Prism transverse double longitudinal mode four-frequency operation laser gyro

Abstract

The application discloses a prism reflection type double longitudinal mode four-frequency working laser gyroscope, and belongs to the technical field of high-precision optical inertial navigation gyroscopes. The prism reflection type double longitudinal mode four-frequency working laser gyroscope comprises two full reflection prisms with a 90-degree light beam rotation angle and two spherical mirrors which jointly form a closed ring-shaped light path. The small right-angle surface of the full reflection prism is provided with an outer convex spherical surface with a curvature radius of 8 meters, and the mirror is provided with an inner concave spherical surface with a curvature radius of 6 meters, so that the oscillation light beam in the ring laser generates a micrometer-level light splitting distance according to the difference of the frequency in the range of about 650MHz, and the stability of the light path is maintained in the environment temperature of-40 DEG C to 60 DEG C. The prism reflection type double longitudinal mode four-frequency working laser gyroscope adopts the above structure, adopts a radio frequency low-voltage mode to excite a He-Ne gain medium, reduces the thermal effect in the working process of the laser, and maintains the stability of the linear profile of the light intensity harmonic curve.

Description

Technical Field

[0001] This invention relates to the field of high-precision optical inertial navigation gyroscope technology, and in particular to a prism-reflecting dual longitudinal mode four-frequency laser gyroscope. Background Technology

[0002] The dual-longitudinal-mode four-frequency laser gyroscope relies on the nonlinear frequency coupling effect between two pairs of four frequencies propagating in clockwise and counterclockwise directions caused by the splitting of the two longitudinal modes oscillating inside the ring resonant cavity under the action of rotation. This allows for the detection of the celestial component of the Earth's rotational angular velocity without frequency bias, achieving a self-biased state and enabling real-time measurement of the inertial body's angular velocity. Because it does not require additional biasing technology, the self-biased laser gyroscope does not need additional moving parts, has no additional insertion loss components, and requires no additional magnetic field (unlike Zeeman biased and four-frequency differential laser gyroscopes). Therefore, the working stability and theoretical accuracy of this gyroscope are superior to those of traditional laser gyroscopes currently used in engineering applications.

[0003] Further research has shown that for a self-polarized laser gyroscope to be applied in engineering and to achieve stable dual-longitudinal-mode self-polarized laser gyroscope output, the key mechanism is the accurate determination of the asymmetric frequency position of the dual-longitudinal-mode in the same polarization state of the ring laser, and the key technology is the precise frequency stabilization control technology of the dual-longitudinal-mode oscillating ring laser under asymmetric frequency conditions.

[0004] The old technique for precise frequency stabilization control of dual-longitudinal-mode oscillating ring lasers under asymmetric frequency conditions employs a sealed heater to control the refractive index of a section of air within the capillary tube of the ring cavity, thereby achieving servo control of the longitudinal mode state. However, the heat conduction process exhibits a relaxation effect, resulting in persistent hysteresis and overshoot in the thermal control process. Furthermore, self-polarizing gyroscopes require at least one prism to form the cavity. The nonlinear coupling effect between the four frequencies of the dual-longitudinal-mode oscillation within the ring cavity generates within the prism. It has been proven that the frequency repulsion effect of the weak modes provides a stable bias term for the gyroscope, and is the primary cause of the gyroscope's self-polarization phenomenon. Moreover, the gyroscope's self-polarization state relies on the adjusted intensity tuning curve profile for frequency stabilization. Traditional high-voltage excitation methods lead to severe self-heating effects in gas lasers, with increased gain gas temperature causing gas pressure changes, thus affecting the stability of the laser's output intensity tuning curve profile. Summary of the Invention

[0005] The purpose of this invention is to provide a prism-reversed dual-longitudinal-mode four-frequency laser gyroscope, which enables the dual-longitudinal-mode four-frequency laser gyroscope to operate in a stable state under self-biased frequency conditions.

[0006] To achieve the above objectives, this invention provides a prism-reflecting dual-longitudinal-mode four-frequency laser gyroscope, comprising a ring resonant cavity and an external aperture. Total internal reflection prisms are disposed at the lower two corners of the ring resonant cavity, and reflectors are disposed at the upper two corners. Piezoelectric ceramic telescopic structures are disposed on the reflectors, controlling the forward and backward extension of the reflectors to achieve dual-longitudinal-mode frequency discrimination and frequency stabilization servo control of the laser. A gain gas storage chamber is disposed inside the ring resonant cavity, and a getter support frame is disposed within the gain gas storage chamber. The ring resonant cavity is surrounded by... The gain gas storage chamber is provided with a capillary cavity. The lower quarter of the capillary cavity is sealed between the total reflection prism and communicates with the gain gas storage chamber. Electrode grooves are etched on both the upper and lower sides of the lower quarter of the capillary cavity. A laser pump upper electrode plate and a laser pump lower electrode plate are respectively arranged in the electrode grooves. The laser pump upper electrode plate and the laser pump lower electrode plate are connected to a high-frequency oscillator through wires to realize low-voltage radio frequency pumping excitation of the He-Ne gas laser. A protective cover is provided on the outside of the total reflection prism to keep the total reflection prism part dry and avoid moisture and contamination.

[0007] Preferably, the total internal reflection prism and the reflector together form a closed ring optical path with an optical cavity length of 0.47m. According to the frequency interval formula of adjacent longitudinal modes of a ring laser, this cavity length is suitable for generating a dual longitudinal mode asymmetric oscillation state, which meets the requirements for generating the self-biased frequency state of the gyroscope. In addition, the dual longitudinal modes generated by this cavity length correspond exactly to the function profile of the laser gain line shape. The laser is in a critical gain state, which is conducive to the low-loss operation of the gyroscope.

[0008] Preferably, the small right-angled surface of the total reflection prism is set as an outwardly convex spherical surface with a radius of curvature of 8 meters, and the reflector is set as an inwardly concave spherical surface with a radius of curvature of 6 meters, so as to generate a micrometer-level beam splitting distance in the ring laser with a frequency range of about 650MHz, and to maintain the stability of the optical path in an ambient temperature range of -40℃ to 60℃.

[0009] Preferably, the movement of the closed annular optical path on one side of the reflector is less than the movement of the optical path on one side of the total internal reflection prism, and the outer aperture is mounted on the side with the smaller movement.

[0010] Preferably, the outer aperture has a square pyramidal structure, and wedge-shaped gaps are symmetrically distributed on both sides of the outer aperture.

[0011] Preferably, the bottom surface of the outer aperture, except for the wedge-shaped gap, is set as a glossy surface and processed according to the requirements of an ultra-smooth surface.

[0012] Therefore, this invention employs a prism-reflector dual-longitudinal-mode four-frequency laser gyroscope with the aforementioned structure. It utilizes a closed-loop optical path structure combining a total internal reflection prism and a reflector. Taking advantage of the near-zero backscattering characteristic of the prism, the latch-up threshold of the laser gyroscope is reduced. The nonlinear optical coupling effect within the total internal reflection prism generates a self-polarized frequency state. Based on the evanescent wave principle, a unique external aperture structure, assembly position (the position where the beam movement with temperature change is minimal, with the central axis of the external aperture perpendicular to the meridional plane during assembly), and assembly method (verifying the assembly result by the change in the laser threshold voltage before and after aperture assembly) are designed. This achieves precise control of cavity loss based on the frequency difference within a 650MHz range of the oscillating beam, thereby further refining the contour of the light intensity tuning curve to meet the requirements for stable operation of the gyroscope in a self-polarized frequency state. Two total internal reflection prisms enclose the He-Ne gain gas, thus creating conditions for the application of radio frequency excitation technology; through the set reflectors, piezoelectric ceramic controlled reflectors can be used to achieve dual longitudinal mode frequency stabilization servo control, avoiding the drawbacks of traditional thermal frequency stabilization, and enabling the gyroscope to work stably in the self-biased frequency state for a long time.

[0013] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the total internal reflection prism structure of an embodiment of the prism-type dual longitudinal mode four-frequency working laser gyroscope of the present invention; (a) is a cross-sectional view of the total internal reflection prism; (b) is an overall view of the total internal reflection prism.

[0015] Figure 2 (a) is a schematic diagram of the optical path stability analysis of an embodiment of the prism-reflecting dual-longitudinal-mode four-frequency laser gyroscope of the present invention; (b) is a schematic diagram of the changes in the optical path structure at high temperature;

[0016] Figure 3 This is a schematic diagram of the structure of the present invention;

[0017] Figure 4 This is a schematic diagram of the outer aperture structure in this invention;

[0018] Figure 5 This is a schematic diagram of the external aperture loss control in this invention;

[0019] Figure 6 This is the light intensity tuning curve obtained by adjusting the Ne isotope mixing ratio of the gain medium in this invention;

[0020] Figure 7 This is the measured result of the light intensity harmonic curve obtained by continuing to assemble the external aperture in this invention;

[0021] Figure 8This is a schematic diagram illustrating the stable (frequency) working principle of the light intensity tuning curve based on contour control in this invention under self-biased frequency state.

[0022] Reference numerals in the attached figures: 1. Ring resonant cavity; 2. Total internal reflection prism; 3. Reflector; 4. Piezoelectric ceramic telescopic structure; 5. Gain gas storage chamber; 6. Capillary cavity; 7. Brewster angle refraction; 8. Protective cover; 9. Getter support frame; 10. Laser pump upper electrode plate; 11. Laser pump lower electrode plate; 12. High-frequency oscillator; 13. External aperture; 14. Wedge gap; 15. Bottom surface of external aperture; 16. Reflected spot. Detailed Implementation

[0023] Example

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0025] like Figure 1 and 3As shown, a prism-reflecting dual-longitudinal-mode four-frequency laser gyroscope includes a ring resonant cavity 1 and an external aperture 13. The ring resonant cavity, made of low-expansion-coefficient microcrystalline glass, serves as the support for the gyroscope's optical structure. Total internal reflection prisms 2 are positioned at the lower two corners of the ring resonant cavity 1 to form a ring optical path. Through optical adhesive and indium-sealed He-Ne gain gas, the beam is refracted at Brewster's angle 7 and exits through the total internal reflection prisms 2, maximizing the linear polarization of the oscillating beam within the ring resonant cavity 1. Reflectors 3 are positioned at the upper two corners of the ring resonant cavity 1, each with a piezoelectric ceramic telescopic structure 4. The piezoelectric ceramic telescopic structure 4 controls the forward and backward extension of the reflectors 3, achieving dual-longitudinal-mode frequency discrimination and frequency stabilization servo control of the laser. A gain gas storage chamber 5 is located inside the ring resonant cavity 1. The gain gas storage chamber 5 is equipped with a getter support frame 9 and a getter to adsorb stray gas particles released during the ionization of the gain medium of the gas laser. A capillary cavity 6 is arranged around the gain gas storage chamber 5 on the ring resonant cavity 1. The lower quarter of the capillary cavity 6 is sealed between the total reflection prisms 2 and is connected to the gain gas storage chamber 5 to form a sealed gas storage space. Electrode grooves are etched on the upper and lower parts of the lower quarter of the capillary cavity 6. The upper laser pump electrode plate 10 and the lower laser pump electrode plate 11 are respectively arranged in the electrode grooves. The upper laser pump electrode plate 10 and the lower laser pump electrode plate 11 are connected to a high-frequency oscillator 12 through wires to realize low-voltage radio frequency pumping excitation of the He-Ne gas laser. A protective cover 8 is arranged on the outside of the total reflection prism 2 to keep the total reflection prism 2 part dry and avoid moisture and contamination.

[0026] The total reflection prism 2 and the reflector 3 together form a closed ring optical path with an optical cavity length of 0.47m. According to the frequency interval formula of adjacent longitudinal modes of the ring laser, this cavity length is suitable for generating a dual longitudinal mode asymmetric oscillation state, which meets the requirements for generating the self-biased frequency state of the gyroscope. In addition, the dual longitudinal modes generated by this cavity length correspond exactly to the function profile of the laser gain line shape. The laser is in the critical gain state, which is conducive to the low-loss operation of the gyroscope.

[0027] To achieve micrometer-level beam splitting distances at approximately 650MHz intervals within the ring laser's oscillating beam, and to maintain optical path stability within an ambient temperature range of -40℃ to 60℃, the small right-angled facet of the total internal reflection prism 2 is configured as a convex spherical surface with a radius of curvature of 8 meters, while the reflector 3 is configured as a concave spherical surface with a radius of curvature of 6 meters. Under high and low temperature environments, the optical path changes as follows: Figure 2 As shown, the high-temperature optical path structure changes as follows: Figure 2 As shown in (a), the solid line represents the optical path at 25℃ (normal temperature), and the dashed line represents the optical path at 60℃ (high temperature); the structural changes of the low-temperature optical path are as follows. Figure 2 As shown in (b) in the figure, the solid line represents the optical path at 25℃ and the dashed line represents the optical path at -40℃.

[0028] The amount of movement of the optical path on the side of the reflector 3 is less than the amount of movement of the optical path on the side of the total internal reflection prism 2. The outer aperture 13 is mounted on the side with smaller movement and is a patch aperture, such as... Figure 4 As shown, the outer aperture 13 has a square pyramidal structure, and wedge-shaped gaps 14 are symmetrically distributed on both sides of the outer aperture 13. The gap thickness is calculated and determined according to the evanescent wave principle and the specific requirements of coupling energy. Currently, the wedge angle used in the prism-type self-biased frequency gyroscope is 2. 〃 The wedge width is 5mm, and the coupling output of light energy at different frequencies is controlled according to the thickness of the wedge gap 14. The bottom surface 15 of the outer aperture, except for the wedge gap 14, is set as a photoresist surface and processed according to ultra-smooth surface requirements, i.e.: the surface profile N = -0.5 in the photoresist area, and the local surface profile ΔN = 0.1; the surface roughness Ra of the fused silica photoresist area is less than... Defect level: Level 2 in glossy adhesive area, Level 0 in light-transmitting area, with no bidirectional through scratches in glossy adhesive area.

[0029] When the external aperture 13 is working, it is optically bonded to the two large inclined surfaces of the total internal reflection prism. The specific bonding position is determined by the change in the laser threshold voltage before and after bonding the external aperture 13 (for example, for a prism-type self-polarizing gyroscope, the threshold voltage change is required to be 0.75V). Figure 4 For example, according to the prism-reflection ring optical path design, the reflected light spot 16 is elliptical, with the center of its major axis corresponding to the output center frequency of the He-Ne laser. The two sides are the directions of decreasing and increasing light frequency, respectively. The outer aperture 13, with its loss-limiting working edge, partially blocks the reflected light spot 16 on the surface of the total internal reflection prism 2. The side view of the blockage is shown below. Figure 5 As shown, the area within the dashed circle represents the working edge of the outer aperture 13. Figure 5 Taking a clockwise rotating beam as an example, the light energy in the upper half of the beam's center line will pass through the wedge-shaped gap 14 layers, with some energy being coupled out of the cavity. Among these, the energy near the center frequency experiences the most coupling due to the fused silica optical adhesive; the energy at the high and low frequency ends couples relatively less. The specific amount of coupled energy is determined by the thickness and assembly depth of the wedge-shaped gap 14. The lower half of the beam's center line does not pass through the optical adhesive region and the wedge-shaped gap 14, so its energy is not coupled outward and continues to maintain laser resonant cavity oscillation within the cavity.

[0030] In summary, with the help of the external aperture 13, the He-Ne ring laser can achieve a controllable state of high loss at the center frequency and low loss at the low and high frequency ends on both sides of the center frequency.

[0031] With the aforementioned external aperture 13, the He-Ne laser employs Ne dual isotope gas filling, and Ne... 20 and Ne 24 When isotopes are mixed in a 7:3 ratio, the following can be obtained: Figure 6The light intensity harmonic curve shown initially exhibits a bimodal structure, but the dip between the two peaks is not significant and further adjustments are needed. By continuing to assemble the external aperture 13, a result similar to... Figure 7 The intensity tuning curve shown has a peak-to-peak ratio of 1.4:1, with a significant dip in the middle of the two peaks. The slopes on either side of each peak have opposite signs, which can serve as a reference for low-jitter frequency stabilization, thereby achieving frequency stabilization at the asymmetric frequency position of the dual longitudinal modes. This enables steady-state operation of the laser gyroscope under self-biased frequency conditions. Figure 8 As shown.

[0032] Therefore, the present invention adopts the above-mentioned structure of a prism-type dual longitudinal mode four-frequency laser gyroscope, which uses radio frequency excitation to stabilize the frequency. Through optimized design of the radio frequency pump, the excitation voltage is reduced to about 5V, which greatly reduces the heat generation of the gain gas section and maintains the stability of the dual longitudinal mode self-biased frequency state.

[0033] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A prism-reversing dual-longitudinal-mode four-frequency laser gyroscope, characterized in that: The device includes a ring resonant cavity and an external aperture. A total internal reflection prism is positioned at each of the two lower corners of the ring resonant cavity, and a reflector is positioned at each of the two upper corners. Each reflector has a piezoelectric ceramic telescopic structure. An gain gas storage chamber is located inside the ring resonant cavity, and a getter support frame is positioned within the gain gas storage chamber. A capillary cavity is positioned around the gain gas storage chamber on the ring resonant cavity. The lower quarter of the capillary cavity is sealed between the total internal reflection prisms and communicates with the gain gas storage chamber. Electrode grooves are etched at the top and bottom of the lower quarter of the capillary cavity, and a laser pump upper electrode plate and a laser pump lower electrode plate are respectively positioned within the electrode grooves. The upper and lower laser pump electrode plates are connected to a high-frequency oscillator via wires. A protective cover is positioned on the outside of the total internal reflection prisms. The small right-angled facet of the total internal reflection prism is set as an outwardly convex spherical surface with a radius of curvature of 8 meters, and the reflector is set as an inwardly concave spherical surface with a radius of curvature of 6 meters. The outer aperture has a square pyramidal structure, and wedge-shaped gaps are symmetrically distributed on both sides of the outer aperture; The bottom surface of the outer aperture is configured as a glossy surface, except for the wedge-shaped gap.

2. The prism-reversing dual-longitudinal-mode four-frequency laser gyroscope according to claim 1, characterized in that: The total internal reflection prism and the reflector together form a closed annular optical path with an optical cavity length of 0.47m.

3. The prism-reversing dual-longitudinal-mode four-frequency laser gyroscope according to claim 2, characterized in that: The amount of movement of the closed annular optical path on one side of the reflector is less than the amount of movement of the optical path on one side of the total internal reflection prism, and the outer aperture is mounted on the side with the smaller amount of movement.

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