CN109556591B - Passive laser gyroscope based on ultrastable laser - Google Patents

Abstract

The invention discloses a passive laser gyroscope based on an ultra-stable laser, comprising an ultra-stable laser light source device, a high-Q value ring cavity interferometer device and a beat frequency detection device. , at the same time locked to the femtosecond optical comb linked to the atomic frequency standard to obtain an ultra-stable laser source with both short and long stability; the circumference of the ring cavity is locked to the frequency of the ultra-stable laser source injected in the counterclockwise direction, and the The frequency of the laser injected in the clockwise direction is locked to the same resonance peak of the cavity; the beat frequency detection device detects the beat frequencies of the overflowing light in two directions in the cavity to obtain the Sagnac signal, and the rotation angular velocity is determined by this signal. The invention improves the interference signal-to-noise ratio of the laser gyroscope by using the ultra-stable laser as the passive laser gyroscope injection light source, and at the same time, the stability of the scale factor of the gyroscope can be improved, thereby improving the stability of the whole gyroscope system and prolonging the integral Averaging time for better rotational measurement resolution.

Description

A passive laser gyroscope based on ultra-stable laser

technical field

The invention belongs to the field of laser gyroscopes, and more particularly, relates to a passive laser gyroscope based on ultra-stable laser technology.

Background technique

其中f_sagnac是我们测量的两个方向谐振激光的频率差，也被称为Sagnac频率，其中

称为标度因子，A是环形腔的环绕面积，λ是激光的波长，P是环形腔的周长，Ω是环形腔的旋转角速度。可以看出，激光陀螺仪的环绕面积越大，其标度因子越大，其测量灵敏度越高。Laser gyroscopes are used in inertial navigation, geophysics, fundamental physics and other fields due to their excellent rotational rate measurement performance. In the past 40 years, laser gyroscopes have become the most important instruments in the fields of inertial navigation and precision rotation measurement, and are favored by researchers in scientific and industrial circles due to their high resolution, good stability, and wide dynamic range. The laser gyroscope is based on the Sagnac effect and was proposed by the French scientist Sagnac in 1913. In a ring cavity, if the system rotates in the light propagation plane, then the light propagating in the clockwise direction and the light propagating in the counterclockwise direction actually travel. The optical paths are not equal. If two beams of light resonate with the same resonance peak of the ring cavity at the same time, the relationship between the difference between their resonance frequencies and the rotational angular velocity can be expressed as:

where f _sagnac is the frequency difference between the two directions of the resonant laser that we measure, also known as the Sagnac frequency, where

Called the scaling factor, A is the encircling area of the ring cavity, λ is the wavelength of the laser, P is the perimeter of the ring cavity, and Ω is the rotational angular velocity of the ring cavity. It can be seen that the larger the surrounding area of the laser gyroscope, the larger the scale factor and the higher the measurement sensitivity.

Most of the existing gyroscopes are active laser gyroscopes, that is, the ring laser interferometer composed of four high anti-cavity mirrors is filled with He-Ne gas gain medium, and they are themselves an active ring laser. / The frequency difference of the laser output resonating in the counterclockwise direction is the Sagnac frequency. The design idea of this active laser gyroscope is relatively simple and straightforward. At present, the limiting factors mainly come from two aspects: one is limited by the spontaneous emission noise and the disturbance of the cavity medium; the other is to overcome the frequency blocking phenomenon of the laser gyroscope. Dither biasing and other biasing techniques can compromise the stability of the laser gyroscope.

The laser source of the passive laser gyroscope is located outside the ring cavity, which can effectively avoid the spontaneous emission noise and the disturbance of the medium in the cavity. However, passive gyroscopes are usually limited by the stability of the injected laser source and the stability of their own annular cavity. They can neither obtain good rotational angular velocity detection sensitivity nor obtain a long integration time average to obtain good rotational angular velocity resolution. Rate. In order to solve this problem, the patent document CN103047979 B provides a method to lock the center frequency of the laser signal at the resonant frequency of the Fabry-Perot cavity by means of feedback, so as to realize the narrowing of the output laser line width of the laser device and the stability of the laser frequency , to improve the measurement accuracy and sensitivity of the rotational angular velocity of the laser gyroscope, but it does not solve the long-term drift of the resonant frequency of the Fabry-Perot cavity, and the integration and averaging time of the passive laser gyroscope will be very limited. A passive laser gyroscope stabilization or post-processing solution is developed.

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 ultra-stable laser, the purpose of which is to solve the problem of detection caused by injected laser noise and poor stability of the gyroscope in the existing passive laser gyroscope. For the problem that the resolution is not high enough, by improving the stability of the laser source injected into the passive laser gyroscope and the stability of the scale factor, the laser linewidth is much smaller than the linewidth of the ring cavity, which improves the signal-to-noise ratio of the interference signal of the laser gyroscope, and at the same time improves the laser gyroscope. The rotation detection sensitivity and long-term running integration time of the instrument are improved, and the rotation detection resolution is finally improved.

In order to achieve the above object, according to one aspect of the present invention, a passive laser gyroscope based on ultra-stable laser is provided, including: an ultra-stable laser light source device, a high-Q value ring cavity interferometer device and a beat frequency detection device; the The ultra-stable laser light source device includes: a laser device, a Fabry-Perot cavity device, a femtosecond optical comb device and an atomic frequency standard device; The Q-value ring cavity interferometer device provides a laser signal, and the frequency of the laser signal is locked to the Fabry-Perot cavity device and the femtosecond optical comb device at the same time. At the same time, the femtosecond optical comb device changes its own repetition frequency and zero offset The frequency is locked to the atomic frequency standard device, so that the final output laser signal frequency of the laser device has both the short-term stability of the Fabry-Perot cavity device and the long-term stability of the atomic frequency standard device; the high-Q ring cavity interferometer device It is used to construct a passive laser gyroscope interference optical path. After the long-term and short-term frequency stabilization of the laser device, the output laser signal is divided into two channels, which are respectively injected into the high-Q ring cavity interferometer device along the counterclockwise direction and the clockwise direction; The laser signal is injected counterclockwise as the length reference, the resonant frequency of the high-Q ring cavity interferometer device is locked to the frequency of the laser signal by the cavity length frequency locking device, and the laser signal is injected clockwise into the high-Q ring The cavity interferometer device locks the frequency of the laser signal to the resonant frequency of the high-Q value annular cavity interferometer device; the beat frequency detection device is used to detect the counterclockwise directions in the high-Q value annular cavity interferometer device respectively. The difference between the frequency of the laser signal and the Sagnac signal propagating clockwise is used to determine the rotational angular velocity of the entire device.

Among them, the atomic frequency standard device in the ultra-stable laser light source device can be realized by using a stable reference source, such as rubidium clock, cesium clock, hydrogen maser, optical frequency standard, etc.; femtosecond optical comb device and frequency standard device in the ultra-stable laser light source device The combination of iodine molecules, rubidium atoms, and cesium atoms can be replaced by frequency stabilization systems.

Further, the passive laser gyroscope further includes: a first laser transmission unit, a first feedback unit, a second laser transmission unit and a second feedback unit; the first input end of the second laser transmission unit is connected to the femtosecond optical comb device The output end of the second laser transmission unit is connected to the output end of the laser device, the input end of the second feedback unit is connected to the output end of the second laser transmission unit, and the output end of the second feedback unit is connected to the laser The first input end of the device; the input end of the first laser transmission unit is connected to the output end of the laser device, the input and output end of the first laser transmission unit is connected to the Fabry-Perot cavity device, and the input end of the first feedback unit is connected to the output end of the first laser transmission unit, and the output end of the first feedback unit is connected to the second input end; the first laser transmission unit is used to transmit the laser signal output by the laser device to the Fabry-Perot cavity device the first feedback unit is used for frequency-locking the laser signal output by the laser device to the Fabry-Perot cavity; the second laser transmission unit is used for transmitting the laser signal output by the laser device to the femtosecond optical comb device; The second feedback unit is used for frequency locking the laser signal output by the laser device to the femtosecond optical comb device.

Furthermore, the frequency of the laser signal output by the laser device is stabilized by the Fabry-Perot cavity device and the femtosecond optical comb device linked to the atomic frequency standard device.

Furthermore, the short-term stability of the frequency of the laser signal output by the laser device is stabilized by the Fabry-Perot cavity device, and the laser signal reflected by the second beam splitter is phase-modulated by the first electro-optic modulator, and then is The isolator is reflected into the Fabry-Perot cavity device, the laser signal is reflected after interacting with the Fabry-Perot cavity device, the signal is detected at the first photodetector, and the obtained error signal is demodulated and passed through the first servo amplifier After feeding back to the laser device, the frequency of the laser signal output by the laser device is locked to the resonance peak of the Fabry-Perot cavity device, so as to obtain the superior short-term stability of the Fabry-Perot cavity device; the frequency of the laser signal output by the laser device is The long-term stability is stabilized by the femtosecond optical comb device linked to the atomic frequency standard device. The laser signal reflected by the first beam splitter and the outgoing laser signal of the femtosecond optical comb device linked to the atomic frequency standard device pass through After the third beam splitter, a beam of laser light is synthesized, and the beat frequency signal is detected on the second photodetector. The obtained signal is fed back to the laser device after passing through the second servo amplifier, and the frequency of the output laser signal of the laser device is locked to the atomic frequency standard device. On the femtosecond optical comb device, the laser device has the long-term stability of the atomic frequency standard device.

Further, the high-Q ring cavity interferometer device includes: a gyro laser preparation unit, a third laser transmission unit, a fourth laser transmission unit, a ring cavity, a third feedback unit, and a fourth feedback unit; the first laser signal is connected to the gyro The input end of the laser preparation unit, the first output end of the gyro laser preparation unit is connected to the input end of the third laser transmission unit, the second output end of the gyro laser preparation unit is connected to the input end of the fourth laser transmission unit, the third laser transmission unit The input and output ends of the transmission unit are connected to the ring cavity, the input and output ends of the fourth laser transmission unit are connected to the ring cavity; the input end of the third feedback unit is connected to the second output end of the fourth laser transmission unit, and the The input end is connected to the second output end of the third laser transmission unit; the output end of the third feedback unit is connected to the other input end of the ring cavity, and the output end of the fourth feedback unit is connected to the other input end of the fourth laser transmission unit The gyro laser preparation unit is used to phase modulate the first laser signal and divide it into two equal beams; the third laser transmission unit is used to transmit and inject the laser signal output from the gyro laser preparation unit into the ring cavity; the fourth laser The transmission unit is used for transmitting and injecting another laser signal output by the gyro laser preparation unit into the ring cavity; the ring cavity is used for the two beams of injected laser signals to resonate and interfere with each other; the third feedback unit is used for the ring cavity resonance peak The error signal between the laser signal injected in the counterclockwise direction is servo-feedback to the piezoelectric ceramic; the fourth feedback unit is used for servo feedback of the error signal between the resonance peak of the ring cavity and the laser signal injected in the clockwise direction to the first feedback unit. Two acousto-optic modulators.

Further, the cavity length of the ring cavity is stabilized by the ultra-stable laser injected in the counterclockwise direction: the first laser signal injected in the counterclockwise direction is phase-modulated by the second electro-optical modulator, and the laser carrier signal and the two phase modulation are generated after the phase modulation. A sideband signal with equal and opposite amplitudes. The sideband is directly reflected by the ring cavity. After the carrier interacts with the cavity, it is reflected by the second Faraday isolator together with the sideband to the third photodetector and detected by the third photodetector. The detuning amount between the laser carrier frequency and the resonance peak of the ring cavity is demodulated to obtain an error signal, which is finally fed back to the piezoelectric ceramic to push the fourth high reflectivity cavity mirror, change the cavity length of the ring cavity, and lock the cavity length of the ring cavity to the frequency of the laser signal injected counterclockwise.

Further, the ultra-stable laser signal injected in the clockwise direction passes through the second acousto-optic modulator, and the frequency is locked to the cavity length of the ring cavity, wherein: the sideband of the laser signal injected in the clockwise direction is reflected by the ring cavity, After the carrier interacts with the cavity, it is reflected by the first Faraday isolator to the fourth photodetector together with the sideband. The fourth photodetector detects the detuning between the laser carrier frequency and the resonance peak of the ring cavity, and demodulates the error signal. Finally, it is fed back to the second acousto-optic modulator to drive the voltage-controlled oscillator to change the modulation frequency f ₂ of the second acousto-optic modulator, so that the frequency of the laser injected in the clockwise direction resonates with the ring cavity, and the laser will be injected in the clockwise direction. The frequency is locked to the length of the annular cavity.

Furthermore, the Sagnac signal is obtained by using the difference between the modulation frequencies of the first acousto-optic modulator and the second acousto-optic modulator, or by detecting the beat frequencies of spillover light from two directions behind the cavity.

In general, compared with the prior art, the above technical solutions conceived by the present invention have the following beneficial effects:

(1) The present invention enables the passive laser gyroscope to be injected into the light source with both short-term stability and long-term stability by injecting the passive laser gyroscope into the light source and stabilizing it to the ultra-stable Fabry-Perot cavity and the femtosecond optical comb linked to the hydrogen maser. The stability makes the laser linewidth much smaller than the ring cavity linewidth, improves the signal-to-noise ratio of the interference signal of the laser gyroscope, improves the rotational detection sensitivity of the passive laser gyroscope by 2-3 orders of magnitude, and improves the detection resolution under long integration time.

(2) A piezoelectric ceramic is installed on one of the cavity mirrors of the annular cavity, and the method of locking the annular cavity to an ultra-stable laser source is used to improve the scale factor stability of the laser gyroscope.

Description of drawings

Fig. 1 is a kind of general structure diagram of passive laser gyroscope based on ultra-stable laser of the present invention;

2 is a schematic diagram of a specific embodiment of an ultra-stable laser light source device in the present invention;

3 is a schematic diagram of a specific embodiment of a high-Q annular cavity interferometer device in the present invention;

FIG. 4 is a schematic diagram of a specific embodiment of the beat frequency detection device in the present invention.

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.

The present invention provides a passive laser gyroscope based on ultra-stable lasers. Device 300 . The ultra-stable laser light source device 100 includes: a laser device 101 , a Fabry-Perot cavity device 102 , a femtosecond optical comb device 103 , and an atomic frequency standard device 104 .

Among them, a part of the laser signal output by the laser device 101 is output to the Fa-Per cavity device 102, and an error signal is obtained after interacting with it, and the error signal is fed back to the laser device 101 to lock the frequency of the output laser signal of the laser device 101 to the Fa-Per cavity device 102. It is used to stabilize the short-term stability of the frequency of the output laser signal of the laser device 101 on the resonant peak of the Fa-Per cavity;

The other part of the laser signal output by the laser device 101 is output to the femtosecond optical comb device 103. The femtosecond optical comb device 103 uses its own characteristics and the device has been locked to the atomic frequency standard device 104, and has the stability of the hydrogen maser. The laser signal output by the device 101 to the femtosecond optical comb device 103 interacts with the output light of the femtosecond optical comb device 103, and the obtained error signal is fed back to the laser device 101 to stabilize the long-term stability of the output laser signal frequency of the laser device 101;

According to a specific implementation example of the present invention, the Fa-Per cavity device 102 can adopt a super-stable Fa-Per cavity, and the short-term stability Allan deviation of the laser signal locked to the Fa-Per cavity can be better than 10 ⁻¹² , preferably, better than ^10-13 , ^10-14 , ^10-15 , ^10-16 , ^10-17 or ^10-18 ;

According to a specific embodiment of the present invention, a hydrogen maser can be used as the atomic frequency standard device 104, which is a long-term stable reference source, and the femtosecond optical comb device 103 is used to link to the hydrogen maser, and the laser signal locked to the femtosecond optical comb is stable for a long time. Sexual Allen deviation can be better than 10 ^-12 , preferably, better than 10 ^-13 , 10 ^-14 , 10 ^-15 , 10 ^-16 ; preferably, other reference sources can be used, such as iodine molecular frequency standard, optical clock etc., preferably, the long-term stability may be better than ^10-13 , ^10-14 , ^10-15 , ^10-16 , ^10-17 , ^10-18 or ^10-19 .

FIG. 2 is a schematic diagram of a specific embodiment of the ultra-stable laser light source device in the present invention. In the drawings of the present invention, a thick solid line indicates an optical path, and a thick broken line indicates an electric circuit. The ultra-stable laser light source device 100 includes: a laser device 101, a Fabry-Perot cavity device 102, a femtosecond optical comb device 103, an atomic frequency standard device 104, a first laser transmission unit 105, a first feedback unit 106, a second laser The transmission unit 107, the second feedback unit 108; the laser device 101 is used to provide the laser signal to the whole system, the Fabry-Perot cavity device 102 is used for the short-term stable reference source of the laser signal, and the femtosecond optical comb device 103 is used to link the laser The signal and the output signal of the atomic frequency standard, the atomic frequency standard device 104 is used as a short-term stable reference source for the laser signal, and the first laser transmission unit 105 is used to transmit the laser signal output by the laser device 101 to the Fabry-Perot cavity 102 , the first feedback unit 106 is used to frequency-lock the laser signal output by the laser device 101 to the Fabry-Perot cavity 102, and the second laser transmission unit 107 is used to transmit the laser signal output by the laser device 101 to the The second optical comb device 103 and the second feedback unit 108 are used to lock the frequency of the laser signal output by the laser device 101 to the femtosecond optical comb device 103 .

Wherein, the laser device 101 includes: a laser 1011 and a first beam splitter 1012 arranged on the outgoing optical path of the laser 1011; the laser 1011 is used to emit the original laser signal, and the first beam splitter 1012 is used to equally divide the laser into two beams;

The first laser transmission unit 105 includes: a second beam splitter 1051, a first electro-optical modulator 1052, and an optical isolator 1053; one of the laser signals emitted by the laser device 101 is partially reflected by the second beam splitter 1051 and then passes through the first electro-optical device in turn. The modulator 1052 and the optical isolator 1053 reach the Fibre cavity 102; the second beam splitter 1051 is used to partially reflect and transmit the laser signal, the first electro-optical modulator 1052 is used to phase modulate the laser signal, and the optical isolator 1053 is used to The laser signal is reflected to the Faber cavity 102 and the laser signal returned by the Faber cavity 102 is received.

The first feedback unit 106 includes: a first photodetector 1061 and a first servo amplifier 1062; the first photodetector 1061 is placed behind the optical isolator 1053 to detect the laser signal returned from the Fiddler cavity 102, and the first servo amplifier 1062 is located between the first photodetector 1061 and the laser 1011, and is used for demodulation, amplification and servo feedback of the short stable loop error signal.

The second laser transmission unit 107 includes: a third beam splitter 1071; the third beam splitter 1071 is placed between the laser device 101 and the femtosecond optical comb 103, and is used for the laser signal output by the laser device 101 and the output signal of the femtosecond optical comb 103 The transmission signal is combined.

The second feedback unit 108 includes: a second photodetector 1081 and a second servo amplifier 1082; the second photodetector 1081 is placed behind the third beam splitter 1071 to detect the laser signal output by the laser device 101 and the femtosecond optical comb 103 For the beat frequency signal of the output signal, the second servo amplifier 1082 is located between the second photodetector 1081 and the laser 1011 for demodulation, amplification and servo feedback of the long stable loop error signal.

The outgoing laser signal of the laser 1011 passes through the first beam splitter 1012, and a beam of laser light is reflected by the second beam splitter 1051 and then phase-modulated by the first electro-optic modulator 1052, and then reflected to the Fa-Per cavity 102 by the optical isolator 1053. The laser signal interacts with the Faber cavity 102 and is reflected, and detects the signal at the first photodetector 1061. After demodulation, the obtained error signal passes through the first servo amplifier 1062 and is fed back to the laser 1011, and the laser device 101 outputs the frequency of the laser signal. Locked to the resonance peak of the Far-Pere cavity 102 to obtain the excellent short-term stability of the Far-Pert cavity 102; the obtained laser beam and the outgoing laser signal of the femtosecond optical comb device 103 linked to the hydrogen maser 104 pass through the third beam splitting After the mirror 1071 is combined, the beat frequency signal is detected on the second photodetector 1081, and the obtained signal is fed back to the laser 1011 after passing through the second servo amplifier 1082, and the frequency of the output laser signal of the laser device 101 is locked to the Feather connected to the hydrogen maser 104. On the second optical comb device 103 , the laser device 101 has the long-term stability of the hydrogen maser 104 ; the two-way feedback is performed simultaneously, realizing the long-term frequency stability and short-term frequency stability of the laser signal output by the laser device 101 .

The laser signal transmitted by the second beam splitter 1051 is denoted as the first laser signal. The first laser signal is provided to the high-Q ring cavity interferometer device 200, which is used as a passive laser gyroscope light source.

In this specific embodiment, the laser may be an Nd:YAG solid-state laser.

According to another specific embodiment of the present invention, the laser may be a fiber laser.

According to another specific embodiment of the present invention, the hydrogen maser can be replaced by other atomic or optical clocks or other frequency standards.

FIG. 3 is a schematic diagram of a specific embodiment of a high-Q annular cavity interferometer device 200 in the present invention. In the drawings of the present invention, a thick solid line indicates an optical path, and a thick broken line indicates an electric circuit. The high-Q ring cavity interferometer device 200 includes: a gyro laser preparation unit 201 , a third laser transmission unit 202 , a fourth laser transmission unit 203 , a ring cavity 204 , a third feedback unit 205 , and a fourth feedback unit 206 . The gyro laser preparation unit 201 is used to phase modulate the first laser signal and divide it into two equal beams. The third laser transmission unit 202 is used to transmit and inject the laser signal output by the gyro laser preparation unit 201 into the ring cavity 204. The four laser transmission units 203 are used for transmitting and injecting another laser signal output from the gyro laser preparation unit 201 into the ring cavity 204 . The ring cavity 204 is used for the two injected laser signals to resonate and interfere with each other. The third feedback unit 205 The error signal between the resonance peak of the ring cavity 204 and the laser signal injected in the counterclockwise direction is servo-feedback to the piezoelectric ceramic 2045. The error signal between the laser signals is servo-feedback to the second acousto-optic modulator 2031 .

Wherein, the gyro laser preparation unit 201 includes: a second electro-optical modulator 2011, a half-wave plate 2012 and a polarization beam splitter prism 2013 arranged on the outgoing optical path of the first laser signal; the second electro-optical modulator 2011 is used for the first laser signal Phase modulation, the half-wave plate 2012 is used to adjust the polarization state of the laser signal, and the polarization beam splitter prism 2013 is used to divide the first laser signal into two equal parts;

The third laser transmission unit 202 includes: a first acousto-optic modulator 2021, a first mirror 2022, and a first Faraday isolator 2023; one of the laser signals emitted by the gyro laser preparation unit 201 sequentially passes through the first acousto-optic modulator 2021 , the first reflection mirror 2022 and the first Faraday isolator 2023 to reach the ring cavity 204; the first acousto-optic modulator 2021 is used to frequency shift the laser signal to be injected into the ring cavity in the counterclockwise direction, and the first reflection mirror 2022 uses In order to adjust the directivity of the laser signal, the first Faraday isolator 2023 is used for isolating and extracting the laser signal returning from the annular cavity 204 and propagating in the clockwise direction.

The fourth laser transmission unit 203 includes: a second acousto-optic modulator 2031, a second mirror 2032, and a second Faraday isolator 2033; the other laser signal emitted by the gyro laser preparation unit 201 sequentially passes through the second acousto-optic modulator 2031 , the second reflection mirror 2032 and the second Faraday isolator 2033 to reach the ring cavity 204; the second acousto-optic modulator 2031 is used to shift the frequency of the laser signal to be injected into the ring cavity in the clockwise direction, and the second reflection mirror 2032 For adjusting the directivity of the laser signal, the second Faraday isolator 2033 is used for isolating and extracting the laser signal propagating in the counterclockwise direction returned by the annular cavity 204 .

The annular cavity 204 includes: a first high-reflection cavity mirror 2041, a second high-reflection cavity mirror 2042, a third high-reflection cavity mirror 2043, a fourth high-reflection cavity mirror 2044, and a piezoelectric ceramic 2045; The reflectivity cavity mirror 2041, the second high reflectivity cavity mirror 2042, the third high reflectivity cavity mirror 2043, and the fourth high reflectivity cavity mirror 2044 are arranged in sequence to form a closed square ring cavity 204 for injecting two beams of laser signals Resonance and interference are generated respectively, and the piezoelectric ceramics 2045 are arranged behind the fourth high-reflection cavity mirror 2044 to push the cavity mirror to change the cavity length of the annular cavity 204 .

The third feedback unit 205 includes: a third photodetector 2051 and a third servo amplifier 2052; the third photodetector 2051 is placed behind the second Faraday isolator 2033 for detecting the counterclockwise propagating back from the annular cavity 204 For the laser signal, the third servo amplifier 2052 is located between the third photodetector 2051 and the piezoelectric ceramic 2045, and is used for demodulation, amplification and servo feedback of the cavity length locked loop error signal.

The fourth feedback unit 206 includes: a fourth photodetector 2061, a fourth servo amplifier 2062, and a second acousto-optic modulator to drive a voltage-controlled oscillator 2063; the fourth photodetector 2061 is placed after the first Faraday isolator 2023, after Connect the fourth servo amplifier 2062, the second acousto-optic modulator to drive the voltage-controlled oscillator 2063, and the second acousto-optic modulator 2031 in sequence; Laser signal, the fourth servo amplifier 2062 is used for demodulation, amplification and servo feedback of the locked loop error signal at this frequency, and the second acousto-optic modulator drives the voltage-controlled oscillator 2063 for driving the second acousto-optic modulator 2031 signal, the second acousto-optic modulator 2031 is used for frequency shifting of the laser signal through it.

The first laser signal provided by the ultra-stable laser light source device 100 is phase-modulated by the second electro-optical modulator 2011. After phase modulation, a laser carrier signal and two sideband signals with equal and opposite amplitudes are generated. The sideband signals are the same as The frequency interval of the carrier signal depends on the modulation frequency of the electro-optical modulator 201. The phase-modulated first laser signal is equally divided into two laser signals by the half-wave plate 2012 and the polarization beam splitter prism 2013. The laser signal is then frequency-shifted by the first acousto-optic modulator f ₁ , then passed through the first mirror 2022 and the first Faraday isolator 2023, and injected counterclockwise by the first high-reflection cavity mirror 2041, the second high-reflection cavity mirror 2041, the second high-reflection mirror The annular cavity 204 formed by the cavity mirror 2042, the third high reflectivity cavity mirror 2043, the fourth high reflectivity cavity mirror 2044 and the piezoelectric ceramic 2045; the laser signal transmitted by the polarized beam splitter prism 2013 is then modulated by the second acousto-optical After the frequency is shifted by f2, it is injected into the annular cavity 204 in a clockwise direction through the _second mirror 2032 and the second Faraday isolator 2033.

The first Faraday isolator 2023 and the second Faraday isolator 2033 are respectively used to extract the laser signal reflected by the clockwise injected laser through the annular cavity and the laser signal reflected by the counterclockwise injected laser through the annular cavity. The isolation degree of the Faraday isolator used is better than 60dB, preferably better than 90dB.

Among them, the sideband of the laser signal injected in the counterclockwise direction is directly reflected by the annular cavity, and the carrier interacts with the cavity and is reflected by the second Faraday isolator 2033 together with the sideband to the third photodetector 2051, and is detected by the third photoelectric The device 2051 detects the detuning amount between the laser carrier frequency and the resonance peak of the ring cavity, demodulates the error signal, and finally feeds it back to the piezoelectric ceramic 2045 to push the fourth high reflectivity cavity mirror 2044 and change the cavity length of the ring cavity. The cavity length of the ring cavity is locked to the frequency of the laser signal injected counterclockwise.

Assuming that the frequency of the first laser signal is v ₀ , the frequency of the laser propagating in the counterclockwise direction in the ring cavity is: v _ccw =v ₀ +f ₁ ; the sidebands of the laser signal injected in the clockwise direction are also affected by the ring cavity. Reflection, after the carrier interacts with the cavity, it is reflected by the first Faraday isolator 2023 together with the sideband to the fourth photodetector 2061, and the fourth photodetector 2061 detects the detuning amount between the laser carrier frequency and the resonance peak of the ring cavity , demodulate the error signal, which is finally fed back to the second acousto-optic modulator to drive the voltage-controlled oscillator 2063 to change the modulation frequency f ₂ of the second acousto-optic modulator, so that the frequency of the injected laser in the clockwise direction resonates with the ring cavity , which locks the frequency of the laser injected in the clockwise direction to the length of the ring cavity. Assuming that the frequency of the first laser signal is v ₀ , the frequency of the laser propagating in the clockwise direction in the ring cavity is: v _cw =v ₀ +f ₂ ; the first acousto-optic modulator 2021 and the second acousto-optic modulator 2031 is the same type of modulation device, and the frequency shift direction is also the same, so the two laser beams resonate with the same longitudinal mode of the ring cavity. Due to the existence of the ring cavity rotation, they will produce a frequency shift, denoted as f _sagnac , which can be expressed as: f _sagnac =f ₁ −f ₂ , that is, the difference between the modulation frequencies of the first acousto-optic modulator 2021 and the second acousto-optic modulator 2031 is equal to the Sagnac frequency.

FIG. 4 is a schematic diagram of a specific embodiment of the beat frequency detection device in the present invention. Including: reflecting mirror 301, reflecting mirror 302, beam combining prism 303 and fifth photodetector 304; reflecting mirror 301 is arranged between the third high reflectivity cavity mirror 2043 and beam combining prism 303 to reflect and adjust counterclockwise The overflow laser signal in the direction, the mirror 302 is arranged between the third high reflectivity cavity mirror 2043 and the beam combining prism 303 to reflect and adjust the overflow laser signal in the clockwise direction, and the beam combining prism 303 is used for two in the cavity. For the beam combining of the directional overflow laser signals, the fifth photodetector 304 placed behind the beam combining prism is used for the beat frequency detection of the overflow laser signals in two directions in the cavity. Its beat frequency is the Sagnac frequency we need to detect.

Aiming at the detection sensitivity and detection resolution of the current large-scale laser gyroscope, the present invention proposes a passive laser gyroscope based on an ultra-stable laser, which can further improve the detection sensitivity of the passive laser gyroscope and make the scale factor stability more stable. It is improved, thereby improving the stability of the whole gyroscope system, and obtaining a long-term integral averaging effect to obtain better rotational measurement resolution.

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 (7)

1. A passive laser gyroscope based on ultrastable laser, the passive laser gyroscope comprising: the system comprises an ultrastable laser light source device (100), a high-Q ring cavity interferometer device (200) and a beat frequency detection device (300);

the ultrastable laser light source device comprises: the device comprises a laser device (101), a Fabry-Perot cavity device (102), a femtosecond optical comb device (103) and an atomic frequency standard device (104);

the laser device (101) provides laser signals to the Fabry-Perot cavity device (102), the femtosecond optical comb device (103) and the high-Q-value ring cavity interferometer device (200) respectively, the frequency of the laser signals is simultaneously locked to the Fabry-Perot cavity device (102) and the femtosecond optical comb device (103), meanwhile, the femtosecond optical comb device (103) locks the self repetition frequency and the zero-bias frequency to the atomic frequency standard device (104), and the laser signal frequency finally output by the laser device is enabled to have both the short-term stability of the Fabry-Perot cavity device and the long-term stability of the atomic frequency standard device;

the high-Q-value annular cavity interferometer device (200) is used for constructing a passive laser gyroscope interference light path, and the laser device outputs laser signals which are divided into two paths after the frequency is stabilized for a long time and a short time and respectively injected into the high-Q-value annular cavity interferometer device along the anticlockwise direction and the clockwise direction; injecting a laser signal in the anticlockwise direction to serve as a length reference, locking the resonant frequency of the high-Q-value annular cavity interferometer device to the frequency of the laser signal through a cavity length frequency locking device, and injecting the laser signal in the clockwise direction to the high-Q-value annular cavity interferometer device and locking the frequency of the laser signal to the resonant frequency of the high-Q-value annular cavity interferometer device;

the beat frequency detection device (300) is used for detecting that the difference between the frequencies of the laser signals respectively propagating along the counterclockwise direction and the clockwise direction in the high-Q-value ring cavity interferometer device (200) is a Sagnac signal, so as to determine the rotation angular velocity of the whole device;

the passive laser gyro further includes: a first laser transmission unit (105), a first feedback unit (106), a second laser transmission unit (107) and a second feedback unit (108);

a first input end of a second laser transmission unit (107) is connected to an output end of the femtosecond optical comb device (103), a second input end of the second laser transmission unit (107) is connected to an output end of the laser device (101), an input end of a second feedback unit (108) is connected to an output end of the second laser transmission unit (107), and an output end of the second feedback unit (108) is connected to a first input end of the laser device (101);

the input end of a first laser transmission unit (105) is connected to the output end of the laser device (101), the input end and the output end of the first laser transmission unit (105) are connected with the Fabry-Perot cavity device (102), the input end of a first feedback unit (106) is connected to the output end of the first laser transmission unit (105), and the output end of the first feedback unit (106) is connected to the second input end of the laser device (101);

the first laser transmission unit (105) is used for transmitting a laser signal output by a laser device (101) to the Fabry-Perot cavity device (102);

the first feedback unit (106) is used for locking the frequency of a laser signal output by the laser device (101) to the Fabry-Perot cavity device (102);

the second laser transmission unit (107) is used for transmitting the laser signal output by the laser device (101) to the femtosecond optical comb device (103);

the second feedback unit (108) is used for locking the frequency of the laser signal output by the laser device (101) to the femtosecond optical comb device (103).

2. The passive laser gyroscope of claim 1, characterized in that the frequency of the laser signal output by the laser device (101) is stabilized by a fabry-perot cavity device (102) and a femtosecond optical comb device (103) linked to an atomic frequency scale device (104).

3. The passive laser gyro of claim 2, wherein the short term stability of the frequency of the laser signal output by the laser device (101) is stabilized by the Fabry-Perot cavity device (102), and a laser beam reflected by the second beam splitter (1051) is phase-modulated by the first electro-optical modulator (1052) and then reflected by the optical isolator (1053) into the Fabry-Perot cavity device (102), the laser signal is reflected after interacting with the Fabry-Perot cavity device (102), the signal is detected at a first photoelectric detector (1061), the obtained error signal is demodulated and then fed back to the laser device (101) through a first servo amplifier (1062), the frequency of the laser signal output by the laser device (101) is locked to the resonance peak of the Fabry-Perot cavity device (102), and the excellent short-term stability of the Fabry-Perot cavity device (102) is obtained;

the long-term stability of the frequency of the laser signal output by the laser device (101) is stabilized by the femtosecond optical comb device (103) which is linked to the atomic frequency standard device (104), the laser signal is synthesized into a laser beam by a laser beam reflected by the first beam splitter (1012) and an emergent laser signal of the femtosecond optical comb device (103) which is linked to the atomic frequency standard device (104) after passing through the third beam splitter (1071), a beat frequency signal is detected on the second photoelectric detector (1081), the obtained signal is fed back to the laser device (101) after passing through the second servo amplifier (1082), the frequency of the laser signal output by the laser device is locked to the femtosecond optical comb device (103) which is linked to the atomic frequency standard device (104), and the laser device (101) has the long-term stability of the atomic frequency standard device (104).

4. The passive laser gyroscope of claim 1, characterized in that the high-Q ring cavity interferometer apparatus (200) comprises: a gyro laser preparation unit (201), a third laser transmission unit (202), a fourth laser transmission unit (203), a ring cavity (204), a third feedback unit (205) and a fourth feedback unit (206);

the first laser signal is connected with the input end of a gyro laser preparation unit (201), the first output end of the gyro laser preparation unit (201) is connected to the input end of a third laser transmission unit (202), the second output end of the gyro laser preparation unit (201) is connected to the input end of a fourth laser transmission unit (203), the input and output end of the third laser transmission unit (202) is connected with an annular cavity (204), and the input and output end of the fourth laser transmission unit (203) is connected with the annular cavity (204); the input end of the third feedback unit (205) is connected to the second output end of the fourth laser transmission unit (203), and the input end of the fourth feedback unit (206) is connected to the second output end of the third laser transmission unit (202); the output end of the third feedback unit (205) is connected to the other input end of the ring cavity (204), and the output end of the fourth feedback unit (206) is connected to the other input end of the fourth laser transmission unit (203);

the gyro laser preparation unit (201) is used for carrying out phase modulation on a first laser signal and equally dividing the first laser signal into two beams;

the third laser transmission unit (202) is used for transmitting and injecting the laser signal output by the gyro laser preparation unit (201) into the ring cavity (204);

the fourth laser transmission unit (203) is used for transmitting and injecting another laser signal output by the gyro laser preparation unit (201) into the ring cavity (204);

the ring cavity (204) is used for generating resonance and interference for the two injected laser signals respectively;

the third feedback unit (205) is used for servo-feeding an error signal between a resonant peak of the annular cavity (204) and the laser signal injected along the anticlockwise direction to the piezoelectric ceramic (2045);

the fourth feedback unit (206) is used for servo-feeding an error signal between a resonance peak of the annular cavity (204) and the laser signal injected in the clockwise direction to the second acousto-optic modulator (2031).

5. The passive laser gyroscope of claim 4, characterized in that the cavity length of the ring cavity (204) is stabilized by ultrastable laser light injected in a counter-clockwise direction:

injecting a first laser signal along the anticlockwise direction, carrying out phase modulation through a second electro-optic modulator (2011), generating a carrier signal of laser and two sideband signals with equal amplitude and opposite amplitude after phase modulation, directly reflecting the sidebands by a ring cavity, reflecting the carrier signal and the sidebands together to a third photoelectric detector (2051) through a second Faraday isolator (2033) after interaction of the carrier and the cavity, detecting the detuning quantity of the carrier frequency of the laser and the resonant peak of the ring cavity through the third photoelectric detector (2051), demodulating to obtain an error signal, finally feeding the error signal back to a piezoelectric ceramic (2045) to push a fourth high reflectivity (2044), changing the cavity length of the ring cavity, and locking the cavity length of the ring cavity (204) to the frequency of the laser signal injected along the anticlockwise direction.

6. The passive laser gyro of claim 4 or 5, characterized in that the ultrastable laser signal injected in the clockwise direction is frequency-locked to the cavity length of the ring cavity (204) by a second acousto-optical modulator (2031), wherein:

injecting a laser signal sideband along the clockwise direction to be reflected by the ring cavity, reflecting the sideband with the sideband by a first Faraday isolator (2023) to a fourth photoelectric detector (2061) after the carrier interacts with the cavity, detecting the detuning quantity of the laser carrier frequency and the ring cavity resonance peak by the fourth photoelectric detector (2061), demodulating to obtain an error signal, and finally feeding the error signal back to a second sound optical modulator to drive a voltage-controlled oscillator (2063) to change the modulation frequency f of the second sound optical modulator₂So that the frequency of the laser injected in the clockwise direction resonates with the ring cavity, and the frequency of the laser injected in the clockwise direction is locked to the length of the ring cavity.

7. Passive laser gyro according to claim 1, characterized in that the Sagnac signal is obtained by the difference between the modulation frequencies of the first acousto-optic modulator (2021) and the second acousto-optic modulator (2031), or by the detection of the beat frequency of the overflow light from the two directions behind the cavity.

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