Laser frequency stabilization device, system and method

Abstract

The application discloses a laser frequency stabilization device, system and method, and relates to the technical field of super-stable lasers. The device comprises a photoelectric detection unit for converting a pre-cavity reflected light signal into a first electrical signal; a gain unit configured to amplify the first electrical signal to obtain a second electrical signal; a locking unit configured to constrain the laser frequency to a reference cavity resonance frequency based on the second electrical signal; and a controller configured to: in a first gain stage, control the gain value of the gain unit to be an initial gain value; in response to a preset locking condition being met, enter a second gain stage; in the second gain stage, perform spectral analysis on the second electrical signal, extract a first characteristic quantity reflecting the effective signal intensity and a second characteristic quantity reflecting the background noise intensity; calculate the ratio of the first characteristic quantity and the second characteristic quantity; and in response to the difference between the ratio and a target ratio, gradually adjust the gain value so that the ratio approaches the target ratio. In this way, the lock-in success rate and the frequency stabilization accuracy are improved.

Description

Technical Field

[0001] This application relates to the technical field of ultrastable lasers, and more specifically, to a laser frequency stabilization device, system, and method. Background Technology

[0002] Ultrastable lasers are the core fundamental light source in cutting-edge fields such as optical atomic clocks, quantum precision measurement, gravitational wave detection, and long-distance optical frequency transmission. Their frequency stability directly determines the ultimate performance of precision measurement systems. Currently, the industry mainstream adopts PDH (Pound-Drever-Hall) frequency stabilization technology, which locks the seed laser frequency to the resonance peak of a high-precision, narrow-linewidth optical reference cavity, thereby achieving ultrastable constraint of the laser frequency.

[0003] The basic working principle of the PDH frequency stabilization system is as follows: after phase modulation, the seed laser is incident on a high-precision optical reference cavity. The reflected light in front of the cavity is received by a photodetector and converted into an electrical signal. After demodulation, the electrical signal reflects the error signal that reflects the deviation between the laser frequency and the resonant frequency of the reference cavity. The error signal controls the frequency execution mechanism of the laser (such as an acousto-optic modulator or an electro-optic modulator) through a feedback loop to lock the laser frequency at the resonant point of the reference cavity.

[0004] In a PDH frequency stabilization system, the output signal of the pre-cavity photodetector needs to be amplified by radio frequency before being sent to the demodulation circuit. The setting of the amplification gain directly affects the frequency discrimination performance of the system: when the gain is low, the frequency discrimination dynamic range is large, which can tolerate a large laser frequency drift, but the frequency discrimination resolution is low; when the gain is high, the frequency discrimination resolution is improved, but the dynamic range is reduced, and the laser frequency drift is more likely to exceed the frequency discrimination linear range, resulting in loss of lock.

[0005] Currently, most existing PDH frequency stabilization systems employ a fixed-gain design, meaning the RF amplification gain remains constant throughout operation. While this allows the system to tolerate significant laser frequency drift and achieve a high locking success rate, the frequency discrimination resolution is insufficient in the locked state, failing to fully utilize the frequency stabilization potential of the high-precision reference cavity and thus limiting laser frequency stability.

[0006] Therefore, a new laser frequency stabilization solution is urgently needed. Summary of the Invention

[0007] To address the technical problem that existing PDH frequency stabilization systems cannot simultaneously achieve high lock-in success rates and stable laser frequencies, this application provides a laser frequency stabilization device, system, and method.

[0008] In a first aspect, embodiments of this application provide a laser frequency stabilization device. The device includes: The photoelectric detection unit is used to convert the cavity front reflected light signal into a first electrical signal, wherein the cavity front reflected light signal reflects the deviation information between the laser frequency and the reference cavity resonant frequency; The gain unit is configured to amplify the first electrical signal to obtain the second electrical signal; The locking unit is configured to constrain the laser frequency to the reference cavity resonant frequency based on the second electrical signal; The controller is configured as follows: In the first gain stage, the gain value of the gain unit is controlled to be the initial gain value in order to broaden the frequency discrimination dynamic range; In response to the satisfaction of the preset locking condition, the system enters the second gain phase. In the second gain stage, the second electrical signal is subjected to spectrum analysis to extract a first feature quantity reflecting the effective signal strength and a second feature quantity reflecting the background noise strength. Calculate the ratio of the first feature quantity to the second feature quantity; In response to the difference between the ratio and the target ratio, the gain value is gradually adjusted so that the ratio approaches the target ratio.

[0009] Optionally, the initial gain value satisfies: During the first gain phase, the signal-to-noise ratio of the second electrical signal is made greater than or equal to 20dB.

[0010] Optionally, the preset locking condition includes: the fluctuation of the amplitude of the second electrical signal within a first preset time period is less than a first preset threshold.

[0011] Optionally, the device further includes a detection unit; The detection unit includes a first detection channel and a second detection channel; The first detection channel is configured to filter the second electrical signal in a first frequency band to obtain the first feature quantity; The second detection channel is configured to filter the second electrical signal in the second frequency band to obtain the second feature quantity; The frequency of the first frequency band is lower than the frequency of the second frequency band.

[0012] Optionally, the first frequency band is from 100 kHz to 800 kHz; and the second frequency band is from 1 MHz to 2 MHz.

[0013] Optionally, the controller is further configured to: In the second gain stage, if the difference between the ratio and the target ratio is greater than the second preset threshold, the gain value is adjusted by a preset step size. Within a first preset time period, the amplitude fluctuation of the second electrical signal is monitored; once the amplitude fluctuation is less than a first preset threshold, the ratio of the first feature quantity and the second feature quantity is recalculated. The difference between the ratio and the target ratio is repeatedly calculated, and the gain value is adjusted in response to the difference by a preset step size until the difference is less than or equal to the second preset threshold, at which point the gain adjustment is stopped.

[0014] Optionally, the second preset threshold is greater than 0 and less than or equal to 1 dB.

[0015] Optionally, the preset step size is greater than or equal to 0.1 dB and less than or equal to 1 dB.

[0016] Optionally, the target ratio is greater than or equal to 1 dB and less than or equal to 20 dB.

[0017] Optionally, the first preset duration is greater than or equal to 1 second, and the first preset threshold is less than or equal to 1 / 10 of the peak value of the second electrical signal in the first gain phase.

[0018] Optionally, the first characteristic quantity includes the amplitude of the gain peak of the second electrical signal.

[0019] Optionally, the second characteristic quantity includes the intensity of the background noise.

[0020] Secondly, this application also provides a laser frequency stabilization system, including a seed laser, an acousto-optic modulator, an electro-optic modulator, a cavity pre-coupled optical path, a reference cavity, and a laser frequency stabilization device according to any of the above embodiments; The seed laser emitted by the seed laser is modulated sequentially by the acousto-optic modulator and the electro-optic modulator, then enters the reference cavity through the pre-cavity coupling optical path, and returns to the pre-cavity coupling optical path after being reflected by the reference cavity. The photoelectric detection unit of the laser frequency stabilization device is used to convert the optical signal reflected by the reference cavity into a first electrical signal; The controller controls the gain unit and the locking unit, and by gradually adjusting the gain value, makes the ratio of the first characteristic quantity reflecting the effective signal strength to the second characteristic quantity reflecting the background noise strength approach the target ratio.

[0021] Thirdly, this application provides a laser frequency stabilization method for use with the laser frequency stabilization device and the laser frequency stabilization system provided according to any of the above embodiments, the method comprising: The cavity front reflected light signal is converted into a first electrical signal, which reflects the deviation information between the laser frequency and the reference cavity resonant frequency; The gain of the first electrical signal is adjusted to output the second electrical signal; In the first gain stage, the gain value of the gain unit is controlled to be the initial gain value in order to broaden the frequency discrimination dynamic range; In response to the satisfaction of the preset locking condition, the system enters the second gain phase. In the second gain stage, the second electrical signal is subjected to spectrum analysis to extract a first feature quantity reflecting the effective signal strength and a second feature quantity reflecting the background noise strength. Calculate the ratio of the first feature quantity to the second feature quantity; In response to the difference between the ratio and the target ratio, the gain value is gradually adjusted so that the ratio approaches the target ratio.

[0022] Optionally, the preset locking condition includes: the fluctuation of the amplitude of the second electrical signal within a first preset time period is less than a first preset threshold.

[0023] Optionally, the method further includes: The second electrical signal is filtered in the first frequency band to obtain the first feature quantity; The second electrical signal is filtered in the second frequency band to obtain the second characteristic quantity; The frequency of the first frequency band is lower than the frequency of the second frequency band.

[0024] Optionally, the first frequency band is from 100 kHz to 800 kHz; and the second frequency band is from 1 MHz to 2 MHz.

[0025] Optionally, the method further includes: In the second gain stage, if the difference between the ratio and the target ratio is greater than the second preset threshold, the gain value is adjusted by a preset step size. Within a first preset time period, the amplitude fluctuation of the second electrical signal is monitored; once the amplitude fluctuation is less than a first preset threshold, the ratio of the first feature quantity and the second feature quantity is recalculated. The difference between the ratio and the target ratio is repeatedly calculated, and the gain value is adjusted in response to the difference by a preset step size until the difference is less than or equal to the second preset threshold, at which point the gain adjustment is stopped.

[0026] The technical solutions provided in the embodiments of this application have achieved at least the following technical effects: The laser frequency stabilization device provided in this application amplifies the first electrical signal with an initial gain value in the first gain stage, thereby widening the frequency discrimination dynamic range and improving the locking success rate. In the second gain stage, it extracts a first feature quantity reflecting the effective signal strength and a second feature quantity reflecting the background noise intensity, and calculates the ratio of the first and second feature quantities. Responding to the difference between this ratio and the target ratio, the gain value is gradually adjusted so that the ratio gradually approaches the target ratio, thereby achieving adaptive gain adjustment and ensuring frequency stabilization accuracy. By using segmented gain, both locking success rate and frequency stabilization accuracy are considered. The first and second feature quantities are extracted through spectrum analysis, and the gain value is controlled so that their ratio tracks the target ratio. It eliminates the need for a high-speed analog-to-digital converter and a field-programmable gate array (FPGA) digital spectrum analysis architecture; only a common microcontroller and analog detection circuit are required to complete the spectral feature quantization and determination, reducing hardware costs, optimizing circuit space utilization, and improving system stability. This facilitates system miniaturization, portability, and engineering. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of this application or the background art, the accompanying drawings used in the embodiments of this application or the background art will be described below.

[0028] Figure 1 A schematic diagram of an optional architecture of the laser frequency stabilization system provided in an embodiment of this application is shown.

[0029] Figure 2 A schematic diagram of an optional laser frequency stabilization method provided in an embodiment of this application is shown.

[0030] Figure 3 This illustration shows another optional flowchart of the laser frequency stabilization method provided in the embodiments of this application.

[0031] The reference numerals in the figure represent: 100-Laser frequency stabilization device; 10-Photoelectric detection unit; 20-Gain unit; 30-Lock unit; 40-Controller; 50-Seed laser; 60-Acousto-optic modulator; 70-Electro-optic modulator; 80-Cavity pre-coupling optical path; 90-Optical reference cavity. Detailed Implementation

[0032] The following description is exemplary in nature and is not intended to limit this disclosure or its application or use. It should be understood that corresponding reference numerals in the drawings always indicate the same or corresponding parts and features. This teaching is suitable for integration into many different types of laser frequency stabilization devices.

[0033] Exemplary implementations are provided to make this application sufficiently disclosed and to fully convey the scope to those skilled in the art. Numerous specific details, such as examples of specific components, apparatuses, and methods, are set forth to provide a comprehensive understanding of embodiments of this disclosure. It will be apparent to those skilled in the art that the exemplary implementations may be practiced in many different forms without employing the specific details, and none of these should be construed as limiting the scope of this disclosure. In some exemplary implementations, well-known methods, well-known apparatus structures, and well-known technologies are not described in detail.

[0034] When an element or layer is referred to as being “on”, “joined to,” “connected to,” or “attached to” another element or layer, the element or layer may be directly located on, directly joined to, connected to, or attached to the other element or layer, or there may be an intervening element or layer. Conversely, when an element is referred to as being “directly located” on, directly joined to, directly connected to, or directly attached to another element or layer, there is no intervening element or layer. Other terms used to describe relationships between elements should be interpreted in the same manner (e.g., “located between” versus “directly located between,” “proximately” versus “directly proximately to,” etc.). As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0035] Although the terms first, second, third, etc., are used herein to describe different elements, components, regions, layers, and / or portions, these elements, components, regions, layers, and / or portions should not be limited by these terms. These terms may be used only to distinguish one element, component, region, layer, and / or portion from another. Terms such as “first,” “second,” and other numerical terms, when used herein, do not imply order or sequence unless clearly indicated by the context. Thus, the first element, component, region, layer, or portion discussed below may be referred to as a second element, component, region, layer, or portion without departing from the teachings of the exemplary embodiments.

[0036] Given that existing laser frequency stabilization technologies using fixed gain parameters cannot simultaneously achieve high locking success rates and stable laser frequencies, the following solutions are provided: (1) Phase modulation depth segmented adjustment and back-end PID loop gain adjustment scheme: Only the optical path phase modulation depth is optimized, and the adjustment range is small because the optimal phase modulation depth is about 1 rad, and the adjustable space is very limited. If it exceeds the optimal phase modulation depth, it will affect the signal-to-noise ratio. The back-end feedback parameters are used for PID gain adjustment, which does not improve the front-end detection signal-to-noise ratio and frequency discrimination limit accuracy. Moreover, the increase in gain may cause the circuit noise to be amplified by the synchronous broadband, and the performance improvement is limited. (2) Fully digital adaptive gain scheme: This also belongs to back-end feedback parameter adjustment and does not fundamentally improve the signal-to-noise ratio and frequency discrimination accuracy. Moreover, it relies on high-speed ADC and FPGA high-speed digital spectrum analysis architecture, which requires real-time fast Fourier transform (FFT) spectrum calculation. The hardware cost is high, the circuit size is large, the power consumption is high, and the development difficulty is high. It is difficult to adapt to the application requirements of portable, miniaturized, low-cost ultra-stable laser equipment, and the engineering implementation is poor.

[0037] In addition, traditional laser frequency stabilization relies on manual gain adjustment, which depends on the operator's experience. This results in poor adjustment consistency, lack of quantifiable standards, and inability to automate operation, making it difficult to achieve long-term unattended stable locking.

[0038] In view of this, such as Figure 1 As shown in the figure, this application provides a laser frequency stabilization device 100. The laser frequency stabilization device 100 includes a photoelectric detection unit 10, a gain unit 20, a locking unit 30, and a controller 40.

[0039] Specifically, the input terminal of the photodetector unit 10 is connected to the pre-cavity coupling optical path 80, and the output terminal is connected to the gain unit 20. The photodetector unit 10 is used to convert the pre-cavity reflected light signal into a first electrical signal, wherein the pre-cavity reflected light signal reflects the deviation information between the laser frequency and the reference cavity resonant frequency. Exemplarily, the pre-cavity reflected light signal includes a reflected light component spatially matched with the reference cavity fundamental mode, which reflects the error between the laser frequency and the reference cavity resonant frequency; the first electrical signal includes a radio frequency signal encoded with information on the deviation between the laser frequency and the reference cavity resonant frequency, which, after demodulation, can form an error signal for laser locking. According to some optional embodiments, the photodetector unit 10 includes a photodetector (e.g., a photodiode or a balanced photodetector), a transimpedance amplifier circuit, and a polarization separation element. The photodetector generates a photocurrent signal in response to the incident light signal, its response bandwidth covering the laser carrier modulation frequency Ω and its harmonics, and possesses low dark current and high linearity characteristics to avoid introducing nonlinear distortion or additional intensity noise. The transimpedance amplifier is electrically connected to the photodetector and is used to convert the weak photocurrent into a voltage signal (i.e., the first electrical signal). A polarization separation element is disposed between the input end of the photodetector unit 10 and the photodetector, and is used to separate the cavity-front reflected light from the cavity-front coupled optical path and guide it to the photodetector. Optionally, the extinction ratio of the polarization separation element is greater than or equal to 30 dB.

[0040] Gain unit 20 is configured to adjust the gain of the first electrical signal to obtain a second electrical signal. The signal-to-noise ratio of the second electrical signal meets the requirements for frequency locking in ultra-stable lasers. For example, the ultra-stable laser involved in this application refers to an Allan variance better than 1×10⁻⁶ over a 1s integration time. -14Optionally, the initial gain is obtained experimentally by observing the error signal in the second electrical signal before locking and adjusting the gain value according to the error signal, so that the signal-to-noise ratio of the second signal reaches a preset target. For example, the signal-to-noise ratio of the second electrical signal is greater than or equal to 10. Here, the signal-to-noise ratio is an amplitude ratio. That is, the ratio of the error signal amplitude in the second electrical signal to the system's inherent noise floor amplitude is greater than or equal to 20 dB. Optionally, the gain unit 20 includes a low-noise amplifier, a variable gain amplifier, and a buffer amplifier. For example, the gain unit 20 also includes at least one of an impedance matching network, an RF filter, a temperature sensor, and a DC-DC converter.

[0041] The locking unit 30 is configured to constrain the laser frequency to the reference cavity resonant frequency based on a second electrical signal. Specifically, the locking unit 30 obtains frequency deviation information between the laser frequency and the reference cavity resonant frequency based on the second electrical signal, and then generates a feedback control signal that acts on the seed laser 50 and / or the modulation unit (e.g., an acousto-optic modulator and an electro-optic modulator), so that the laser frequency is constrained to near the reference cavity resonant frequency, thereby achieving laser frequency stabilization and locking. Optionally, the locking unit 30 may include a mixer, demodulator, low-pass filter, servo controller, actuator drive circuit, etc., for extracting the baseband error signal from the radio frequency signal and feeding back to control the laser frequency.

[0042] The controller 40 is communicatively connected to the gain unit 20 and the locking unit 30. Optionally, this communication connection can be wireless or wired. The controller 40 is configured to: In the first gain stage, the gain value of the control gain unit 20 is set to the initial gain value in order to broaden the frequency discrimination dynamic range; In response to the satisfaction of the preset locking condition, the system enters the second gain phase. In the second gain stage, the second electrical signal is subjected to spectrum analysis to extract the first feature quantity reflecting the effective signal strength and the second feature quantity reflecting the background noise strength. Calculate the ratio of the first characteristic quantity to the second characteristic quantity; In response to the difference between the ratio and the target ratio, the gain value is gradually adjusted to bring the ratio closer to the target ratio.

[0043] Because the seed laser lacks feedback loop constraints in the open-loop unlocked state, its frequency and amplitude noise are significant, resulting in a wide frequency drift range. This necessitates a large frequency discrimination dynamic range to achieve locking. However, after the laser is locked in a closed-loop system, a high-bandwidth servo loop suppresses the seed laser's native noise in real time, confining frequency jitter within a very small linear range. At this point, the laser frequency stabilization device needs high-resolution frequency discrimination capabilities.

[0044] This application discovers that by using the aforementioned two-stage gain, a smaller RF gain is forced during the locking stage (i.e., the first gain stage), widening the frequency discrimination dynamic range and improving the success rate of laser locking. After the preset locking condition (successful locking) is met, in the second gain stage, a first characteristic quantity reflecting the effective signal strength and a second characteristic quantity reflecting the background noise strength are extracted, and the ratio of the first and second characteristic quantities is calculated. Responding to the difference between this ratio and the target ratio, if the difference exceeds a preset range, the gain value is gradually adjusted to bring the ratio closer to the target ratio, thus achieving adaptive high-precision stable frequency locking. Optionally, according to the implementation of this application, when the ratio of the first and second characteristic quantities is less than the target ratio, the gain value is gradually increased. By automatically tracking the preset target ratio, the frequency locking signal link can be maintained in an optimal operating state, thereby providing a high-quality error signal for the servo loop and ensuring long-term stable locking of the laser frequency relative to the reference cavity resonant frequency. This achieves automated, high-precision, and high-stability laser frequency stabilization locking. By gradually adjusting the gain in small increments, lockout caused by instantaneous gain jumps is avoided.

[0045] According to some optional implementations, the initial gain value must at least satisfy the following conditions: In the first gain phase, the signal-to-noise ratio of the second electrical signal is made to be greater than or equal to 10.

[0046] According to the embodiments of this application, the initial gain value can be obtained experimentally. By observing the error signal before locking, the gain is adjusted to ensure that the second electrical signal has a sufficiently high signal-to-noise ratio. Optionally, the initial gain value makes the signal-to-noise ratio of the second electrical signal greater than or equal to 20dB. It should be understood that the initial gain value can be a fixed value or an adjustable value within a preset range.

[0047] According to some optional implementations, the preset locking condition includes: the fluctuation of the amplitude of the second electrical signal within a first preset duration is less than a first preset threshold. Optionally, the first preset duration is greater than or equal to 1 second, and the first preset threshold is less than or equal to 1 / 10 of the peak value of the second electrical signal. As another example, the controller 40 detects fluctuations in the second electrical signal; when the amplitude of the error signal in the second electrical signal remains stable without any jumps or loss of lock-up, and the stabilization duration reaches a preset threshold, it determines that steady-state closed-loop locking is complete and automatically enters the second gain stage. Optionally, the threshold for the stabilization duration is preset to 10 seconds.

[0048] According to embodiments of this application, the first characteristic quantity and the second characteristic quantity have the same dimensions. When the first characteristic value is the amplitude or power value of the gain peak characteristic value of the second electrical signal, the corresponding second characteristic value is the amplitude or power value of the noise floor. According to some optional embodiments, the first characteristic quantity includes the amplitude of the gain peak of the second electrical signal. According to some optional embodiments, the second characteristic quantity includes the intensity of the noise floor of the second electrical signal, such as the peak voltage of the noise plateau. Exemplarily, the dimensions of both the first and second characteristic quantities are voltages obtained from bandpass filtering and peak detection.

[0049] According to some optional implementations, in order to balance the stability and frequency stabilization accuracy of laser locking, the target ratio is greater than or equal to 1dB and less than or equal to 20dB. Preferably, the target ratio is 10dB. To avoid loss of lock caused by instantaneous changes in gain value, optionally, the preset step size is greater than or equal to 0.1dB and less than or equal to 1dB.

[0050] According to some optional implementations, the controller 40 is also configured to: in the second gain phase, if the difference between the ratio of the first and second feature quantities and the target ratio is greater than or equal to a second preset threshold, adjust the gain value by a preset step size. Within a first preset time period, the amplitude fluctuation of the second electrical signal is monitored; once the amplitude fluctuation is less than the first preset threshold, the ratio of the first characteristic quantity and the second characteristic quantity is recalculated. Repeatedly calculate the difference between the ratio and the target ratio, and adjust the gain value according to the difference by a preset step size until the difference is less than the second preset threshold, then stop the gain adjustment.

[0051] Optionally, if the ratio of the first and second characteristic quantities is less than the target ratio, and the difference between them is greater than or equal to a second preset threshold, then the current gain value is determined to be too low, and the frequency discrimination resolution has not reached the optimal level. The controller outputs a command to increase the gain value by a preset step size. After a single adjustment is completed, the difference between the new ratio of the first and second characteristic quantities and the target ratio is calculated. Based on the difference, it is determined whether to adjust the gain. This process is repeated until the difference between the ratio of the first and second characteristic quantities and the target ratio is less than the second preset threshold. Alternatively, if the ratio of the first and second characteristic quantities is greater than the target ratio, and the difference between them (or the absolute value of the difference) is greater than or equal to the second preset threshold, then the current gain value is determined to be too high, and the system has a risk of losing lock beyond the frequency discrimination linear range. The controller outputs a command to decrease the gain value by a preset step size. For example, if the difference between the ratio of the first and second characteristic quantities and the target ratio (or the absolute value of the difference) is less than the second preset threshold, then the current gain value is determined to have reached the optimal balance range. The controller outputs a command to stop gain adjustment, lock and maintain the current gain value, and the system enters the steady-state high-precision maintenance stage. Optionally, the difference between the ratio of the first feature quantity and the second feature quantity and the target ratio can refer to the absolute value of the difference.

[0052] Optionally, the second preset threshold is greater than 0 and less than or equal to 1 dB. For example, when the difference between the ratio of the first feature quantity to the second feature quantity and the target ratio is less than 1 dB, gain adjustment is stopped and the current gain parameter is locked; when the difference between the ratio of the first feature quantity to the second feature quantity and the target ratio is greater than or equal to 1 dB, the gain value is gradually increased by a preset step size until the difference between the ratio of the first feature quantity to the second feature quantity and the target ratio is less than 1 dB.

[0053] According to an embodiment of this application, the laser frequency stabilization device 100 further includes a detection unit. The detection unit includes a first detection channel and a second detection channel. The first detection channel is configured to filter the second electrical signal in a first frequency band to obtain a first feature value; the second detection channel is configured to filter the second electrical signal in a second frequency band to obtain a second feature value; wherein the frequency of the first frequency band is lower than the frequency of the second frequency band. Optionally, the aforementioned filtering is bandpass filtering. Optionally, the first frequency band is 100kHz to 800kHz. Further optional, the second frequency band is 1MHz to 2MHz.

[0054] For example, after the locking unit achieves stable locking, the first and second detection channels in the detection unit operate synchronously. The first detection channel (100kHz to 800kHz) detects the effective signal gain peak height in real time, and the second detection channel (1 to 2MHz) detects the system's noise floor height in real time. Both detection channels output corresponding DC analog voltages in real time. The controller 40 periodically acquires the voltage signals output by the two detection channels from the detection unit and calculates the ratio of the gain peak to the noise floor. For example, the ratio of the gain peak to the noise floor is the dB value obtained by dividing the peak voltage of the gain peak by the peak voltage of the noise floor by 20log, i.e., 20log 10 (V1 / V2), where V1 is the peak-to-peak gain voltage and V2 is the peak-to-peak noise plateau voltage. It should be noted that the height mentioned in this application refers to the height, i.e., the amplitude, in the gain peak and noise plateau spectrum.

[0055] Optionally, the controller 40 also integrates a low-speed analog-to-digital converter (ADC). Optionally, the ADC has a sampling rate of 100Hz and completes a ratio calculation every 10ms. For example, the controller 40 uses a general-purpose, low-cost microcontroller, such as the STM32F103RCT6, to acquire signals using its built-in ordinary low-speed ADC, and performs decibel difference calculation, lockout state determination, and gain step adjustment control. Optionally, the detection unit includes dual-channel analog hardware circuitry. The dual-channel analog hardware circuitry includes dual-channel analog bandpass filtering and peak detection circuitry.

[0056] This approach replaces the high-speed digital architecture with dual-band spectral feature detection. It employs two analog bandpass filters and peak detection circuits to extract the effective bandwidth gain peak and high-frequency noise platform, respectively. This eliminates the need for high-speed ADCs, FPGAs, and complex FFT digital calculations; spectral feature quantization and determination can be completed using only a standard microcontroller, significantly reducing the system's hardware requirements.

[0057] Secondly, such as Figure 1 As shown, this application embodiment also provides a laser frequency stabilization system, including a seed laser 50, an acousto-optic modulator 60 (AOM), an electro-optic modulator 70 (EOM), a cavity pre-coupled optical path 80, an optical reference cavity 90, and a laser frequency stabilization device 100 provided in any of the above embodiments.

[0058] The seed laser emitted by the seed laser 50 is modulated sequentially by the acousto-optic modulator 60 and the electro-optic modulator 70, and then enters the optical reference cavity 90 through the pre-cavity coupling optical path 80. After being reflected by the optical reference cavity 90, it returns to the pre-cavity coupling optical path 80. The photoelectric detection unit 10 of the laser frequency stabilization device 100 is used to convert the optical signal reflected by the optical reference cavity 90 into a first electrical signal. The controller 40 controls the gain unit 20 and the locking unit 30, and by gradually adjusting the gain value, makes the ratio of the first characteristic quantity reflecting the effective signal strength to the second characteristic quantity reflecting the background noise strength approach the target ratio.

[0059] Thirdly, such as Figure 2 As shown, this application also provides a laser frequency stabilization method for use in any of the laser frequency stabilization devices and systems provided in the above embodiments, comprising the following steps: The cavity front reflected light signal is converted into a first electrical signal, which reflects the deviation information between the laser frequency and the reference cavity resonant frequency. The gain of the first electrical signal is adjusted to output the second electrical signal; In the first gain stage, the gain value of the control gain unit 20 is kept within the initial gain range to broaden the frequency discrimination dynamic range; In response to the satisfaction of the preset locking condition, the system enters the second gain phase. In the second gain stage, the second electrical signal is subjected to spectrum analysis to extract the first feature quantity reflecting the effective signal strength and the second feature quantity reflecting the background noise strength. Calculate the ratio of the first characteristic quantity to the second characteristic quantity; In response to the difference between the ratio and the target ratio, the gain value is gradually adjusted to bring the ratio closer to the target ratio.

[0060] Optionally, the amplitude fluctuation of the second electrical signal within a first preset duration is less than a first preset threshold. The first preset duration is greater than or equal to 1 second, and the first preset threshold is less than or equal to 1 / 10 of the peak value of the second electrical signal during the first gain phase.

[0061] Optionally, such as Figure 3 As shown, the laser frequency stabilization method provided in this application embodiment further includes: The second electrical signal is filtered in the first frequency band to obtain the first characteristic quantity; The second electrical signal is filtered in the second frequency band to obtain the second characteristic quantity; The frequency of the first frequency band is lower than the frequency of the second frequency band.

[0062] Optionally, the first frequency band is from 100kHz to 800kHz. Alternatively, the second frequency band is from 1MHz to 2MHz.

[0063] Optionally, the laser frequency stabilization method provided in this application embodiment further includes: In the second gain stage, if the difference between the ratio of the first and second feature quantities and the target ratio is greater than the second preset threshold, the gain value is adjusted by a preset step size. Within a first preset time period, the amplitude fluctuation of the second electrical signal is monitored; once the amplitude fluctuation is less than the first preset threshold, the ratio of the first characteristic quantity and the second characteristic quantity is recalculated. Repeatedly calculate the difference between the ratio of the first and second feature quantities and the target ratio, and adjust the gain value according to the difference by a preset step size until the difference is less than or equal to the second preset threshold, then stop the gain adjustment.

[0064] Optionally, the second preset threshold is greater than 0 and less than or equal to 1dB. For example, when the ratio of the first feature quantity to the second feature quantity is less than 1dB, gain adjustment is stopped and the current gain parameter is locked; when the ratio of the first feature quantity to the second feature quantity is greater than or equal to 1dB, the gain value is gradually increased by a preset step size until the ratio of the first feature quantity to the second feature quantity is less than 1dB.

[0065] Example 1

[0066] Example 1 provides an example of ultra-stable laser locking using the laser frequency stabilization device provided in this application. Example 1 uses a 5kHz linewidth laser as the seed laser for the ultra-stable laser system. The optical reference cavity consists of a 6cm long ULE glass substrate and a high-reflectivity cavity mirror with a precision of approximately 500,000. The controller uses a microprocessor. The gain unit is an RF gain adjustment unit. The locking unit is a PDH locking unit.

[0067] First, the first electrical signal output by the photoelectric detection unit 10 is connected to the gain unit. After the system starts, the microprocessor forces the gain of the gain unit to a preset small initial gain value to widen the effective frequency discrimination dynamic range of the locking stage (i.e., the first gain stage). In this embodiment, the microprocessor is an STM32F103RCT6. Experimental calibration shows that when the initial gain value is set to 12dB, the signal-to-noise ratio of the second electrical signal output by the gain unit before locking (including the error signal between the laser frequency and the reference cavity resonant frequency) is approximately 12dB within the corresponding measurement bandwidth, which can meet the signal discriminability required for locking capture.

[0068] Subsequently, the PDH locking unit is activated. The PDH locking unit searches for the resonant point of the optical reference cavity and uses the PDH error signal generated by the cavity front reflected light signal to provide feedback control over the seed laser frequency, initially locking the laser frequency to near the resonant frequency of the optical reference cavity. Because the first gain stage uses a relatively low RF gain, the second electrical signal is less likely to exceed the linear operating range of the subsequent circuits during the search and acquisition process, thereby reducing the probability of locking failure or repeated frequency sweeps due to excessive error signals. After multiple tests, the single-shot locking success rate in this embodiment can reach over 99%.

[0069] After initial locking is achieved, the controller continuously monitors the amplitude changes of the second electrical signal. When the amplitude of the second electrical signal remains stable within a preset time and no jumps or loss of lock occur, the system is determined to have entered a steady-state closed-loop locking state and automatically switches to the second gain stage. In this embodiment, the preset threshold for the stabilization time is 10 seconds.

[0070] After entering steady-state lockout, the first and second detection channels of the detection unit operate synchronously. The first detection channel has a bandwidth of 100kHz to 800kHz and is used to detect the effective signal gain peak height in the spectrum of the second electrical signal; the second detection channel has a bandwidth of 1MHz to 2MHz and is used to detect the system's noise floor height. The two detection channels output corresponding DC analog voltages through analog filtering and peak detection circuits, respectively. The controller periodically acquires the two DC voltage signals using a built-in ADC and calculates the ratio between the gain peak height and the noise floor height. In this embodiment, the ADC sampling rate is 100 Hz, meaning that dual-spectral feature acquisition and ratio calculation are completed every 10ms.

[0071] In the second gain stage, the controller performs closed-loop gain adjustment based on the calculated spectral characteristic ratio. Specifically, if the ratio of the current gain peak height to the noise plateau height is lower than the target ratio, it is determined that the current RF gain is too low and the error signal resolution in the second electrical signal has not yet met the preset requirements. The controller then outputs a control command to the gain unit, causing the gain to increase slightly by a preset step size. In this embodiment, the single-step gain adjustment is 1 dB. To balance lock-in stability and frequency stabilization accuracy, the target ratio of the gain peak height to the noise plateau height is set to 10 dB.

[0072] After each gain adjustment, the system delays for the signal link to stabilize before acquiring the two spectral feature data again and recalculating the ratio. In this embodiment, the delay after a single gain adjustment is 20ms. The controller cyclically executes the spectral feature acquisition, ratio calculation, difference judgment, and gain adjustment processes. When the difference between the current ratio and the target ratio is detected to be less than a preset threshold, gain adjustment stops, and the current RF gain parameter is maintained. In this embodiment, the difference threshold is set to 1dB.

[0073] After completing the above tuning, the system enters a high-precision, ultra-stable locking state. At this point, the RF gain is in an operating range that matches the current system noise level, ensuring high frequency discrimination resolution for the PDH error signal while preventing excessive gain from causing saturation in subsequent circuits or instability in the locking loop. During system operation, the controller continuously monitors the dual-spectrum characteristic signals and makes small dynamic corrections to the RF gain based on changes in the ratio of gain peak height to noise plateau height, adapting to environmental changes, changes in optical coupling state, and seed laser state drift.

[0074] Tests have shown that, using the method described in this embodiment, the ultra-stable laser system can operate continuously for several months without losing lock, and achieves a performance better than 2×10⁻⁶. -15 @1s frequency stability, meaning that the Allan deviation of the laser is less than 2×10⁻⁶ within 1 second. -15 .

[0075] In summary, the laser frequency stabilization device, system, and method provided in this application amplify the first electrical signal with an initial gain value in the first gain stage, thereby widening the frequency discrimination dynamic range and improving the locking success rate. In the second gain stage, a first feature quantity reflecting the effective signal strength and a second feature quantity reflecting the background noise strength are extracted, and the ratio of the first feature quantity and the second feature quantity is calculated. In response to the difference between this ratio and the target ratio, the gain value is gradually adjusted so that the ratio gradually approaches the target ratio, thereby achieving adaptive gain adjustment and ensuring frequency stabilization accuracy. Segmented gain balances both locking success rate and frequency stabilization accuracy. Spectrum analysis extracts the first and second feature quantities, and the gain value is controlled so that their ratio tracks the target ratio. No high-speed analog-to-digital converter and field-programmable gate array digital spectrum analysis architecture are required; only a common microcontroller and analog detection circuit are needed to complete the spectral feature quantization and determination, reducing hardware costs, optimizing circuit space utilization, and improving system stability. This facilitates system miniaturization, portability, and engineering.

[0076] The above description is merely a specific implementation of the embodiments of this application, but the protection scope of the embodiments of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the embodiments of this application should be covered within the protection scope of the embodiments of this application.

Claims

1. A laser frequency stabilization device, characterized in that, include: The photoelectric detection unit is used to convert the cavity front reflected light signal into a first electrical signal, wherein the cavity front reflected light signal reflects the deviation information between the laser frequency and the reference cavity resonant frequency; A gain unit is configured to adjust the gain of the first electrical signal to obtain a second electrical signal; The locking unit is configured to constrain the laser frequency to the reference cavity resonant frequency based on the second electrical signal; The controller is configured as follows: In the first gain stage, the gain value of the gain unit is controlled to be the initial gain value in order to broaden the frequency discrimination dynamic range; In response to the satisfaction of the preset locking condition, the system enters the second gain phase. In the second gain stage, the second electrical signal is subjected to spectrum analysis to extract a first feature quantity reflecting the effective signal strength and a second feature quantity reflecting the background noise strength. Calculate the ratio of the first feature quantity to the second feature quantity; In response to the difference between the ratio and the target ratio, the gain value is gradually adjusted so that the ratio approaches the target ratio.

2. The laser frequency stabilization device according to claim 1, characterized in that, The initial gain value satisfies: During the first gain phase, the signal-to-noise ratio of the second electrical signal is made greater than or equal to 20dB.

3. The laser frequency stabilization device according to claim 1, characterized in that, The preset locking condition includes: the fluctuation of the amplitude of the second electrical signal within a first preset time period is less than a first preset threshold.

4. The laser frequency stabilization device according to claim 1, characterized in that, The device also includes a detection unit; The detection unit includes a first detection channel and a second detection channel; The first detection channel is configured to filter the second electrical signal in a first frequency band to obtain the first feature quantity; The second detection channel is configured to filter the second electrical signal in the second frequency band to obtain the second feature quantity; The frequency of the first frequency band is lower than the frequency of the second frequency band.

5. The laser frequency stabilization device according to claim 4, characterized in that, The first frequency band is from 100 kHz to 800 kHz; and the second frequency band is from 1 MHz to 2 MHz.

6. The laser frequency stabilization device according to claim 3, characterized in that, The controller is also configured to: In the second gain stage, if the difference between the ratio and the target ratio is greater than the second preset threshold, the gain value is adjusted by a preset step size. Within a first preset time period, the amplitude fluctuation of the second electrical signal is monitored; once the amplitude fluctuation is less than a first preset threshold, the ratio of the first feature quantity and the second feature quantity is recalculated. The difference between the ratio and the target ratio is repeatedly calculated, and the gain value is adjusted in response to the difference by a preset step size until the difference is less than or equal to the second preset threshold, at which point the gain adjustment is stopped.

7. The laser frequency stabilization device according to claim 6, characterized in that, The second preset threshold is greater than 0 and less than or equal to 1 dB.

8. The laser frequency stabilization device according to claim 6, characterized in that, The preset step size is greater than or equal to 0.1 dB and less than or equal to 1 dB.

9. The laser frequency stabilization device according to claim 1 or 6, characterized in that, The target ratio is greater than or equal to 1 dB and less than or equal to 20 dB.

10. The laser frequency stabilization device according to claim 3 or 6, characterized in that, The first preset duration is greater than or equal to 1 second, and the first preset threshold is less than or equal to 1 / 10 of the peak value of the second electrical signal in the first gain phase.

11. The laser frequency stabilization device according to any one of claims 1, 4, or 6, characterized in that, The first characteristic quantity includes the amplitude of the gain peak of the second electrical signal.

12. The laser frequency stabilization device according to any one of claims 1, 4, or 6, characterized in that, The second characteristic quantity includes the intensity of the background noise.

13. A laser frequency stabilization system, characterized in that, It includes a seed laser, an acousto-optic modulator, an electro-optic modulator, a pre-cavity coupled optical path, a reference cavity, and a laser frequency stabilization device according to any one of claims 1 to 12; The seed laser emitted by the seed laser is modulated sequentially by the acousto-optic modulator and the electro-optic modulator, then enters the reference cavity through the pre-cavity coupling optical path, and returns to the pre-cavity coupling optical path after being reflected by the reference cavity. The photoelectric detection unit of the laser frequency stabilization device is used to convert the optical signal reflected by the reference cavity into a first electrical signal; The controller controls the gain unit and the locking unit, and by gradually adjusting the gain value, makes the ratio of the first characteristic quantity reflecting the effective signal strength to the second characteristic quantity reflecting the background noise strength approach the target ratio.

14. A laser frequency stabilization method, characterized in that, For the laser frequency stabilization device according to any one of claims 1 to 12 and the laser frequency stabilization system according to claim 13, the method comprises: The cavity front reflected light signal is converted into a first electrical signal, which reflects the deviation information between the laser frequency and the reference cavity resonant frequency; The gain of the first electrical signal is adjusted to output the second electrical signal; In the first gain stage, the gain value of the gain unit is controlled to be the initial gain value in order to broaden the frequency discrimination dynamic range; In response to the satisfaction of the preset locking condition, the system enters the second gain phase. In the second gain stage, the second electrical signal is subjected to spectrum analysis to extract a first feature quantity reflecting the effective signal strength and a second feature quantity reflecting the background noise strength. Calculate the ratio of the first feature quantity to the second feature quantity; In response to the difference between the ratio and the target ratio, the gain value is gradually adjusted so that the ratio approaches the target ratio.

15. The method according to claim 14, characterized in that, The preset locking condition includes: the fluctuation of the amplitude of the second electrical signal within a first preset time period is less than a first preset threshold.

16. The method according to claim 15, characterized in that, The method further includes: The second electrical signal is filtered in the first frequency band to obtain the first feature quantity; The second electrical signal is filtered in the second frequency band to obtain the second characteristic quantity; The frequency of the first frequency band is lower than the frequency of the second frequency band.

17. The method according to claim 16, characterized in that, The first frequency band is from 100 kHz to 800 kHz; and the second frequency band is from 1 MHz to 2 MHz.

18. The method according to claim 14, characterized in that, The method further includes: In the second gain stage, if the difference between the ratio and the target ratio is greater than the second preset threshold, the gain value is adjusted by a preset step size. Within a first preset time period, the amplitude fluctuation of the second electrical signal is monitored; once the amplitude fluctuation is less than a first preset threshold, the ratio of the first feature quantity and the second feature quantity is recalculated. The difference between the ratio and the target ratio is repeatedly calculated, and the gain value is adjusted in response to the difference by a preset step size until the difference is less than or equal to the second preset threshold, at which point the gain adjustment is stopped.

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