of the period synchronous frequency measurement method is: 。

[0049] 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 a synchronous gate, thus eliminating the quantization error of ±1 and achieving equal - precision measurement of measured signals with different frequencies.

[0050] Example 3, refer to Figure 1 A method for adjusting the current tuning sensitivity of a DFB semiconductor laser according to the present invention is given, including the following steps:

[0051] Step S1: The photodetector in the signal acquisition module acquires a beat signal with high signal - to - noise ratio, and the power divider evenly distributes the power of this beat signal to the digital frequency pre - control module and the feed - forward control module;

[0052] Step S2: In the digital frequency pre - control module, the beat signal is filtered, amplified, frequency - divided, and shaped;

[0053] Step S3: In the digital frequency pre - control module, the digital frequency measurement unit measures the frequency value of the beat signal in real - time for the shaped signal;

[0054] Step S4: The digital frequency stabilization control module compares the frequency value with the target set frequency, and calculates the feedback control quantity in real - time through the PID control algorithm;

[0055] Step S5: The above - mentioned feedback control quantity is converted by digital - to - analog conversion and then 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.

[0056] Based on Embodiment 1 and Embodiment 2, a digital frequency stabilization control unit is added. 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 a data transmission line, then the microcontroller obtains a digital control signal according to the frequency value, and finally gives an analog control voltage to the current tuning port of the laser driver through the digital - to - analog converter, thereby achieving control of the semiconductor laser frequency. Among them, the digital frequency stabilization control module uses the PID control algorithm to calculate the real - time feedback control quantity. Let be the transfer function of the PID controller, be the proportional gain, be the integral gain, be the derivative gain. The transfer function form of the PID algorithm is: , where s is the complex frequency variable in the Laplace transform.

[0057] In a digital frequency stabilization system, the dynamic characteristics of the controlled object may vary due to factors such as model and working environment. By using the PID algorithm and adjusting the three parameters of proportional, integral, and differential, it can flexibly adapt to the characteristics of various controlled objects. The actual digital frequency stabilization system will be subject to various external interferences, such as temperature changes and power fluctuations. These interferences may cause frequency changes. The PID algorithm can adjust the control signal in a timely manner according to the frequency deviation and its change situation, effectively resisting these interferences.

[0058] Embodiment 4 provides a method for adjusting the current tuning sensitivity of a DFB semiconductor laser according to the present invention, including the following steps:

[0059] Step S1: The photodetector in the signal acquisition module acquires a beat signal with high signal-to-noise ratio, and the power splitter evenly distributes the power of the beat signal to the digital frequency pre-control module and the feed-forward control module.

[0060] Step S2: In the digital frequency pre-control module, the beat signal is filtered, amplified, frequency-divided, and shaped.

[0061] Step S3: In the digital frequency pre-control module, the digital frequency measurement unit measures the frequency value of the beat signal in real time for the shaped signal.

[0062] Step S4: The digital frequency stabilization control module compares the frequency value with the target set frequency, and calculates the feedback control quantity in real time through the PID control algorithm.

[0063] Step S5: The above feedback control quantity is converted by digital-to-analog conversion and then 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.

[0064] Step S6: In the feed-forward control module, the other branch of the power splitter extracts the controlled beat signal through band-pass filtering.

[0065] Step S7: The beat signal is frequency-shifted to the vicinity of the AOFS center frequency through a mixer and a high-pass filter, and is directly driven by the AOFS after being amplified in power by a radio frequency power amplifier to achieve fast control of the laser frequency. In this step, the feed-forward time delay and the frequency offset size are closely related to the phase noise suppression index. Specifically, the longer the delay time, the larger the frequency offset, and the corresponding larger the phase noise suppression index, which will lead to a worse feed-forward control effect on the frequency. The delay time of the feed-forward control system mainly includes the optoelectronic conversion time, the delay time of radio frequency devices and transmission lines, and the AOFS frequency rise time.

[0066] Step S8: Use the phase-locked loop technology to lock the beat frequency to the reference frequency, achieve the same frequency stability as the reference frequency, and reach the frequency stability limit.

[0067] Based on Embodiments 1-3, a feedforward control module is added. The output signal of the feedforward control module is , and the frequency output by the local oscillator is , which is used to mix with the beat signal. After mixing, two frequency components are obtained, which are and . After passing through a high-pass filter, the low-frequency component is filtered out, so as to obtain the driving frequency of AOFS as . Let be the frequency of the closest comb teeth of the optical frequency comb, be the laser frequency output by the semiconductor laser, and the frequency of the positive first-order diffracted light diffracted by AOFS is: .

[0068] Among them, the feedforward time delay and the frequency offset size 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 feedforward control effect of the frequency. The delay time of the feedforward control system mainly includes the optoelectronic conversion time, the radio frequency device and transmission line delay time, and the AOFS frequency rise time. Use the phase-locked loop technology to lock the beat frequency to the reference frequency, 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, instead of waiting for the system output to deviate before making adjustments, it directly makes corresponding control actions according to the interference situation in a timely manner, compensates 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 amount adjustment according to the pre-established model or algorithm, so that the system output can quickly follow the change of the set value and achieve fast dynamic tracking. By compensating for the known system changes in advance, the error of the system at steady state can be effectively reduced or even eliminated.

[0069] The above embodiments can be implemented in whole or in part by software, hardware, firmware, or any other combination. When implemented using software, the above embodiments can be implemented in whole or in part in the form of a computer program product.

[0070] Those of ordinary skill in the art can realize that the modules and algorithm steps of each example described in combination with the embodiments disclosed herein can be implemented by electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. Professional technicians can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of this application.

[0071] In addition, the functional modules in each embodiment of this application can be integrated into one processing module, or each module can exist physically alone, or two or more modules can be integrated into one module.

[0072] As mentioned above, the above is only the specific implementation manner of this application, but the protection scope of this application is not limited thereto. Any person skilled in the art within the technical scope disclosed by this application can easily think of changes or substitutions, which should all be covered by the protection scope of this application. Therefore, the protection scope of this application should be subject to the protection scope of the claims.

[0073] Finally: The above is only the preferred embodiment of the present invention and is not used to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall 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, It includes the following steps: Step S1: Obtain a beat signal with high signal-to-noise ratio through a photodetector in the signal acquisition module, and evenly distribute the power of the beat signal to the digital frequency pre-control module and the feed-forward control module through a power splitter; Step S2: In the digital frequency pre-control module, filter, amplify, divide, and shape the obtained beat signal; Step S3: Use a digital frequency measurement unit to perform real-time measurement of the frequency value of the beat signal after shaping in Step S2; Step S4: Compare the frequency value measured in Step S3 with the target set frequency through a digital frequency stabilization control module, and calculate the feedback control quantity in real time through a PID control algorithm; Step S5: After digital-to-analog conversion of the feedback control quantity in Step S4, output 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; Step S6: In the feed-forward control module, process the signal of the other branch of the power splitter through band-pass filtering to extract the controlled beat signal; Step S7: Shift the frequency of the beat signal in Step S6 to near the center frequency of the AOFS through a mixer and a high-pass filter, and directly drive the AOFS after power amplification through a radio frequency power amplifier to achieve fast control of the laser frequency; Step S8: Use phase-locked loop technology to lock the beat frequency to the reference frequency 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 photodetector and a power splitter, where: The photodetector receives the optical signal and generates an electrical pulse signal corresponding to the optical signal; The electrical signal output by the photodetector is transmitted to the power splitter; The power splitter evenly distributes the electrical pulse signal to the digital frequency pre-control module and the feed-forward control module by using an impedance matching network.

3. A 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 the step S2 filters the beat signal. Let be the output voltage after filtering, be the noise power of the beat signal, be the reference power of the continuous wave light source, be the transimpedance gain, be the scaling factor, and the filtering formula is: .

4. A 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 signal, specifically including: Amplification: The beat frequency signal after filtering is amplified in two stages by the triode in the amplification circuit. Let be the amplification factor, be the current amplification factor of the triode, be the collector resistance, be the input resistance of the triode. The amplification formula is: ; Frequency division: Let be the output beat frequency signal, be the frequency of the input beat frequency signal, be the frequency division coefficient, and the beat frequency signal frequency division formula is: ; Shaping: Assume the input beat frequency signal is , after passing through a comparator, the output signal is a square wave, the high-level signal is , the low-level signal is , and the beat frequency signal shaping formula is: .

5. A 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-period synchronous frequency measurement method, and this method includes: Generate a preset gate signal with a duty cycle of 50% by frequency division processing of the crystal oscillator; When the preset gate is at a high level, after the synchronization circuit receives the rising edge of the measured signal, it immediately generates a synchronous gate signal to make the rising edge of the synchronous gate signal synchronous with the rising edge of the measured signal; When the synchronous gate is at a high level, start counters A and B to perform edge-triggered counting on the measured signal and the time-base signal respectively; When the preset gate signal becomes low, when the synchronization circuit receives the rising edge of the measured signal, it sets the synchronous gate signal to low, so that counters A and B stop counting and latch the count values; The arithmetic unit collects the latched 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 high-level time of the synchronization gate and the magnitude of the time-base frequency. Let be the frequency of the signal to be measured, be the duration of the high level of the synchronization gate, be the time-base frequency, d be the small change amount of , which is used to measure the uncertainty of the frequency measurement. The relative uncertainty of the frequency measurement result of the periodic synchronization frequency measurement method is: .

6. A 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 frequency discrimination result of the digital frequency measurement unit through a 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 by a digital-to-analog converter and output to the current tuning port of the laser driver, thereby realizing the control of the frequency of the semiconductor laser.

7. A 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 the step S4 calculates the real-time feedback control quantity by using the PID control algorithm. Let be the transfer function of the PID controller, be the proportional gain, be the integral gain, be the derivative gain. The transfer function form of the PID control algorithm is: , where s is the complex frequency variable in the Laplace transform.

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

9. A 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 the magnitude of the 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 feedforward control effect of the frequency; The delay time of the feedforward control system mainly includes the optoelectronic conversion time, the delay time of the radio frequency device and the transmission line, and the AOFS frequency rise time.

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

Images