Laser gyroscope frequency stabilization system and frequency stabilization method thereof

Abstract

The invention belongs to the technical field of optoelectronic devices, and provides a laser gyroscope frequency stabilization system and a frequency stabilization method thereof.The laser gyroscope frequency stabilization system comprises a large laser gyroscope to be subjected to frequency stabilization, an electro-optical modulator, an adjusting light path, a signal generator, a mode matching mirror set, a PID regulator, a frequency mixer, a photoelectric detector, an ultra-stable cavity, a low-pass filter, a computer and a data acquisition card; and a square transmission light path is arranged in the ultra-stable cavity. According to the invention, the problem of insufficient isolation caused by an optical isolator consisting of a polarization splitting prism and a 1 / 4 wave plate is effectively avoided, the influence of an optical feedback effect is reduced, and the optical isolator is better adapted to the field of high-precision measurement related to a large laser gyroscope.

Description

Technical Field

[0001] The invention belongs to the technical field of optoelectronic devices, and in particular relates to a laser gyro frequency stabilization system and a frequency stabilization method thereof. Background Art

[0002] As a typical application of the Sagnac effect in the field of inertial navigation and a typical representative of the first quantum technology revolution, the laser gyroscope can accurately measure angular velocity without the need for inertial mass conditions, bringing disruptive changes to fields such as ultra-precision inertial navigation and attitude control, and becoming an indispensable core component from inertial sensing control to basic science. With the continuous advancement of related process technologies, the measurement accuracy of laser gyroscopes is gradually approaching the theoretical limit. People increase the proportional factor by increasing the size of the gyroscope, and large laser gyroscopes are born, which successfully achieves a breakthrough in accuracy based on traditional laser gyroscopes. At present, the measurement accuracy of mainstream large laser gyroscopes in the world has reached 10 -13 Up to 10 -11 The minimum theoretical accuracy is reduced to 2×10 -15 rad / s, which can basically meet the stringent requirements of a series of high-precision fields such as relativistic effect testing.

[0003] As a type of large scientific device used in the field of high-precision measurement of weak signals, it is crucial to maintain a large laser gyro to work stably for a long time at a high-precision measurement level. The core of this is to maintain the stability of the frequency in its resonant cavity, including short-term stability and long-term stability. Short-term stability ensures the accuracy and repeatability of instant signal measurement, while long-term stability requires reducing or even eliminating the impact of long-term drift. At present, the mainstream frequency stabilization solution for large laser gyros widely used internationally is the "external absolute frequency standard + PDH frequency stabilization technology". This solution is based on the beat frequency between the gyro output frequency and the absolute frequency standard to generate an error signal. After a series of complex processing processes, the control signal is fed back to the piezoelectric ceramic, thereby achieving precise control of the cavity length, and ultimately achieving the purpose of outputting a stable laser frequency. In this process, the frequency stability of the output laser depends to a large extent on the stability of the absolute frequency standard. In traditional PDH frequency stabilization technology, the resonant transmission peak line of the straight FP cavity is generally used as the absolute frequency standard. The reason is that by increasing the reflectivity of the two reflecting mirrors that constitute the FP cavity, the fineness of the FP cavity can be increased, making its resonant transmission peak line width narrower; at the same time, the high stability of microcrystalline glass ensures the extremely small offset of the resonant transmission peak center of the FP cavity itself, making the straight FP cavity a relatively ideal external frequency standard.

[0004] In traditional PDH technology, it is often necessary to add an electro-optic modulator (EOM) driven by a certain local oscillator frequency in front of the straight FP cavity. The electro-optic modulator will impose two symmetrical sideband frequencies on the original frequency of the laser to be stabilized to reflect the error information between the frequency of the laser to be stabilized and the resonant transmission peak of the straight FP cavity. In the actual optical path design, in order to prevent the light reflected from the straight FP cavity from returning to the electro-optic modulator and the resonant cavity of the laser to be stabilized along the incident optical path to cause an optical feedback effect, it is necessary to introduce optical isolation means between the electro-optic modulator and the straight FP cavity. A common method is to add a quarter wave plate after a polarizing beam splitter (PBS) to form an optical isolation module. When incident in the forward direction, the quarter wave plate will produce a phase difference of 1 / 4 wavelength on the two orthogonal components of the linearly polarized light emitted by the polarizing beam splitter, thereby converting the linearly polarized light into circularly polarized light. When incident in the reverse direction, the quarter wave plate again acts on the circularly polarized light reflected back from the straight FP cavity, and the phase difference between the two orthogonal components becomes 1 / 2 wavelength, and the circularly polarized light is converted into linearly polarized light. At this time, the polarization direction of the linearly polarized light is perpendicular to the polarization direction of the original incident light and cannot pass through the polarization beam splitter, thereby achieving optical isolation.

[0005] However, for large-scale laser gyroscopes and other high-precision scientific devices, the use of the above optical isolation modules will inevitably lead to the following problems: 1. Insertion loss is introduced. The polarization beam splitter and the quarter wave plate will reflect and absorb the laser to a certain extent, which will introduce insertion loss to the already weak light intensity signal and affect the subsequent signal processing effect; 2. Poor isolation effect. The optical isolation module composed of a polarization beam splitter and a quarter wave plate has high requirements for the polarization degree of the incident light, and the isolation effect for light with a lower polarization degree will be greatly reduced; and even if the incident light has a high polarization degree, its isolation is relatively limited, usually around 20dB~40dB, which may not meet the isolation requirements in some applications in the field of extremely high-precision measurement; 3. The frequency stabilization system is complex to control. First, the phase delay characteristics of the 1 / 4 wave plate are sensitive to temperature changes, and temperature fluctuations will greatly affect the optical isolation performance; secondly, in order to achieve effective optical isolation, the relative position and angle of the polarization beam splitter and the 1 / 4 wave plate need to be precisely designed and aligned, which increases the overall debugging difficulty of the frequency stabilization system; in addition, the 1 / 4 wave plate has the best phase delay effect for light of a specific wavelength, and the optical isolation performance for other wavelengths will decrease, so the wavelength drift under different conditions will weaken the optical isolation effect. Summary of the invention

[0006] In order to solve the technical problems existing in the actual application of an optical isolation module composed of a polarization beam splitter prism and a quarter wave plate in the PDH technology, the present invention provides a laser gyro frequency stabilization system and a frequency stabilization method thereof.

[0007] In order to solve the technical problems existing in the above-mentioned prior art, the technical solution adopted by the present invention is: On the one hand, a laser gyro frequency stabilization system is proposed, which includes a large laser gyro to be stabilized, an electro-optic modulator, an adjustment optical path, a signal generator, a mode matching mirror group, a PID regulator, a mixer, a photodetector, an ultra-stable cavity, a low-pass filter, a computer, and a data acquisition card; The large laser gyro to be stabilized outputs the laser to be stabilized; The electro-optic modulator receives the laser to be stabilized, and the signal generator is connected to the electro-optic modulator and the mixer through cables, and outputs two radio frequency signals with the same frequency, one radio frequency signal is used as a working signal to excite the electro-optic modulator, and the other radio frequency signal is used as a local oscillator signal in the mixing process of the mixer. The electro-optic modulator applies two symmetrical sidebands to the frequency of the laser to be stabilized under the action of the radio frequency signal generated by the signal generator; Adjust the optical path to transmit the laser to be stabilized emitted by the electro-optic modulator to the mode matching mirror group; The mode matching mirror group adjusts the mode and phase of the laser to be stabilized and then outputs the laser to be stabilized to the ultra-stable cavity; The laser output from the ultrastable cavity is incident on the photodetector, which is connected to the mixer and the data acquisition card, and the data acquisition card is connected to the computer through the network port / serial port; The mixer is connected to a low-pass filter, and the mixing signal from the mixer is low-pass filtered to extract the error signal; the low-pass filter is respectively connected to a PID regulator and a computer, and the PID regulator is connected to a piezoelectric ceramic fixedly connected to the rear side of one of the resonant cavity reflectors in the large laser gyroscope to be stabilized, and the error signal from the low-pass filter is converted into a voltage signal for driving the piezoelectric ceramic, and transmitted to the piezoelectric ceramic. The piezoelectric ceramic movement synchronously drives the resonant cavity reflector fixedly connected to the piezoelectric ceramic, thereby realizing precise control of the resonant cavity length inside the large laser gyroscope to be stabilized, thereby maintaining the stability of the output laser frequency of the large laser gyroscope to be stabilized.

[0008] Furthermore, the large laser gyroscope to be frequency stabilized is placed on an air-floating optical platform to reduce environmental vibration.

[0009] Furthermore, the adjustment optical path includes a front reflector and a rear reflector. The reflective surface of the front reflector receives the laser to be stabilized emitted by the clear aperture of the electro-optic modulator, and reflects it to the reflective surface of the rear reflector. The rear reflector reflects the laser to be stabilized from the front reflector to the mode matching mirror group. The front reflector and the rear reflector cooperate to enable the laser to be stabilized to be smoothly incident into the ultra-stable cavity and overlap with the intrinsic light field in the ultra-stable cavity.

[0010] Furthermore, the mode matching mirror group is composed of n reflectors, which are the first reflector M1, the nth reflector M2, the nth reflector M3, the nth reflector M4, the nth reflector M5, the nth reflector M6, the nth reflector M7, the nth reflector M8, the nth reflector M9, the nth reflector M10, the nth reflector M11, the nth reflector M12, the nth reflector M13, the nth reflect n The n reflecting mirrors include a plane mirror and a spherical mirror coated with a high-reflection film. By adjusting the curvature radius of the spherical mirror in the mode matching mirror group and the relative position of the plane mirror and the spherical mirror, the laser to be stabilized incident on the mode matching mirror group can match the position and size of the intrinsic waist spot of the light beam when it is emitted into the ultra-stable cavity after passing through the mode matching mirror group. The mode and phase of the laser to be stabilized are adjusted by the mode matching mirror group so that the laser to be stabilized can effectively resonate after entering the ultra-stable cavity.

[0011] Furthermore, the ultra-stable cavity is placed in a temperature-controlled cover and fixedly connected to an air-floating optical platform.

[0012] Furthermore, the main material of the ultra-stable cavity is microcrystalline glass, and the ultra-stable cavity has a square transmission light path inside. The reflection of the laser in the square transmission light path is realized by four high-reflectivity mirrors. Piezoelectric ceramics are installed on the outside of the cavity of two adjacent mirrors of the four mirrors. The other two mirrors are the incident end mirror S1 and the output end mirror S2. The incident end mirror S1 and the output end mirror S2 serve as the entrance and exit of external laser injection. The laser to be stabilized after the mode and phase are adjusted by the mode matching mirror group is incident on the incident end mirror S1. The incident end mirror S1 transmits the laser to be stabilized into the ultra-stable cavity, and the output end mirror S2 transmits the laser to be stabilized to the reflection surface of the rear mirror of the cavity. The rear mirror of the cavity then reflects the laser to be stabilized to the photosensitive surface of the photodetector.

[0013] Furthermore, the electrical signal generated by the photodetector includes three parts: a DC term reflecting the respective strengths of the carrier and the sideband, an interference term between the carrier and the sideband, and an interference term between the two sidebands. The interference term between the carrier and the sideband includes the error information between the frequency of the laser to be stabilized and the resonance peak of the ultra-stable cavity.

[0014] The mixing signal output by the mixer includes three parts: the amplitude of the interference term between the carrier and the sideband, the first-time frequency term, and the second-time frequency term, wherein the amplitude of the interference term between the carrier and the sideband is used as an error signal.

[0015] The computer has a built-in data reading and visualization program and a driver adapted to the temperature regulator on the wall of the temperature control cover to achieve the following purposes: The electrical signal from the photodetector is read out to observe the resonance inside the ultra-stable cavity. When resonance occurs in the ultra-stable cavity, an obvious light intensity transmission peak will be seen on the computer. Correspondingly, the transmitted light emitted by the incident end reflector S1 of the ultra-stable cavity will coherently cancel the primary reflected light of the laser to be stabilized on the incident end reflector S1, which is manifested as a depression in the light intensity signal. Receive the error signal processed by the low-pass filter and display its curve; The temperature inside the ultra-stable cavity is monitored and adjusted to keep it stable.

[0016] The beneficial technical effects of the present invention are: The present invention effectively avoids the problem of insufficient isolation caused by the optical isolator composed of a polarization beam splitter prism and a 1 / 4 wave plate, reduces the influence of the optical feedback effect, and better adapts to the high-precision measurement field involved in large laser gyroscopes. The present invention has better thermal stability and vibration resistance. The ultra-stable cavity provided by the present invention has a square transmission light path inside. Compared with a straight cavity, the thermal expansion is more uniform in all directions, and the heat conduction path is more complex and dispersed. It will not have local overheating or excessive temperature gradients like a straight cavity, so it has better thermal stability and temperature control effects; at the same time, the structure of the square cavity makes its stiffness in all directions relatively uniform, and the distribution of external vibration energy inside the cavity is relatively more dispersed, so it can better resist the interference of external vibrations and is more compact and stable.

[0017] The ultrastable cavity of the present invention has a square transmission optical path inside. During the electro-optical modulation process, the residual amplitude modulation generated will be less than that of a straight cavity, which helps to reduce interference with the error signal and further improve the frequency stabilization accuracy of the system.

[0018] On the premise of ensuring the same length of the resonant cavity, this scheme can effectively reduce the scale of the optical path part of the frequency stabilization system compared to the straight cavity scheme, and enhance the practicality and flexibility of the frequency stabilization system. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0020] Figure 11 is a schematic diagram of the structure of a laser gyro frequency stabilization system in an embodiment, wherein: 1: a large laser gyro to be stabilized; 2: an electro-optic modulator; 3: a front reflector; 4: a rear reflector; 5: a signal generator; 6: a mode matching mirror group; 7: a PID regulator; 8: a mixer; 9: a photodetector; 10: an ultra-stable cavity; 11: a temperature control cover; 12: a rear reflector of the cavity; 13: a low-pass filter; 14: a computer; 15: a data acquisition card; Figure 2 for Figure 1 The composition of the mode matching mirror group and the relative positions of each mirror surface, where: P1 and P2 are the first spot observation position and the second spot observation position; M1 to M n To adjust the incident laser mode and phase, the first reflector is n Reflector.

[0021] Figure 3 for Figure 1 Schematic diagram of the structure of the ultrastable cavity, where: S1 is the incident end reflector, S2 is the output end reflector; there are two laser beams propagating in the ultrastable cavity in the clockwise and counterclockwise directions at the same time, of which the clockwise beam is the externally injected stabilized laser, and the counterclockwise beam is the backscattered beam of the stabilized laser, and its intensity can be ignored relative to the stabilized laser; Figure 4 for Figure 1 Flowchart of the frequency stabilization method of the laser gyro frequency stabilization system of the structure shown. DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] Refer to the attached Figure 1 To Attachment Figure 4 , Figure 1 is a schematic diagram of the structure of a laser gyro frequency stabilization system in an embodiment, Figure 2 for Figure 1 The composition of the mode matching mirror set and the relative positions of the mirror surfaces; Figure 3 for Figure 1 Schematic diagram of the structure of the superstable cavity. Figure 4 for Figure 1 Flowchart of the frequency stabilization method of the laser gyro frequency stabilization system of the structure shown.

[0024] like Figure 1As shown, a laser gyro frequency stabilization system is provided by an embodiment, comprising: a large laser gyro to be frequency stabilized 1, an electro-optical modulator 2, an adjustment optical path, a signal generator 5, a mode matching mirror group 6, a PID regulator 7, a mixer 8, a photodetector 9, an ultra-stable cavity 10, a low-pass filter 13, a computer 14, and a data acquisition card 15; The large laser gyro 1 to be stabilized is placed on an air-floating optical platform to reduce environmental vibration. The output frequency of the large laser gyro 1 to be stabilized is ω 0 laser to be stabilized; The electro-optic modulator 2 is located at the light outlet of the large laser gyro 1 to be stabilized. The electro-optic modulator 2 receives the laser to be stabilized emitted by the large laser gyro 1 to be stabilized. The electro-optic modulator 2 is connected to a signal generator 5. Under the action of the radio frequency signal generated by the signal generator 5, two symmetrical sidebands are applied to the frequency of the laser to be stabilized. The signal generator 5 is used to generate a working signal to excite the electro-optic modulator 2 and a local oscillator signal for the mixing process. The signal generator 5 is connected to the electro-optic modulator 2 and the mixer 8 through cables, and the output frequency is the same. f 0, wherein the RF signal input to the electro-optic modulator 2 is used as the working signal to excite the electro-optic modulator 2, and the RF signal input to the mixer 8 is used as the local oscillator signal of the mixing process.

[0025] The optical path is adjusted to receive the laser light to be stabilized emitted from the optical aperture of the electro-optic modulator 2, and transmit the laser light to be stabilized to the mode matching mirror group 6; wherein the optical path includes a front reflector 3 and a rear reflector 4, wherein the front reflector 3 is placed at the rear side of the optical aperture of the electro-optic modulator 2, and the rear reflector 4 is placed at the rear end of the front reflector 3, and the two are used to coordinately adjust the optical path. The reflective surface of the front reflector 3 receives the laser light to be stabilized emitted from the optical aperture of the electro-optic modulator 2, and reflects it to the reflective surface of the rear reflector 4, and the rear reflector 4 reflects the laser light to be stabilized from the front reflector 3 to the mode matching mirror group 6, and the front reflector 3 and the rear reflector 4 cooperate to allow the laser light to be stabilized to be smoothly incident into the ultra-stable cavity 10, and to coincide with the intrinsic light field in the ultra-stable cavity 10.

[0026] The mode matching mirror group 6 is placed at the rear end of the rear reflector 4 to adjust the mode and phase of the laser to be stabilized. The mode matching mirror group 6 adjusts the mode and phase of the laser to be stabilized and then outputs the laser to be stabilized to the ultra-stable cavity 10. The mode matching mirror group 6 adjusts the mode and phase of the laser to be stabilized so that the laser to be stabilized can effectively resonate after entering the ultra-stable cavity 10.

[0027] Reference Figure 2 The mode matching mirror group 6 is composed of n reflectors, which are the first reflector M1, the nth reflector M2, the nth reflector M3, the nth reflector M4, the nth reflector M5, the nth reflector M6, the nth reflector M7, the nth reflector M8, the nth reflector M9, the nth reflector M10, the nth reflector M11, the nth reflector M12, the nth reflector M13, the nth reflect nThe n reflecting mirrors include a plane mirror and a spherical mirror coated with a high-reflection film. By adjusting the curvature radius of the spherical mirror in the mode matching mirror group 6 and the relative positions of the plane mirror and the spherical mirror, the laser to be stabilized incident on the mode matching mirror group 6 can match the position and size of the intrinsic waist spot of the light beam when it is emitted into the ultra-stable cavity 10 after passing through the mode matching mirror group 6. The mode and phase of the laser to be stabilized are adjusted by the mode matching mirror group 6 so that the laser to be stabilized can effectively resonate after entering the ultra-stable cavity 10.

[0028] The ultrastable cavity 10 is placed in a temperature control cover 11 and fixedly connected to an air-floating optical platform, wherein the temperature control cover 11 is used for heat insulation and temperature control. Figure 3 The main material of the ultra-stable cavity 10 is microcrystalline glass. The ultra-stable cavity 10 has a square transmission optical path inside. The laser is reflected in the square transmission optical path by four high-reflectivity mirrors. Two adjacent mirrors of the four mirrors are installed with piezoelectric ceramics outside the cavity. The other two adjacent mirrors are the incident end mirror S1 and the exit end mirror S2. The incident end mirror S1 and the exit end mirror S2 serve as the entrance and exit of external laser injection. The laser to be stabilized after the mode and phase are adjusted by the mode matching mirror group 6 is incident to the incident end mirror S1. The incident end mirror S1 transmits the laser to be stabilized into the ultra-stable cavity 10, and the exit end mirror S2 transmits the laser to be stabilized to the reflection surface of the cavity rear mirror 12. The cavity rear mirror 12 is placed behind the transmission light outlet of the ultra-stable cavity 10. The photodetector 9 is placed behind the cavity rear mirror 12 to convert the light intensity signal into an electrical signal. The post-cavity reflector 12 reflects the laser light to be frequency-stabilized onto the photosensitive surface of the photodetector 9 .

[0029] The laser output from the ultrastable cavity 10 is incident on the photosensitive surface of the photodetector 9. The photodetector 9 is connected to the mixer 8 and the data acquisition card 15 through cables to convert the collected laser signal into an electrical signal. The electrical signal generated by the photodetector 9 includes three parts: a DC term reflecting the strength of the carrier and the sideband, an interference term between the carrier and the sideband, and an interference term between the two sidebands. The interference term between the carrier and the sideband includes the error information between the frequency of the laser to be stabilized and the resonance peak of the ultrastable cavity 10.

[0030] After receiving the RF signal from the signal generator 5 and the electrical signal from the photodetector 9, the mixer 8 mixes the two and outputs the mixed signal to the low-pass filter 13. The mixed signal output by the mixer 8 includes three parts: the amplitude of the interference term between the carrier and the sideband, the one-time frequency term, and the two-time frequency term, wherein the amplitude of the interference term between the carrier and the sideband is used as an error signal. The amplitude of the interference term between the carrier and the sideband is a DC term, and when the laser frequency to be stabilized is consistent with the cavity resonance frequency, the amplitude curve passes through the zero point, and when the two are close but not equal, the amplitude curve is either positive or negative, so it fully meets the frequency discrimination characteristic and can be used as an error signal.

[0031] The low-pass filter 13 is connected to the mixer 8 and the PID regulator 7 through a cable, and performs low-pass filtering on the mixing signal from the mixer 8, filters out irrelevant high-frequency impurities in the mixing signal, and extracts the error signal. The PID regulator 7 is used to convert the error signal into a voltage signal that drives the piezoelectric ceramic. The PID regulator 7 is connected to the piezoelectric ceramic fixedly connected to the rear side of one of the resonant cavity reflectors in the large laser gyroscope 1 to be stabilized through a cable, converts one error signal from the low-pass filter 13 into a voltage signal that drives the piezoelectric ceramic, and transmits it to the piezoelectric ceramic. The piezoelectric ceramic moves synchronously to drive the resonant cavity reflector fixedly connected to the piezoelectric ceramic, thereby realizing precise control of the resonant cavity length inside the large laser gyroscope 1 to be stabilized, thereby maintaining the stability of the output laser frequency of the large laser gyroscope 1 to be stabilized.

[0032] The low-pass filter 13 is connected to the computer 14 through a cable. The computer 14 is used for resonant state observation, data reading, data processing and temperature control driving. The data acquisition card 15 is connected to the computer 14 through the network port / serial port, receives the electrical signals from the photodetector 9 and the temperature sensor on the wall of the temperature control cover 11, and transmits them to the computer 14 in a centralized manner. The computer 14 has a built-in data reading and visualization program and a driver adapted to the temperature regulator on the wall of the temperature control cover 11 to achieve the following purposes: The electrical signal from the photodetector 9 is read out to observe the resonance inside the ultrastable cavity 10. When resonance occurs inside the ultrastable cavity 10, an obvious light intensity transmission peak will be seen on the computer 14. Correspondingly, the transmitted light emitted by the incident end reflector S1 of the ultrastable cavity 10 will be coherently destructed with the primary reflected light of the laser to be stabilized on the incident end reflector S1, which is manifested as a depression in the light intensity signal. receiving the error signal processed by the low-pass filter 13 and displaying its curve; The temperature inside the ultrastable cavity 10 is monitored and adjusted to keep it stable.

[0033] In the above-mentioned large laser gyro frequency stabilization system based on ultra-stable cavity, combined with the characteristics of the large laser gyro single-channel output laser, the device selection should meet the following requirements: the response range of the electro-optic modulator 2, the signal generator 5, and the photodetector 9 to the wavelength of the light field should be consistent with the response range of the large laser gyro 1 to be stabilized and the ultra-stable cavity 10 to the wavelength of the light field. When the large laser gyro 1 to be stabilized is fixed on the air-floating optical platform, the linear polarization direction of its output light beam should be consistent with the polarization direction of the ultra-stable cavity 10. The electro-optic modulator 2 used should have a low-frequency modulation range including DC coupling, and low insertion loss to reduce the further loss of the weak optical signal emitted by the large laser gyro. The mode matching mirror group 6 is composed of a plane mirror and a spherical mirror coated with a high reflection film. The design is based on the Gaussian beam self-reproduction transformation method described in [Zhou Bingkun et al., Laser Principles [M]. 7th edition. Beijing: National Defense Industry Press, 2014: 81-91]. By adjusting the curvature radius of the spherical mirror inside the mode matching mirror group 6 and the relative position of the plane mirror and the spherical mirror, the stabilized light beam emitted by the large laser gyro to be stabilized 1 can match the position and size of the intrinsic waist spot of the light beam when it passes through the electro-optic modulator 2, the front side reflector 3, the rear side reflector 4, and the mode matching mirror group 6 and enters the ultra-stable cavity 10. The frequency range of the output RF signal of the signal generator 5 should cover the minimum driving frequency of the electro-optic modulator 2 and the mixer 8, and have good output signal accuracy and stability. The PID regulator 7 should have a high bandwidth to quickly respond to signal changes; at the same time, the output voltage range should be wide enough to ensure a sufficiently large cavity length tuning range and a sufficiently small cavity length tuning accuracy of the piezoelectric ceramic. The photodetector 9 should have high sensitivity to detect weak signals, and its response bandwidth should be greater than the free spectrum range of the ultrastable cavity 10. The ultrastable cavity 10 should have excellent cavity length stability. It is essentially a small laser gyroscope. The reflectivity of the incident end reflector S1 and the output end reflector S2 should be as large as possible to improve the fineness of the ultrastable cavity 10, but it is necessary to ensure that it matches the cavity length tuning accuracy of the piezoelectric ceramic; in addition, the resonance peak center of the ultrastable cavity 10 should match the frequency of the laser output by the large laser gyroscope 1 to be stabilized. The temperature control cover 11 should have good thermal stability and thermal insulation, the temperature sensor on the wall should respond quickly, and the matching temperature regulator should support multi-channel input and output to ensure the spatial uniformity of the ambient temperature of the ultrastable cavity 10, and the adjustment accuracy should match the ambient temperature change. The passband range of the low-pass filter 13 should cover the frequency range of the error signal output by the mixer 8, and the stopband frequency should be slightly larger than the maximum frequency in the error signal frequency range to filter out unnecessary high-frequency signals as much as possible. The sampling frequency and resolution of the data acquisition card 15 should match the frequency and resolution of the electrical signal from the photoelectric detector 9 and the temperature sensor on the wall of the temperature control cover 11.

[0034] Further, refer to Figure 4, a frequency stabilization method for a laser gyro frequency stabilization system is proposed, comprising the following steps: Step 1: Turn on the excitation power supply of the large laser gyro 1 to be stabilized, so that it lights up and smoothly emits the laser to be stabilized; Step 2: by adjusting the optical path, the laser to be stabilized emitted by the large laser gyro to be stabilized 1 is injected into the ultra-stable cavity 10 and resonates, the adjustment optical path includes a front side reflector 3 and a rear side reflector 4, the reflective surface of the front side reflector 3 receives the laser to be stabilized emitted by the clear aperture of the electro-optic modulator 2, and reflects it to the reflective surface of the rear side reflector 4, and the rear side reflector 4 reflects the laser to be stabilized from the front side reflector 3 to the mode matching mirror group 6; Step 2.1: Adjust the position of the front reflector 3 so that the laser spot to be stabilized emitted from the aperture of the electro-optic modulator 2 falls on the center of the reflective surface of the front reflector 3; Step 2.2: Adjust the position of the rear reflector 4 so that the laser spot to be stabilized reflected by the front reflector 3 falls on the center of the reflective surface of the rear reflector 4; Step 2.3: Adjust the deflection and pitch of the rear reflector 4 so that the laser spot to be stabilized falls on the center of the reflective surface of the first reflector M1 in the mode matching mirror assembly 6; Step 2.4: Adjust the nth reflector M in the pattern matching mirror set 6 n The deflection and pitch of the laser beam to be stabilized are made to fall on the center of the incident end reflector S1 of the ultra-stable cavity 10; Step 2.5: Turn on the excitation power supply of the ultrastable cavity 10, so that it lights up and emits the reference laser smoothly; Step 2.6: Adjust the nth reflector M in the pattern matching mirror set 6 n , so that the laser to be stabilized output by the large laser gyro 1 and the reference laser output by the ultrastable cavity 10 overlap at the first spot observation position P1; Step 2.7: Adjust the first reflector M1 in the mode matching mirror group 6 so that the laser to be stabilized output by the large laser gyro 1 to be stabilized and the reference laser output by the ultrastable cavity 10 (i.e., the square cavity) at the second spot observation position P2 overlap; Step 2.8: Repeat the adjustment according to steps 2.6 and 2.7 until the laser to be stabilized output by the large laser gyro 1 and the reference laser output by the ultrastable cavity 10 overlap at the first spot observation position P1 and the second spot observation position P2, and the laser to be stabilized is successfully injected into the ultrastable cavity 10; Step 2.9: Turn off the excitation power supply of the ultrastable cavity 10, turn on the photodetector 9 and the data acquisition card 15, collect the light intensity signal transmitted from the ultrastable cavity 10 on the computer 14, fine-tune the deflection and pitch of the front reflector 3, the rear reflector 4, and the mode matching mirror group 6, and manually adjust the piezoelectric ceramics to fine-tune the resonant cavity length of the large laser gyroscope 1 to be stabilized, until the brightest transmission light spot is observed on the rear reflector 12 of the cavity, and at the same time, the transmission peak of the transmission light intensity signal in the computer 14 reaches the highest, and at this time, the laser to be stabilized has achieved resonance in the ultrastable cavity 10; Step 3: Collect the error signal: Step 3.1: Turn on the electro-optic modulator 2, the signal generator 5, the mixer 8, and the low-pass filter 13 in sequence, and use the signal generator 5 to generate two frequencies of f 0, are added to the electro-optic modulator 2 and the mixer 8 respectively, and the low-pass frequency of the low-pass filter 13 is set according to the frequency of the radio frequency signal; Step 3.2: The error signal output by the low-pass filter 13 is converted into a voltage signal for driving the piezoelectric ceramic, and the piezoelectric ceramic is used to scan the cavity length of the large-scale laser gyroscope 1 to be stabilized, and the error signal curve input by the low-pass filter 13 is observed on the computer 14; Step 4: Stop scanning the cavity length of the large laser gyro 1 to be stabilized, turn on the PID regulator 7, adjust the P, I, and D parameters of the PID regulator 7, and observe the changes in the error signal and the transmitted light intensity signal on the computer 14. When the transmitted light intensity remains at the maximum value and the error signal disappears, it means that the frequency of the laser to be stabilized has been successfully locked on the resonant frequency of the ultra-stable cavity 10.

[0035] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0036] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention. It should be pointed out that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. Laser gyro frequency stabilization system, characterized in that: include: The large laser gyro to be stabilized (1) outputs the laser to be stabilized; The electro-optic modulator (2) receives the laser to be stabilized, and the signal generator (5) is connected to the electro-optic modulator (2) and the mixer (8) through cables, and outputs two radio frequency signals with the same frequency, one radio frequency signal is used as a working signal to excite the electro-optic modulator (2), and the other radio frequency signal is used as a local oscillator signal in the mixing process of the mixer (8). Under the action of the radio frequency signal, the electro-optic modulator (2) applies two symmetrical sidebands to the frequency of the laser to be stabilized; Adjusting the optical path to transmit the laser light to be stabilized emitted by the electro-optic modulator (2) to the mode matching mirror group (6); The mode matching mirror group (6) adjusts the mode and phase of the laser to be stabilized and then outputs the laser to be stabilized to the ultra-stable cavity (10); The laser output from the ultrastable cavity (10) is incident on the photodetector (9), the photodetector (9) is connected to the mixer (8) and the data acquisition card (15), and the data acquisition card (15) is connected to the computer (14) via the network port / serial port; The mixer (8) is connected to a low-pass filter (13), and a mixing signal from the mixer (8) is low-pass filtered to extract an error signal; the low-pass filter (13) is respectively connected to a PID regulator (7) and a computer (14); the PID regulator (7) is connected to a piezoelectric ceramic fixedly connected to the rear side of one of the resonant cavity reflectors in the large laser gyroscope (1) to be stabilized, and the error signal from the low-pass filter (13) is converted into a voltage signal for driving the piezoelectric ceramic, and transmitted to the piezoelectric ceramic; the piezoelectric ceramic moves synchronously to drive the resonant cavity reflector fixedly connected to the piezoelectric ceramic, thereby achieving precise control of the resonant cavity length inside the large laser gyroscope (1) to be stabilized, thereby maintaining the stability of the output laser frequency of the large laser gyroscope (1) to be stabilized.

2. The laser gyro frequency stabilization system according to claim 1, characterized in that: The large laser gyroscope to be stabilized (1) is placed on an air-floating optical platform to reduce environmental vibrations; the ultra-stable cavity (10) is placed in a temperature-controlled cover (11) and fixedly connected to the air-floating optical platform; a data acquisition card (15) receives electrical signals from a photoelectric detector (9) and from a temperature sensor on the wall of the temperature-controlled cover (11), and transmits the electrical signals to a computer (14).

3. The laser gyro frequency stabilization system according to claim 2, characterized in that: The adjustment optical path comprises a front reflector (3) and a rear reflector (4); the reflective surface of the front reflector (3) receives the laser light to be frequency-stabilized emitted from the light aperture of the electro-optic modulator (2) and reflects it onto the reflective surface of the rear reflector (4); the rear reflector (4) reflects the laser light to be frequency-stabilized from the front reflector (3) to a mode matching mirror group (6); the front reflector (3) and the rear reflector (4) cooperate to enable the laser light to be frequency-stabilized to be smoothly incident into the ultra-stable cavity (10) and to coincide with the intrinsic light field in the ultra-stable cavity (10).

4. The laser gyro frequency stabilization system according to claim 1, 2 or 3, characterized in that: The mode matching mirror group (6) is composed of n reflectors, which are arranged in the order of the first reflector (M1), the nth reflector (M2), the nth reflector (M3), the nth reflector (M4), the nth reflector (M5), the nth reflector (M6), the nth reflector (M7), the nth reflector (M8), the nth reflector (M9), the nth reflector (M11), the nth reflector (M12), the nth reflector n ), the n reflecting mirrors include a plane mirror and a spherical mirror coated with a high reflection film, and by adjusting the curvature radius of the spherical mirror in the mode matching mirror group (6) and the relative positions of the plane mirror and the spherical mirror, the laser to be frequency stabilized incident on the mode matching mirror group (6) can match the position and size of the intrinsic waist spot of the light beam when it is emitted into the ultra-stable cavity (10) after passing through the mode matching mirror group (6), and the mode and phase of the laser to be frequency stabilized are adjusted by the mode matching mirror group (6) so that the laser to be frequency stabilized can effectively resonate after entering the ultra-stable cavity (10).

5. The laser gyro frequency stabilization system according to claim 4, characterized in that: After receiving the radio frequency signal from the signal generator (5) and the electrical signal from the photodetector (9), the mixer (8) mixes the two and outputs the mixed signal to a low-pass filter (13).

6. The laser gyro frequency stabilization system according to claim 5, characterized in that: The main material of the ultra-stable cavity (10) is microcrystalline glass. The ultra-stable cavity (10) has a square transmission light path inside. Four high-reflectivity reflectors are used to realize the reflection of laser in the square transmission light path. Two adjacent reflectors of the four reflectors are installed with piezoelectric ceramics on the outside of the cavity. The other two reflectors are an incident end reflector (S1) and an output end reflector (S2). The incident end reflector (S1) and the output end reflector (S2) serve as an inlet and an output outlet for external laser injection. The laser to be stabilized after the mode and phase are adjusted by the mode matching mirror group (6) is incident on the incident end reflector (S1). The incident end reflector (S1) transmits the laser to be stabilized into the ultra-stable cavity (10). The output end reflector (S2) transmits the laser to be stabilized to the reflection surface of the cavity rear reflector (12). The cavity rear reflector (12) then reflects the laser to be stabilized to the photosensitive surface of the photodetector (9).

7. The laser gyro frequency stabilization system according to claim 6, characterized in that: The electrical signal generated by the photoelectric detector (9) includes three parts: a DC term reflecting the respective strengths of the carrier and the sideband, an interference term between the carrier and the sideband, and an interference term between the two sidebands, wherein the interference term between the carrier and the sideband includes error information between the frequency of the laser to be stabilized and the resonance peak of the ultra-stable cavity (10).

8. The laser gyro frequency stabilization system according to claim 7, characterized in that: The mixing signal output by the mixer (8) includes three parts: the amplitude of the interference term between the carrier and the sideband, the first-time frequency term, and the second-time frequency term, wherein the amplitude of the interference term between the carrier and the sideband is used as an error signal.

9. The laser gyro frequency stabilization system according to claim 8, characterized in that: The computer (14) has a built-in data reading and visualization program and a driver adapted to the temperature regulator on the wall of the temperature control cover (11) to achieve the following purposes: The electrical signal from the photodetector (9) is read out to observe the resonance inside the ultrastable cavity (10). When resonance occurs inside the ultrastable cavity (10), an obvious light intensity transmission peak will be seen on the computer (14). Correspondingly, the transmitted light emitted by the incident end reflector (S1) of the ultrastable cavity (10) will coherently cancel the primary reflected light of the laser to be stabilized on the incident end reflector (S1), which is manifested as a depression in the light intensity signal. receiving the error signal processed by the low-pass filter (13) and displaying its curve; The temperature inside the ultra-stable cavity (10) is monitored and adjusted to keep it stable.

10. The frequency stabilization method of the laser gyro frequency stabilization system as claimed in claim 1, characterized in that: include: Step 1: Turn on the excitation power supply of the large laser gyro (1) to be stabilized, so that it lights up and smoothly emits the laser to be stabilized; Step 2: by adjusting the optical path, the laser to be stabilized emitted from the large laser gyro to be stabilized (1) is injected into the ultra-stable cavity (10) and resonates, the adjustment optical path comprises a front side reflector (3) and a rear side reflector (4), the reflective surface of the front side reflector (3) receives the laser to be stabilized emitted from the clear aperture of the electro-optic modulator (2), and reflects it to the reflective surface of the rear side reflector (4), and the rear side reflector (4) reflects the laser to be stabilized from the front side reflector (3) to the mode matching mirror group (6); Step 2.1: adjusting the position of the front reflector (3) so that the laser spot to be stabilized emitted from the clear aperture of the electro-optic modulator (2) falls on the center of the reflective surface of the front reflector (3); Step 2.2: Adjust the position of the rear reflector (4) so ​​that the laser spot to be stabilized reflected by the front reflector (3) falls on the center of the reflective surface of the rear reflector (4); Step 2.3: Adjust the deflection and pitch of the rear reflector (4) so ​​that the laser spot to be stabilized falls on the center of the reflective surface of the first reflector (M1) in the mode matching mirror assembly (6); Step 2.4: Adjust the nth reflector (M n ) so that the emitted laser spot to be stabilized falls on the center of the incident end reflector (S1) of the ultra-stable cavity (10); Step 2.5: Turn on the excitation power supply of the ultrastable cavity (10) to light it up and emit the reference laser smoothly; Step 2.6: Adjust the nth reflector (M n ), so that the light spots of the laser to be stabilized output by the large laser gyro to be stabilized (1) and the reference laser output by the ultra-stable cavity (10) overlap at the first light spot observation position (P1); Step 2.7: adjusting the first reflector (M1) in the mode matching mirror assembly (6) so that the light spots of the laser to be stabilized outputted by the large laser gyro to be stabilized (1) and the reference laser outputted by the ultrastable cavity (10) at the second light spot observation position (P2) overlap; Step 2.8: Repeat the adjustment according to steps 2.6 and 2.7 until the laser to be stabilized outputted by the large laser gyro to be stabilized (1) and the reference laser outputted by the ultra-stable cavity (10) overlap at the first spot observation position (P1) and the second spot observation position (P2), and at this time, the laser to be stabilized is successfully injected into the ultra-stable cavity (10); Step 2.9: Turn off the excitation power supply of the ultrastable cavity (10), turn on the photodetector (9) and the data acquisition card (15), collect the light intensity signal transmitted from the ultrastable cavity (10) on the computer (14), fine-tune the deflection and pitch of the front side reflector (3), the rear side reflector (4), and the mode matching mirror group (6), and adjust the piezoelectric ceramic to achieve fine-tuning of the resonant cavity length of the large laser gyroscope (1) to be stabilized, until the brightest transmission light spot is observed on the rear reflector (12) of the cavity, and at the same time, the transmission peak of the transmission light intensity signal in the computer (14) reaches the highest, and at this time, the laser to be stabilized has achieved resonance in the ultrastable cavity (10); Step 3: Collect the error signal: Step 3.1: Turn on the electro-optic modulator (2), signal generator (5), mixer (8), and low-pass filter (13) in sequence, and use the signal generator (5) to generate two frequencies of f 0, respectively applied to the electro-optic modulator (2) and the mixer (8), and setting the low-pass frequency of the low-pass filter (13) according to the frequency of the radio frequency signal; Step 3.2: The error signal output by the low-pass filter (13) is converted into a voltage signal for driving the piezoelectric ceramic, and the piezoelectric ceramic is used to scan the cavity length of the large laser gyro (1) to be stabilized, and the error signal curve input by the low-pass filter (13) is observed on a computer (14); Step 4: Stop scanning the cavity length of the large laser gyro (1) to be stabilized, turn on the PID regulator (7), adjust the P, I, and D parameters of the PID regulator (7), and observe the changes in the error signal and the transmitted light intensity signal on the computer (14). When the transmitted light intensity remains at the maximum value and the error signal disappears, it means that the frequency of the laser to be stabilized has been successfully locked on the resonant frequency of the ultra-stable cavity (10).

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