A mode-hop-free scanning control method for narrow-linewidth lasers

Abstract

The application discloses a mode-hop-free scanning control method for a narrow-linewidth laser, and belongs to the technical field of laser control. The method comprises the following steps: generating a reference current scanning signal and a reference voltage scanning signal; generating a high-frequency jitter signal and superimposing the high-frequency jitter signal on the reference current scanning signal to generate a total injection current for driving the narrow-linewidth laser; acquiring a real-time optical power feedback signal of the narrow-linewidth laser; demodulating a mode margin error signal according to the optical power feedback signal and the high-frequency jitter signal, wherein the mode margin error signal is used for representing the mode stability of the current working state of the narrow-linewidth laser; and generating a dynamic correction voltage according to the mode margin error signal and superimposing the dynamic correction voltage on the reference voltage scanning signal to generate a total driving voltage for driving the piezoelectric ceramic of the narrow-linewidth laser. The application can effectively suppress the mode-hopping phenomenon by means of predictive feedforward correction and real-time compensation control mismatch.

Description

Technical Field

[0001] This invention relates to the field of laser control technology, and in particular to a mode-skipping scanning control method for narrow linewidth lasers. Background Technology

[0002] Narrow-linewidth tunable lasers play a crucial role in cutting-edge technologies such as coherent optical communication, high-precision spectral measurement, lidar, and atomic physics. These applications typically require lasers to perform continuous, smooth scanning over a wide wavelength range, maintaining a single longitudinal mode output throughout the scan—i.e., mode hopping-free. However, laser wavelength tuning usually relies on the coordinated control of both injection current and cavity length. Due to the significant difference in their physical response speeds, control mismatch is highly likely to occur during scanning, leading to mode hopping and severely compromising measurement continuity and accuracy. Existing technologies primarily address this issue through pre-calibrated open-loop control, but this approach is extremely sensitive to environmental changes and device aging, exhibiting poor robustness. Therefore, developing a control method that can adaptively compensate for dynamic disturbances and ensure continuous, mode-hopping-free scanning over a wide range is a pressing technical challenge in this field. Summary of the Invention

[0003] The purpose of this application is to provide a mode-skipping-free scanning control method, system, and computer-readable storage medium for narrow linewidth lasers, aiming to solve the technical problems of easy mode skipping and poor robustness to dynamic disturbances in the wide-range scanning of lasers in the prior art.

[0004] In a first aspect, this application provides a mode-hopping-free scanning control method for a narrow-linewidth laser, the method comprising: generating a reference current scanning signal and a reference voltage scanning signal; generating a high-frequency jitter signal and superimposing the high-frequency jitter signal with the reference current scanning signal to generate a total injection current for driving the narrow-linewidth laser; acquiring a real-time optical power feedback signal of the narrow-linewidth laser; demodulating and generating a mode margin error signal based on the real-time optical power feedback signal and the high-frequency jitter signal, wherein the mode margin error signal is used to characterize a mode stability of the current operating state of the narrow-linewidth laser; generating a dynamic correction voltage based on the mode margin error signal and superimposing the dynamic correction voltage with the reference voltage scanning signal to generate a total driving voltage for driving a piezoelectric ceramic of the narrow-linewidth laser.

[0005] Optionally, the step of demodulating and generating a mode margin error signal based on the real-time optical power feedback signal and the high-frequency jitter signal includes: using a lock-in amplification principle to perform quadrature phase-sensitive detection on the real-time optical power feedback signal and a reference signal, wherein the reference signal is in phase with the high-frequency jitter signal; demodulating to obtain a co-phase response component and a quadrature response component in the real-time optical power feedback signal that have the same frequency as the high-frequency jitter signal; and using the co-phase response component as the mode margin error signal.

[0006] Optionally, the step of generating a dynamic correction voltage based on the mode margin error signal includes: presetting a target error value, the target error value corresponding to the expected value of the mode margin error signal under the stable operating state of the narrow linewidth laser; calculating a deviation between the mode margin error signal and the target error value; and using a proportional-integral-derivative control algorithm to calculate and generate the dynamic correction voltage based on the deviation.

[0007] Optionally, the high-frequency jitter signal is a sinusoidal signal, and its frequency range is [range missing]. to .

[0008] Optionally, the amplitude of the high-frequency jitter signal is a threshold current of the narrow-linewidth laser. to .

[0009] Optionally, the step of obtaining a real-time optical power feedback signal of the narrow linewidth laser includes: using a beam splitter to split a portion of the beam from a main optical path of the narrow linewidth laser; and using a photodetector to convert the portion of the beam into a voltage signal proportional to the optical power, as the real-time optical power feedback signal.

[0010] Secondly, this application provides a mode-hopping-free scanning control system for a narrow-linewidth laser. The system includes: a scanning parameter generation module for generating a reference current scanning signal and a reference voltage scanning signal; a laser co-driving module including a current driving unit and a voltage driving unit, wherein the current driving unit generates a high-frequency jitter signal and superimposes the high-frequency jitter signal with the reference current scanning signal to generate a total injection current for driving the narrow-linewidth laser; and an optical power feedback module for acquiring a real-time optical power feedback signal from the narrow-linewidth laser. The system includes: a mode margin demodulation module for demodulating and generating a mode margin error signal based on the real-time optical power feedback signal and the high-frequency jitter signal, wherein the mode margin error signal is used to characterize the mode stability of the current operating state of the narrow-linewidth laser; a predictive feedforward correction module for generating a dynamic correction voltage based on the mode margin error signal; wherein the voltage driving unit of the laser co-drive module is further used to superimpose the dynamic correction voltage with the reference voltage scanning signal to generate a total driving voltage for driving a piezoelectric ceramic of the narrow-linewidth laser.

[0011] Optionally, the mode margin demodulation module is specifically used to: employ a lock-in amplifier to perform quadrature phase-sensitive detection on the real-time optical power feedback signal and a reference signal, wherein the reference signal is in phase with the high-frequency jitter signal; demodulate to obtain a co-phase response component and a quadrature response component in the real-time optical power feedback signal that have the same frequency as the high-frequency jitter signal; and use the co-phase response component as the mode margin error signal.

[0012] Optionally, the predictive feedforward correction module includes a proportional-integral-derivative (PID) controller, which is configured to: receive a target error value, the target error value corresponding to the expected value of the mode margin error signal under the stable operating state of the narrow linewidth laser; calculate a deviation between the mode margin error signal and the target error value; and calculate and generate the dynamic correction voltage based on the deviation.

[0013] Thirdly, this application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method described in the first aspect.

[0014] The technical solution of this application embodiment obtains a mode margin error signal that can predict mode hopping trends in advance by actively injecting a high-frequency jitter signal into the main scanning current and demodulating the phase response of the laser optical power in real time. This error signal is used in a high-speed predictive feedforward correction loop to dynamically fine-tune the driving voltage of the PZT, thereby actively compensating and correcting before the physical response delay mismatch accumulates to the point of triggering mode hopping. This method does not rely on expensive external wavelength measurement equipment, but extracts steady-state information from the laser's own physical response, achieving adaptive suppression of dynamic disturbances such as changes in ambient temperature and device aging. This enables high-speed, continuous, mode-hopping-free scanning over a wider wavelength range, improving scanning range and robustness. Attached Figure Description

[0015] Figure 1 This is a schematic flowchart illustrating a mode-skipping scanning control method for a narrow-linewidth laser provided in an embodiment of this application.

[0016] Figure 2 This is a structural block diagram of a mode-skipping scanning control system for a narrow linewidth laser provided in an embodiment of this application. Detailed Implementation

[0017] 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 the accompanying drawings and specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0018] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0019] This embodiment provides a mode-hopping-free scanning control method and system for narrow-linewidth lasers. In one specific implementation, the method actively superimposes a high-frequency, low-amplitude sinusoidal jitter signal onto a reference current scanning ramp signal, and uses a photodetector to monitor the weak fluctuations in the laser's output optical power caused by the jitter signal in real time. Then, it uses lock-in amplification technology to demodulate the phase information directly related to the laser's mode stability from the optical power fluctuations, thereby converting the phase information into a mode margin error signal that can predict mode-hopping trends.

[0020] This method solves the mode hopping problem caused by the severe mismatch between the physical response speed of current tuning and cavity length tuning in the prior art. It can perform high-speed closed-loop adaptive adjustment according to the instantaneous changes in the internal state of the laser and actively eliminate the risk of mode hopping, thereby achieving the beneficial effect of wide-range and highly robust continuous scanning.

[0021] The following reference Figure 1 This application provides a detailed description of a mode-skipping-free scanning control method for narrow-linewidth lasers, as provided in the embodiments of this application.

[0022] S100 generates a reference current scan signal and a reference voltage scan signal.

[0023] In this embodiment, at the start of the mode-skipping-free scanning process, the scanning task parameters need to be initialized and corresponding reference drive signals generated. The scanning task is defined by the user or the upper-level control system, and its core parameters include the starting wavelength of the scan. The termination wavelength of the scan and the desired speed for scanning within the wavelength range. To drive a narrow-linewidth laser and achieve continuous wavelength tuning, the control system must coordinately change two physical quantities: the current injected into the laser gain medium and the voltage applied to a piezoelectric ceramic (PZT) actuator. The piezoelectric ceramic is used to change the physical length of the laser resonant cavity.

[0024] The scanning parameter generation module converts user-defined wavelength domain scanning parameters into electrical domain drive signal parameters. This conversion process relies on a pre-calibration of the specific laser used. Through this calibration, the functional relationships between the injection current and the output wavelength, and between the PZT drive voltage and the output wavelength, can be obtained. Based on these relationships, the starting wavelength... and termination wavelength It can then be uniquely mapped to a set of initial current values. With termination current value and a set of starting voltage values With termination voltage value After obtaining the start and end points of the electrical domain scan, the scan parameter generation module generates scan parameters according to the user-set scan speed. This is used to determine the rate at which the driving signal changes over time.

[0025] Specifically, the total time required for the scan It can be determined by the total wavelength range With scanning speed The calculation is then performed. Subsequently, the reference current scan signal is obtained. Constructed as a from linearly increase to The slope of the ramp signal. Similarly, the reference voltage scanning signal Constructed as a from linearly increase to The slope of the ramp signal. These two ramp signals together form the open-loop driving baseline for achieving laser wavelength scanning.

[0026] For example, this embodiment uses a unit with a center wavelength of An external cavity tunable laser (ECL) is used as the controlled object. The user-defined scanning task is: from the starting wavelength... Scan to the termination wavelength wavelength range Approximately equivalent to The optical frequency range. The set total scan time is... That is, corresponding to the scanning speed .

[0027] By consulting the laser's calibration datasheet, it was found that the driving parameter range corresponding to this wavelength range is: injection current from Change to At the same time, the PZT drive voltage needs to be changed from... Change to Accordingly, the scan parameter generation module (e.g., a digital signal generator built into a microcontroller) will calculate and generate two linear ramp signals. The reference current scan signal The mathematical expression is time The unit is milliseconds (ms), and Simultaneously, the reference voltage scanning signal The mathematical expression is time The unit is also milliseconds (ms), and .

[0028] S200. Generate a high-frequency jitter signal and superimpose the high-frequency jitter signal with the reference current scanning signal to generate a total injection current for driving the narrow linewidth laser.

[0029] In this embodiment, to detect the mode stability state inside the laser in real time, a small perturbation is injected into the system, and the internal state is deduced by observing the system's response to the perturbation. The perturbation is a high-frequency jitter signal, which is selectively superimposed on an injected current that has a fast response to the laser wavelength. Exemplarily, the high-frequency jitter signal can be designed as a sine wave signal, whose mathematical form can be expressed as: Among them, frequency It must be much higher than the amount generated during the scanning process. and Any dynamic frequency introduced by the change must be ensured so that the jitter response can be clearly separated from the macroscopic changes in the scan in the frequency domain; at the same time, this frequency must also be lower than the response bandwidth of the current modulation of the photodetector and laser itself used to ensure that the system can respond to this jitter without distortion. In a preferred embodiment, the frequency... The range of values ​​is limited to to Between. Amplitude It must also be large enough so that the slight modulation it causes in the laser's output power can be captured by the subsequent detection system with a sufficient signal-to-noise ratio (SNR); however, it must also be small enough to avoid any adverse effects on the laser's average output power and linewidth, i.e., the detection behavior itself should not interfere with the normal operation of the laser. In a preferred embodiment, the amplitude... The current set as the laser's operating threshold current to After the reference current scan signal was generated... and the high-frequency jitter signal Then, the two are linearly superimposed using an adder circuit to generate the total injection current ultimately used to drive the laser semiconductor gain chip. .

[0030] For example, a direct digital frequency synthesizer (DDS) within the laser co-drive module is configured to generate a highly stable sinusoidal signal. The dithering frequency is selected according to design requirements. This frequency is within the bandwidth of a typical photodetector and is much higher than the scanning dynamic range. The jitter amplitude is selected. This value is relative to This is a tiny disturbance in terms of the operating current (approximately) This is sufficient to ensure the non-invasiveness of the detection process. Therefore, the generated high-frequency jitter signal is... At any given scan time, for example The reference current scan value at this time is The adder circuit adds this DC bias to the instantaneous high-frequency jitter value to obtain the total injected current. The synthesized current signal is output by a wide-bandwidth current source and directly injected into the anode of the laser. Simultaneously, in the initial state or when no calibration is required, the total driving voltage used to drive the PZT is temporarily equal to the reference voltage scanning signal, i.e. .exist At that moment, its value is This voltage drives the PZT actuator via a high-voltage amplifier.

[0031] S300: Obtain a real-time optical power feedback signal from the narrow linewidth laser.

[0032] In this embodiment, when the total injected current When applied to a laser, the output optical power of the laser This will change accordingly. This change comprises two parts: one is the change caused by the reference current scanning signal. The other is a slowly changing macroscopic power curve caused by high-frequency jitter signals. This results in weak, high-frequency power modulation superimposed on the macroscopic curve. This application aims to extract this high-frequency modulation information from the total optical power signal. To achieve this, an optical power feedback branch is needed. Specifically, a beam-splitting device, such as a free-space beam splitter or a fiber coupler, is placed in the main output optical path of the laser. The function of this beam-splitting device is to split a small proportion of the beam (e.g., [missing information]) without significantly affecting the main optical path output power. to The light is then directed to a photodetector. This photodetector can be an InGaAs PIN photodiode, sensitive to the operating wavelength, whose core function is to linearly convert the received optical power signal into a current signal. For easier subsequent signal processing, a transimpedance amplifier (TIA) can convert this photocurrent signal into a voltage signal. This final output voltage signal is the real-time optical power feedback signal. Its amplitude is proportional to the instantaneous output optical power of the laser at any given moment. To ensure distortion-free transmission of high-frequency optical power modulation caused by jitter current, the total response bandwidth of the entire optical power feedback module, consisting of the photodetector and its subsequent TIA amplifier circuit, should be significantly greater than the jitter frequency. .

[0033] For example, the power of the main beam output by the laser is Insert a [something] into the main optical path. The fiber optic coupler will The optical power, i.e. It is coupled to the optical power feedback module. This module uses a response bandwidth of... The InGaAs PIN photodiode has a responsivity of When received When the average optical power is reached, the diode generates The average photocurrent. This current signal is input to a transimpedance amplifier, whose transimpedance gain is set to... Therefore, the real-time optical power feedback signal output by this TIA... The DC bias (average voltage) is approximately Superimposed on this DC bias is... This results in a weak AC voltage signal. Assume that at the current operating point, the derivative of the optical power with respect to the current... for ,So The peak value caused is Current fluctuations will cause [a problem] in the total optical power. The power fluctuations. These power fluctuations, after photoelectric detection and transimpedance amplification, will... A peak value is formed on the upper part. The frequency is The communication signal. This The communication signal is the target information that needs to be extracted in subsequent steps.

[0034] S400. Based on the real-time optical power feedback signal and the high-frequency jitter signal, a mode margin error signal is generated by demodulation, wherein the mode margin error signal is used to characterize the mode stability of the current operating state of the narrow linewidth laser.

[0035] In this embodiment, the purpose of this step is to obtain the real-time optical power feedback signal, which contains a large DC component and noise. In this process, specific information related to the high-frequency modulation signal and its mode stability is extracted.

[0036] Understandably, the in-phase component of the optical power response excited by high-frequency current modulation can serve as an effective and predictive indicator of laser mode stability. Its theoretical basis can be derived from the rate equations of semiconductor lasers. The single-mode rate equations describe the photon number density inside the laser. and carrier number density The dynamic relationship that changes over time. Output optical power. With photon number density Proportional to the injected current This directly affects the carrier number density. Near a certain operating point, the response of optical power to injection current can be approximated as linear, with its first derivative (i.e., slope efficiency) being... This is a key parameter. When the laser operates in a stable single-mode region, this slope is mainly determined by the material's differential gain and the cavity's output loss, and is a relatively stable positive value. However, when the combination of scanning parameters (current and cavity length) approaches the mode boundary, neighboring side modes begin to compete with the main mode for gain. This mode competition phenomenon, through nonlinear effects such as spatial hole burning, leads to a decrease in the effective gain of the main mode, thereby affecting the slope efficiency. A significant, measurable drop occurs before the actual mode hopping actually happens. Therefore, Changes in this pattern are a predictive physical indicator of impending instability.

[0037] This invention injects high-frequency dithering current. (in ), actually is to The slope of the relationship curve is measured dynamically and locally. Based on Taylor expansion, from... Caused optical power response Under the first-order approximation:

[0038]

[0039] This formula shows that the optical power response signal It is a sine wave with the same frequency as the jitter signal, and its amplitude is proportional to the local slope. Lock-in amplifier technology is an ideal tool for extracting this weak signal from noise. The lock-in amplifier converts the input signal... (proportional to) ) and in-phase reference signal and quadrature reference signals After multiplying, a low-pass filter is applied. Its in-phase output... The value is proportional to the input signal. The coefficient of the component, and according to the above formula, this coefficient is exactly... Therefore, in-phase components It directly and linearly reflects the slope efficiency as a predictive indicator. Orthogonal components This reflects the phase delay in the optical power response relative to current modulation. This delay is mainly determined by relaxation times such as carrier lifetime, and its change is less sensitive and direct than the slope itself when the mode becomes unstable. Therefore, this application selects the in-phase component. The core error signal characterizes the mode margin.

[0040] In some embodiments, the demodulation process is implemented using the lock-in amplification principle. Lock-in amplification is essentially a filter with an extremely narrow bandwidth, whose center frequency is precisely locked by an external reference signal. In this application, the reference signal is naturally the original high-frequency signal used to generate the jitter, i.e., the signal that is... Strictly in-phase and frequency-in-sync signals. The mode margin demodulation module receives... Then, quadrature phase-sensitive detection is performed internally.

[0041] Specifically, the module will Simultaneously, it is mixed (i.e. multiplied) with two orthogonal reference signals: one of which is a reference signal in phase with the original jitter signal. The other path is a reference signal that is orthogonal to it (phase shifted by 90 degrees). The two mixed signals are then passed through a low-pass filter (LPF) with an extremely low cutoff frequency. According to Fourier transform theory, this operation is equivalent to accurately extracting the input signal. In the middle, the frequency is strictly equal to The amplitude and phase information of the components. The filter outputs two quasi-DC signals: one is the in-phase response component. Its amplitude is proportional to The amplitude of the in-phase portion of the reference signal; the other is the quadrature response component. Its amplitude is proportional to the amplitude of the portion orthogonal to the reference signal. Based on the foregoing theoretical explanation, in this embodiment, the in-phase response component... Directly defined as the mode margin error signal As a quantitative indicator, it characterizes the mode stability of the laser's current operating state, or in other words, the margin from the mode hopping boundary.

[0042] For example, the mode margin demodulation module (which may be implemented by an analog lock-in amplifier chip or an FPGA-based digital lock-in algorithm) receives the real-time optical power feedback signal from the S300. At the same time, it also receives a signal from the jitter source of the S200 that is related to... A synchronous, TTL-level square wave signal is used as the reference for phase-locked loop. At a given moment, assuming that a slight drift in ambient temperature causes the actual cavity length change of the PZT to lag behind the ideal scanning curve, the laser's operating point begins to drift towards the mode-hopping boundary. This drift manifests as... The curve's slope decreases locally. During the stable scanning phase, the demodulated in-phase response components Stable at a small positive value, for example (This value corresponds to a healthy, stable slope). In As the slope decreases, the demodulated in-phase component also decreases, for example, becoming... At this point, the orthogonal components It may still be close to zero. The system will use this in-phase component. The output is directly used as the mode margin error signal, i.e. This non-zero and negative error signal is a clear predictive warning, indicating that the laser's mode margin is decreasing and mode hopping is imminent if no intervention is taken.

[0043] S500. Based on the mode margin error signal, a dynamic correction voltage is generated, and the dynamic correction voltage is superimposed with the reference voltage scanning signal to generate a total driving voltage for driving a piezoelectric ceramic of the narrow linewidth laser.

[0044] In this embodiment, when the mode margin demodulation module generates an error signal that can reflect mode stability in real time... Then, this error signal can be used to construct a closed-loop feedback to actively pull the laser, which is about to become unstable, back to a stable region. This task can be accomplished by a predictive feedforward correction module. The core of this module is a controller used to calculate a suitable correction output based on the input error signal. In a preferred embodiment, the controller employs a proportional-integral-derivative (PID) control algorithm. First, a target error value is set for the system. This target value corresponds to the mode margin error signal that the laser should possess under ideal and stable single-mode operation. In most cases, this ideal value can be set to zero, i.e. Subsequently, the controller calculates the actual error signal in real time at each time step. With target value Deviation between The three components of the PID algorithm act on this deviation: the proportional term (P) provides an immediate corrective force proportional to the current deviation; the integral term (I) eliminates long-term static deviations, ensuring the system remains stable at the target value without error; and the derivative term (D) provides a predictive, damped correction based on the rate of change of the deviation to suppress overshoot and oscillations. Finally, the contributions of these three terms are linearly weighted and summed to generate a dynamic correction voltage. Its mathematical expression is ,in These are PID parameters that need to be tuned according to system characteristics. The physical meaning of this correction voltage is that it represents the additional fine-tuning amount that needs to be applied on top of the ideal PZT scan voltage baseline to maintain mode stability. Finally, the dynamic correction voltage is added by an adder circuit along with the reference voltage scan signal from S100. The voltages are superimposed to generate the total driving voltage ultimately applied to the PZT high-voltage amplifier. In this way, the control loop dynamically adjusts the rate of change of the PZT cavity length in real time, enabling it to accurately follow the refractive index change caused by the current change, thereby fundamentally eliminating the physical response delay mismatch that causes mode skipping.

[0045] For example, continuing with the S400 scenario. The PID controller in the predictive feedforward correction module has its target value set to... Its control parameters are pre-tuned to (dimensionless) , In one specific embodiment, to ensure that the PID controller can effectively control the controlled system (mainly including dynamic components such as the PZT actuator and the laser cavity length response), the PID parameters... The determination can follow the following exemplary tuning steps:

[0046] Set the PID controller to pure proportional control mode (i.e.) In an informal scan, at the dynamic correction voltage A tiny step voltage signal (e.g., a) is injected into the output terminal. (the step), and use a data acquisition card to monitor the mode margin error signal at high speed. The response curve. Gradually increase the proportional gain. Start with a small value until the error signal is observed. The response exhibits sustained, constant-amplitude oscillations. The proportional gain at this point is recorded as the critical gain. The period of oscillation is measured as the critical period. Based on the Ziegler-Nichols tuning rule (critical oscillation method) well-known in the art, and based on the measured... and Calculate a set of initial PID parameters. For example, the following classic rule can be used for calculation: ; ; The calculated initial PID parameters were applied to the controller, and a real-world mode-skip-free sweep test was performed. During the test, adjustments were made based on the actual vibration damping effect and response speed. Perform small-scale online fine-tuning to achieve optimal control performance. For example, if the system response exhibits overshoot, the range can be appropriately reduced. or increase Using the tuning method described above, those skilled in the art can configure corresponding PID parameters for a specific laser system.

[0047] exist At that time, due to the continued disturbance, the mode margin error signal further deteriorated. At this moment, the PID controller calculates the deviation. To simplify the calculation, only the effect of the proportional term is considered, and the instantaneous correction voltage it produces is: The integral and differential terms also contribute corresponding voltage values ​​based on historical errors and the rate of change of error. Assuming the total correction voltage is... The reference PZT voltage at this time should be Therefore, the total driving voltage finally applied to the PZT is corrected to This additional positive voltage slightly increases the elongation of the PZT, thereby fine-tuning the cavity length of the resonant cavity and compensating for insufficient cavity length variation caused by temperature disturbances. Thanks to this timely correction, at the next sampling time... The mode stability of the laser was restored, and the mode margin error signal was... Start moving towards the target value Regression, for example, becoming The entire system continues to perform closed-loop correction in this manner until the entire system... The scanning process ends, thus ensuring mode-free operation throughout the entire process.

[0048] In an optional embodiment, this application also provides a mode-skipping-free scanning control system for narrow linewidth lasers, as described below. Figure 2 The system will be described in detail.

[0049] The system includes:

[0050] A scan parameter generation module, which can be implemented by a microcontroller (MCU) or a field-programmable gate array (FPGA), contains digital signal generator logic. This module is configured to perform step S100 of the aforementioned method, that is, to calculate and generate a reference current scan signal and a reference voltage scan signal in digital form based on the scan range and speed parameters input by the user, and output them through two independent digital-to-analog converter (DAC) channels.

[0051] A laser co-drive module, which can be implemented based on analog circuitry, provides all necessary electrical drive signals to the laser. Logically, this module can be divided into a current drive unit and a voltage drive unit. The current drive unit internally includes a direct digital frequency synthesizer (DDS) for generating a high-stability sine wave as a high-frequency jitter signal source, and an adder circuit that superimposes the reference current scan signal from the scan parameter generation module with the high-frequency jitter signal output from the DDS, outputting the superimposed total injected current through a precision constant current source. The voltage drive unit internally includes another adder circuit that superimposes the reference voltage scan signal with the dynamic correction voltage from the predictive feedforward correction module, outputting the superimposed total drive voltage through a high-voltage amplifier.

[0052] An optical power feedback module, which can be composed of optical components and photoelectric conversion circuits, includes a fiber coupler or beam splitter placed in the main optical path of the laser to extract a small portion of the optical signal. A high-speed, high-sensitivity InGaAs PIN photodiode receives this portion of the optical signal and generates a corresponding photocurrent. A wide-bandwidth transimpedance amplifier (TIA) linearly converts the photocurrent into a voltage signal, which is then output as the real-time optical power feedback signal.

[0053] A mode margin demodulation module, functionally equivalent to a high-performance lock-in amplifier, can be implemented using a dedicated analog lock-in amplifier integrated circuit or by sampling the optical power feedback signal using a high-speed analog-to-digital converter (ADC) and then implementing it in a digital signal processor (DSP) or FPGA through digital mixing and digital filtering algorithms. Regardless of the implementation method, this module is used to receive the optical power feedback signal and the synchronization reference signal from the jitter source, and outputs the demodulated in-phase response component as the mode margin error signal.

[0054] A predictive feedforward correction module is responsible for implementing the PID control algorithm. It can be implemented using an analog PID circuit built with operational amplifiers, or more flexibly, using a microcontroller or DSP. In the digital implementation, this module samples the mode margin error signal via an ADC, executes discrete-time PID algorithm calculations internally by the processor, and then outputs a smooth, analog dynamic correction voltage via a DAC.

[0055] In system operation, the above modules work in concert. The scanning parameter generation module generates a reference signal, the laser co-drive module synthesizes and applies the drive, the optical power feedback module monitors the response, the mode margin demodulation module extracts state information, and the predictive feedforward correction module calculates and applies correction, forming a complete, high-speed, adaptive closed-loop control system, thereby realizing the mode-skipping-free scanning control method described in this application.

[0056] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

[0057] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit described above can be implemented in hardware.

Claims

1. A mode-skipping-free scanning control method for narrow linewidth lasers, characterized in that, The method includes: Generate a reference current scan signal and a reference voltage scan signal; A high-frequency jitter signal is generated and superimposed with the reference current scanning signal to generate a total injection current for driving the narrow linewidth laser. Obtain a real-time optical power feedback signal from the narrow-linewidth laser; Based on the real-time optical power feedback signal and the high-frequency jitter signal, a mode margin error signal is generated by demodulation. The mode margin error signal is used to characterize the mode stability of the current operating state of the narrow linewidth laser and predict the mode hopping trend. Based on the mode margin error signal, a dynamic correction voltage is generated in a predictive feedforward manner, and the dynamic correction voltage is superimposed on the reference voltage scanning signal to generate a total driving voltage for driving a piezoelectric ceramic for the narrow linewidth laser.

2. The method according to claim 1, characterized in that, The step of demodulating and generating a mode margin error signal based on the real-time optical power feedback signal and the high-frequency jitter signal includes: The real-time optical power feedback signal and a reference signal are subjected to quadrature phase-sensitive detection, wherein the reference signal is in phase with the high-frequency jitter signal. Demodulation yields a co-phase response component with the same frequency as the high-frequency jitter signal and a quadrature response component in the real-time optical power feedback signal. The in-phase response component is used as the mode margin error signal.

3. The method according to claim 2, characterized in that, The step of generating a dynamic correction voltage based on the mode margin error signal includes: A target error value is preset, which corresponds to the expected value of the mode margin error signal under the stable operating state of the narrow linewidth laser; Calculate the deviation between the mode margin error signal and the target error value; A proportional-integral-derivative control algorithm is used to calculate and generate the dynamic correction voltage based on the deviation.

4. The method according to claim 1, characterized in that, The high-frequency jitter signal is a sinusoidal signal with a frequency range of 100kHz to 10MHz.

5. The method according to claim 1, characterized in that, The amplitude of the high-frequency jitter signal is 0.1% to 1% of a threshold current of the narrow linewidth laser.

6. The method according to claim 1, characterized in that, The step of obtaining a real-time optical power feedback signal of the narrow linewidth laser includes: A beam splitter is used to separate a portion of the beam from a main optical path of the narrow linewidth laser; A photodetector is used to convert a portion of the light beam into a voltage signal proportional to the optical power, which serves as the real-time optical power feedback signal.

7. A mode-skipping-free scanning control system for narrow linewidth lasers, characterized in that, The system includes: A scan parameter generation module is used to generate a reference current scan signal and a reference voltage scan signal; A laser co-driving module includes a current driving unit and a voltage driving unit, wherein the current driving unit is used to generate a high-frequency jitter signal and superimpose the high-frequency jitter signal with the reference current scanning signal to generate a total injection current for driving the narrow linewidth laser. An optical power feedback module is used to acquire a real-time optical power feedback signal from the narrow linewidth laser. A mode margin demodulation module is used to demodulate and generate a mode margin error signal based on the real-time optical power feedback signal and the high-frequency jitter signal, wherein the mode margin error signal is used to characterize the mode stability of the current operating state of the narrow linewidth laser. A predictive feedforward correction module is used to generate a dynamic correction voltage based on the mode margin error signal; The voltage driving unit of the laser co-driving module is further configured to superimpose the dynamic correction voltage with the reference voltage scanning signal to generate a total driving voltage for driving a piezoelectric ceramic of the narrow linewidth laser.

8. The system according to claim 7, characterized in that, The mode margin demodulation module is specifically used for: A lock-in amplifier is used to perform quadrature phase-sensitive detection on the real-time optical power feedback signal and a reference signal, wherein the reference signal is in phase with the high-frequency jitter signal; Demodulation yields a co-phase response component with the same frequency as the high-frequency jitter signal and a quadrature response component in the real-time optical power feedback signal. The in-phase response component is used as the mode margin error signal.

9. The system according to claim 8, characterized in that, The predictive feedforward correction module includes a proportional-integral-derivative (PI-DI) controller, which is used for: Receive a target error value, the target error value corresponding to the expected value of the mode margin error signal under the stable operating state of the narrow linewidth laser; Calculate the deviation between the mode margin error signal and the target error value; The dynamic correction voltage is generated based on the deviation.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the method as described in any one of claims 1 to 6.

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