CN109489651B - Four-frequency differential laser gyro Faraday magneto-optical glass installation method - Google Patents
Four-frequency differential laser gyro Faraday magneto-optical glass installation method Download PDFInfo
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- CN109489651B CN109489651B CN201811287531.8A CN201811287531A CN109489651B CN 109489651 B CN109489651 B CN 109489651B CN 201811287531 A CN201811287531 A CN 201811287531A CN 109489651 B CN109489651 B CN 109489651B
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Abstract
The invention relates to a method for installing Faraday magneto-optical glass of a four-frequency differential laser gyroscope, which is characterized in that the orientation of the Faraday magneto-optical glass is adjusted to ensure that reflected light on the surface of the Faraday magneto-optical glass is transmitted to a proper position outside a cavity with the least energy loss as possible, and a photoelectric detector is used for converting the reflected light into an electric signal to stabilize the frequency. Because the frequency stabilization is carried out without using the light transmitted by the reflector, the reflectivity of the reflector can be improved as much as possible during film coating, and the loss of the whole annular cavity is reduced. The method has the advantages that the light energy is fully utilized, the loss of the ring cavity can be reduced, and the intensity of the frequency stabilization signal is basically unchanged.
Description
Technical Field
The invention relates to a four-frequency differential laser gyro, in particular to a Faraday chamber installation method suitable for frequency stabilization of the four-frequency differential laser gyro.
Background
The laser gyro has the advantages of large dynamic range, no acceleration effect, simple structure and the like, is an ideal element of an inertial system, particularly a strapdown inertial system, and is widely applied to the fields of military affairs and civil use. The principle of a laser gyro is the Sagnac (Sagnac) effect, in which at least one pair of counter-propagating light waves runs within its optical cavity. When the laser gyro rotates around the sensitive axis relative to the inertial space, the frequency of opposite traveling waves is split to form beat frequency proportional to the rotation rate, so that the rotation information of the laser gyro relative to the inertial space can be obtained by measuring the beat frequency.
Due to the back scattering of the reflector and other reasons, weak coupling occurs between opposite traveling waves in the annular resonant cavity, and as a result, the laser gyro has a locking effect, so that the laser gyro cannot measure a low rotating speed. The most common method for overcoming the blocking effect is mechanical dithering offset frequency, and the principle is that a mechanical dithering device is used for providing high-frequency small-amplitude angular velocity input, namely 'dithering', for a laser gyro, and then a signal processing technology is adopted for deducting the dithering angular velocity input from an output signal of the laser gyro, so that the actually measured angular velocity is obtained. However, the mechanical shaking device increases the random walk of the laser gyro, reduces the signal bandwidth, and mechanical vibration can generate mechanical interference on other instruments in the inertial system, such as another gyro, an accelerometer, an optical sighting device and the like in the inertial system.
Another widely used scheme for overcoming latch-up is four-frequency differential, which adopts an optical offset frequency method to overcome latch-up, and has great advantages, such as large bandwidth, no mechanical interference, etc. Four traveling wave modes are operated in a resonant cavity of the four-frequency differential laser gyro, a quartz optical rotator or a non-planar ring cavity is adopted to enable a left-handed polarization (LCP) traveling wave and a right-handed polarization (RCP) traveling wave to generate frequency splitting, and a Faraday frequency offset device or a longitudinal magnetic field is applied to a gain medium to establish nonreciprocal frequency splitting between opposite traveling waves with the same polarization so as to avoid a blocking area. The left-hand polarized pair of traveling waves constitutes a left-hand polarized two-frequency single gyroscope (called a left-hand gyroscope), and the right-hand polarized pair of traveling waves constitutes a right-hand polarized two-frequency single gyroscope (called a right-hand gyroscope).
The gain curve of the four-frequency differential laser gyro is shown in fig. 1, the frequency division between the left-handed gyro and the right-handed gyro is called reciprocal division, and the typical value is hundreds of MHz; the frequency split between the two oppositely running traveling waves of each single gyroscope is called a nonreciprocal split, and is typically 0.1MHz-3 MHz. The four-frequency differential laser gyro at least comprises four modes, wherein the frequency of the mode running in the left-handed polarization clockwise direction is f1Amplitude of A1(ii) a The mode frequency for left hand polarization running counter-clockwise is f2Amplitude of A2(ii) a The mode frequency of the counterclockwise operation of the right-hand polarization is f3Amplitude of A3(ii) a The mode frequency of the clockwise operation of the right-hand polarization is f4Amplitude of A4. Frequency difference f of two modes of left-handed gyroscopeLComprises the following steps:
fL＝f2-f1＝F+SΩ (1)
where F is the Faraday offset frequency, S is the geometric scale factor of the ring cavity, and Ω is the input angular velocity.
Frequency difference f of two modes of right-handed gyroscopeRComprises the following steps:
fR＝f4-f3＝F-SΩ (2)
the photoelectric detection device and the corresponding signal processing circuit are adopted to respectively measure the frequency difference of the left-handed gyro and the right-handed gyro and then calculate the difference to obtain the final output of the four-frequency differential laser gyro:
fout＝fL-fR＝2SΩ (3)
namely, the scale factor of the four-frequency differential laser gyro is enhanced by one time compared with that of the two-frequency laser gyro.
In order to obtain a sufficiently high performance, a four-frequency differential laser gyro usually needs frequency stabilization (or cavity length control) to make the loop path length an integer multiple of the resonance wavelength. Us patent "4963026 Cavity length control apparatus for a multi-oscillator" proposes a method for directly detecting a pair of clockwise or counterclockwise mode optical signals transmitted from a ring Cavity mirror of a four-frequency differential laser gyro, then performing radio frequency amplification and performing frequency stabilization by using the extreme value of the amplitude. However, since the reflector of the four-frequency differential laser gyroscope is plated with a high-reflection film, and in order to reduce cavity loss, the light intensity transmittance of the reflector outputting the frequency stabilization optical signal is not too high, and the frequency stabilization optical signal is weak, so that the signal-to-noise ratio of the frequency stabilization circuit is low, and the frequency stabilization precision is influenced. Furthermore, the reflectivity of a general high reflective film can be more than 99.998%, and in order to make the partial light intensity transmitted from the mirror lens enough for frequency stabilization, the transmittance of the mirror needs to be ensured to be about 100ppm, which inevitably increases the cavity Loss by about 80ppm, and the reduction of the cavity Loss is the fundamental means for improving the Limit precision of the Laser gyro [5] Wang Zhiguo, Long Xingwu, Wang Fei.Quantum Limit in Low Loss Ring Laser Gyros [ J ]. Chinese optics Letters,2012,10(6):061404 ].
In a four-frequency differential laser gyro, in order to perform a nonreciprocal offset frequency, it is necessary to use a faraday cell, which is composed of a magnetic field generating device such as a permanent magnet and faraday magneto-optical glass. In order to reduce the reflection loss of Faraday magneto-optical glass, the light-passing surface of the Faraday magneto-optical glass is coated with an antireflection film. The residual reflectivity after plating the antireflection film is about 100ppm generally, and the difficulty of further reducing the reflectivity is very high, so that the Faraday magneto-optical glass always has about 100ppm of partial reflected light on the surface. In a typical four-frequency differential laser gyro design, this portion of reflected light is not utilized and is completely wasted. More detailed information on the faraday cage can be found in the relevant literature cited herein.
Disclosure of Invention
The invention provides a method for adjusting the orientation of Faraday magneto-optical glass to enable surface reflected light to penetrate out of a cavity and stabilizing frequency by utilizing the reflected light.
The invention adopts the following technical scheme:
when Faraday magneto-optical glass is installed in the assembly stage of the four-frequency differential laser gyroscope, the surface normal of the magneto-optical glass is adjusted to form a small included angle with a light beam passing through the Faraday magneto-optical glass, so that reflected light cannot propagate along the optical path of the ring cavity. On the basis of ensuring that the reflected light cannot enter a reverse light path, the orientation of Faraday magneto-optical glass is further finely adjusted, so that the reflected light is transmitted out of the annular cavity from a proper angle and position, and the reflected light is received by a photoelectric detector and subjected to signal processing such as amplification detection and the like to realize frequency stabilization. The light beam is reflected and passes through Faraday magneto-optical glass to become a transmitted light beam, and a considerable part of the light beam is reflected although the surface of the magneto-optical glass is coated with an antireflection film. The orientation of the magneto-optical glass is suitably adjusted so that the reflected light is transmitted from the mirror substrate. For the reflecting mirror using quartz glass as a substrate, the transmittance of the non-film region reaches 96%, and thus the reflected light is effectively utilized. A photoelectric detection assembly is arranged on the outer surface of the reflector to convert the optical signal into an electric signal so as to be processed for frequency stabilization;
the high-reflection film is arranged on the reflector substrate, and the transmittance of the non-film area reaches 96 percent, so that the reflected light is effectively utilized;
for a detailed principle of frequency stabilization, reference may be made to the U.S. patent "4963026 Cavity length control apparatus for a multi-oscillator".
The invention has the advantages that the reflection light on the surface of the Faraday magneto-optical glass is fully utilized, so that the reflectivity of the reflector is improved as much as possible, and the cavity loss is reduced.
Drawings
FIG. 1 is a schematic diagram of the structure of a four-frequency differential laser gyro and the frequency spectrum of its intracavity traveling wave,
figure 2 is a schematic diagram of an apparatus for frequency stabilization using mirror transmitted light,
figure 3 is a schematic representation of the reflection of a laser beam at the surface of faraday magneto-optical glass,
figure 4 is a schematic diagram of one way to obtain faraday magneto-optical glass surface reflection,
figure 5 is another schematic diagram of obtaining faraday magneto-optical glass surface reflection light.
Detailed Description
The following detailed description of specific embodiments is provided in connection with the accompanying drawings
Fig. 1 is a schematic diagram of a four-frequency differential laser gyro structure and mode distribution on a gain curve thereof. An air inflation and light transmission pipeline is processed on the low expansion cavity 1, and four reflectors 5, 6, 7 and 8 are arranged at four corners of the cavity. Two anodes 2, 3 and one cathode 4 are used to provide gain. Reference numeral 10 is a reciprocal frequency offset device, which may be implemented as a crystal or non-planar cavity, and functions to provide an offset frequency between gyroscopes 1 and 2 of a four-frequency differential laser gyroscope to avoid mode competition. 9 is a nonreciprocal offset frequency device, which generates nonreciprocal offset frequency between two modes with the same polarization of the four-frequency differential laser gyro to avoid locking. The four-frequency differential laser gyro operates in a cavity with 4 modes, wherein the modes 12 and 13 form a gyro 1, and the modes 14 and 151 form a gyro 2;
fig. 2 is a schematic diagram of an apparatus for frequency stabilization by using mirror transmitted light, laser in a cavity of a four-frequency differential laser gyro partially penetrates out of a mirror 7 and is incident on a photosensitive surface of a photodetector 15, a current-voltage converter 16 is used for converting a current output by the detector into a voltage signal, the voltage signal is amplified to a proper amplitude by a high-frequency amplifier 19, and then the amplitude of the signal is detected by an amplitude detector 20. The oscillator 24 outputs a sine waveform or a square wave with a certain frequency, the output signal is connected to the reference input end of the phase sensitive detector 21, and the output of the amplitude detector 20 is input to the signal input end of the phase sensitive detector 21. The phase-sensitive detection output is an error signal for frequency stabilization, and is processed by a PID controller 22 to obtain a correction voltage, and the correction voltage is processed by a piezoelectric ceramic driver 23 to generate a voltage signal for driving piezoelectric ceramic. The oscillating voltage of the oscillator output is connected to the piezoelectric ceramic at the adder 25 in superposition with the output of the piezoelectric ceramic driver 23, so that the position of the piezoelectric ceramic is moved to a position where the amplitude of the signal of the amplitude detector 20 is maximized, and the oscillating voltage is used to modulate the position of the piezoelectric ceramic.
Figure 3 shows the reflection path diagram of light on the surface of faraday magneto-optical glass. The light beam 40 is incident on the surface of faraday magneto-optical glass 41 and most of the light is transmitted and only a small part of the light 43 is reflected. The position and direction of the reflected light are related to the position and orientation of the Faraday magneto-optical glass in the loop. To avoid that the reflected light 43 enters the path of the light beam opposite to the direction of travel of the light beam 40, the normal to the surface of the faraday magneto-optical glass 41 is typically at a small angle to the direction of the light beam 40. Typically, the reflected light 43 is randomly positioned outside the annular cavity and may be blocked from passing out by other components, such as magnets.
In the invention, the reflected light 43 is transmitted out of the annular cavity with the loss as small as possible by adjusting the orientation of Faraday magneto-optical glass 41, and is received by a photoelectric detector to be used as an optical signal for frequency stabilization;
one proposed solution is shown in figure 4. In the figure 40 is the beam running in a clockwise loop, 44 is a mirror substrate, typically quartz glass, and 45 is a highly reflective film on the mirror substrate. The mirrors composed of a mirror substrate and a highly reflective film on the mirror substrate include the mirrors of mirrors 5, 6, 7, 8 of fig. 1, 2. The light beam 40 is reflected and passes through a faraday magneto-optical glass 41 as a transmitted light beam 42, a substantial part of which is reflected despite the anti-reflection coating on the surface of the magneto-optical glass 41. The orientation of the magneto-optical glass is suitably adjusted to allow transmission of reflected light from the mirror substrate 44. Taking fig. 4 as an example, if an angle θ is formed between the surface of the faraday magneto-optical glass 41 and the light ray 40, and if the distance between the light ray incidence point on the surface of the faraday magneto-optical glass 41 and the light ray incidence point of the high reflection film 45 is tried to be d, the angle θ satisfies the requirement
Wherein r is1Is high film reflection radius, r2The radius of the light-transmitting pipeline; in the mirror using quartz glass as a substrate, the transmittance of the non-film region reaches 96%, and thus the reflected light 43 is effectively utilized. Photoelectric detection assembly arranged on the outer surface of the reflector for converting optical signals into electric signalsSo as to carry out processing and frequency stabilization;
considering that the adhesion of the photodetector assembly to the surface of the mirror may generate thermal stress when the temperature changes, and the mechanical stress when the photodetector assembly is adhered, the solution of penetrating the mirror may cause the performance degradation of the mirror, such as stress birefringence, mirror deformation, etc., another proposed solution is to transmit the reflected light from the surface of the faraday magneto-optical glass from other places of the glass-ceramic cavity, and fix the photodetector assembly in the corresponding position, as shown in fig. 5. In fig. 5, the reflected light 43 reflected from the surface of the faraday magneto-optical glass passes through the cavity and exits the cavity, and a suitable structure is formed on the microcrystalline glass cavity to place a photodetector to receive the reflected light 43. The angle of the faraday magneto-optical glass 41 with the slot and the position at which the photo detection assembly 46 is mounted are designed according to the law of reflection of light. The advantage of this scheme is that the light-combining component and the detecting component are not fixed on the reflector, so that no stress is generated on the reflector;
the principles of this patent may be modified slightly by those skilled in the art to better utilize reflected light for frequency stabilization, but the basic principles are not changed.
Claims (1)
1. The method for installing Faraday magneto-optical glass of four-frequency differential laser gyro includes regulating the orientation of Faraday magneto-optical glass to make the reflected light on its surface not lose energy and transmit out of cavity, converting the reflected light into electric signal with photoelectric detector, and further processing the signal to stabilize frequency,
when Faraday magneto-optical glass is installed in the assembly stage of the four-frequency differential laser gyroscope, adjusting the surface normal of the magneto-optical glass to form an included angle with a light beam passing through the Faraday magneto-optical glass, so that reflected light cannot propagate along the optical path of the annular cavity, further finely adjusting the orientation of the Faraday magneto-optical glass on the basis of ensuring that the reflected light cannot enter a reverse optical path, transmitting the reflected light out of the annular cavity, receiving the reflected light by using a photoelectric detector, and amplifying and detecting signals to realize frequency stabilization;
the reflecting mirror with quartz glass as substrate has high reflecting film, Faraday magneto-optical glass surface and light beam forming angle theta, and the distance between the light incident point on the Faraday magneto-optical glass surface and the light incident point of the high reflecting film is d, so that the angle theta satisfies the requirement
Wherein r is1Is high film reflection radius, r2The radius of the light-transmitting pipeline; the transmittance of the non-membrane region reaches 96%, and a photoelectric detection assembly is arranged on the outer surface of the reflector to convert optical signals into electric signals so as to be processed for frequency stabilization;
the light beam is incident on the surface of the Faraday magneto-optical glass, most light is transmitted, only a small part of light is reflected, the position and the direction of the reflected light are related to the position and the direction of the Faraday magneto-optical glass in a loop, in order to avoid the reflected light entering a light path opposite to the running direction of the light beam, a small included angle is formed between the normal line of the surface of the Faraday magneto-optical glass and the direction of the light beam, the reflected light is enabled to be transmitted out of the annular cavity with the smallest loss as possible by adjusting the direction of the Faraday magneto-optical glass, and the reflected light is received by a photoelectric detector to serve as a light signal.
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| CN112556679B (en) * | 2020-11-19 | 2022-03-18 | 中国人民解放军国防科技大学 | Positive and negative plug-cock Raman space four-frequency differential laser gyro |
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| CN101008568A (en) * | 2006-01-27 | 2007-08-01 | 泰勒斯公司 | No-blind-area four-mode stable solid state laser gyroscope |
| CN102003957A (en) * | 2010-10-01 | 2011-04-06 | 中国人民解放军国防科学技术大学 | Four-frequency laser gyro zero offset compensation method |
| CN102023006A (en) * | 2010-10-01 | 2011-04-20 | 中国人民解放军国防科学技术大学 | Four-frequency laser gyro electronic reading system |
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| JPS5861689A (en) * | 1981-10-07 | 1983-04-12 | Nec Corp | Multi-wavelength ring laser gyroscope |
| CN103674487B (en) * | 2012-09-07 | 2016-04-20 | 中国航空工业第六一八研究所 | A kind of laser gyro ultra-smooth catoptron backscattering measurement mechanism and method |
| CN103033178B (en) * | 2012-09-20 | 2015-05-27 | 中国人民解放军国防科学技术大学 | Laser gyroscope offset frequency method based on external cavity feedback |
| CN203615937U (en) * | 2013-12-10 | 2014-05-28 | 中国航空工业第六一八研究所 | Optical demodulating device for four-frequency differential laser gyro |
| CN103994774A (en) * | 2013-12-16 | 2014-08-20 | 西安北方捷瑞光电科技有限公司 | Double-longitudinal mode frequency self-offset detection system and detection method of prism laser gyro |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101008568A (en) * | 2006-01-27 | 2007-08-01 | 泰勒斯公司 | No-blind-area four-mode stable solid state laser gyroscope |
| CN102003957A (en) * | 2010-10-01 | 2011-04-06 | 中国人民解放军国防科学技术大学 | Four-frequency laser gyro zero offset compensation method |
| CN102023006A (en) * | 2010-10-01 | 2011-04-20 | 中国人民解放军国防科学技术大学 | Four-frequency laser gyro electronic reading system |
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