CN113916211B - Passive laser gyroscope based on critical coupling annular cavity - Google Patents

Abstract

The invention discloses a passive laser gyroscope based on a critical coupling annular cavity, which is characterized by comprising a laser system, a critical coupling annular cavity and a signal acquisition system, wherein the laser system is used for injecting first laser and second laser into the critical coupling annular cavity; the critical coupling annular cavity is used for receiving the first laser and the second laser, enabling the carrier resonant with the critical coupling annular cavity to completely enter the cavity and enabling the sideband to be reflected outside the cavity; the signal acquisition system is used for acquiring the first laser and the second laser which pass through the critical coupling ring cavity. The carrier wave resonating with the critical coupling ring cavity can not be reflected by the ring cavity, and the sideband without resonance can be reflected, so that the resonant laser can not interfere with the sideband at the reflection end of the ring cavity, and is not influenced by the RAM effect.

Description

A Passive Laser Gyroscope Based on Critically Coupled Ring Cavity

technical field

The invention belongs to the field of laser gyroscopes, and more particularly relates to a passive laser gyroscope based on a critically coupled annular cavity.

Background technique

其中f_s为萨格纳克频率，Ω为环形腔所在光学平面的旋转角速度，λ为激光的波长，A为环形腔的环绕面积，P为环形腔的环绕周长。只要测量出萨格纳克频率，就可以计算出激光陀螺仪所在参考系目前的旋转角速度。Laser gyroscopes have excellent rotational rate measurement performance and are widely used in inertial navigation, geophysics and basic physics research. A laser gyroscope is a rotation sensor based on the Sagnac Effect. The Sagnac effect is to make two beams of homologous light propagate in the clockwise and counterclockwise directions in the annular optical cavity, respectively. If the annular cavity rotates in its optical plane, its clockwise and counterclockwise There will be a small difference in the propagation optical path in the clockwise direction, and this small optical path difference will cause a slight difference in the resonance frequency of the two beams of light in the ring cavity. This frequency difference is called the Sagnac Frequency. ), the Sagnac frequency f _s satisfies:

where f _s is the Sagnac frequency, Ω is the rotational angular velocity of the optical plane where the ring cavity is located, λ is the wavelength of the laser, A is the surrounding area of the ring cavity, and P is the surrounding perimeter of the ring cavity. As long as the Sagnac frequency is measured, the current rotational angular velocity of the reference frame where the laser gyroscope is located can be calculated.

There is no gain medium inside the optical cavity of the passive laser gyroscope, and the two laser beams need to be locked to the clockwise and counterclockwise resonance modes by external injection. At this time, the frequency difference between the two includes the Sagnac frequency. In order to lock the external laser to the resonant peak of the ring cavity, the passive laser gyroscope generally adopts the Pound-Drever-Hall (PDH) frequency locking technology. Ideally, according to the PDH frequency-locking technology, the laser will generate a carrier wave and two sidebands with opposite phases and equal amplitudes after phase modulation by an electro-optical modulator (EOM). to get the reflected signal. Then use the local signal to demodulate the reflected signal, and then the error signal required for laser frequency locking can be obtained. In practice, due to imperfect phase modulation, the phases of the two sidebands are not completely opposite, and the amplitudes are not exactly equal, resulting in an amplitude modulation signal mixed into the modulation signal, that is, residual amplitude modulation (RAM). This amplitude modulation signal is indistinguishable from the error signal in the frequency locking process, so there is usually a changing voltage offset V _RAM in the error signal obtained by final demodulation, and the laser locking frequency in the ring cavity determined according to the error signal produces an offset , thereby affecting the stability of the Sagnac frequency measurement.

SUMMARY OF THE INVENTION

In view of the above defects or improvement requirements of the prior art, the present invention provides a passive laser gyroscope based on a critically coupled annular cavity, the purpose of which is to improve the stability of Sagnac frequency measurement.

In order to achieve the above object, according to an aspect of the present invention, a passive laser gyroscope based on a critically coupled annular cavity is provided, which includes a laser system (100), a critically coupled annular cavity (200) and a signal acquisition system (300), in,

The laser system (100) is used for injecting a first laser and a second laser into the critically coupled annular cavity (200);

The critically coupled annular cavity (200) is configured to receive the first laser and the second laser, and make the carrier resonating with the critically coupled annular cavity (200) completely enter the cavity and reflect sidebands to the cavity outside;

The signal acquisition system (300) is used for acquiring the first laser light and the second laser light via the critically coupled annular cavity (200).

Preferably, the critically coupled annular cavity comprises an input mirror (201), a first reflection mirror (202), a second reflection mirror (203) and an output mirror (204). The sidebands are reflected outside the cavity by the input mirror (201), and the carrier waves of the first laser and the second laser resonating with the critically coupled annular cavity (200) penetrate the input mirror (201) and enter The critically coupled annular cavity (200) is reflected to the output mirror (204) by the first reflection mirror (202) and the second reflection mirror (203) respectively, and then penetrates the output mirror (204) Enter the signal acquisition system (300).

所述阻抗匹配系数

其中，L₁为输入镜(201)的吸收散射损耗，所述r₁、r₂、r₃、r₄分别为输入镜(201)、第一反射镜(202)、第二反射镜(203)和输出镜(204)的反射系数。Preferably, the impedance matching coefficient κ and the laser mode matching efficiency ρ of the critically coupled annular cavity (200) satisfy

The impedance matching coefficient

Wherein, L ₁ is the absorption and scattering loss of the input mirror (201), and the r ₁ , r ₂ , r ₃ , and r ₄ are the input mirror ( 201 ), the first reflecting mirror ( 202 ), and the second reflecting mirror ( 203 ), respectively ) and the reflection coefficient of the output mirror (204).

Preferably, the transmittance of the input mirror (201) in the critically coupled annular cavity (200) is greater than or equal to the first mirror (202), the second mirror (203) and the output The sum of the transmittances of the mirrors (204).

Preferably, the first laser light and the second laser light respectively penetrate the input mirror (201) in different directions and enter the critically coupled annular cavity (200), and the first laser light enters the critically coupled annular cavity in the critically coupled annular cavity (200) propagates in a clockwise direction, and the second laser propagates in a counterclockwise direction in the critically coupled annular cavity (200).

Preferably, the emission directions of the first laser and the second laser output through the output mirror (204) are perpendicular to each other.

Preferably, the laser system (100) comprises a laser source (101) and a frequency locking system (102), the frequency locking system (102) is used to lock the first laser and the second laser to a critical coupling On two adjacent or two identical longitudinal modes of the annular cavity (200).

Preferably, the laser source (101) comprises a narrow linewidth solid-state laser or a semiconductor laser.

Preferably, the signal acquisition system includes a beat frequency optical circuit, a photodetector (306) and a frequency counter (307). The photodetector (306) receives, and the frequency counter (307) is connected to the photodetector (306) for calculating the beat signal frequency of the beat signal.

Preferably, the beat frequency optical path includes a third reflection mirror (303), a fourth reflection mirror (304), and a half mirror (305), and the first laser light is reflected by the third reflection mirror (303) to the front of the half mirror (305), the second laser is reflected to the back of the half mirror (305) by the fourth mirror (304), the first laser and The beat frequency signal is formed by the second laser after passing through the half mirror (305).

The applicant has found through research that the reason for the bias of the error signal is that when the laser enters the ring cavity, in addition to the sidebands, part of the carrier wave will also be reflected, and the reflected carrier wave will not be completely opposite to the two sides. The interference will cause the frequency-locking system to generate an offset according to the error signal demodulated by the reflected signal, and finally shift the locking point.

In this application, since the carrier wave resonating with the critically coupled ring cavity will not be reflected by the receiving end of the ring cavity when entering the ring cavity, the two sidebands that are reflected back and whose phases are not completely opposite will not interfere with the carrier wave, so Even if the phases of the two sidebands are not completely opposite, it will not affect the value of the demodulated error signal at the laser locking frequency point, thus avoiding the offset of the error signal modulated by the frequency locking system, thereby avoiding the frequency locking point. , which reduces RAM noise and improves the rotational detection performance of passive laser gyroscopes.

Description of drawings

1 is an overall structural diagram of a passive laser gyroscope based on a critically coupled annular cavity according to an embodiment of the present invention;

与激光模式匹配效率ρ之间的关系图。Figure 2 is the conversion coefficient under different impedance matching coefficient κ

Plot against laser mode matching efficiency ρ.

Throughout the drawings, the same reference numerals are used to refer to the same elements or structures, and the reference numerals are as follows:

Laser system 100, laser source 101, frequency locking system 102, critical coupling ring cavity 200, input mirror 201, first mirror 202, second mirror 203, output mirror 204, signal acquisition system 300, first laser 301, Two lasers 302 , a third mirror 303 , a fourth mirror 304 , a half mirror 305 , a photodetector 306 , and a frequency counter 307 .

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

As shown in FIG. 1 , in an embodiment, a passive laser gyroscope based on a critically coupled ring cavity includes a laser system 100 , a critically coupled ring cavity 200 and a signal acquisition system 300 , wherein the laser system 100 is used to The critically coupled ring cavity 200 injects the first laser and the second laser; the critically coupled ring cavity 200 is used to receive the first laser and the second laser and make the carrier resonating with the critically coupled ring cavity 200 enter the cavity The signal collection system 300 is used to collect the first laser 301 and the second laser 302 passing through the critically coupled annular cavity 200 . Based on the laser signal collected by the signal collection system 300, the calculation is performed to obtain the Sagnac frequency.

In this application, the critically coupled cavity theory is applied to passive laser gyroscopes, so that the ring cavity is in a critically coupled state, that is, the carrier resonating with the critically coupled ring cavity does not reflect and completely enters the cavity, while the sidebands are The ring cavity is reflected back, so the carrier resonating with the cavity will not interfere with the reflected sideband at this time, so it is not affected by the RAM effect, that is, it is not sensitive to the RAM effect, which effectively suppresses the interference caused by the PDH frequency locking system. The offset of the laser locking frequency caused by the RAM effect reduces the RAM noise and improves the rotational detection performance of the passive laser gyroscope.

光学腔的阻抗匹配系数描述了腔对激光的反射特性，当注入腔的激光反射为零时称为阻抗匹配；激光模式匹配效率表征了入射激光的空间横模与腔本征模式的匹配程度，等于入腔激光功率与入射激光总功率之比。In one embodiment, the impedance matching coefficient κ and the laser mode matching efficiency ρ of the critically coupled ring cavity 200 satisfy

The impedance matching coefficient of the optical cavity describes the reflection characteristics of the cavity to the laser. When the reflection of the laser injected into the cavity is zero, it is called impedance matching; the laser mode matching efficiency represents the matching degree between the spatial transverse mode of the incident laser and the cavity eigenmode. It is equal to the ratio of the laser power into the cavity to the total power of the incident laser.

In passive laser gyroscopes, the laser locking frequency shift caused by the RAM effect can be expressed by the following formula:

为二者之间的转换关系，是光学腔阻抗匹配系数κ和激光模式匹配效率ρ的函数，S为PDH系统的鉴频斜率，是一个常数。当临界耦合环形腔200的阻抗匹配系数κ和激光模式匹配效率ρ满足

时，

光学腔达到临界耦合状态，RAM效应引入的电压偏置V_RAM对激光锁定频率的影响f_RAM被降为零。图2是不同阻抗匹配系数κ下，转换系数

与激光模式匹配效率ρ之间的关系，由于在实际操作中，临界耦合环形腔200的激光模式匹配效率ρ不可能等于或大于1，即只能是ρ<1，对应的，光学腔阻抗匹配系数κ<0，也即，只有当环形腔的阻抗匹配系数κ<0时，才能使

实现对RAM效应的完全抑制。where f _RAM is the offset of the laser locking frequency, and V _RAM is the voltage bias introduced by the RAM effect.

is the conversion relationship between the two, and is a function of the optical cavity impedance matching coefficient κ and the laser mode matching efficiency ρ, and S is the frequency discrimination slope of the PDH system, which is a constant. When the impedance matching coefficient κ and the laser mode matching efficiency ρ of the critically coupled annular cavity 200 satisfy

hour,

The optical cavity reaches a critical coupling state, and the effect of the voltage bias V _RAM introduced by the RAM effect on the laser locking frequency f _RAM is reduced to zero. Figure 2 is the conversion coefficient under different impedance matching coefficient κ

The relationship between the laser mode matching efficiency ρ, because in actual operation, the laser mode matching efficiency ρ of the critically coupled annular cavity 200 cannot be equal to or greater than 1, that is, it can only be ρ<1, correspondingly, the optical cavity impedance matching The coefficient κ<0, that is, only when the impedance matching coefficient κ<0 of the annular cavity can be used.

Complete suppression of RAM effects is achieved.

In one embodiment, as shown in FIG. 1 , the critically coupled annular cavity 200 includes an input mirror 201 , a first mirror 202 , a second mirror 203 and an output mirror 204 . The sidebands of the first laser and the second laser are reflected outside the cavity by the input mirror 201; the carrier waves of the first and second lasers resonating with the critically coupled annular cavity 200 completely penetrate The critically coupled annular cavity 200 is passed through the input mirror 201 . The first laser light entering the critically coupled annular cavity 200 is reflected to the output mirror 204 by the first mirror 202 and penetrates the output mirror 204 to enter the signal acquisition system 300 ; the second laser entering the critically coupled annular cavity 200 The laser light is reflected by the second mirror 203 to the output mirror 204 and penetrates the output mirror 204 to enter the signal acquisition system 300 .

Further, the impedance matching coefficient of the critically coupled annular cavity 200

Wherein, L ₁ is the absorption and scattering loss of the input mirror 201 , and the r ₁ , r ₂ , r ₃ , and r ₄ are the reflection coefficients of the input mirror 201 , the first mirror 202 , the second mirror 203 and the output mirror 204 respectively . When the reflection coefficients of the first reflection mirror 202, the second reflection mirror 203 and the output mirror 204 are the same as r, the impedance matching coefficient

时，便能使环形腔达到上文所述的临界耦合状态。In this embodiment, by adjusting the optical characteristics of the optical path and the cavity mirror, the impedance matching coefficient κ and the laser mode matching efficiency ρ are satisfied

, the annular cavity can reach the critical coupling state described above.

其中t₁为输入镜的透射系数，L_total为环形腔的各项损耗总和，包含输入镜、第一反射镜、第二反射镜、输出镜的透射损耗和吸收散射损耗等。在本实施例中，只有输入镜201的透射系数满足上述关系，才能使环形腔的阻抗匹配系数κ<0，从而能使

实现对RAM效应的完全抑制。In one embodiment, the transmission loss of the input mirror 201 in the critically coupled annular cavity 200 is greater than or equal to the sum of the remaining losses of the annular cavity, that is,

where t ₁ is the transmission coefficient of the input mirror, and L _total is the sum of various losses of the annular cavity, including the transmission loss and absorption and scattering loss of the input mirror, the first mirror, the second mirror, and the output mirror. In this embodiment, only if the transmission coefficient of the input mirror 201 satisfies the above relationship, the impedance matching coefficient κ of the annular cavity can be made <0, so that the

Complete suppression of RAM effects is achieved.

In one embodiment, the first laser and the second laser respectively penetrate the input mirror 201 in different directions and enter the critically coupled annular cavity 200 , and the first laser penetrates the critically coupled annular cavity 200 Propagating in a clockwise direction, the second laser propagates in a counterclockwise direction in the critically coupled annular cavity 200 . Further, the emission directions of the first laser 301 and the second laser 302 output by the output mirror 204 are perpendicular to each other.

其中c为真空中的光速，P为环形光学腔的周长，N取整数。在另一具体的实施例中，从激光系统中分出的第一激光和第二激光可以锁定在临界耦合环形腔200相同的纵模上，即N＝0，其频率关系满足f₁-f₂＝f_s，其中f_s为萨格纳克频率。优选地，所述所有激光来自窄线宽固体激光器或半导体激光器。In one embodiment, the laser system 100 includes a laser source 101 and a frequency locking system 102 , and the frequency locking system 102 is used to lock the first laser and the second laser to two parts of the critically coupled ring cavity 200 . on two adjacent or two identical longitudinal modes. In a specific embodiment, the first laser and the second laser separated from the laser system can be locked on the longitudinal modes adjacent to the critically coupled ring cavity 200, and the frequencies are f ₁ and f ₂ respectively, and the frequency relationship is Satisfy f ₁ -f ₂ =f _s +N·f _FRS , where f _s is the Sagnac frequency, and f _FRS is the double free spectral frequency of the ring optical cavity, which satisfies the relation

where c is the speed of light in vacuum, P is the perimeter of the annular optical cavity, and N is an integer. In another specific embodiment, the first laser and the second laser split from the laser system can be locked on the same longitudinal mode of the critically coupled ring cavity 200, that is, N=0, and their frequency relationship satisfies f ₁ -f ₂ = f _s , where f _s is the Sagnac frequency. Preferably, all the lasers are from narrow linewidth solid-state lasers or semiconductor lasers.

In an embodiment, the signal acquisition system 300 includes a beat frequency optical circuit, a photodetector 306 and a frequency counter 307. After the first laser 301 and the second laser 302 form a beat frequency signal through the beat frequency optical circuit It is received by the photodetector 306, and the frequency counter 307 is connected to the photodetector 306 to calculate the beat signal frequency of the beat signal, and then calculate the Sagnac frequency according to the beat signal frequency.

Specifically, the beat frequency optical path includes a third mirror 303 , a fourth mirror 304 , and a half mirror 305 , and the first laser 301 is reflected by the third mirror 303 to the half mirror The front side of the mirror 305, the second laser 302 is reflected by the third mirror 303 to the back of the half mirror 305, the first laser 301 and the second laser 302 are reflected by the half mirror 305 The above-mentioned beat signal is formed after the half mirror 305 .

计算得到需要的模式匹配效率ρ，然后通过调节腔前光路来调节模式匹配效率以得到我们所需要的模式匹配效率值。在本申请中，无需将激光的模式匹配效率调节至接近100％，可以为60％～80％，只要满足

即可，特定的模式匹配效率可以通过调节腔前光路来实现。In the specific operation, a cavity mirror with suitable reflectivity can be selected to make the impedance matching coefficient κ of the annular cavity negative, and then according to the formula

Calculate the required mode matching efficiency ρ, and then adjust the mode matching efficiency by adjusting the optical path in front of the cavity to obtain the required mode matching efficiency value. In this application, it is not necessary to adjust the mode matching efficiency of the laser to be close to 100%, it can be 60% to 80%, as long as it satisfies

That is, a specific mode matching efficiency can be achieved by adjusting the optical path in front of the cavity.

吸收散射损耗L₁＝10ppm，第一反射镜202、第二反射镜203和输出镜的反射率均为R＝r²＝0.99996，经计算，所述临界耦合环形腔的阻抗匹配系数为

根据公式

对应激光模式匹配效率为65.71％，此时，

有效抑制了由PDH锁频系统引入的RAM效应对激光锁定频率造成的偏移。若两束注入激光103、104在PDH锁频系统102的作用下被锁定到临界耦合环形腔200相邻的两个纵模上，即N＝1，其频率关系满足f₁-f₂＝f_s+f_FRS，其中，分别为信号采集系统300采集到的第一激光和第二光的频率，f_s为萨格纳克频率，f_FRS为临界耦合环形腔的一倍自由光谱区频率。第一激光和第二激光从临界耦合环形腔200的输出镜204出射，方向互为垂直，与两面反射镜303、304和一面半透半反镜305组成拍频光路，拍频信号被光电探测器306接收，从频率计数器307可读出拍频信号频率f_beat，满足关系f_beat＝f_s+f_FRS，由此计算出萨格纳克频率f_s。For example, in a specific embodiment, the reflectivity of the input mirror

The absorption and scattering loss L ₁ =10ppm, the reflectivity of the first reflector 202, the second reflector 203 and the output mirror are all R=r ² =0.99996, after calculation, the impedance matching coefficient of the critically coupled annular cavity is

According to the formula

The corresponding laser mode matching efficiency is 65.71%, at this time,

The offset of the laser locking frequency caused by the RAM effect introduced by the PDH frequency locking system is effectively suppressed. If the two injected laser beams 103 and 104 are locked to the two adjacent longitudinal modes of the critically coupled annular cavity 200 under the action of the PDH frequency locking system 102 , that is, N=1, the frequency relationship satisfies f ₁ -f ₂ =f _s +f _FRS , wherein, are the frequencies of the first laser and the second light collected by the signal collection system 300 respectively, f _s is the Sagnac frequency, and f _FRS is one time of the free spectral region frequency of the critically coupled ring cavity. The first laser and the second laser are emitted from the output mirror 204 of the critically coupled ring cavity 200, the directions are perpendicular to each other, and form a beat frequency optical path with the two mirrors 303, 304 and a half mirror 305, and the beat frequency signal is detected by photoelectricity The frequency counter 306 receives and reads the beat signal frequency f _beat from the frequency counter 307 , which satisfies the relation f _beat =f _s +f _FRS , thereby calculating the Sagnac frequency f _s .

吸收散射损耗L₁＝100ppm，所述第一反射镜、第二反射镜和输出镜的反射率均为R＝r²＝0.99999，经计算，所述临界耦合环形腔的阻抗匹配系数为

根据公式

对应激光模式匹配效率为75.75％。此时，

有效抑制了由PDH锁频系统引入的RAM效应对激光锁定频率造成的偏移。若所述两束注入激光103、104从输入镜201的两个方向注入临界耦合环形腔200，分别沿顺时针方向和逆时针方向在腔内传播。所述两束注入激光103、104在PDH锁频系统102的作用下被锁定到临界耦合环形腔200相同的纵模上，即N＝0，其频率关系满足f₁-f₂＝f_s，其中f_s为萨格纳克频率。所述信号采集系统300中的两束出射激光301、302从临界耦合环形腔200的输出镜204出射，方向互为垂直，与两面反射镜303、304和一面半透半反镜305组成拍频光路，拍频信号被光电探测器306接收，从频率计数器307可读出拍频信号频率f_beat，满足关系f_beat＝f_s，由此得出萨格纳克频率f_s。In another specific embodiment, the reflectivity of the input mirror

The absorption and scattering loss L ₁ =100ppm, the reflectivity of the first mirror, the second mirror and the output mirror are all R=r ² =0.99999, after calculation, the impedance matching coefficient of the critically coupled annular cavity is

According to the formula

The corresponding laser mode matching efficiency is 75.75%. at this time,

The offset of the laser locking frequency caused by the RAM effect introduced by the PDH frequency locking system is effectively suppressed. If the two injected laser beams 103 and 104 are injected into the critically coupled annular cavity 200 from two directions of the input mirror 201 , they propagate in the cavity in a clockwise direction and a counterclockwise direction, respectively. The two injected laser beams 103 and 104 are locked to the same longitudinal mode of the critically coupled annular cavity 200 under the action of the PDH frequency locking system 102, that is, N=0, and their frequency relationship satisfies f ₁ -f ₂ =f _s , where _fs is the Sagnac frequency. The two outgoing lasers 301 and 302 in the signal acquisition system 300 are emitted from the output mirror 204 of the critically coupled annular cavity 200 , and the directions are perpendicular to each other, and form a beat frequency with the two mirrors 303 and 304 and the half mirror 305 . In the optical path, the beat signal is received by the photodetector 306 , and the frequency f _beat of the beat signal can be read from the frequency counter 307 , which satisfies the relationship f _beat =f _s , thereby obtaining the Sagnac frequency f _s .

Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, etc., All should be included within the protection scope of the present invention.

Claims (8)

1. A passive laser gyroscope based on a critically coupled annular cavity, characterized in that, comprising a laser system (100), a critically coupled annular cavity (200) and a signal acquisition system (300), wherein, The laser system (100) is used for injecting the first laser light and the second laser light emitted in different directions into the critically coupled annular cavity (200); The critically coupled annular cavity (200) is configured to receive the first laser and the second laser, and make the carrier resonating with the critically coupled annular cavity (200) completely enter the cavity and reflect sidebands to the cavity In addition, the first laser light and the second laser light entering the critically coupled annular cavity (200) are incident on the signal acquisition system (300) after being reflected; The signal acquisition system (300) is configured to acquire and analyze the first laser and the second laser emitted through the critically coupled annular cavity (200); The critically coupled annular cavity includes an input mirror (201), a first reflection mirror (202), a second reflection mirror (203) and an output mirror (204), and the edges of the first laser and the second laser are The band is reflected outside the cavity by the input mirror (201), and the carrier waves of the first laser and the second laser resonating with the critically coupled annular cavity (200) completely penetrate the input mirror (201) and enter The critically coupled annular cavity (200) is reflected to the output mirror (204) by the first reflection mirror (202) and the second reflection mirror (203) respectively, and then penetrates the output mirror (204) enter the signal acquisition system (300); Wherein, the impedance matching coefficient κ and the laser mode matching efficiency ρ of the critically coupled ring cavity (200) satisfy

The impedance matching coefficient

Wherein, L ₁ is the absorption and scattering loss of the input mirror (201), and the r ₁ , r ₂ , r ₃ , and r ₄ are the input mirror ( 201 ), the first reflecting mirror ( 202 ), and the second reflecting mirror ( 203 ), respectively ) and the reflection coefficient of the output mirror (204). 2. The passive laser gyroscope according to claim 1, wherein the transmittance of the input mirror (201) in the critically coupled annular cavity (200) is greater than or equal to the first mirror (202) ), the sum of the transmittances of the second mirror (203) and the output mirror (204). 3. The passive laser gyroscope according to claim 1, wherein the first laser and the second laser respectively penetrate the input mirror (201) in different directions and enter the critically coupled annular cavity ( 200), the first laser propagates in a clockwise direction in the critically coupled annular cavity (200), and the second laser propagates in a counterclockwise direction in the critically coupled annular cavity (200). 4. The passive laser gyroscope according to claim 3, characterized in that the emission directions of the first laser and the second laser output through the output mirror (204) are perpendicular to each other. 5. The passive laser gyroscope according to claim 1, wherein the laser system (100) comprises a laser source (101) and a frequency locking system (102), wherein the frequency locking system (102) is used to make The first laser and the second laser are locked to two adjacent or two identical longitudinal modes of the critically coupled annular cavity (200). 6. The passive laser gyroscope according to claim 1, wherein the laser source (101) comprises a narrow linewidth solid-state laser or a semiconductor laser. 7. The passive laser gyroscope according to claim 1, wherein the signal acquisition system (300) comprises a beat frequency optical circuit, a photodetector (306) and a frequency counter (307), the first laser and The second laser is received by the photodetector (306) after forming a beat signal through the beat optical path, and the frequency counter (307) is connected to the photodetector (306) for calculating the The beat signal frequency of the beat signal. 8. The passive laser gyroscope according to claim 7, wherein the beat frequency optical path comprises a third reflection mirror (303), a fourth reflection mirror (304), and a half mirror (305), so The first laser is reflected to the front of the half mirror (305) by the third mirror (303), and the second laser is reflected to the half mirror by the fourth mirror (304) On the back of the half mirror (305), the first laser and the second laser pass through the half mirror (305) to form the beat frequency signal.

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