Method and system for suppressing intensity noise in a resonant frequency-doubled laser

Abstract

This invention provides a method and system for suppressing intensity noise in a resonant frequency-doubled laser, relating to the field of data processing technology. By acquiring the cavity detuning error signal of the resonant frequency-doubled cavity and performing normalization and frequency band separation processing, low-frequency error signals and mid-to-high-frequency error signals are obtained. The piezoelectric actuator of the resonant frequency-doubled laser is driven to compensate the cavity length of the resonant frequency-doubled cavity, and multi-source state signals are collected during the driving compensation process. Based on the multi-source state signals, the resonant frequency drift of the resonant frequency-doubled cavity is predicted, and a target radio frequency is generated. A frequency control signal and an intensity compensation control signal are generated based on the target radio frequency. The equivalent optical frequency of the seed light is adjusted based on the frequency control signal, and the output power fluctuation during the frequency modulation process is synchronously compensated based on the intensity compensation control signal. This effectively compensates for the fluctuation of output optical power during the process of adjusting the seed light frequency to track the cavity resonant drift, achieving high stability and low intensity noise output of the resonant frequency-doubled laser.

Description

Technical Field

[0001] This invention relates to data processing technology, and more particularly to a method and system for suppressing intensity noise in a resonant frequency-doubled laser. Background Technology

[0002] Resonant frequency doubling technology is a core technology for obtaining high-power, high-stability frequency-doubled laser output. In fields such as precision measurement, quantum optics, and laser spectroscopy, the output intensity noise of resonant frequency-doubled lasers can affect system performance. Therefore, suppressing the output intensity noise of frequency doubling has always been one of the core issues in resonant frequency doubling technology research.

[0003] Currently, most existing noise suppression schemes for resonant frequency-doubled lasers rely on single cavity length feedback control to maintain the cavity resonance state. Under complex environmental disturbances, the resonant frequency of the resonant cavity will drift over a wide bandwidth. Traditional single actuator compensation bandwidth is limited and it is difficult to effectively suppress cavity length disturbances at both low and mid-to-high frequencies simultaneously. When seed light frequency adjustment is used to track cavity resonance drift, due to the high frequency sensitivity of the resonant cavity, changes in the radio frequency will cause changes in the diffraction efficiency of the acousto-optic modulator, which will in turn cause fluctuations in the output optical power, thereby introducing additional intensity noise and reducing the stability of the output optical power.

[0004] Therefore, how to effectively compensate for the fluctuation of output optical power during the process of adjusting the seed light frequency to track the cavity resonance drift, and achieve high stability and low noise output of the resonant frequency doubling laser, has become an urgent problem to be solved. Summary of the Invention

[0005] This invention provides a method and system for suppressing intensity noise in a resonant frequency-doubled laser. It can effectively compensate for fluctuations in output optical power during the process of adjusting the seed light frequency to track the resonant drift of the cavity, thereby achieving high stability and low intensity noise output of the resonant frequency-doubled laser.

[0006] A first aspect of the present invention provides a method for suppressing intensity noise in a resonant frequency-doubled laser, comprising:

[0007] The cavity detuning error signal of the resonant frequency doubling cavity is obtained, and the cavity detuning error signal is normalized and frequency band separated to obtain the low-frequency error signal and the mid-to-high frequency error signal, respectively.

[0008] The first and second piezoelectric actuators of the resonant frequency-doubled laser are driven according to the low-frequency error signal and the medium-to-high-frequency error signal, respectively, to perform cavity length compensation of the resonant frequency-doubled cavity, and the multi-source state signals of the resonant frequency-doubled laser are collected during the driving compensation process;

[0009] The resonant frequency drift of the resonant frequency doubling cavity is predicted based on the multi-source state signal, a target radio frequency is generated based on the resonant frequency drift, and a frequency control signal and an intensity compensation control signal are generated based on the target radio frequency.

[0010] The equivalent optical frequency of the seed light is adjusted based on the frequency control signal, and the output power fluctuation during the frequency modulation process is synchronously compensated based on the intensity compensation control signal.

[0011] Optionally, in one possible implementation of the first aspect, before acquiring the cavity detuning error signal of the resonant frequency doubling cavity, the method further includes:

[0012] The seed light is controlled to pass through an acousto-optic modulator and an electro-optic modulator in sequence for frequency shifting and phase modulation, generating a probe light containing modulation sidebands;

[0013] The probe light is amplified by an optical amplifier and then injected into the resonant frequency doubling cavity.

[0014] Optionally, in one possible implementation of the first aspect, the step of acquiring the cavity detuning error signal of the resonant frequency doubling cavity, and performing normalization and frequency band separation processing on the cavity detuning error signal to obtain low-frequency error signals and mid-to-high-frequency error signals respectively includes:

[0015] The reflected light signal after the probe light is reflected by the resonant frequency doubling cavity is acquired;

[0016] The reflected light signal is demodulated to extract the cavity detuning error signal corresponding to the modulation sideband;

[0017] The cavity detuning error signal is normalized by dividing it by the fundamental frequency optical power to obtain the normalized error signal.

[0018] The normalized error signal is separated into frequency bands by a complementary filter to obtain the low-frequency error signal and the mid-to-high-frequency error signal, respectively.

[0019] Optionally, in one possible implementation of the first aspect, the first piezoelectric actuator and the second piezoelectric actuator, which drive the resonant frequency-doubled laser according to the low-frequency error signal and the mid-to-high-frequency error signal respectively, perform cavity length compensation on the resonant frequency-doubled cavity, and acquire the multi-source state signal of the resonant frequency-doubled laser during the driving compensation process, include:

[0020] The low-frequency error signal is input to the first feedback controller, which drives the first piezoelectric actuator via the first piezoelectric driver to perform low-frequency cavity length compensation on the resonant frequency doubling cavity;

[0021] The mid-to-high frequency error signal is input to the second feedback controller, which drives the second piezoelectric actuator via the second piezoelectric driver to perform mid-to-high frequency residual error compensation on the resonant frequency doubling cavity;

[0022] The residual error signal of the resonant frequency doubling cavity after compensation by the first piezoelectric actuator and the second piezoelectric actuator, the first driving voltage of the first piezoelectric actuator, the second driving voltage of the second piezoelectric actuator, and the operating state parameters of the resonant frequency doubling laser are collected to obtain a multi-source state signal.

[0023] Optionally, in one possible implementation of the first aspect, the acquisition of the residual error signal of the resonant frequency doubling cavity after compensation by the first piezoelectric actuator and the second piezoelectric actuator, the first driving voltage of the first piezoelectric actuator, the second driving voltage of the second piezoelectric actuator, and the operating status parameters of the resonant frequency doubling laser includes:

[0024] After compensation by the first piezoelectric actuator and the second piezoelectric actuator, the cavity detuning error signal of the resonant frequency doubling cavity at the current moment is obtained as the residual error signal;

[0025] The output voltages of the first piezoelectric actuator and the second piezoelectric actuator are collected respectively, and used as the first driving voltage and the second driving voltage;

[0026] At least four of the following parameters are obtained as operating status parameters: the current radio frequency of the acousto-optic modulator, the fundamental frequency optical power, the frequency doubling optical power, the transmission peak signal of the resonant frequency doubling cavity, the cavity temperature, and the frequency doubling crystal temperature.

[0027] Optionally, in one possible implementation of the first aspect, the step of predicting the resonant frequency drift of the resonant frequency doubling cavity based on the multi-source state signal, generating a target radio frequency based on the resonant frequency drift, and generating a frequency control signal and an intensity compensation control signal based on the target radio frequency includes:

[0028] The multi-source state signal is input into the model prediction controller, which predicts the resonant frequency drift of the resonant frequency doubling cavity within a preset time period based on a preset objective function and constraints.

[0029] The target radio frequency is generated based on the resonant frequency drift, and a corresponding frequency control signal is generated based on the target radio frequency.

[0030] Based on the pre-calibrated correspondence between radio frequency, amplitude control quantity and output optical power, and in combination with the target radio frequency and the preset target output optical power, the corresponding radio frequency amplitude control quantity is determined.

[0031] The corresponding intensity compensation control signal is generated based on the radio frequency amplitude control quantity and output to the acousto-optic driver.

[0032] Optionally, in one possible implementation of the first aspect, generating the target radio frequency based on the resonant frequency drift and generating a corresponding frequency control signal based on the target radio frequency includes:

[0033] The target radio frequency is calculated by superimposing the resonant frequency drift with the current radio frequency of the acousto-optic modulator.

[0034] The target radio frequency is converted from digital to analog to generate the frequency control signal and output to the acousto-optic driver.

[0035] Optionally, in one possible implementation of the first aspect, adjusting the equivalent optical frequency of the seed light based on the frequency control signal and synchronously compensating for output power fluctuations during frequency modulation based on the intensity compensation control signal includes:

[0036] The frequency control signal and the intensity compensation control signal are respectively input to the frequency control port and amplitude control port of the acousto-optic driver;

[0037] The acousto-optic driver is controlled to generate a radio frequency drive signal corresponding to the target radio frequency according to the frequency control signal, and the acousto-optic modulator is driven to frequency shift the seed light based on the radio frequency drive signal to adjust the equivalent optical frequency of the seed light.

[0038] The acoustic-optical driver is controlled to adjust the amplitude of the radio frequency drive signal according to the intensity compensation control signal to obtain the target radio frequency amplitude;

[0039] The diffraction efficiency of the acousto-optic modulator is adjusted according to the obtained target radio frequency amplitude, and the output power fluctuation during the frequency modulation process is compensated based on the adjusted diffraction efficiency.

[0040] Optionally, in one possible implementation of the first aspect, when the current radio frequency of the acousto-optic modulator deviates from the center operating frequency by more than a preset threshold, the cavity length of the resonant frequency doubling cavity is adjusted based on the first piezoelectric actuator until the radio frequency of the acousto-optic modulator is within the center operating range.

[0041] A second aspect of the present invention provides an intensity noise suppression system for a resonant frequency-doubled laser, comprising:

[0042] The processing module is used to acquire the cavity detuning error signal of the resonant frequency doubling cavity, and to normalize and perform frequency band separation processing on the cavity detuning error signal to obtain low-frequency error signal and mid-to-high frequency error signal respectively.

[0043] The acquisition module is used to drive the first piezoelectric actuator and the second piezoelectric actuator of the resonant frequency-doubled laser to perform cavity length compensation of the resonant frequency-doubled cavity according to the low-frequency error signal and the medium-high frequency error signal, respectively, and to acquire the multi-source state signal of the resonant frequency-doubled laser during the driving compensation process;

[0044] The generation module is used to predict the resonant frequency drift of the resonant frequency doubling cavity based on the multi-source state signal, generate a target radio frequency based on the resonant frequency drift, and generate a frequency control signal and an intensity compensation control signal based on the target radio frequency.

[0045] The adjustment module is used to adjust the equivalent optical frequency of the seed light based on the frequency control signal, and to synchronously compensate for the output power fluctuations during the frequency modulation process based on the intensity compensation control signal.

[0046] The beneficial effects of this invention are as follows:

[0047] 1. This invention can generate a probe light containing modulation sidebands by frequency shifting and phase modulation of the seed light, and demodulate the reflected light signal of the resonant frequency doubling cavity to obtain the cavity detuning error signal. By normalizing the error signal by dividing it by the fundamental frequency optical power, and separating the normalized error signal into frequency bands, the first piezoelectric actuator and the second piezoelectric actuator are driven to perform coordinated cavity length compensation, respectively. This can eliminate the interference of incident light power fluctuations on the amplitude of the error signal, ensure that the error signal truly reflects the frequency deviation, and improve the locking accuracy and stability of the resonant frequency doubling cavity.

[0048] 2. This invention simultaneously acquires residual error signals, first driving voltage, second driving voltage, and multi-source state signals such as the current RF frequency of the acousto-optic modulator, fundamental frequency optical power, frequency doubling optical power, transmission peak signal, cavity temperature, and frequency doubling crystal temperature during the dual piezoelectric actuator drive compensation process. Based on the multi-source state signals, the drift direction and amplitude of the cavity resonant frequency are predicted and compensated, thereby improving the ability of the resonant frequency doubling laser to suppress complex environmental disturbances and achieving accurate prediction and compensation of resonant frequency drift.

[0049] 3. This invention can synchronously adjust the frequency and amplitude of the radio frequency drive signal by inputting the frequency control signal and the intensity compensation control signal into the frequency control port and amplitude control port of the acousto-optic driver, respectively. By adjusting the sound field intensity inside the acousto-optic modulator by the change of radio frequency amplitude, the diffraction efficiency can be corrected. While adjusting the equivalent optical frequency of the seed light to track the cavity frequency drift, the change in diffraction efficiency caused by the frequency change can be offset in real time, thereby eliminating the intensity noise introduced by the frequency modulation process and ensuring the stability of the frequency doubling light output power. Attached Figure Description

[0050] Figure 1This is a schematic flowchart of a method for suppressing intensity noise in a resonant frequency-doubled laser, provided in an embodiment of the present invention.

[0051] Figure 2 This is a schematic diagram of the composition architecture of a resonant frequency doubling laser intensity noise suppression system provided in an embodiment of the present invention;

[0052] Figure 3 This is a schematic diagram of the structure of a resonant frequency doubling laser intensity noise suppression system provided in an embodiment of the present invention. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] The technical solution of the present invention will be described in detail below with reference to specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments.

[0055] See Figure 1 This is a schematic flowchart of a method for suppressing intensity noise in a resonant frequency-doubled laser, provided in an embodiment of the present invention. Figure 1 The execution entity of the method shown can be a software and / or hardware device. The execution entity of this application can include, but is not limited to, at least one of the following: user equipment, network equipment, etc. User equipment can include, but is not limited to, computers, smartphones, personal digital assistants (PDAs), and the aforementioned electronic devices. Network equipment can include, but is not limited to, a single network server, a server group consisting of multiple network servers, or a cloud based on cloud computing consisting of a large number of computers or network servers. Cloud computing is a type of distributed computing, consisting of a super virtual computer composed of a group of loosely coupled computers. This embodiment does not limit this. Steps S1 to S4 are detailed as follows:

[0056] S1, acquire the cavity detuning error signal of the resonant frequency doubling cavity, normalize and perform frequency band separation processing on the cavity detuning error signal to obtain low-frequency error signal and mid-to-high frequency error signal respectively.

[0057] Among them, the resonant frequency doubling cavity refers to an optical resonant cavity with a frequency doubling crystal placed inside. The fundamental frequency light is reflected back and forth in the cavity to form power enhancement, and part of it is converted into frequency doubling light output in the frequency doubling crystal. The cavity detuning error signal refers to an electrical signal obtained by detecting the reflected light of the resonant frequency doubling cavity and demodulating it. The magnitude and sign of this signal reflect the degree of deviation between the incident fundamental frequency light frequency and the cavity resonant frequency. Normalization refers to the data processing process that eliminates the influence of incident light power fluctuations on the amplitude of the error signal. Frequency band separation processing refers to the processing process that splits the signal into different frequency components according to a preset frequency threshold. The low-frequency error signal refers to the slowly changing part of the error signal, mainly caused by factors such as temperature changes. The mid-to-high frequency error signal refers to the rapidly changing part of the error signal, mainly caused by factors such as mechanical vibration.

[0058] It is understandable that the cavity detuning error signal can reflect the degree of mismatch between the incident light frequency and the cavity resonant frequency. However, the fluctuation of the incident light power itself will interfere with the amplitude of the error signal. Therefore, normalization can be performed first to eliminate this interference. The normalized error signal contains both slow changes caused by temperature drift and rapid changes caused by mechanical vibration. These two types of changes have different requirements for the actuator's stroke and response speed. Therefore, the error signal can be split into low-frequency and mid-to-high-frequency paths according to frequency, which are then used for compensation by actuators with different characteristics.

[0059] Specifically, the resonant frequency doubling cavity can be probed to obtain the cavity detuning error signal, which reflects the deviation between the incident light frequency and the cavity resonant frequency. The cavity detuning error signal is then normalized to eliminate the influence of interference factors on the signal accuracy. The normalized signal is then subjected to frequency band separation processing, which can split it into two outputs, a low-frequency error signal and a mid-to-high-frequency error signal, according to the rate of change.

[0060] Before obtaining the cavity detuning error signal of the resonant frequency doubling cavity, the following steps are also included:

[0061] A1 controls the seed light to pass through an acousto-optic modulator and an electro-optic modulator in sequence for frequency shifting and phase modulation, generating a probe light containing modulation sidebands.

[0062] Among them, seed light refers to single-frequency continuous laser light generated by the laser, which serves as the original light source for the entire resonant frequency-doubled laser; acousto-optic modulator refers to a device that changes the frequency of passing light by changing the radio frequency driving frequency; electro-optic modulator refers to a device that changes the phase of light by applying an electric field to light and generates sideband signals on both sides of the optical frequency; frequency shift refers to the operation of changing the frequency of light; phase modulation refers to the operation of applying periodic phase changes to the light wave; modulation sideband refers to the new frequency components generated on both sides of the original center frequency after phase modulation of light; and probe light refers to the optical signal carrying the modulation sideband after frequency shift and phase modulation.

[0063] Understandably, subsequent steps require obtaining the cavity detuning error signal from the resonant frequency doubling cavity. This signal can be obtained by injecting a probe beam carrying a specific frequency marker into the resonant frequency doubling cavity. The seed light first undergoes frequency shifting via an acousto-optic modulator, and then phase modulation is applied via an electro-optic modulator, thereby generating modulation sidebands on both sides of the optical frequency. When this light with sidebands enters the resonant cavity and is reflected back, the reflection patterns of the center frequency and the sidebands are different. Using this difference, the magnitude and direction of the frequency deviation can be calculated relatively accurately.

[0064] Specifically, the single-frequency continuous laser output from the seed light source is input into an acousto-optic modulator via an optical fiber. A radio frequency drive signal of a certain frequency is applied to the acousto-optic modulator. The acousto-optic modulator uses the acousto-optic effect to diffract the input light, and selects the first-order diffracted light as the output. The frequency of the output light is shifted relative to the input light by the same frequency as the radio frequency. The frequency-shifted light is input into an electro-optic modulator, and a sinusoidal modulation signal with a fixed frequency is applied to the electro-optic modulator. The refractive index of the crystal in the electro-optic modulator changes periodically with the modulation signal, causing the phase of the transmitted light wave to be periodically modulated. This generates two modulation sidebands at symmetrical positions on both sides of the original light frequency, resulting in a probe light containing the modulation sidebands.

[0065] A2, the probe light is amplified by an optical amplifier and then injected into the resonant frequency doubling cavity.

[0066] An optical amplifier is a device that amplifies the power of an input optical signal.

[0067] Understandably, the probe light has low power after passing through the acousto-optic modulator and electro-optic modulator, which is insufficient to form an effective resonance in the resonant frequency doubling cavity and generate sufficient frequency doubling light output. Therefore, the power can be boosted to the required level by the optical amplifier before being injected into the resonant frequency doubling cavity.

[0068] Specifically, the output probe light can be input into an optical amplifier through an optical fiber. The optical amplifier uses a gain medium to stimulate the amplification of the input light, resulting in a probe light with increased output power. The amplified probe light is then injected into the input end of the resonant frequency doubling cavity through an optical fiber and coupling optical elements, and enters the cavity to participate in resonance.

[0069] Based on the above embodiments, step S1 can be implemented in the following ways:

[0070] S11, Collect the reflected light signal after the resonant frequency doubling cavity reflects the probe light.

[0071] Among them, the reflected light signal refers to the light signal that returns from the reflection end of the resonant frequency doubling cavity after the probe light is injected into the cavity.

[0072] It is understandable that after the probe light is injected into the resonant frequency doubling cavity, part of the light enters the cavity to resonate, while the other part of the light returns from the cavity's reflection end. The reflected light carries information about whether the incident light frequency matches the cavity's resonant frequency. By collecting the reflected light signal, the original signal source can be provided for the subsequent extraction of the cavity detuning error signal.

[0073] Specifically, a photodetector can be set in the direction of the reflected light path of the resonant frequency doubling cavity. The photosensitive surface of the detector receives the reflected light returning from the cavity reflection end. The photodetector converts the received light intensity change into a corresponding electrical signal. The waveform and amplitude of the electrical signal reflect the characteristics of the reflected light, which is the collected reflected light signal.

[0074] S12, demodulate the reflected light signal and extract the cavity detuning error signal corresponding to the modulation sideband.

[0075] It is understandable that the reflected light signal contains the response of the modulation sideband applied in step A1 after being reflected by the cavity. When the modulation sideband is outside the cavity resonant frequency, it is almost entirely reflected, while the carrier partially enters the cavity near the resonant frequency. The amplitude and phase relationship between the two at the reflection end changes with the frequency deviation. By demodulating the reflected light signal with the modulation frequency as a reference, the error signal reflecting the frequency deviation can be extracted from the interaction between the sideband and the carrier.

[0076] Specifically, the collected reflected light signal can be input into the demodulation circuit, and the modulation signal used by the electro-optic modulator can also be input into the demodulation circuit as a reference signal. The demodulation circuit mixes the reflected light signal and the reference signal and performs low-pass filtering to remove the high-frequency carrier component, and outputs a low-frequency or DC voltage signal. This voltage signal is the cavity detuning error signal. The sign of the signal indicates the direction of the frequency deviation, and the amplitude of the signal indicates the magnitude of the frequency deviation.

[0077] S13, the cavity detuning error signal is divided by the fundamental frequency optical power and normalized to obtain the normalized error signal.

[0078] Among them, the fundamental frequency optical power refers to the optical power of the fundamental frequency light before it is injected into the resonant frequency doubling cavity, and the normalized error signal refers to the error signal after being processed by dividing by the fundamental frequency optical power and eliminating the influence of optical power fluctuation.

[0079] It is understandable that the fundamental frequency optical power injected into the resonant frequency doubling cavity may fluctuate over time. This fluctuation will proportionally affect the amplitude of the cavity detuning error signal obtained by demodulation. If this effect is not eliminated, the rise and fall of optical power will be misjudged as a change in frequency deviation. Dividing the error signal by the fundamental frequency optical power at the current moment can eliminate the influence of optical power change on the amplitude of the error signal, so that the normalized error signal only reflects the true situation of frequency detuning.

[0080] Specifically, a beam splitter can be set at the input end of the resonant frequency doubling cavity to extract a small portion of the fundamental frequency light before it is injected into the cavity. The light is then converted into an electrical signal representing the fundamental frequency optical power by a monitoring photodetector. The cavity detuning error signal and the current fundamental frequency optical power signal are simultaneously input into a division circuit. The division circuit outputs the result of dividing the two signals, which is the normalized error signal.

[0081] The normalized error signal can be expressed as:

[0082]

[0083] in This is the cavity detuning error signal. This represents the fundamental frequency optical power.

[0084] S14, the normalized error signal is separated into frequency bands by a complementary filter to obtain the low-frequency error signal and the mid-to-high frequency error signal respectively.

[0085] Among them, a complementary filter refers to a filter network composed of a low-pass filter and a high-pass filter, and the sum of their frequency responses remains constant throughout the entire frequency band. Frequency band separation refers to the operation of using a complementary filter to split the normalized error signal into low-frequency and high-frequency parts without distortion.

[0086] It is understandable that the normalized error signal contains both slow changes caused by temperature drift and rapid changes caused by mechanical vibration. These two types of changes have different detuning amplitudes and rates of change, and can be processed separately by actuators with different stroke and response characteristics. The complementary filter can split the signal into two paths according to the preset frequency division, and the sum of the two signals is consistent with the original signal, without introducing signal distortion near the frequency division point.

[0087] Specifically, the obtained normalized error signal can be simultaneously input into the input terminals of a low-pass filter and a high-pass filter. The cutoff frequencies of the low-pass and high-pass filters are set to the same division frequency value. The low-pass filter allows signal components below the division frequency to pass through and outputs a low-frequency error signal, while the high-pass filter allows signal components above the division frequency to pass through and outputs a mid-to-high frequency error signal. The amplitude-frequency responses of the two filters at the division frequency compensate for each other, so that the sum of the amplitudes of the two outputs is consistent with the amplitude of the input signal.

[0088] S2, the first piezoelectric actuator and the second piezoelectric actuator of the resonant frequency doubling laser are driven according to the low-frequency error signal and the medium-high frequency error signal, respectively, to perform cavity length compensation of the resonant frequency doubling cavity, and the multi-source state signal of the resonant frequency doubling laser is collected during the driving compensation process.

[0089] Among them, the resonant frequency-doubled laser refers to the entire laser including the seed light source, optical frequency adjustment device, optical amplifier, resonant frequency-doubled cavity and control module. The first piezoelectric actuator refers to the piezoelectric driving element with a large displacement stroke and a low response frequency, which is used to perform low-frequency cavity length compensation of the resonant frequency-doubled cavity. The second piezoelectric actuator refers to the piezoelectric driving element with a small displacement stroke and a high response frequency, which is used to perform mid-to-high frequency residual error compensation of the resonant frequency-doubled cavity. Cavity length compensation refers to the process of adjusting the physical length of the cavity by changing the position of the cavity mirror of the resonant frequency-doubled cavity, so that the cavity resonant frequency is restored to match the incident light frequency. Multi-source state signals refer to multiple signals reflecting the laser's operating state that are collected simultaneously during the driving compensation process.

[0090] Understandably, after splitting the error signal into low-frequency and mid-to-high-frequency categories, these two types of signals correspond to different types of disturbances and can be processed separately by actuators with different characteristics. Low-frequency error signals are mainly caused by temperature drift, characterized by potentially large amplitude changes but slow speed of change. For example, the temperature difference between day and night in a laboratory causes the cavity to expand slowly, and the cavity resonant frequency may drift by tens of megahertz. However, this drift occurs on a time scale of minutes or even hours. Mid-to-high-frequency error signals are mainly caused by table vibration, acoustic noise, etc., characterized by small amplitude changes but fast speed of change. For example, vibrations caused by people walking cause the cavity length to jitter on the order of microseconds. Although the amplitude is small, if it is not suppressed, it will still cause significant intensity noise. Two actuators can be used to process them separately. The first piezoelectric actuator has a large stroke and slow response, and is responsible for compensating for the large low-frequency detuning caused by temperature drift. The second piezoelectric actuator has a small stroke and fast response, and is responsible for suppressing the rapid mid-to-high-frequency jittering caused by vibration. During the drive compensation process, although most of the detuning is suppressed, a small amount of residual error still exists. Collecting these signals at the same time can provide a data basis for subsequent prediction of resonant frequency drift.

[0091] Specifically, the obtained low-frequency error signal is processed by the controller and applied to the first piezoelectric actuator, which generates a corresponding displacement to compensate for the low-frequency cavity length of the resonant frequency doubling cavity. At the same time, the obtained mid-to-high frequency error signal is processed by the controller and applied to the second piezoelectric actuator, which generates a corresponding rapid displacement to compensate for the mid-to-high frequency residual error of the resonant frequency doubling cavity. During the drive compensation process, the compensated residual error signal, the drive voltage corresponding to each actuator, and various state parameters of the laser during operation are collected synchronously to form a multi-source state signal.

[0092] Based on the above embodiments, step S2 can be implemented in the following ways:

[0093] S21, the low-frequency error signal is input to the first feedback controller, and the first piezoelectric actuator is driven by the first piezoelectric driver to perform low-frequency cavity length compensation on the resonant frequency doubling cavity.

[0094] The first feedback controller refers to a PID controller operating in the low-frequency compensation channel. It receives low-frequency error signals and calculates the compensation amount to be applied at the current moment according to a preset proportional, integral, and derivative control algorithm, and outputs a low-voltage control signal representing the compensation amount. The first piezoelectric actuator refers to a high-voltage amplifier circuit connected to the output of the first feedback controller. It amplifies the low-voltage control signal output by the first feedback controller into a high-voltage drive signal that can directly drive the first piezoelectric actuator. The first piezoelectric actuator refers to a piezoelectric element with a large stroke and slow response speed, which is installed on one cavity mirror of the resonant frequency doubling cavity. It receives the high-voltage drive signal output by the first piezoelectric actuator and converts it into mechanical displacement. Low-frequency cavity length compensation refers to changing the cavity length by generating a large displacement through the first piezoelectric actuator, correcting the slow detuning of the cavity resonant frequency caused by factors such as temperature drift.

[0095] Understandably, the low-frequency error signal is a voltage signal that changes slowly over time. Its amplitude is small and insufficient to directly drive the piezoelectric actuator to produce displacement. The feedback controller needs to calculate the compensation control quantity to be applied based on the magnitude and trend of the error signal. Then, the piezoelectric driver amplifies this control quantity into a high-voltage drive signal to drive the piezoelectric actuator to produce a displacement of sufficient amplitude to compensate for the low-frequency detuning.

[0096] Specifically, the obtained low-frequency error signal can be connected to the input terminal of the first feedback controller. The internal arithmetic circuit of the first feedback controller performs proportional, integral, and differential operations on the error signal, and then adds the three operation results to obtain a low-voltage control signal. This low-voltage control signal is sent out from the output terminal of the first feedback controller and connected to the input terminal of the first piezoelectric actuator. The high-voltage amplifier circuit inside the first piezoelectric actuator amplifies the voltage of the signal and outputs a high-voltage drive signal with sufficient amplitude to drive the actuator. This high-voltage drive signal is applied to the first piezoelectric actuator, and the piezoelectric ceramic inside the first piezoelectric actuator undergoes mechanical deformation under the action of the high-voltage electric field, pushing the cavity mirror to move and completing the low-frequency cavity length compensation.

[0097] S22, the mid-to-high frequency error signal is input to the second feedback controller, and the second piezoelectric actuator is driven by the second piezoelectric driver to perform mid-to-high frequency residual error compensation on the resonant frequency doubling cavity.

[0098] Among them, the second feedback controller refers to the PID controller operating in the mid-to-high frequency compensation channel. The difference between it and the first feedback controller is that its control parameters are configured differently for the rapid changes of mid-to-high frequency signals. The second piezoelectric actuator refers to the high-voltage amplifier circuit connected to the output of the second feedback controller. The difference between it and the first piezoelectric actuator is that it has a higher response bandwidth and can amplify rapidly changing low-voltage control signals without distortion. The second piezoelectric actuator refers to a piezoelectric element with a small stroke and fast response speed, which is installed on another cavity mirror of the resonant frequency doubling cavity. Mid-to-high frequency residual error compensation refers to suppressing the rapid jitter of the cavity resonant frequency caused by mechanical vibration and other factors by generating a rapid and small displacement through the second piezoelectric actuator.

[0099] Understandably, the control signal output by the second feedback controller changes rapidly, requiring the second piezoelectric driver to have a high response bandwidth to track the rapid changes in the control signal and accurately amplify it into a high-voltage signal in a short time. Otherwise, the delay and distortion generated during the amplification process will render the mid-to-high frequency compensation ineffective.

[0100] Specifically, the obtained mid-to-high frequency error signal can be input to the input terminal of the second feedback controller. The second feedback controller mainly uses enhanced proportional and differential operations, combined with weakened integral operations, to calculate a rapidly changing low-voltage control signal. This low-voltage control signal is sent out from the output terminal of the second feedback controller and input to the second piezoelectric actuator. The high-bandwidth amplifier circuit inside the second piezoelectric actuator rapidly amplifies it into a high-voltage drive signal. This high-voltage drive signal is applied to the second piezoelectric actuator. The piezoelectric ceramic inside the second piezoelectric actuator undergoes rapid and minute deformation under the action of the rapidly changing electric field, driving the cavity mirror to move rapidly and complete the mid-to-high frequency residual error compensation.

[0101] S23, acquire the residual error signal of the resonant frequency doubling cavity after compensation by the first piezoelectric actuator and the second piezoelectric actuator, the first driving voltage of the first piezoelectric actuator, the second driving voltage of the second piezoelectric actuator, and the operating status parameters of the resonant frequency doubling laser to obtain a multi-source status signal.

[0102] Among them, the residual error signal refers to the cavity detuning error signal that remains in the resonant frequency doubling cavity after the first and second piezoelectric actuators simultaneously apply cavity length compensation. It reflects the frequency deviation that has not yet been eliminated by the compensation at the current moment. The first driving voltage refers to the voltage value of the high-voltage driving signal applied to the first piezoelectric actuator at the current moment, which can reflect the magnitude of the compensation currently being output by the low-frequency compensation channel. The second driving voltage refers to the voltage value of the high-voltage driving signal applied to the second piezoelectric actuator at the current moment, which can reflect the magnitude of the compensation currently being output by the mid-to-high frequency compensation channel. The operating status parameters refer to the various measurable physical quantities related to the frequency matching stability and output optical power stability in the resonant frequency doubling laser.

[0103] Understandably, after the dual piezoelectric actuators apply compensation, the cavity detuning error signal is significantly reduced. However, since the compensation is not instantaneous, a small amount of residual error still exists. The residual error signal represents the remaining deviation of the frequency matching. The first driving voltage and the second driving voltage represent the compensation amount currently applied by the two compensation channels, respectively. The operating status parameters reflect the overall working state of the laser from multiple dimensions such as optical power and temperature. These types of signals describe the state of the resonant frequency-doubled laser during the compensation process from different perspectives. Each type can only reflect local information when viewed alone. Only by collecting them synchronously and aggregating them together can a complete data foundation be provided for subsequent prediction of the drift trend of the cavity resonant frequency.

[0104] Specifically, during the simultaneous operation of low-frequency compensation and mid-to-high-frequency compensation, the compensation error signal at the current moment is extracted from the cavity detuning error signal acquisition channel as the residual error signal. The first driving voltage at the output of the first piezoelectric driver and the second driving voltage at the output of the second piezoelectric driver are read in real time through the voltage acquisition circuit. Various physical quantities related to the operating state are acquired from various monitoring points of the laser as operating state parameters. The residual error signal, the first driving voltage, the second driving voltage and the operating state parameters are aligned according to the acquisition time and then collected to form a multi-source state signal.

[0105] Based on the above embodiments, step S23 can be implemented in the following ways:

[0106] S231, after the compensation effect of the first piezoelectric actuator and the second piezoelectric actuator, the cavity detuning error signal of the resonant frequency doubling cavity at the current moment is obtained as the residual error signal.

[0107] It is understandable that the first and second piezoelectric actuators have adjusted the cavity length respectively, and the deviation between the cavity resonant frequency and the incident light frequency has been greatly reduced, but it usually will not be completely zero. At this time, the small deviation remaining in the cavity detuning error signal is the error that is still left after compensation by the dual piezoelectric actuators. The magnitude and direction of this residual error signal reflect the remaining deviation of the cavity resonant frequency relative to the incident light frequency at the current moment, and can be used to determine whether the cavity resonant frequency is continuing to drift and what the drift direction is.

[0108] Specifically, the reflected light signal of the resonant frequency doubling cavity after compensation by the first and second piezoelectric actuators can be demodulated again to obtain the cavity detuning error signal at the current moment, and this signal can be directly used as the residual error signal.

[0109] S232, the output voltages of the first piezoelectric driver and the second piezoelectric driver are collected respectively, and used as the first driving voltage and the second driving voltage.

[0110] Specifically, a voltage sampling circuit can be set at the output terminal of the first piezoelectric driver to read the high-voltage signal voltage value output to the first piezoelectric actuator at the current moment, and use it as the first driving voltage. Similarly, a voltage sampling circuit can be set at the output terminal of the second piezoelectric driver to read the high-voltage signal voltage value output to the second piezoelectric actuator at the current moment, and use it as the second driving voltage.

[0111] S233, acquire at least four of the following parameters as operating status parameters: current RF frequency of the acousto-optic modulator, fundamental frequency optical power, frequency doubling optical power, transmission peak signal of the resonant frequency doubling cavity, cavity temperature, and frequency doubling crystal temperature.

[0112] Among them, the current radio frequency refers to the frequency value of the radio frequency drive signal applied by the acousto-optic modulator at the current moment, which can reflect the current adjustment state of the seed light frequency; the frequency doubling optical power refers to the optical power of the frequency doubling light output by the resonant frequency doubling cavity; the transmission peak signal of the resonant frequency doubling cavity refers to the light intensity signal detected from the transmission end of the resonant frequency doubling cavity, and the strength of this signal reflects the intensity of the fundamental frequency optical resonance in the cavity. The stronger the resonance, the higher the transmission peak signal; the cavity temperature refers to the temperature of the cavity mechanical structure of the resonant frequency doubling cavity at the current moment; and the frequency doubling crystal temperature refers to the temperature of the frequency doubling crystal itself in the resonant frequency doubling cavity.

[0113] Understandably, the radio frequency of the acousto-optic modulator determines the frequency offset of the seed light, the fundamental frequency optical power and the frequency-doubled optical power reflect the input and output optical power levels, respectively, the transmission peak signal reflects the resonant state within the cavity, and the cavity temperature and the frequency-doubled crystal temperature are key environmental factors affecting the cavity resonant frequency drift and frequency doubling conversion efficiency. These parameters reflect the operating state of the resonant frequency-doubled laser from different perspectives, and their changes are related to the drift trend of the cavity resonant frequency. By simultaneously acquiring these operating state parameters and combining them with the residual error signal and the driving voltage, the current operating state and future trend of the resonant frequency-doubled cavity can be comprehensively judged from multiple dimensions.

[0114] Specifically, the applied radio frequency value at the current moment can be read from the radio frequency drive module of the acousto-optic modulator as the current radio frequency. The fundamental frequency optical power value at the current moment can be collected from the beam splitting monitoring point at the input end of the resonant frequency doubling cavity. The frequency doubling optical power value at the current moment can be collected from the frequency doubling optical output end of the resonant frequency doubling cavity. The transmission peak signal can be obtained by detecting the transmitted light signal at the transmission end of the resonant frequency doubling cavity. The cavity temperature can be read from the temperature sensor installed on the cavity structure. The frequency doubling crystal temperature can be read from the temperature sensor installed on the frequency doubling crystal. Then, at least four of the above parameters can be selected together with the residual error signal and the driving voltage to form the operating status parameters.

[0115] S3, predict the resonant frequency drift of the resonant frequency doubling cavity based on the multi-source state signal, generate a target radio frequency based on the resonant frequency drift, and generate a frequency control signal and an intensity compensation control signal based on the target radio frequency.

[0116] Among them, resonant frequency drift refers to the phenomenon that the resonant frequency of the resonant frequency doubling cavity shifts over time under the influence of environmental factors; resonant frequency drift amount refers to the predicted shift value of the cavity resonant frequency over a future period; target RF frequency refers to the RF signal frequency value that needs to be applied to the optical frequency modulation device based on the predicted drift amount; frequency control signal refers to the electrical signal used to control the optical frequency modulation device to adjust the seed light frequency; and intensity compensation control signal refers to the electrical signal used to synchronously adjust the driving power of the optical frequency modulation device during frequency modulation to maintain its output optical power stability.

[0117] It is understandable that the compensation of the dual piezoelectric actuator is a feedback control. From the drift of the cavity resonant frequency to the detection of the error signal and the completion of the actuator response, the accumulated delay of each link causes the compensation to lag. The multi-source state signal contains the current state of the residual error, the amount of compensation being applied by the actuator, and parameters such as the temperature and power of the resonant frequency doubling laser. This information together reflects the current state and trend of the cavity resonant frequency. By analyzing this information, the direction and amplitude of the resonant frequency drift can be predicted, so as to actively adjust the seed light frequency for compensation before the error changes significantly. In addition, when the optical frequency adjustment device changes the output light frequency, its output light power will fluctuate with the frequency change. If only the frequency is changed without synchronously adjusting the driving power, new intensity noise will be introduced. Therefore, an intensity compensation control signal can be generated at the same time.

[0118] Specifically, the collected multi-source state signals are used as the basis for analysis. Based on the cavity resonant frequency change trend information contained in these signals, the drift direction and drift amount of the cavity resonant frequency in the future period are predicted. The required radio frequency adjustment amount is calculated based on the predicted drift amount, and a target radio frequency is generated. A corresponding frequency control signal is generated based on the target radio frequency. At the same time, based on the predetermined correspondence between the radio frequency and the output optical power, the required drive power adjustment amount to maintain the stability of the output optical power at the current target radio frequency is determined, and a corresponding intensity compensation control signal is generated.

[0119] Based on the above embodiments, step S3 can be implemented in the following ways:

[0120] S31, the multi-source state signal is input to the model prediction controller, and the model prediction controller predicts the resonant frequency drift of the resonant frequency doubling cavity within a preset time period according to the preset objective function and constraint conditions.

[0121] The Model Predictive Controller (MMC) is a controller that predicts future states and generates control quantities based on a mathematical model through optimization calculations. It consists of two core components: a prediction model and an objective function. The prediction model is a mathematical equation describing the dynamic relationship between the multi-source state signals and the cavity resonant frequency drift in a resonant frequency-doubled laser. Its role is to answer how the future state will evolve if a certain control quantity is applied in the current state. The objective function is a mathematical expression that the MMC needs to minimize or maximize during calculations. It is usually used to measure the magnitude of the prediction error. The constraints are the restrictions that the MMC must follow during optimization calculations. For example, the radio frequency of the acousto-optic modulator cannot exceed its effective operating range. The preset time period is the length of the time window for the MMC to predict the future state, which can also be called the prediction time domain.

[0122] It is understandable that each signal in the multi-source state signal reflects the state information of different aspects of the resonant frequency doubling laser. It is difficult to accurately judge the future trend of cavity resonant frequency by looking at any single signal alone. The mathematical model configured inside the model predictive controller describes the dynamic relationship between cavity resonant frequency and multiple factors such as residual error, actuator drive voltage, temperature, and power. After the multi-source state signals are input simultaneously, the model predictive controller can calculate the evolution trajectory of cavity resonant frequency in the current state based on the mathematical model.

[0123] It should be noted that the working process of a model predictive controller is an iterative process of repeated assumptions, deductions, and evaluations. A model predictive controller can first generate multiple sets of candidate control sequences, each set of which is generated by future... The change in the radio frequency of the acousto-optic modulator within one control cycle The composition of values, in different candidate sequences Different values ​​represent different control strategies. Then, for each candidate sequence, the prediction model uses the multi-source state signal collected at the current moment as the initial state, and sequentially calculates the corresponding control strategy applied in each control cycle. Subsequently, the evolution trajectory of the cavity detuning residual error and frequency doubling optical power at various future moments was obtained. and To determine the predicted future states, and in order to select the optimal evolution trajectory from multiple possible paths, the model predictive controller needs an evaluation criterion, which is the objective function. This criterion combines the predicted future states of each candidate sequence with... Substituting the values ​​into the objective function for scoring, the objective function typically focuses on reducing cavity detuning residual error and frequency doubling optical power fluctuations, while also considering the smoothness of control variable changes. Its mathematical form can be expressed as:

[0124]

[0125] in, Indicates the future number residual error of cavity detuning in the step. Indicates the future number The frequency doubling optical power of the step, This represents the expected reference value for frequency-doubled optical power. This indicates the change in the radio frequency of the acousto-optic modulator. , and These are the weight coefficients for the corresponding items. To predict the length of the time domain, that is, the length of the preset time period, To control the time domain length, the first term of the objective function represents the number of steps of frequency control signals actually generated and executed by the model predictive controller within a preset time period in the future. The second term measures the magnitude of the residual error due to cavity detuning during the prediction process. The third item measures the degree to which the frequency-doubled optical power deviates from the expected value. Measure the magnitude of frequency changes in an acousto-optic modulator.

[0126] By minimizing this objective function, the model predictive controller can iteratively optimize and output the optimal predicted value of the resonant frequency drift, while satisfying constraints such as the frequency range of the acousto-optic modulator. Furthermore, in the candidate sequence... The value of is not arbitrarily chosen, but is constrained by the effective RF operating range of the acousto-optic modulator and the maximum frequency change in a single control cycle. It can also be strategically adjusted in the direction of decreasing the objective function value based on the scoring results of each candidate sequence. The value of is gradually approached to the optimal solution.

[0127] Before the resonant frequency-doubled laser is put into operation, a prediction model is established in advance through experiments. Specifically, under the normal locked state of the dual piezoelectric feedback loop, small-amplitude sweep signals and step signals are applied to the radio frequency of the acousto-optic modulator, the first piezoelectric actuator, and the second piezoelectric actuator as known excitation inputs. The change data of each signal in the multi-source state signals with excitation is collected synchronously as the output response. From the correspondence between the excitation input and the output response, the mathematical equation describing the dynamic relationship between each state quantity can be determined. This mathematical equation is the prediction model. During the operation of the resonant frequency-doubled laser, when each control cycle arrives, the collected multi-source state signals are used to form a state vector input model predictive controller.

[0128] For each candidate sequence, the prediction model starts with the current state vector and sequentially calculates the application of each... The state evolution trajectory after the initial state is obtained, and the predicted values ​​of cavity detuning residual error and frequency doubling optical power at each future time are obtained. The predicted values ​​corresponding to each candidate sequence are then combined with... Substitute the scores into the objective function to calculate the score, and then adjust the optimization algorithm in the direction of decreasing the objective function value based on the score results. The value of is used to generate new candidate sequences. The deduction and scoring are repeated. After multiple iterations, the optimal control sequence that minimizes the objective function is found. The model predictive controller extracts the radio frequency change corresponding to the first control cycle in the optimal sequence. This change is numerically equal to the drift of the cavity resonant frequency. It is output as the predicted value of the resonant frequency drift. In the next control cycle, the multi-source state signal is reacquired and the entire process is repeated.

[0129] The state vector input to the model predictive controller can be represented as:

[0130]

[0131] in, and These represent the first driving voltage and the second driving voltage, respectively. Indicates the current radio frequency of the acousto-optic modulator. Indicates fundamental frequency optical power. Indicates frequency-doubled optical power. This indicates the transmission peak signal. Indicates the temperature status.

[0132] S32, generate the target radio frequency based on the resonant frequency drift, and generate a corresponding frequency control signal based on the target radio frequency.

[0133] Based on the above embodiments, step S32 can be implemented in the following ways:

[0134] S321, The resonant frequency drift is superimposed with the current radio frequency of the acousto-optic modulator to calculate the target radio frequency.

[0135] The current radio frequency refers to the frequency value of the radio frequency drive signal that the acousto-optic modulator is currently using.

[0136] It is understandable that the resonant frequency drift is numerically equal to the RF frequency compensation. The acousto-optic modulator is already operating at a certain RF frequency, and the target RF frequency is the current frequency plus this compensation. When the resonant frequency drift is positive, it indicates that the cavity resonant frequency has drifted towards a higher frequency, and the RF frequency of the acousto-optic modulator needs to be increased to compensate. When the drift is negative, the RF frequency needs to be decreased.

[0137] Specifically, the current RF frequency value can be read from the RF drive module of the acousto-optic modulator, and the output resonant frequency drift can be used as the RF frequency compensation amount. This is then added to the current RF frequency, and the result is the target RF frequency.

[0138] S322, the target radio frequency is converted from digital to analog, the frequency control signal is generated and output to the acousto-optic driver.

[0139] Among them, digital-to-analog conversion refers to the process of converting the target radio frequency value represented by a digital quantity into an analog voltage signal, and the acousto-optic driver refers to the electronic device that provides radio frequency drive signals for the acousto-optic modulator. It contains two independent control interfaces: a frequency control port and an amplitude control port.

[0140] It is understandable that the target radio frequency calculated in step S321 is a digital quantity, while the frequency control port of the acousto-optic driver receives an analog voltage signal. Therefore, the digital frequency value needs to be converted into an analog voltage signal with the corresponding amplitude in order to be recognized and executed by the acousto-optic driver.

[0141] Specifically, the obtained target radio frequency digital value can be converted into an analog voltage signal of corresponding amplitude through a digital-to-analog converter. This analog voltage signal is the frequency control signal, which is then output to the frequency control port of the acousto-optic driver.

[0142] S33. Based on the pre-calibrated correspondence between the radio frequency, amplitude control quantity and output optical power, and in combination with the target radio frequency and the preset target output optical power, determine the corresponding radio frequency amplitude control quantity.

[0143] Among them, amplitude control quantity refers to the parameter value used to control the amplitude of the radio frequency drive signal of the acousto-optic modulator, output optical power refers to the optical power of the first-order diffracted light output by the acousto-optic modulator, target output optical power refers to the pre-set output optical power value that the acousto-optic modulator is expected to maintain during frequency modulation, radio frequency amplitude control quantity refers to the amplitude control quantity required to achieve the target output optical power at the target radio frequency, and the pre-calibrated correspondence refers to the correspondence of the output optical power of the acousto-optic modulator at different radio frequency and different radio frequency drive amplitudes, which is pre-configured before the operation of the resonant frequency doubling laser.

[0144] It is understandable that the diffraction efficiency of an acousto-optic modulator is not the same at all radio frequency frequencies. When the radio frequency changes, the output optical power will change even if the drive amplitude remains unchanged. After determining the target radio frequency, if the drive amplitude remains unchanged, the output optical power will fluctuate with the frequency, introducing new intensity noise. Therefore, while changing the frequency, the required drive amplitude adjustment can be determined according to the pre-calibrated correspondence.

[0145] Specifically, the target RF frequency and the preset target output optical power can be used as a basis to determine the corresponding RF amplitude control quantity from the pre-calibrated correspondence between RF frequency, amplitude control quantity and output optical power.

[0146] S34, generate a corresponding intensity compensation control signal according to the radio frequency amplitude control amount and output it to the acousto-optic driver.

[0147] Specifically, the determined digital value of the radio frequency amplitude control can be input to the digital-to-analog converter, which converts it into a corresponding analog voltage signal and outputs it as an intensity compensation control signal to the amplitude control terminal of the acousto-optic driver. This signal is used to synchronously adjust the diffraction efficiency of the acousto-optic modulator during frequency modulation and maintain stable output optical power.

[0148] S4, adjust the equivalent optical frequency of the seed light based on the frequency control signal, and synchronously compensate for the output power fluctuation during the frequency modulation process based on the intensity compensation control signal.

[0149] Among them, the equivalent optical frequency refers to the actual optical frequency exhibited by the seed light after passing through the optical frequency modulation device, the frequency modulation process refers to the process of changing the output optical frequency by changing the frequency of the radio frequency signal applied to the optical frequency modulation device, and the output power fluctuation refers to the phenomenon that the output optical power fluctuates due to its own physical characteristics when the optical frequency modulation device changes the output optical frequency.

[0150] It is understandable that optical frequency modulation devices change the frequency of output light by changing the frequency of the radio frequency signal applied to them. However, their diffraction efficiency changes with the radio frequency, causing the output light power to fluctuate. If only the frequency control signal is applied to adjust the seed light frequency to follow the cavity resonant frequency drift, the power fluctuations that accompany the frequency modulation process will introduce new intensity noise. Therefore, the frequency control signal and the intensity compensation control signal can be applied to the optical frequency modulation device simultaneously to compensate for the power fluctuations while adjusting the seed light frequency.

[0151] Specifically, the generated frequency control signal is applied to the optical frequency modulation device. The optical frequency modulation device changes the radio frequency driving frequency according to the signal, and shifts the seed light frequency accordingly, thereby changing the equivalent optical frequency of the seed light. At the same time, the generated intensity compensation control signal is applied synchronously to the same optical frequency modulation device. The optical frequency modulation device adjusts the radio frequency driving power according to the signal to compensate for the fluctuation of output optical power caused by frequency change.

[0152] Based on the above embodiments, step S4 can be implemented in the following ways:

[0153] S41, the frequency control signal and the intensity compensation control signal are respectively input to the frequency control port and amplitude control port of the acousto-optic driver.

[0154] The frequency control port refers to the input port on the acousto-optic driver used to receive frequency control signals. The analog voltage signal received by this port determines the frequency of the radio frequency signal output by the acousto-optic driver. The amplitude control port refers to the input port on the acousto-optic driver used to receive intensity compensation control signals. The analog voltage signal received by this port determines the amplitude of the radio frequency signal output by the acousto-optic driver.

[0155] It is understandable that the frequency control and amplitude control of the acousto-optic driver are two independent channels, receiving control signals from different ports. The voltage value received by the frequency control port determines the frequency of the RF drive signal, and the voltage value received by the amplitude control port determines the power of the RF drive signal. The two ports can work simultaneously without affecting each other, allowing frequency adjustment and power compensation to be performed synchronously.

[0156] Specifically, the generated frequency control signal can be connected to the frequency control port of the acousto-optic driver via a signal line, and the generated intensity compensation control signal can be connected to the amplitude control port of the acousto-optic driver via a signal line. The two control signals are delivered synchronously within the same control cycle to ensure that the acousto-optic driver can respond to both frequency and amplitude commands simultaneously.

[0157] S42, control the acousto-optic driver to generate a radio frequency drive signal corresponding to the target radio frequency according to the frequency control signal, and drive the acousto-optic modulator to frequency shift the seed light based on the radio frequency drive signal, thereby adjusting the equivalent optical frequency of the seed light.

[0158] Among them, the radio frequency drive signal refers to the radio frequency electrical signal output by the acousto-optic driver to the acousto-optic modulator. The frequency of this signal determines the amount of frequency shift applied by the acousto-optic modulator to the seed light.

[0159] Understandably, after receiving the frequency control signal, the internal circuit of the acousto-optic driver determines the required radio frequency (RF) output based on the voltage amplitude of the signal. It can generate an RF drive signal with a frequency equal to the target RF frequency. This RF drive signal is applied to the piezoelectric transducer of the acousto-optic modulator. Under the excitation of the RF signal, the piezoelectric transducer generates ultrasonic waves. The ultrasonic waves propagate in the acousto-optic medium to form a periodic refractive index grating. When the seed light passes through this grating, it undergoes diffraction. The frequency of the first-order diffracted light is equal to the incident light frequency plus or minus the frequency of the RF drive signal, thereby enabling the adjustment of the equivalent optical frequency of the seed light.

[0160] Specifically, after the frequency control port of the acousto-optic driver receives the frequency control signal, the internal oscillation circuit generates a radio frequency oscillation signal of the corresponding frequency according to the voltage amplitude of the signal. After power amplification, it forms a radio frequency drive signal and is output to the piezoelectric transducer of the acousto-optic modulator. When the seed light passes through the acousto-optic modulator, it interacts with the ultrasonic grating, and the frequency of its first-order diffracted light shifts accordingly, thus adjusting the equivalent optical frequency.

[0161] S43, control the acoustic-optical driver to adjust the amplitude of the radio frequency drive signal according to the intensity compensation control signal to obtain the target radio frequency amplitude.

[0162] The target RF amplitude refers to the amplitude value that the RF drive signal should reach after adjustment by the intensity compensation control signal. This amplitude value enables the acousto-optic modulator to output diffracted light corresponding to the preset target output optical power at the current target RF frequency.

[0163] It is understandable that when the acousto-optic driver generates the radio frequency drive signal, its initial amplitude is output according to the set value before frequency modulation. However, the diffraction efficiency of the acousto-optic modulator at the target radio frequency is different from that before frequency modulation. If the amplitude remains unchanged, the output optical power will deviate from the preset value. The function of the intensity compensation control signal is to tell the acousto-optic driver how much the amplitude of the radio frequency drive signal needs to be adjusted to compensate for the change in diffraction efficiency. The acousto-optic driver increases or decreases the amplitude of the radio frequency drive signal accordingly based on the voltage amplitude of the intensity compensation control signal to obtain the target radio frequency amplitude.

[0164] Specifically, after the amplitude control port of the acousto-optic driver receives the intensity compensation control signal, the internal amplitude adjustment circuit can adjust the output amplitude of the radio frequency drive signal according to the voltage amplitude of the signal. When the intensity compensation control signal indicates that the amplitude needs to be increased, the amplitude adjustment circuit increases the power of the radio frequency drive signal. When it indicates that the amplitude needs to be decreased, the power is reduced. The adjusted radio frequency drive signal amplitude is the target radio frequency amplitude.

[0165] S44, adjust the diffraction efficiency of the acousto-optic modulator according to the obtained target radio frequency amplitude, and compensate for the output power fluctuation during the frequency modulation process based on the adjusted diffraction efficiency.

[0166] Diffraction efficiency refers to the efficiency by which an acousto-optic modulator converts input optical power into first-order diffraction optical power, that is, the ratio of first-order diffraction optical power to input optical power. This efficiency changes with the frequency and amplitude of the radio frequency drive signal.

[0167] It is understandable that the diffraction efficiency of the acousto-optic modulator is determined by both the frequency and amplitude of the radio frequency drive signal. In step S42, the frequency of the radio frequency drive signal has been changed to the target radio frequency, which will cause the diffraction efficiency to deviate from the value before frequency modulation. By adjusting the amplitude of the radio frequency drive signal to the target radio frequency amplitude, the diffraction efficiency can be restored to the level that can output the preset target output optical power. Through the synchronous adjustment of frequency and amplitude, the diffraction efficiency of the acousto-optic modulator after frequency modulation is consistent with that before frequency modulation, and the output first-order diffraction optical power is maintained within the preset allowable fluctuation range, thereby compensating for the output power fluctuation caused by the change in diffraction efficiency during frequency modulation.

[0168] Specifically, after receiving a generated radio frequency drive signal with a target radio frequency and adjusted to the target radio frequency amplitude, the acousto-optic modulator's piezoelectric transducer can generate ultrasonic waves of corresponding frequency and intensity under the drive of the signal, forming a grating with a corresponding period and refractive index modulation depth in the acousto-optic medium. When the seed light passes through the grating, it undergoes diffraction. The frequency of the first-order diffracted light shifts according to the target radio frequency, while its power remains stable due to the amplitude compensation of the diffraction efficiency. The output power fluctuation during the frequency modulation process is compensated.

[0169] See Figure 2 This is a schematic diagram of the composition architecture of a resonant frequency-doubled laser intensity noise suppression system provided in an embodiment of the present invention, as shown below. Figure 1 As shown, it mainly includes a seed light source, an acousto-optic modulator, an electro-optic modulator, an optical amplifier, a resonant frequency doubling cavity, an acousto-optic driver, a cavity detuning error signal acquisition module, a PID controller, a PZT-1 driver, a PZT-2 driver, a model prediction controller (MPC), and an acousto-optic frequency modulation power holding control module. Each module works in sequence to complete the generation of probe light, extraction of error signal, dual piezoelectric layered compensation, feedforward prediction, and synchronous control of frequency modulation power.

[0170] The seed light source outputs a single-frequency continuous laser, which is then passed through an acousto-optic modulator for frequency shifting, an electro-optic modulator for phase modulation to generate a modulation sideband, and then amplified by an optical amplifier before being injected into a resonant frequency doubling cavity. The cavity detuning error signal acquisition module collects the reflected photoelectric signal from the resonant frequency doubling cavity and demodulates it to extract the cavity detuning error signal. The error signal is then normalized and frequency band separated to obtain low-frequency error signals and mid-to-high-frequency error signals, respectively.

[0171] like Figure 2 As shown in the figure, this system includes a PID controller, corresponding to the first feedback controller and the second feedback controller in this scheme, and also includes a PZT-1 driver, corresponding to the first piezoelectric driver, and a PZT-2 driver, corresponding to the second piezoelectric driver. The first feedback controller receives the low-frequency error signal and drives the first piezoelectric actuator through the first piezoelectric driver to perform low-frequency large-stroke cavity length compensation. The second feedback controller receives the mid-to-high frequency error signal and drives the second piezoelectric actuator through the second piezoelectric driver to perform mid-to-high frequency fast small displacement compensation. During the dual piezoelectric actuator driving compensation process, residual error signals, first driving voltage, second driving voltage, and multi-source state signals such as the current RF frequency of the acousto-optic modulator, fundamental frequency optical power, frequency doubling optical power, transmission peak signal, cavity temperature, and frequency doubling crystal temperature are collected simultaneously. The MPC in the figure corresponds to the model prediction controller in this scheme. The model prediction controller receives multi-source state signals and predicts the resonant frequency drift of the resonant frequency doubling cavity within a preset time period according to the preset objective function and constraint conditions.

[0172] The acousto-optic frequency modulation power maintenance control module generates a target radio frequency based on the predicted resonant frequency drift, and generates a frequency control signal and an intensity compensation control signal based on the target radio frequency. These signals are input to the frequency control port and amplitude control port of the acousto-optic driver, respectively, to drive the acousto-optic modulator to adjust the equivalent optical frequency of the seed light while correcting the diffraction efficiency by adjusting the radio frequency amplitude, thereby compensating for output power fluctuations during the frequency modulation process in real time.

[0173] Based on the above steps, this solution also includes the following embodiments:

[0174] When the current radio frequency of the acousto-optic modulator deviates from the center operating frequency by more than a preset threshold, the cavity length of the resonant frequency doubling cavity is adjusted based on the first piezoelectric actuator until the radio frequency of the acousto-optic modulator is within the center operating range.

[0175] Among them, the current radio frequency refers to the radio frequency drive signal frequency value that the acousto-optic modulator is currently using; the center operating frequency refers to the radio frequency value where the acousto-optic modulator has the highest diffraction efficiency and the most stable operating characteristics, which is usually the center point of the effective operating frequency range of the acousto-optic modulator; the preset threshold refers to the maximum allowable deviation of the radio frequency from the center operating frequency; when the deviation exceeds the threshold, a return-to-center operation is triggered; and the center operating range refers to the frequency range centered on the center operating frequency where the radio frequency is allowed to operate normally.

[0176] It is understandable that the RF frequency adjustment range of the acousto-optic modulator is limited. When the model predictive controller compensates for the cavity resonant frequency drift in the same direction for a long time, the RF frequency of the acousto-optic modulator will gradually deviate from the center operating frequency. If the deviation continues without intervention, the RF frequency may approach or even exceed the boundary of the effective operating range, resulting in the exhaustion of the tuning range. At the same time, when the acousto-optic modulator deviates far from the center frequency, the diffraction efficiency decreases and the operating characteristics deteriorate. Therefore, when it is detected that the current RF frequency of the acousto-optic modulator deviates from the center operating frequency by more than a preset threshold, the cavity length of the resonant frequency doubling cavity can be slowly adjusted by the first piezoelectric actuator to move the cavity resonant frequency in the direction corresponding to the center frequency of the acousto-optic modulator. At the same time, the RF frequency of the acousto-optic modulator returns to the center operating range in the opposite direction. During the return process, the cavity length adjustment of the first piezoelectric actuator and the frequency return of the acousto-optic modulator are coordinated to keep the relative matching relationship between the incident light frequency and the cavity resonant frequency basically unchanged and will not cause lockout. When the RF frequency of the acousto-optic modulator returns to the center operating range, the return operation stops and normal predictive compensation control is restored.

[0177] Specifically, during the operation of the resonant frequency-doubled laser, the current radio frequency of the acousto-optic modulator is continuously monitored, and the difference between it and the center operating frequency is calculated. When the absolute value of the difference exceeds a preset threshold and the duration exceeds a preset time, the centering control is initiated. During the centering process, the first piezoelectric actuator adjusts the cavity length of the resonant frequency-doubled cavity at a slow rate, so that the cavity resonant frequency gradually moves. At the same time, the radio frequency of the acousto-optic modulator is gradually adjusted in the opposite direction until the radio frequency of the acousto-optic modulator returns to within the center operating range. After the centering is completed, the normal dual piezoelectric layered cavity locking and model prediction feedforward compensation control are restored.

[0178] See Figure 3 This is a schematic diagram of a resonant frequency doubling laser intensity noise suppression system provided in an embodiment of the present invention. The system includes:

[0179] The processing module is used to acquire the cavity detuning error signal of the resonant frequency doubling cavity, and to normalize and perform frequency band separation processing on the cavity detuning error signal to obtain low-frequency error signal and mid-to-high frequency error signal respectively.

[0180] The acquisition module is used to drive the first piezoelectric actuator and the second piezoelectric actuator of the resonant frequency-doubled laser to perform cavity length compensation of the resonant frequency-doubled cavity according to the low-frequency error signal and the medium-high frequency error signal, respectively, and to acquire the multi-source state signal of the resonant frequency-doubled laser during the driving compensation process;

[0181] The generation module is used to predict the resonant frequency drift of the resonant frequency doubling cavity based on the multi-source state signal, generate a target radio frequency based on the resonant frequency drift, and generate a frequency control signal and an intensity compensation control signal based on the target radio frequency.

[0182] The adjustment module is used to adjust the equivalent optical frequency of the seed light based on the frequency control signal, and to synchronously compensate for the output power fluctuations during the frequency modulation process based on the intensity compensation control signal.

[0183] Figure 3 The apparatus of the illustrated embodiment can be used to perform corresponding actions. Figure 1 The steps in the method embodiments shown are implemented in a similar manner and have similar technical effects, and will not be repeated here.

[0184] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for suppressing intensity noise in a resonant frequency-doubled laser, characterized in that, include: The cavity detuning error signal of the resonant frequency doubling cavity is obtained, and the cavity detuning error signal is normalized and frequency band separated to obtain the low-frequency error signal and the mid-to-high frequency error signal, respectively. The first and second piezoelectric actuators of the resonant frequency-doubled laser are driven according to the low-frequency error signal and the medium-to-high-frequency error signal, respectively, to perform cavity length compensation of the resonant frequency-doubled cavity, and the multi-source state signals of the resonant frequency-doubled laser are collected during the driving compensation process; The resonant frequency drift of the resonant frequency doubling cavity is predicted based on the multi-source state signal, a target radio frequency is generated based on the resonant frequency drift, and a frequency control signal and an intensity compensation control signal are generated based on the target radio frequency. The equivalent optical frequency of the seed light is adjusted based on the frequency control signal, and the output power fluctuation during the frequency modulation process is synchronously compensated based on the intensity compensation control signal.

2. The method according to claim 1, characterized in that, Before obtaining the cavity detuning error signal of the resonant frequency doubling cavity, the following steps are also included: The seed light is controlled to pass through an acousto-optic modulator and an electro-optic modulator in sequence for frequency shifting and phase modulation, generating a probe light containing modulation sidebands; The probe light is amplified by an optical amplifier and then injected into the resonant frequency doubling cavity.

3. The method according to claim 2, characterized in that, The process of acquiring the cavity detuning error signal of the resonant frequency doubling cavity, normalizing and separating the cavity detuning error signal to obtain low-frequency error signals and mid-to-high-frequency error signals includes: The reflected light signal after the probe light is reflected by the resonant frequency doubling cavity is acquired; The reflected light signal is demodulated to extract the cavity detuning error signal corresponding to the modulation sideband; The cavity detuning error signal is normalized by dividing it by the fundamental frequency optical power to obtain the normalized error signal. The normalized error signal is separated into frequency bands by a complementary filter to obtain the low-frequency error signal and the mid-to-high-frequency error signal, respectively.

4. The method according to claim 3, characterized in that, The first and second piezoelectric actuators, which drive the resonant frequency-doubled laser according to the low-frequency error signal and the mid-to-high-frequency error signal respectively, perform cavity length compensation on the resonant frequency-doubled cavity and acquire multi-source state signals of the resonant frequency-doubled laser during the driving compensation process, including: The low-frequency error signal is input to the first feedback controller, which drives the first piezoelectric actuator via the first piezoelectric driver to perform low-frequency cavity length compensation on the resonant frequency doubling cavity; The mid-to-high frequency error signal is input to the second feedback controller, which drives the second piezoelectric actuator via the second piezoelectric driver to perform mid-to-high frequency residual error compensation on the resonant frequency doubling cavity; The residual error signal of the resonant frequency doubling cavity after compensation by the first piezoelectric actuator and the second piezoelectric actuator, the first driving voltage of the first piezoelectric actuator, the second driving voltage of the second piezoelectric actuator, and the operating state parameters of the resonant frequency doubling laser are collected to obtain a multi-source state signal.

5. The method according to claim 4, characterized in that, The acquisition of the residual error signal of the resonant frequency doubling cavity after compensation by the first and second piezoelectric actuators, the first driving voltage of the first piezoelectric actuator, the second driving voltage of the second piezoelectric actuator, and the operating status parameters of the resonant frequency doubling laser includes: After compensation by the first piezoelectric actuator and the second piezoelectric actuator, the cavity detuning error signal of the resonant frequency doubling cavity at the current moment is obtained as the residual error signal; The output voltages of the first piezoelectric actuator and the second piezoelectric actuator are collected respectively, and used as the first driving voltage and the second driving voltage; At least four of the following parameters are obtained as operating status parameters: the current radio frequency of the acousto-optic modulator, the fundamental frequency optical power, the frequency doubling optical power, the transmission peak signal of the resonant frequency doubling cavity, the cavity temperature, and the frequency doubling crystal temperature.

6. The method according to claim 1, characterized in that, The step of predicting the resonant frequency drift of the resonant frequency doubling cavity based on the multi-source state signal, generating a target radio frequency based on the resonant frequency drift, and generating a frequency control signal and an intensity compensation control signal based on the target radio frequency includes: The multi-source state signal is input into the model prediction controller, which predicts the resonant frequency drift of the resonant frequency doubling cavity within a preset time period based on a preset objective function and constraints. The target radio frequency is generated based on the resonant frequency drift, and a corresponding frequency control signal is generated based on the target radio frequency. Based on the pre-calibrated correspondence between radio frequency, amplitude control quantity and output optical power, and in combination with the target radio frequency and the preset target output optical power, the corresponding radio frequency amplitude control quantity is determined. The corresponding intensity compensation control signal is generated based on the radio frequency amplitude control quantity and output to the acousto-optic driver.

7. The method according to claim 6, characterized in that, The step of generating the target radio frequency based on the resonant frequency drift and generating a corresponding frequency control signal based on the target radio frequency includes: The target radio frequency is calculated by superimposing the resonant frequency drift with the current radio frequency of the acousto-optic modulator. The target radio frequency is converted from digital to analog to generate the frequency control signal and output to the acousto-optic driver.

8. The method according to claim 7, characterized in that, The process of adjusting the equivalent optical frequency of the seed light based on the frequency control signal and synchronously compensating for output power fluctuations during frequency modulation based on the intensity compensation control signal includes: The frequency control signal and the intensity compensation control signal are respectively input to the frequency control port and amplitude control port of the acousto-optic driver; The acousto-optic driver is controlled to generate a radio frequency drive signal corresponding to the target radio frequency according to the frequency control signal, and the acousto-optic modulator is driven to frequency shift the seed light based on the radio frequency drive signal to adjust the equivalent optical frequency of the seed light. The acoustic-optical driver is controlled to adjust the amplitude of the radio frequency drive signal according to the intensity compensation control signal to obtain the target radio frequency amplitude; The diffraction efficiency of the acousto-optic modulator is adjusted according to the obtained target radio frequency amplitude, and the output power fluctuation during the frequency modulation process is compensated based on the adjusted diffraction efficiency.

9. The method according to claim 1, characterized in that, Also includes: When the current radio frequency of the acousto-optic modulator deviates from the center operating frequency by more than a preset threshold, the cavity length of the resonant frequency doubling cavity is adjusted based on the first piezoelectric actuator until the radio frequency of the acousto-optic modulator is within the center operating range.

10. A system for suppressing intensity noise in a resonant frequency-doubled laser, characterized in that, include: The processing module is used to acquire the cavity detuning error signal of the resonant frequency doubling cavity, and to normalize and perform frequency band separation processing on the cavity detuning error signal to obtain low-frequency error signal and mid-to-high frequency error signal respectively. The acquisition module is used to drive the first piezoelectric actuator and the second piezoelectric actuator of the resonant frequency-doubled laser to perform cavity length compensation of the resonant frequency-doubled cavity according to the low-frequency error signal and the medium-high frequency error signal, respectively, and to acquire the multi-source state signal of the resonant frequency-doubled laser during the driving compensation process; The generation module is used to predict the resonant frequency drift of the resonant frequency doubling cavity based on the multi-source state signal, generate a target radio frequency based on the resonant frequency drift, and generate a frequency control signal and an intensity compensation control signal based on the target radio frequency. The adjustment module is used to adjust the equivalent optical frequency of the seed light based on the frequency control signal, and to synchronously compensate for the output power fluctuations during the frequency modulation process based on the intensity compensation control signal.

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