Cavity length locking system and method of pulse type optical parametric oscillator

Abstract

The invention belongs to but not limited to the technical field of oscillators, and particularly relates to a cavity length locking system and method for a pulse type optical parametric oscillator, and the system comprises an OPO pulse light source, a pulse width feedback locking loop, and a power-based auxiliary locking loop. The OPO pulse light source comprises a seed pulse light source and an OPO resonant cavity; the pulse width feedback locking loop consists of a pulse width measuring device, a signal processing circuit and a cavity length control element; the auxiliary locking loop based on power is composed of a power signal measuring device, a signal processing circuit and a cavity length control element. The locking system operates simultaneously using a pulse width feedback locking loop and a power-based auxiliary locking loop. Wherein the pulse width feedback locking loop has the characteristics of Hz-level bandwidth and high gain, and the power-based auxiliary locking loop has larger bandwidth of kHz-MHz level. And the two are matched for application, so that more stable OPO cavity length locking can be realized.

Description

Technical Field

[0001] The present invention belongs to but is not limited to the technical field of oscillators, and in particular relates to a cavity length locking system and method for a pulsed optical parametric oscillator. Background Art

[0002] The pulsed optical parametric oscillator (OPO) is based on synchronous pumping and resonant cavity technology. It only needs a single pump light source to generate high-quality pulsed light sources with extremely high power and wide spectrum tunability. It has extensive and important applications in precision spectroscopy, bioimaging, atmospheric environment, optical frequency comb and other fields. However, due to the historical reasons for the development of ultrashort laser technology, the spatially structured pulsed OPO has left a bad impression on people in the past. The main disadvantage is poor structural stability. This is because of the synchronous pumping and stable output requirements. The matching error between the pulsed OPO cavity length and the pump pulse cavity length must be controlled at the sub-micron level. Typical OPO cavity length locking schemes include "position sensing detection" feedback technology [Optics Communications 123:577-582(1996)] and dither-locking technology [Optics Express 25(4):4190-4200(2017)]. The former uses the OPO output wavelength as feedback and uses "position sensing detection" to extract the error signal, but it is very sensitive to the beam directivity of the optical path structure and is easily affected by the external environment. Therefore, it is generally impossible to achieve long-term locking at the OPO resonance peak. The latter obtains the error signal related to the OPO power by applying a cavity length modulation signal. Although this scheme can lock to the OPO resonance peak, the application of the external modulation signal causes the output pulse power and spectral optical frequency after locking to still have slight jitter, which limits its promotion in application fields such as high-precision precision measurement. Recently, scientific and technological workers have discovered a new method to achieve OPO resonance peak locking in experiments. Based on the spectral power of the OPO parasitic light pulse as feedback, they successfully proved that the locking target can be effectively achieved without relying on external modulation methods [Optics Letters 45(3):768-771(2020)]. This discovery is of great significance because parasitic light is commonly present in the leakage light of the OPO, which can greatly simplify the optical path design of the system. Therefore, this solution shows broad application prospects due to its simplicity and effectiveness and is considered to be a highly potential solution.

[0003] However, when the parasitic light pulse spectral power is used as the feedback quantity, the error signal signal-to-noise ratio is limited by the spectral shape, and the signal strength is limited by the detection sensitivity of the spectral power converted into a voltage signal, making the current locking level still not high enough. Therefore, in the parasitic light pulse scheme, how to effectively improve the error signal signal-to-noise ratio and signal strength has become the core issue in achieving high-level locking of the OPO cavity length.

[0004] In order to improve the locking performance, the present invention proposes an innovative solution: using the inverse Fourier transform term of the parasitic light pulse spectrum, that is, using the pulse width in the time domain waveform as a new feedback quantity. This method has benefited from the significant progress in ultrashort pulse measurement technology in recent years, making it possible to measure ultrashort pulses in real time with high sensitivity (microwatt power) and high resolution (femtosecond level). This highly sensitive and high-resolution pulse width signal provides a strong guarantee for obtaining a high signal-to-noise ratio and high-intensity error signal, thereby hopefully achieving an OPO pulse light source with a higher locking level.

[0005] In view of the above analysis, the technical problem that urgently needs to be solved in the prior art is that the modulation-free locking scheme for the OPO cavity length based on the parasitic light spectral power currently has a limiting factor, that is, the signal-to-noise ratio of the generated error signal is limited by the spectral shape, and the signal intensity is limited by the detection sensitivity, which leads to the OPO cavity length locking level is still not high. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides a cavity length locking system and method for a pulsed optical parametric oscillator. By using a commercial autocorrelator, the parasitic light pulse width variable caused by the OPO cavity length jitter is measured in real time. The variable has microwatt detection sensitivity and femtosecond detection resolution, thus greatly improving the signal-to-noise ratio and signal strength of the error signal. Based on a dual-loop locking scheme, the present invention suppresses Hz-level bandwidth and kHz-MHz-level bandwidth noise respectively, and achieves a high level of OPO cavity length locking.

[0007] The present invention is implemented in this way: a cavity length locking system of a pulse optical parametric oscillator includes an OPO pulse light source, a pulse width feedback locking loop and a power-based auxiliary locking loop.

[0008] The OPO pulse light source includes a seed pulse light source and an OPO resonant cavity;

[0009] The pulse width feedback lock loop is composed of a pulse width measurement device, a signal processing circuit, and a cavity length control element; the pulse width measurement device is used to measure the pulse width of the parasitic light pulse output by the OPO in real time and convert it into a digital voltage signal. The signal processing circuit compares the pulse width voltage signal with the reference voltage signal to obtain an error signal, and obtains a servo signal through a digital proportional-integral-differential (PID) circuit, which is used to feed back to the cavity length control element. The cavity length control element adjusts the cavity length according to the servo voltage signal output by the signal processing circuit.

[0010] The power-based auxiliary locking loop consists of a power signal measurement device, a signal processing circuit, and a cavity length control element; the power signal measurement device includes a filter optical path and a low-noise power detector. The filter optical path is based on a wave plate, a filter, and a reflector to extract parasitic light pulses in the OPO leakage spectrum. The low-noise power detector has a kHz bandwidth and a low-noise detection level.

[0011] Furthermore, the seed pulse light source can be a solid or fiber pulse laser, whose output pulse laser is coupled into the OPO resonant cavity, and parameter conversion is performed inside the nonlinear crystal in the cavity to generate the required resonant pulse, and parasitic light pulses are generated by non-phase matching.

[0012] Furthermore, the pulse width measurement device includes a filter optical path and an autocorrelator. The filter optical path is based on a wave plate, a filter and a reflector, and is used to extract parasitic light pulses in the OPO leakage spectrum. The autocorrelator is based on a Michelson interference structure or a Mach-Zehnder interference structure, and measures the pulse width in real time. The power sensitivity of the measurement reaches the microwatt level, and the numerical resolution of the measurement reaches the femtosecond level.

[0013] Furthermore, the signal processing circuit is mainly composed of a digital PID circuit and a digital-to-analog conversion circuit; the digital PID circuit has a high-gain, low-bandwidth feedback loop characteristic, and is mainly used for low-frequency noise suppression within the Hz-level bandwidth of the signal. The digital-to-analog conversion circuit converts the servo digital signal into an analog signal.

[0014] Furthermore, the cavity length control element may be a piezoelectric ceramic or a stepper motor, which will actively control the OPO cavity length according to the output voltage of the signal processing circuit.

[0015] Furthermore, the signal processing circuit is mainly composed of a comparison circuit and an analog PID circuit;

[0016] The comparison circuit compares the power detection voltage with the reference voltage to obtain an error signal. The comparison circuit has a wide bandwidth. The analog PID circuit has a wideband feedback loop characteristic, which is mainly effective in suppressing signal kHz-MHz frequency band noise.

[0017] The cavity length control element is a piezoelectric ceramic or a stepper motor, which will be driven by a servo voltage to actively control the OPO cavity length.

[0018] Another object of the present invention is to provide a cavity length locking method using the pulsed optical parametric oscillator, comprising:

[0019] S1, after OPO resonates, two leaked lights are used to construct a power-based auxiliary locking loop and a pulse width feedback locking loop respectively.

[0020] S2, first operate the power-based auxiliary locking loop, that is, measure the power variable related to the parasitic light pulse and cavity length jitter through the signal measurement device, and obtain the error voltage signal through the comparison circuit. The error voltage signal is used to obtain the servo voltage signal through the analog PID circuit to drive the cavity length control element to achieve one of the cavity length closed-loop locking. The feedback loop has a kHz-MHz bandwidth and actively suppresses the OPO pulse kHz-MHz frequency band noise.

[0021] S3, then operate the pulse width feedback locking loop, obtain the pulse width parameters of the parasitic pulse through the autocorrelator, and obtain a high signal-to-noise ratio, high-intensity error signal and a high-gain low-bandwidth servo signal through the signal processing circuit, which is used to drive another cavity length control element to achieve another cavity length closed-loop locking. The feedback loop has a Hz-level bandwidth and actively suppresses the Hz-level frequency band noise of the OPO pulse.

[0022] S4, the dual loops will work simultaneously, eventually achieving stable locking of the OPO cavity length.

[0023] Another object of the present invention is to provide a cavity length locking method for a pulsed optical parametric oscillator, comprising the following steps:

[0024] (1) extracting the parasitic light pulse output by the OPO, measuring the pulse width in real time through a pulse width measurement device, and converting the measurement result into a digital voltage signal;

[0025] (2) Compare the pulse width voltage signal with the reference voltage signal and generate a servo signal using a digital proportional-integral-differential (PID) circuit;

[0026] (3) Through the cavity length control element, the cavity length of the OPO resonant cavity is adjusted according to the servo signal to achieve real-time locking of the pulse width.

[0027] Further, in step (1), the method for extracting the OPO parasitic light pulse includes:

[0028] The parasitic light pulses in the OPO leakage spectrum are extracted by using a filtering optical path, which is composed of a wave plate, a filter and a reflector;

[0029] The pulse width is measured using an autocorrelator based on a Michelson interference structure or a Mach-Zehnder interference structure, with a measurement sensitivity of microwatts and a resolution of femtoseconds.

[0030] Further, the following steps are included:

[0031] (1) Extract the OPO parasitic light pulse and measure its power signal in real time using a low-noise power detector;

[0032] (2) Compare the power signal with a reference power signal and generate a servo signal using an analog PID circuit;

[0033] (3) Using piezoelectric ceramics or stepper motors, the cavity length of the OPO resonant cavity is dynamically adjusted according to the servo signal to achieve power-assisted cavity length locking.

[0034] Furthermore, in step (1), the low-noise power detector has a kHz bandwidth and a low-noise detection level, and is capable of achieving high-sensitivity detection when the parasitic light pulse power is weak, and converting the power signal into a voltage signal for subsequent processing.

[0035] The basic method of realizing cavity length locking by pulse width measurement includes measurement, signal processing and feedback control steps.

[0036] The pulse width measurement method emphasizes the specific structure and performance of the filtering optical path and the autocorrelator.

[0037] A method of using power signal to assist cavity length locking is proposed, and the basic steps of power detection and feedback control are proposed.

[0038] The characteristics and functions of low-noise power detectors are further clarified to ensure high sensitivity and accuracy of signal measurement.

[0039] These method claims define the key technical steps and equipment features of the locking process, providing a comprehensive scope of protection for the patented technology. In combination with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0040] First, the present invention proposes an OPO cavity length locking scheme based on the pulse width of parasitic light pulses as feedback. The pulse width variable with microwatt detection sensitivity and femtosecond detection resolution is obtained through a commercial autocorrelator, which can greatly improve the signal-to-noise ratio and signal strength of the loop error signal.

[0041] The locking system uses a pulse width feedback locking loop and a power-based auxiliary locking loop to work simultaneously. The pulse width feedback locking loop has Hz-level bandwidth and high gain characteristics, while the power-based auxiliary locking loop has a larger bandwidth of kHz-MHz. The matching application of the two can achieve a more stable OPO cavity length locking.

[0042] The present invention proposes a cavity length locking method and system for a pulsed OPO. The locking system includes a pulse width feedback locking loop and a power-based auxiliary locking loop. The former uses a commercial autocorrelator to obtain pulse width variables with microwatt detection sensitivity and femtosecond detection resolution, and can obtain high signal-to-noise ratio and high-intensity error signals at a Hz bandwidth, thereby achieving efficient suppression of low-frequency noise; the latter uses power feedback and a larger bandwidth locking loop at the kHz-MHz level to achieve medium and high frequency noise suppression. The matching of the two will effectively suppress the noise power spectrum within the MHz bandwidth. More importantly, the invention has a very efficient suppression level for low-frequency noise within the Hz bandwidth, and therefore will greatly improve the long-term stability of the pulsed OPO.

[0043] Second, the expected benefits and commercial value of the technical solution of the present invention after transformation are:

[0044] The technical solution of the present invention adopts the pulse width in the time domain waveform as the feedback quantity, and utilizes the ultrashort pulse measurement technology to improve the signal-to-noise ratio and intensity of the error signal, and is expected to achieve an OPO pulse light source with a higher locking level. This not only simplifies the system design, but also improves the stability and performance of the system. It will bring significant benefits to optical applications and control applications, and has broad market prospects and commercial value in the fields of infrared spectroscopy measurement, biomedical research, atmospheric environment detection, laser radar, optical communication, quantum information processing, and infrared optical frequency precision measurement.

[0045] (2) The technical solution of the present invention fills the technical gap in the industry at home and abroad:

[0046] The technical solution of the present invention fills an important gap in the optical parametric oscillator (OPO) cavity length locking technology at home and abroad. The traditional method mainly relies on external modulation, while this solution innovatively uses the inverse Fourier transform term of the parasitic light pulse spectrum - pulse width as feedback, without external modulation, and combined with the progress of ultrashort pulse measurement technology, it realizes real-time high-sensitivity and high-resolution measurement, effectively improves the error signal signal-to-noise ratio and intensity, and provides a new way to achieve a higher locking level of OPO pulse light source.

[0047] (3) The technical solution of the present invention solves the technical problems that people have been eager to solve but have never been able to solve successfully:

[0048] The technical solution of the present invention solves the technical problem of limited error signal-to-noise ratio and signal strength caused by using the spectral power of parasitic light pulses as feedback when the OPO resonance peak is locked. By adopting pulse width as a new feedback quantity, an OPO pulse light source with a higher locking level is achieved.

[0049] (4) The technical solution of the present invention overcomes technical prejudice:

[0050] The technical prejudice overcome by the technical solution of the present invention mainly lies in the traditional understanding of the OPO resonance peak locking method. In the past, scientific and technological workers may be more inclined to rely on external modulation methods to achieve the locking target, and believe that the parasitic light pulse spectrum power has limitations as a feedback quantity, such as being limited by the spectrum shape and detection sensitivity. However, the new solution innovatively uses the inverse Fourier transform term (i.e., pulse width) of the parasitic light pulse spectrum as a new feedback quantity, and with the help of advances in ultrashort pulse measurement technology, it successfully achieves a higher level of OPO cavity length locking, breaking this traditional technical prejudice. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 1 is a structural diagram of a cavity length locking system of a pulsed OPO provided in an embodiment of the present invention;

[0052] Figure 2 is a schematic diagram of an optical parametric oscillator provided by an embodiment of the present invention;

[0053] Figure 3 Schematic diagram of a pulse width measurement device (autocorrelator) provided in an embodiment of the present invention. In which, (a) Michelson interferometer structure; (b) Mach-Zehnder interferometer structure;

[0054] Figure 4 It is a flow chart of the cavity length locking method of the pulsed OPO provided in an embodiment of the present invention;

[0055] Figure 5 is the relevant OPO leakage spectrum of the technical effect obtained by the embodiment of the present invention;

[0056] Figure 6 It is a response curve between the relevant parasitic pulse width variable, power variable and cavity length variable of the technical effect obtained by the embodiment of the present invention. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0058] like Figure 1 As shown, the present invention proposes a cavity length locking system for a pulsed OPO, which mainly includes an OPO pulse light source, a pulse width feedback locking loop and a power-based auxiliary locking loop.

[0059] 1) OPO pulse light source, including a seed pulse light source and an OPO resonant cavity;

[0060] Furthermore, the seed pulse light source can be a solid or fiber pulse laser, whose output pulse laser is coupled into the OPO resonant cavity, and parameter conversion is performed inside the nonlinear crystal in the cavity to generate the required resonant pulse, and parasitic light pulses are generated by non-phase matching.

[0061] 2) If Figure 3 As shown, the pulse width feedback locking loop is composed of a pulse width measurement device, a signal processing circuit and a cavity length control element;

[0062] The pulse width measurement device is used to measure the pulse width of the parasitic light pulse output by the OPO in real time and convert it into a digital voltage signal. The signal processing circuit compares the pulse width voltage signal with the reference voltage signal to obtain an error signal, and obtains a servo signal through a digital proportional-integral-differential (PID) circuit, which is used to feed back to the cavity length control element. The cavity length control element adjusts the cavity length according to the servo voltage signal output by the signal processing circuit.

[0063] Furthermore, the pulse width measurement device includes a filter optical path and an autocorrelator. The filter optical path is based on a wave plate, a filter and a reflector, and is used to extract parasitic light pulses in the OPO leakage spectrum. The autocorrelator is based on a Michelson interference structure or a Mach-Zehnder interference structure, and measures the pulse width in real time. The power sensitivity of the measurement reaches the microwatt level, and the numerical resolution of the measurement reaches the femtosecond level.

[0064] Furthermore, the signal processing circuit is mainly composed of a digital PID circuit and a digital-to-analog conversion circuit; the digital PID circuit has a high-gain, low-bandwidth feedback loop characteristic, and is mainly used for low-frequency noise suppression within the Hz-level bandwidth of the signal. The digital-to-analog conversion circuit converts the servo digital signal into an analog signal.

[0065] The cavity length control element may be a piezoelectric ceramic or a stepper motor, which actively controls the OPO cavity length according to the output voltage of the signal processing circuit.

[0066] 3) The power-based auxiliary locking loop is composed of a power signal measuring device, a signal processing circuit and a cavity length control element;

[0067] The power signal measurement device includes a filter optical path and a low-noise power detector. The filter optical path is based on a wave plate, a filter, and a reflector to extract parasitic light pulses in the OPO leakage spectrum. The low-noise power detector has a kHz bandwidth and a low-noise detection level.

[0068] Furthermore, the signal processing circuit is mainly composed of a comparison circuit and an analog PID circuit;

[0069] The comparison circuit compares the power detection voltage with the reference voltage to obtain an error signal. The comparison circuit has a wide bandwidth. The analog PID circuit has a wideband feedback loop characteristic, which is mainly effective in suppressing signal kHz-MHz frequency band noise.

[0070] The cavity length control element is a piezoelectric ceramic or a stepper motor, which will be driven by a servo voltage to actively control the OPO cavity length.

[0071] 4) If Figure 4 As shown, the locking steps of the system include:

[0072] After the OPO resonates, the two leaked lights are used to construct a power-based auxiliary locking loop and a pulse width feedback locking loop respectively. First, the power-based auxiliary locking loop is operated, that is, the power variable related to the parasitic light pulse and the cavity length jitter is measured through the signal measurement device, and the error voltage signal is obtained through the comparison circuit. The error voltage signal is used to obtain a servo voltage signal through the analog PID circuit, which is used to drive the cavity length control element to achieve one of the cavity length closed-loop locking. The feedback loop has a kHz-MHz bandwidth and actively suppresses the kHz-MHz frequency band noise of the OPO pulse. Then the pulse width feedback locking loop is operated, the pulse width parameters of the parasitic pulse are obtained through the autocorrelator, and a high signal-to-noise ratio, high-intensity error signal and a high-gain low-bandwidth servo signal are obtained through the signal processing circuit. The signal is used to drive another cavity length control element to achieve another cavity length closed-loop locking. The feedback loop has a Hz bandwidth and actively suppresses the Hz frequency band noise of the OPO pulse. The dual loops will work simultaneously, and finally achieve stable locking of the OPO cavity length.

[0073] The present invention can be widely used in fields that require high-precision and high-stability light sources, such as infrared spectroscopy measurement, biomedical research, atmospheric environment detection, lidar, optical communication, quantum information processing, and infrared optical frequency precision measurement. By improving the OPO locking performance, more reliable and powerful pulse light source support can be provided for these fields.

[0074] Take the high-energy Yb-doped fiber pulse synchronous pumping of MgO:PPLN crystal OPO as an example. The OPO pump pulse has a central wavelength of 1040nm, a pulse width of 200fs, and a peak intensity density of about 1GW / cm 2 MgO:PPLN crystal (temperature controlled at 60℃) with a length of 1mm and a period of 31.3μm is used to generate 1700nm signal light and 2660nm idler light. The OPO cavity mirror coating ensures the single resonance of the signal light pulse. After the final resonance, the leaked spectrum results are as follows: Figure 5In addition to the pump light (p), signal light (s) and idler light (i), there are also parasitic lights of various frequency conversion methods, such as the sum frequency of pump and signal light (p+s), the sum frequency of pump and idler light (p+i), the double frequency of signal light (2s) and the double frequency of pump light (2p).

[0075] The pump and signal light and the frequency parasitic light are used to obtain the error signal. By adjusting the cavity length, the response curves of the parasitic light pulse width, power and cavity length variables are measured in turn, such as Figure 6 As shown. It can be seen that both have a linear response range, indicating that both can be used as feedback for locking the cavity length. After removing the dimension interference and performing normalization, it can be obtained that the response coefficient of the pulse width is higher than that of the power. This shows that within the appropriate working range of the OPO, the pulse width feedback can obtain a higher signal-to-noise ratio error signal than the power feedback. And because the measurement resolution of the autocorrelator can reach one optical cycle (2fs in the 630nm band), the measured light intensity reaches the microwatt level. This measurement accuracy can further improve the measured error signal strength and signal-to-noise ratio.

[0076] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A cavity length locking system for a pulsed optical parametric oscillator, characterized in that: Including OPO pulse light source, pulse width feedback locking loop and power-based auxiliary locking loop; The OPO pulse light source includes a seed pulse light source and an OPO resonant cavity; The pulse width feedback locking loop is composed of a pulse width measurement device, a signal processing circuit and a cavity length control element; the pulse width measurement device is used to measure the pulse width result of the parasitic light pulse output by the OPO in real time and convert it into a digital voltage signal; the signal processing circuit compares the pulse width voltage signal with the reference voltage signal to obtain an error signal, and obtains a servo signal through a digital proportional-integral-differential circuit, which is used to feed back to the cavity length control element, and the cavity length control element adjusts the cavity length according to the servo voltage signal output by the signal processing circuit; The power-based auxiliary locking loop is composed of a power signal measuring device, a signal processing circuit and a cavity length control element; the power signal measuring device includes a filtering optical path and a low-noise power detector; The optical filter path is based on wave plates, filters and reflectors to extract parasitic light pulses from the OPO leakage spectrum. The low-noise power detector has a kHz bandwidth and low-noise detection level.

2. The cavity length locking system of a pulsed optical parametric oscillator according to claim 1, characterized in that: The seed pulse light source can be a solid or fiber pulse laser, whose output pulse laser is coupled into the OPO resonant cavity, and parameter conversion is performed inside the nonlinear crystal in the cavity to generate the required resonant pulse, and parasitic light pulses are generated by non-phase matching.

3. The cavity length locking system of a pulsed optical parametric oscillator according to claim 1, characterized in that: The pulse width measurement device includes a filter optical path and an autocorrelator; the filter optical path is based on a wave plate, a filter and a reflector, and is used to extract parasitic light pulses in the OPO leakage spectrum; The autocorrelator is based on the Michelson interference structure or the Mach-Zehnder interference structure, and measures the pulse width in real time. The power sensitivity of the measurement reaches the microwatt level and the numerical resolution of the measurement reaches the femtosecond level.

4. The cavity length locking system of a pulsed optical parametric oscillator according to claim 1, characterized in that: The signal processing circuit is mainly composed of a digital PID circuit and a digital-to-analog conversion circuit; the digital PID circuit has high-gain, low-bandwidth feedback loop characteristics, and is mainly used to suppress low-frequency noise within the Hz-level bandwidth of the signal, while the digital-to-analog conversion circuit converts the servo digital signal into an analog signal.

5. The cavity length locking system of a pulsed optical parametric oscillator according to claim 1, characterized in that: The cavity length control element can be a piezoelectric ceramic or a stepper motor, which will actively control the OPO cavity length according to the output voltage of the signal processing circuit.

6. The cavity length locking system of a pulsed optical parametric oscillator according to claim 1, characterized in that: The signal processing circuit is mainly composed of a comparison circuit and an analog PID circuit; The comparison circuit compares the power detection voltage with the reference voltage to obtain an error signal; the comparison circuit has a broadband bandwidth; the analog PID circuit has a broadband feedback loop characteristic, which is mainly effective in suppressing signal kHz-MHz frequency band noise; The cavity length control element is a piezoelectric ceramic or a stepper motor, which will be driven by a servo voltage to actively control the OPO cavity length.

7. A method for cavity length locking of a pulsed optical parametric oscillator using the cavity length locking system of a pulsed optical parametric oscillator according to any one of claims 1 to 6, characterized in that: include: (1) extracting the parasitic light pulse output by the OPO, measuring the pulse width in real time through a pulse width measurement device, and converting the measurement result into a digital voltage signal; (2) Compare the pulse width voltage signal with the reference voltage signal and generate a servo signal using a digital proportional-integral-differential (PID) circuit; (3) Through the cavity length control element, the cavity length of the OPO resonant cavity is adjusted according to the servo signal to achieve real-time locking of the pulse width.

8. The cavity length locking method according to claim 7, characterized in that: In step (1), the method for extracting the OPO parasitic light pulse includes: The parasitic light pulses in the OPO leakage spectrum are extracted by using a filtering optical path, which is composed of a wave plate, a filter and a reflector; The pulse width is measured using an autocorrelator based on a Michelson interference structure or a Mach-Zehnder interference structure, with a measurement sensitivity of microwatts and a resolution of femtoseconds.

9. A power-assisted cavity length locking method, characterized in that: The following steps are involved: (1) Extract the OPO parasitic light pulse and measure its power signal in real time using a low-noise power detector; (2) Compare the power signal with a reference power signal and generate a servo signal using an analog PID circuit; (3) Using piezoelectric ceramics or stepper motors, the cavity length of the OPO resonant cavity is dynamically adjusted according to the servo signal to achieve power-assisted cavity length locking.

10. The power-assisted cavity length locking method according to claim 9, characterized in that: In step (1), the low-noise power detector has a kHz bandwidth and a low-noise detection level, and can achieve high-sensitivity detection when the parasitic light pulse power is weak, and convert the power signal into a voltage signal for subsequent processing.

Images