A multi-longitudinal mode selection and stabilization control system for a large optical gyroscope used for time service

Abstract

The present invention discloses a multi-longitudinal mode selection and stabilization control system for a large optical gyroscope for time service, belonging to the technical field of high-precision optical gyroscopes. It includes an annular cavity formed by a prism, a mirror and a partial mirror, and a stable mode servo control loop. The annular cavity is composed of two prisms, a mirror and a partial mirror to form a square symmetric structure. Each prism, mirror and partial mirror is arranged in a metal sealed cabin. A helium-neon gas gain tube is also arranged between the metal sealed cabins of the mirror and the partial mirror. The inside of the helium-neon gas gain tube is filled with helium-neon gas with a mixing ratio of He:Ne = 9:1. The Ne element uses a dual-isotope mixture of Ne<supgt;20< / supgt; and Ne<supgt;27< / supgt>, and the mixing ratio is Ne<supgt;20< / supgt;:Ne<supgt;27< / supgt> = 1:9. External diaphragms are also assembled on the two prisms. The present invention adopts the above multi-longitudinal mode selection and stabilization control system for a large optical gyroscope for time service, and realizes the extreme asymmetric control of the laser intensity tuning curve profile by controlling the gain and loss of the laser.

Description

Technical Field

[0001] The invention relates to the technical field of high-precision optical gyroscopes, in particular to a multi-longitudinal mode selection and stabilization control system for a large optical gyroscope used for timing. Background Art

[0002] The country has a large size and extremely high frequency stability (better than 10 -20 The demand for ring lasers (of the order of magnitude) comes from important fields such as precision timing, aerospace, aircraft navigation, weapon guidance and positioning, and orientation. At present, my country has increasingly higher requirements for the real-time measurement of the universal time UT1 (also known as the unified Greenwich mean solar time).

[0003] After that, the country restarted the independent timing research and development task for UT1. The internationally accepted UT1 measurement scheme is to use a large-size ring laser as a high-precision angular velocity sensor, and write a corresponding solution algorithm to obtain UT1 by sensing the celestial component of the angular velocity of the spherical rotation. Due to the significant extension of the optical cavity length of the large-size ring laser, the number of internal oscillation longitudinal modes has increased sharply. Taking the ring helium-neon laser with an optical cavity length of 4m as an example, the number of internal oscillation longitudinal modes will be close to 20. These longitudinal modes are evenly distributed in the linear shape of the laser gain curve in the form of a "frequency comb". According to the laser principle, with the laser gain center as the boundary, there are 10 longitudinal modes distributed on the left side of the gain center, which act on the left half of the gain with a positive gain slope; there are 10 longitudinal modes distributed on the right side of the gain center, which act on the right half of the gain with a negative gain slope. Under the traditional small jitter frequency stabilization control, the phase difference π of the discrimination signal generated by the longitudinal modes on both sides cancels each other and cannot be directly used for frequency stabilization.

[0004] Related research shows that to be able to accurately measure UT1, a large-size ring laser must have a frequency stability of 10 under long-term continuous operation. -20Magnitude. In addition, in order to achieve precise measurement, this type of laser needs to be in a critical gain state, that is, the cavity loss must be strictly controlled. Therefore, the traditional method of reducing the number of longitudinal mode oscillations by narrowing the linewidth by relying on additional large-loss optical devices such as inserting saturable absorbers is not applicable to the large-scale ring laser for timing. Therefore, the present invention adopts a method of jointly and precisely controlling the laser gain and loss, adjusts the laser intensity tuning curve to an extremely asymmetric state on the left and right, so that the number of longitudinal modes oscillating on the left side of the laser intensity tuning curve is much larger than that on the right side. By using the characteristic that the phase difference between the longitudinal modes oscillating on the left and right remains unchanged and the phase difference value is π, the peak-to-peak value of the frequency discrimination signal can be preset to a fixed value. According to the characteristic that the longitudinal modes slowly move towards the high-frequency end, more longitudinal modes will move into the laser intensity tuning curve, and the synthesized frequency discrimination signal will increase; conversely, the synthesized frequency discrimination signal will decrease. By using the above characteristics, the stable state of the longitudinal mode oscillation can be achieved. In practice, if it is detected that the peak-to-peak value of the frequency discrimination signal is lower than the preset value, the piezoelectric ceramic will push the curved mirror and the curved partial mirror according to the integral of the frequency discrimination signal; if it is detected that the peak-to-peak value of the frequency discrimination signal is higher than the preset value, the piezoelectric ceramic will pull back the curved mirror and the curved partial mirror according to the integral of the frequency discrimination signal. By this method, the selection and stable control of multiple longitudinal modes can be achieved. Summary of the Invention

[0005] The object of the present invention is to provide a multi-longitudinal mode selection and stable control system for a large optical gyroscope for timing, so as to solve the problems existing in the above-mentioned background technology and achieve long-term stable (frequency stabilization) operation of the large optical gyroscope in a critical gain state.

[0006] To achieve the above object, the present invention provides a multi-longitudinal mode selection and stable control system for a large optical gyroscope for timing, including a ring cavity and a stable mode servo control loop formed by prisms, mirrors and partial mirrors. The ring cavity adopts a square symmetric structure composed of two prisms, one mirror and one partial mirror. Each prism, mirror and partial mirror is arranged in a metal sealed cabin. A helium-neon gas gain tube is also arranged between the metal sealed cabins of the mirror and the partial mirror. The inside of the helium-neon gas gain tube is filled with helium-neon gas with a mixing ratio of He:Ne = 9:1. The Ne element adopts Ne 20 and Ne 27 dual-isotope mixed gas, and the isotope Ne 27 needs to be artificially prepared, and the mixing ratio is Ne 20 :Ne 27= 1:9, the inflation pressure is 340 Pa. Through the mixing and inflation of Ne double isotopes, and by combining the conversion between the homogeneous broadening and inhomogeneous broadening mechanisms of the laser helium-neon gain gas, the line shape of the laser light intensity tuning curve is adjusted and controlled to obtain a linear profile that is gentle on the left side (low-frequency side) and drops sharply on the right side (high-frequency side), which is suitable as a reference for frequency stabilization of a large ring laser and provides a new means of frequency stabilization. External diaphragms are also installed on the two prisms.

[0007] Preferably, the optical cavity length of the ring cavity is 4 m, and the single side length is 1 m. According to the correspondence between the optical cavity length of the laser resonator and the frequency interval of adjacent longitudinal modes, it can be known that for a large resonator with an optical cavity length of 4 m, the number of internal oscillating longitudinal modes is about 20. Corresponding to the adjusted light intensity tuning curve, the number of starting longitudinal modes distributed on the left side of the curve extreme value is approximately more than 15, and the number of starting longitudinal modes distributed on the right side of the curve extreme value will be less than 5. Finally, a phenomenon occurs where the number of starting longitudinal modes on the left side of the curve is significantly more than that on the right side. Under the state of the mechanical small jitter driving the mirror and the micro-displacement of the partial mirror, the period of the frequency discrimination signal generated by each of these longitudinal modes is the same, and the phase difference of the frequency discrimination signals generated by the longitudinal modes on the left and right sides is π. The frequency discrimination signals will be synthesized to generate a synthesized frequency discrimination signal with a determined amplitude. Piezoelectric ceramic structures are provided on both the mirror and the partial mirror, and the small jitter of the mirror and the partial mirror controlled by the piezoelectric ceramic structure is used to obtain the frequency discrimination signal required for frequency stabilization.

[0008] Preferably, the prism uses a trapezoidal total reflection prism to achieve weak beam splitting of the oscillating beam. Its large bottom surface is set as a convex spherical surface with a radius of curvature of 8 m, which increases the stability of the ring oscillation optical path, improves the ability to resist environmental temperature changes, and at the same time strengthens the beam splitting effect of the prism, making the part of the optical path between the two prisms have a greater degree of fine beam splitting for oscillating beams of different frequencies, that is, the relatively high-frequency beams move outward and the low-frequency beams move inward. The mirror and the partial mirror use spherical reflection structures and are set as concave spherical surfaces with a radius of curvature of 6 m to cause the oscillating beam in the ring laser to have a micrometer-scale beam splitting distance according to the frequency difference, and the stability of the optical path can be maintained within the environmental temperature range of -10°C to 40°C. The purpose of using the combination design of the prism and the mirror and designing multiple curved surfaces is to achieve micrometer-scale beam splitting of the oscillating beam according to the frequency difference, and at the same time ensure that the resonator is a stable cavity rather than a critical cavity.

[0009] Preferably, the stable-mode servo control loop includes a photoelectric receiver, a frequency-selective amplifier, a phase-sensitive detector, a DC amplifier, an amplitude comparator, a voltage integration circuit, and a rectifier, which are connected in sequence. A small jitter generator is also provided between the phase-sensitive detector and the rectifier. The laser emitted by the ring laser is coupled and output through a partial reflector and incident on the photoelectric receiver. The electrical signal is frequency-selectively amplified by the frequency-selective amplifier, and the 250 Hz frequency discrimination signal with the same frequency as the mechanical small jitter is screened out and amplified. The phase is compared in real time with the signal output by the mechanical small jitter signal source through the phase-sensitive detector to determine whether the frequency discrimination signal is normal (a frequency discrimination signal with exactly the same phase is a normal one). The part of the frequency discrimination signal greater than 0 is filtered and DC amplified, and the signal is sent to the amplitude comparator for amplitude comparison with a preset voltage value. The voltage greater than or less than the preset amplitude is sent to the voltage integration circuit, and a DC voltage is obtained through integration. The piezoelectric ceramic structure arranged behind the spherical reflector and the partial reflector is controlled according to the sign of the DC voltage to perform a push or pull action, changing the optical cavity length of the ring resonator to achieve the stability (frequency stabilization) of the oscillation longitudinal mode state.

[0010] Preferably, the metal seal chamber includes a seal chamber and a seal housing arranged outside the seal chamber. The trapezoidal total reflection prism, the spherical reflector, and the partial reflector are all placed inside the seal chamber. An adjustment bracket is arranged inside the seal chamber. A first cover plate is arranged on the top of the seal chamber, and a transparent observation window is arranged in the center of the cover plate for convenient cavity adjustment. Optical path seal tubes are arranged on both sides of the seal chamber, and the free ends of the optical path seal tubes are connected to the seal housing, and a second cover plate is arranged at the connection.

[0011] Preferably, the seal chamber and the optical path seal tube form a sealed space, and this space needs to be evacuated. The purpose is to isolate heat conduction through the vacuum treatment and control the influence of temperature change on the change of the cavity optical cavity length to the greatest extent, so as to be beneficial to maintaining the stability of the oscillation longitudinal mode frequency.

[0012] Preferably, the external aperture is a patch-type external aperture, which has a fine comb-like structure. Under low-loss conditions, it increases the loss of the high-frequency part of the light beam and the oscillation threshold. The patch-type external aperture is prepared by an optical ultra-smooth surface processing technology. The rear side of the external aperture is set as an optical cement surface, and 6 glass combs are arranged on the front side. The glass combs have a trapezoidal tooth structure, and the gap between the combs is 5 μm. The trapezoidal tooth structure destroys the Brewster angle refraction relationship (the characteristic of light traveling from an optically denser medium to an optically rarer medium), achieving the purpose of increasing the beam oscillation threshold and increasing the loss of the light beam at a specific frequency, thereby coupling out part of the energy of the oscillating light beam in the cavity to the outside of the cavity. The gap between the combs corresponds to the longitudinal mode frequency interval of the ring cavity, so as to better couple out the energy of the oscillating longitudinal mode on the right side of the light intensity tuning curve. This part of the function is realized by observing the amplitude of the frequency discrimination signal in real time during the aperture assembly process. The external aperture assembly needs to keep the amplitude of the frequency discrimination signal at a maximum value in real time. A wedge-shaped gap is also arranged on the front side of the external aperture. The wedge-shaped gap does not affect the Brewster angle refraction effect and does not increase unnecessary loss additionally. The principle of such a design is that there is a light splitting phenomenon for different frequency light components in the light spot at the trapezoidal prism. The width of the wedge-shaped gap exactly corresponds to the splitting distance of the two longitudinal modes, so that the selected and restricted high-frequency longitudinal modes can be restricted from starting oscillation by increasing the loss through precise control of the loss of different frequency light. This design matches the ring cavity design combined with a prism - mirror, which is beneficial for the ring resonator to work with low loss and controlled longitudinal mode state under the critical gain state.

[0013] Preferably, the external aperture is assembled to the inclined surfaces on both sides of the trapezoidal total reflection prism through the optical cement surface. The specific assembly position of the external aperture is controlled by detecting that the change in the threshold voltage of the laser before and after the external aperture assembly is 0.35 V.

[0014] Therefore, the present invention adopts the above-mentioned multi-longitudinal mode selection and stabilization control system for a large optical gyroscope for time service. A 4m-long large closed optical path is formed by combining a prism, a mirror and a partial mirror. By reasonably designing the spherical surfaces of the prism and the mirror, the stability of the optical path is ensured; by utilizing the prism structure, small-range light splitting of the light beam is realized. An external aperture with a unique structure and the assembly position of the external aperture are designed. The Brewster angle refraction process is destroyed through the comb-like structure, so as to perform precise loss control for the high-frequency longitudinal modes that need to be suppressed. By designing parameters such as the gain gas composition, Ne isotope composition, ratio, and inflation pressure, the line profile of the light intensity tuning curve of the laser is controlled to be an extremely skewed line structure. On this basis, small-jitter frequency stabilization of the ring laser is realized. According to setting the frequency discrimination signal to a preset amplitude, multi-longitudinal mode selection and stabilization control of a large optical gyroscope for time service are finally realized.

[0015] The technical solution of the present invention will be further described in detail below with reference to the drawings and embodiments. Description of the Drawings

[0016] Figure 1 Schematic diagram of the optical path structure of the annular cavity in the present invention;

[0017] Figure 2 Schematic diagram of the structure of the metal seal chamber in the present invention;

[0018] Figure 3 Schematic diagram of the annular resonator structure formed by the prism, mirror, partial mirror and all - internal - cavity laser gain tube in the present invention;

[0019] Figure 4 Schematic diagram of the structure of the external diaphragm in the present invention;

[0020] Figure 5 Top - view of the structure of the external diaphragm in the present invention;

[0021] Figure 6 Assembly diagram of the external diaphragm in the present invention;

[0022] Figure 7 Schematic diagram of the stable - mode servo control loop in the present invention;

[0023] Figure 8 Schematic diagram of the frequency - stabilization principle in the present invention; wherein, (a) is the Gaussian - type light - intensity tuning curve of a traditional laser; (b) is the schematic diagram of the frequency - discrimination curve generated when the longitudinal mode is at the center of the gain curve; (c) is the schematic diagram of the frequency - discrimination when the longitudinal mode is on the left side of the gain curve; (d) is the schematic diagram of the frequency - discrimination signal generated when the longitudinal mode is on the right side of the gain curve; (e) is the schematic diagram of the adjusted non - symmetric light - intensity tuning curve; (f) is the synthesized frequency - discrimination signal obtained by synthesizing the frequency - discrimination signals generated by different longitudinal modes;

[0024] Figure 9 Schematic diagram of the light - intensity tuning curve obtained after adjustment in the present invention; wherein, (a) is the schematic diagram of the calculation and simulation curve; (b) is the schematic diagram of the experimental measured curve;

[0025] Reference numerals

[0026] 1. Trapezoidal total - reflection prism; 2. Spherical mirror; 3. Partial mirror; 4. Total - reflection angle; 5. Brewster angle; 6. Piezo - ceramic structure; 7. Seal chamber; 8. Observation window; 9. First cover plate; 10. Optical - path seal tube; 11. Seal housing; 12. Second cover plate; 13. All - internal - cavity laser gain tube; 14. External diaphragm; 15. Optical cement area; 16. Trapezoidal comb teeth; 17. Wedge - shaped gap; 18. Photo - electric receiver; 19. Frequency - selection amplifier; 20. Phase - sensitive detector; 21. DC amplifier; 22. Amplitude comparator; 23. Voltage integration circuit; 24. Rectifier; 25. Small jitter generator. Detailed implementation manners

[0027] Embodiment

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Components of the embodiments of the present invention usually described and illustrated in the accompanying drawings here can be arranged and designed in various different configurations.

[0029] As Figure 1 shown, a multi-longitudinal mode selection and stabilization control system for a large optical gyroscope for timekeeping includes an annular optical path formed by a trapezoidal total reflection prism 1, a spherical mirror 2, and a partial mirror 3. The optical path is refracted and incident on the trapezoidal total reflection prism 1 at the Brewster angle 5, undergoes total reflection on the large bottom surface of the trapezoidal total reflection prism 1, and then is refracted out of the trapezoidal total reflection prism 1 from the side surface of the trapezoidal total reflection prism 1 at the Brewster angle 5 to achieve a 90-degree rotation of the light beam. The purpose of such a design is to make there be 4 Brewster windows in the annular cavity of the two trapezoidal total reflection prisms 1, ensuring the linearly polarized state of the oscillating light beam in the cavity; and reflecting the light beam at the total reflection angle 4, ensuring that the resonant cavity operates with low loss.

[0030] The trapezoidal total reflection prism 1, the spherical mirror 2, and the partial mirror 3 are all placed in a metal sealed chamber, as Figure 2 shown. The trapezoidal total reflection prism 1, the spherical mirror 2, or the partial mirror 3 is placed in the sealed chamber 7, and there is a prism or mirror adjustment bracket inside the sealed chamber 7 for clamping and cavity adjustment. A first cover plate 9 is provided at the top of the sealed chamber 7, and a transparent observation window 8 is provided in the center of the first cover plate 9 for observing the clamping state of the trapezoidal total reflection prism 1 or the spherical mirror 2 and the partial mirror 3. Optical path sealed tubes 10 are provided on both sides of the sealed chamber 7, and a second cover plate 12 made of fused quartz is installed on one side of the optical path sealed tubes 10 close to the sealed outer shell 11. In this way, the sealed chamber 7 and the optical path sealed tubes 10 on both sides of the sealed chamber 7 form a sealed space, and this space needs to be evacuated to avoid the influence of external environmental temperature changes on the refractive indices of the spherical mirror 2 and the trapezoidal total reflection prism 1, the spherical mirror 2 and the partial mirror 3. The trapezoidal total reflection prism 1, the spherical mirror 2, the partial mirror 3, and a full-inner cavity laser gain tube 13 filled with helium-neon gain gas form a self-excited oscillation laser tube, as Figure 3 shown.

[0031] On this basis, it is necessary to control the line profile of the light intensity tuning curve output by the laser to meet the need for stabilizing the multi-longitudinal mode operating mode. For this purpose, a patch-type external aperture 14 is designed, as Figures 4-6 shown. Figure 4It is a schematic three-dimensional structure diagram of the patch external aperture 14. The external aperture 14 includes a photo-resist area 15, which requires processing according to a super-smooth surface, and the photo-resist is assembled on the inclined surface of the trapezoidal total reflection prism 1. At the front end of the external aperture 14, there are trapezoidal comb teeth 16 and a wedge-shaped gap 17. The trapezoidal comb teeth 16 achieve the loss control of specific longitudinal modes by destroying the refraction condition of the Brewster angle 5, thereby restricting the oscillation of some longitudinal modes. The assembly position of the external aperture 14 is as Figure 6 shown. By observing the change in the threshold voltage of the laser before and after the assembly of the external aperture 14, the rationality of the assembly position is measured, and the change in the threshold voltage is required to be 0.35 V.

[0032] Furthermore, the gas in the laser helium-neon gain tube is controlled to control the linear profile of the laser light intensity tuning curve. The gas mixing ratio of helium and neon is He:Ne = 9:1, and the Ne element adopts a dual-isotope gas mixture of Ne 20 and Ne 27 , and the gas mixing ratio is Ne 20 :Ne 27 = 1:9, and the inflation pressure is 340 Pa. By means of Ne dual-isotope gas mixing and inflation, combined with the conversion between the homogeneous broadening and inhomogeneous broadening mechanisms of the laser helium-neon gain gas, the linear type of the laser light intensity tuning curve is adjusted and controlled to obtain a linear profile that is gentle on the left side (low-frequency side) and drops sharply on the right side (high-frequency side).

[0033]

[0034] The above formula is the linear calculation formula of the light intensity tuning curve. Among them: the gain medium is a mixed gas of Ne 20 、Ne 27 、He 4 , F is the proportion of Ne 20 in the isotope, η is the ratio of homogeneous broadening to inhomogeneous broadening, ξ is the frequency parameter, The subscripts "1" and "2" respectively represent the clockwise and counterclockwise directions of the light beam transmitted in the ring cavity, ω is the angular frequency of the counter-propagating wave pair in the ring resonator, ω0 is the central angular frequency of the spectral line type generated by the transition, and ku is the half-width of the inhomogeneous broadening; Z i (ξ,η) is the imaginary part of the plasma dispersion function, b j = Z i (ξ j ,η)-ηZ r ′(ξ j ,η), Z r ′(ξ j ,η) is the first derivative of the real part of the plasma dispersion function. Z i(0, η) is for Ne in Ne isotopes 20 , which is the value of the imaginary part of the plasma dispersion function varying with η when the frequency parameter ξ is 0; is for Ne in Ne isotopes 27 , which is the value of the imaginary part of the plasma dispersion function varying with η when the frequency parameter ξ is 0; L(ξ 12 , η) is a Lorentzian function, L(ξ 12 , η) = η 2 / (η 2 + ξ 2 ), G0 is the peak gain of the Ne 20 mono-isotope, γ is the one-way loss, defined as: γ = G m / k0, where k0 is the locking ratio; G m is the peak gain of the double isotope. According to this formula for simulation, the simulation results of the light intensity tuning curve can be obtained as shown in Figure 9 (a). Based on this theory, experiments are carried out to obtain the measured light intensity tuning curve of the laser, as shown in Figure 9 (b).

[0035] By combining the gain control with the control of the helium-neon gain gas parameters and the loss control with the mode-limiting control of the external aperture 14, an extremely asymmetric light intensity tuning curve type suitable for multi-longitudinal mode frequency stabilization control can be obtained. On this basis, a servo control loop for stabilizing the mode state of a large ring laser is designed, and its control process block diagram is as shown in Figure 7 . The light emitted by the ring laser is coupled and output through the partial mirror 3, incident on the photoelectric receiver 18. The electrical signal is frequency-selected and amplified by the frequency-selective amplifier 19, and the electrical signal with a frequency of 250 Hz (the same frequency as the jitter signal adopted by the mechanical small jitter generator 25) is selected as the frequency discrimination signal. The phase of the frequency discrimination signal is compared with the signal output by the mechanical small jitter signal source in real time through the phase-sensitive detector 20 to determine whether the frequency discrimination signal is normal (the phase being exactly the same is a normal frequency discrimination signal). The part of the frequency discrimination signal greater than 0 is filtered and then DC-amplified by the DC amplifier 21. The signal is sent to the amplitude comparator 22 and compared with the preset voltage value in terms of amplitude. The voltage greater than or less than the preset amplitude is sent to the voltage integration circuit 23. After integration to obtain a DC voltage, it passes through the rectifier 24, and the piezoelectric ceramic structure 6 set behind the spherical mirror 2 and the partial mirror 3 is controlled according to the sign of the DC voltage to perform a push or pull action, changing the optical cavity length of the ring resonator to achieve the stability (frequency stabilization) of the oscillation longitudinal mode state. Its schematic diagram of the stable longitudinal mode state (frequency) is as shown in Figure 8 . Figure 8 (a) is the traditional Gaussian-type light intensity tuning curve type. Under the action of a small sine jitter, different longitudinal modes generate frequency discrimination curves; Figure 8(b) Under the control of the traditional Gaussian line shape, when the longitudinal mode is located at the center of the gain curve, the frequency of the frequency discrimination curve generated is twice the frequency of the small jitter signal; Figure 8 (c) Under the control of the traditional Gaussian line shape, when the longitudinal mode is located on the left side of the gain curve, the generated frequency discrimination signal; Figure 8 (d) Under the control of the traditional Gaussian line shape, when the longitudinal mode is located on the right side of the gain curve, the generated frequency discrimination signal; Figure 8 (e) The adjusted asymmetric light intensity tuning curve line shape, and the frequency discrimination curves generated by different longitudinal modes under the action of sinusoidal small jitter; Figure 8 (f) The synthesis of the frequency discrimination signals generated by different longitudinal modes, and the obtained synthesized frequency discrimination signal: having a definite amplitude. According to Figure 8 the analysis in, for the extremely asymmetric light intensity tuning curve line shape obtained after adjustment, most of the longitudinal modes are distributed on the left side of the extreme value of the light intensity tuning curve. The frequency discrimination signals have the same frequency and the same phase, and the amplitudes are superimposed and enhanced. Only individual longitudinal modes are affected by the external aperture 14 and have difficulty in starting oscillation. Even if these longitudinal modes start oscillation, the phase difference between the obtained frequency discrimination signal and the small jitter signal generated by the small jitter generator 25 is constantly π, which will affect the amplitude of the synthesized frequency discrimination signal, but does not affect the specificity of the synthesized frequency discrimination signal. Therefore, the technical solution for stabilizing the longitudinal mode state (frequency) is feasible.

[0036] Therefore, the present invention adopts the above-mentioned large optical gyroscope multi-longitudinal mode selection and stabilization control system for timing, and adopts a structural method combining a prism, a mirror and a partial mirror to form a quadrilateral large resonant cavity with a cavity length of 4m. In terms of laser gain, helium-neon gas adopts neon double isotopes. In terms of laser loss, the oscillation beam is split by the structure combining the prism and the mirror, and the high-frequency light is screened and coupled out by using the comb-shaped external aperture. By controlling the laser gain and loss, the extreme asymmetric control of the laser light intensity tuning curve profile is realized. On this basis, for the working longitudinal modes oscillating on the left and right sides of the light intensity tuning curve, under the action of the small jitter of the mirror, the generated frequency discrimination signals have the same frequency and a constant phase difference. Therefore, the synthesized frequency discrimination signal has specificity and can be locked at a definite amplitude. According to the increasing or decreasing trend of the frequency discrimination signal, the stable (frequency stabilization) control of the multi-longitudinal mode simultaneous oscillation working state of the large ring laser can be realized.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A multi-longitudinal mode selection and stabilization control system for a large optical gyroscope for timing, characterized in that: The invention comprises an annular cavity formed by a prism, a reflector and a partial reflector and a steady-mode servo control loop. The annular cavity adopts two prisms, a reflector and a partial reflector to form a square symmetrical structure. Each prism, reflector and partial reflector are arranged in a metal sealed cabin. A helium-neon gas gain tube is also arranged between the metal sealed cabins of the reflector and the partial reflector. The interior of the helium-neon gas gain tube is filled with helium-neon gas with a mixed gas ratio of He:Ne=9:

1. The Ne element adopts Ne 20 and Ne 27 Double isotope gas mixture, the mixing ratio is Ne 20 :Ne 27 =1:9, the inflation pressure is 340Pa, and the two prisms are also equipped with external apertures; The outer aperture is a patch-type outer aperture with a fine comb-tooth structure. The rear side of the outer aperture is set as a light plastic surface, and the front side is set with 6 glass combs. The glass combs are trapezoidal comb teeth with a gap of 5μm between combs. The stable mode servo control loop includes a photoelectric receiver, a frequency-selective amplifier, a phase-sensitive detector, a DC amplifier, an amplitude comparator, a voltage integration circuit and a rectifier which are connected in sequence, and a small jitter generator is also arranged between the phase-sensitive detector and the rectifier; The optical cavity length of the annular cavity is 4m, the single side length is 1m, and piezoelectric ceramic structures are arranged on the reflector and the partial reflector.

2. The multi-longitudinal mode selection and stabilization control system for large optical gyroscope for timing according to claim 1, characterized in that: The prism adopts a trapezoidal total reflection prism, and its large bottom surface is set as an outer convex spherical surface with a curvature radius of 8m. The reflector and partial reflector both adopt a spherical structure and are set as an inner concave spherical surface with a curvature radius of 6m.

3. The multi-longitudinal mode selection and stabilization control system for large optical gyroscope for timing according to claim 2, characterized in that: The metal sealed cabin comprises a sealed cabin and a sealed shell arranged outside the sealed cabin, a trapezoidal total reflection prism, a spherical reflector and a spherical partial reflector are placed inside the sealed cabin, an adjustment bracket is arranged inside the sealed cabin, a first cover plate is arranged on the top of the sealed cabin, a transparent observation window is arranged in the center of the cover plate, light path sealing tubes are arranged on both sides of the sealed cabin, the free ends of the light path sealing tubes are connected to the sealed shell, and a second cover plate is arranged at the connection.

4. The multi-longitudinal mode selection and stabilization control system for large optical gyroscope for timing according to claim 3, characterized in that: The sealed cabin and the light path sealed tube form a closed space, and the space is in a vacuum environment.

5. The multi-longitudinal mode selection and stabilization control system for large optical gyroscope for timing according to claim 1, characterized in that: The outer aperture is assembled onto the inclined surfaces on both sides of the trapezoidal total reflection prism through the optical adhesive surface.

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