CN109520491B - Continuous optical track angular momentum resonant cavity gyroscope - Google Patents
Continuous optical track angular momentum resonant cavity gyroscope Download PDFInfo
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- CN109520491B CN109520491B CN201910027396.1A CN201910027396A CN109520491B CN 109520491 B CN109520491 B CN 109520491B CN 201910027396 A CN201910027396 A CN 201910027396A CN 109520491 B CN109520491 B CN 109520491B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C19/00—Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
- G01C19/58—Turn-sensitive devices without moving masses
- G01C19/64—Gyrometers using the Sagnac effect, i.e. rotation-induced shifts between counter-rotating electromagnetic beams
- G01C19/72—Gyrometers using the Sagnac effect, i.e. rotation-induced shifts between counter-rotating electromagnetic beams with counter-rotating light beams in a passive ring, e.g. fibre laser gyrometers
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- G—PHYSICS
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- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
- G02B26/001—Optical devices or arrangements for the control of light using movable or deformable optical elements based on interference in an adjustable optical cavity
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- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
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- G02B27/286—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising for controlling or changing the state of polarisation, e.g. transforming one polarisation state into another
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Abstract
The invention discloses a continuous optical track angular momentum resonant cavity gyroscope, which mainly comprises a laser light source, a conjugated superposition phase plate, a high-quality factor optical resonant cavity, a mode matching lens-prism group, a piezoelectric ceramic servo system and a balance differential detector. By constructing and locking the structure of the optical resonant cavity, the influence of angular velocity on the mode evolution carrying orbital angular momentum is extracted and converted into an electric signal for output. Compared with an optical fiber gyroscope, the optical fiber gyroscope adopts the evolution of the orbital angular momentum mode in the optical resonant cavity, replaces the propagation of light in the optical fiber, and avoids the problem of loss when the light propagates in the optical fiber. The invention has the characteristics of stable structure, large space, convenient data reading and the like, and the precision can be optimized. The invention can be used for precise navigation, positioning, signal sensing and the like.
Description
Technical Field
The invention relates to a gyroscope, in particular to a continuous optical track angular momentum resonant cavity gyroscope.
Background
Gyroscopes are devices that measure the rotational angular velocity relative to an inertial reference frame. Fiber optic gyroscopes are one of the commercial products.
The optical fiber gyroscope divides the monochromatic light beam into two parts, and the two parts are respectively coupled into opposite loop directions of one optical fiber disc, so that interference fringes are generated at an output end. Due to the Sagnac (Sagnac g.) effect, when the fiber optic disc rotates in the plane of the loop, the interference fringes will move by an amount proportional to the angular velocity of rotation and the area of the loop. In order to achieve a large loop area, long fibers are used, so that a part of the light intensity will be lost during propagation, which will reduce the visibility of interference fringes due to the quantum noise, thereby limiting further improvement of the resolution of the fiber optic gyroscope. Loss in the fiber is a bottleneck limiting resolution of today's fiber optic gyroscopes, requiring a new design to avoid loss of light in propagation.
Disclosure of Invention
The invention aims to provide a continuous optical track angular momentum resonant cavity gyroscope which has the advantages of stable structure, large space, convenient data reading and the like, and the precision can be optimized.
The invention aims at realizing the following technical scheme:
a continuous optical orbital angular momentum cavity gyroscope comprising: the system comprises a bicolor laser light source, a conjugated superposition phase plate, a first dichroic mirror, a second dichroic mirror, an optical resonant cavity, a photoelectric detector, a mode matching lens-prism group, a piezoelectric ceramic servo system and a balance differential detector; wherein:
the bicolor laser light source outputs signal light and reference light; a part of signal light A1 is received by a first optical signal input end of the balanced differential detector before passing through the conjugate superposition phase plate; the other part of the signal light A2 carries out mode conversion through a conjugate superposition state phase plate, carries conjugate superposition state orbital angular momentum and is injected into the first dichroic mirror; meanwhile, reference light is also emitted into the first dichroic mirror, the optical axes of the signal light A2 and the reference light are completely overlapped on the first dichroic mirror, the signal light and the reference light enter the optical resonant cavity together, the reference light is reflected by the second dichroic mirror and enters the photoelectric detector, and the piezoelectric ceramic servo system stabilizes the length of the resonant cavity at a resonant point according to an error signal emitted from the optical resonant cavity by the reference light detected by the photoelectric detector; the signal light A2 is transmitted from the second dichroic mirror and then is rotated by a certain angle through the mode matching lens-prism group and the conjugated superposition phase plate, the signal light A2 is received by the second optical signal input end of the balanced differential detector after mode matching and mode conversion, and the result of the amplified difference of the light intensities of the two optical signals is obtained by the balanced differential detector, so that the rotation angle of the gyroscope is determined.
According to the technical scheme provided by the invention, the evolution of the orbital angular momentum mode in the optical resonant cavity is adopted to replace the light propagation in the optical fiber, so that the problem of loss when the light propagates in the optical fiber is avoided, and the higher angular velocity resolution precision can be realized by inputting higher light intensity, increasing the reflectivity of the cavity mirror and improving the orbital angular momentum number of the input mode.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the description of the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a continuous optical orbital angular momentum cavity gyroscope according to an embodiment of the invention;
fig. 2 is a schematic diagram of evolution of an optical mode carrying orbital angular momentum according to an embodiment of the invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to fall within the scope of the invention.
The embodiment of the invention provides a continuous optical track angular momentum resonant cavity gyroscope, which mainly comprises the following components: the system comprises a bicolor laser light source, a conjugated superposition phase plate, a first dichroic mirror, a second dichroic mirror, an optical resonant cavity, a photoelectric detector, a mode matching lens-prism group, a piezoelectric ceramic servo system and a balance differential detector; wherein:
the bicolor laser light source outputs signal light and reference light; a part of signal light A1 is received by a first optical signal input end of the balanced differential detector before passing through the conjugate superposition phase plate; the other part of the signal light A2 carries out mode conversion through a conjugate superposition state phase plate, carries conjugate superposition state orbital angular momentum and is injected into the first dichroic mirror; meanwhile, reference light is also emitted into the first dichroic mirror, the optical axes of the signal light A2 and the reference light are completely overlapped on the first dichroic mirror, the signal light and the reference light enter the optical resonant cavity together, the reference light is reflected by the second dichroic mirror and enters the photoelectric detector, and the piezoelectric ceramic servo system stabilizes the length of the resonant cavity at a resonant point according to an error signal emitted from the optical resonant cavity by the reference light detected by the photoelectric detector; the signal light A2 is transmitted from the second dichroic mirror and then is rotated by a certain angle through the mode matching lens-prism group and the conjugated superposition phase plate, the signal light A2 is received by the second optical signal input end of the balanced differential detector after mode matching and mode conversion, and the result of the amplified difference of the light intensities of the two optical signals is obtained by the balanced differential detector, so that the rotation angle of the gyroscope is determined.
In an embodiment of the present invention, the mode matching lens-prism group includes: the device comprises a dove prism, a first mode matching lens and a second mode matching lens which are sequentially arranged; the signal light A2 passes through the dove prism and the first mode matching lens and then enters the second mode matching lens through the conjugated superposition phase plate.
According to an embodiment of the present invention, the gyroscope further includes: the first half wave plate, the second half wave plate, the first polarization beam splitting prism, the second polarization beam splitting prism, the single mode fiber, the first reflecting mirror, the second reflecting mirror and the third reflecting mirror;
the signal light is modulated into linearly polarized light through a first half wave plate, and a vertically polarized part, namely the signal light A1, is received by a first optical signal input end of the balanced differential detector after being reflected by a first polarization beam splitter prism; the horizontal polarization part, namely the signal light A2, is transmitted by the first polarization beam splitter prism, after entering the conjugated superposition phase plate, the signal light A2 is converted into a conjugated superposition Laguerre-Gaussian mode from the Gaussian mode, and then all the signal light A2 is transmitted out of the second polarization beam splitter prism to enter the first dichroic mirror;
the signal light A2 which is transmitted from the second double color is sequentially transmitted through the first reflecting mirror, the second half wave plate and the second reflecting mirror and then enters the dove prism, the dove prism is rotated by a certain angle, then is reflected to the first mode matching lens through the third reflecting mirror to achieve optimal matching, then enters the conjugated superposition phase plate again through the reflection of the second polarization beam splitting prism to restore to the Gaussian mode, and then is reflected by the first polarization beam splitting prism to be focused by the second mode matching lens, wherein only part of the signal light is restored to the Gaussian mode when entering the conjugated superposition phase plate again, and is received by the second optical signal input end of the balanced differential detector through the single mode fiber; the other part is not restored to the Gaussian mode, cannot be focused by the second mode matching lens, and is finally filtered by the single-mode optical fiber.
According to the embodiment of the invention, the piezoelectric ceramic servo system comprises: piezoelectric ceramics and piezoelectric ceramics servo; the piezoelectric ceramic servo uses the Pound-Drewer-Hall technology, and utilizes error signals emitted by reference light from the optical resonant cavity to control the expansion and contraction of the piezoelectric ceramic.
In the embodiment of the invention, the optical resonant cavity is used for delaying the propagation of signal light A2 carrying orbital angular momentum and comprises two cavity mirrors; the two cavity mirrors are glass plane-concave reflecting mirrors, the two concave surfaces are oppositely arranged, the planes are not coated with films, and the concave surfaces are coated with double-wavelength high-reflection films; the piezoelectric ceramic center portion is hollowed out and glued to the cavity mirror plane near the second dichroic mirror.
Illustratively, the highly reflective film has an amplitude reflectivity of at least 97% for the signal light.
According to an embodiment of the present invention, the gyroscope further includes: a periodic optical switch and a lock-in amplifier; the periodic optical switch and the phase-locked amplifier are connected to the same reference signal source, and the phase-locked amplifier is also connected with the electric signal output end of the balanced differential detector;
the periodic optical switch is a circular turntable with a through window, the turntable is driven by a motor and is locked with a reference signal in frequency and phase, and the periodic optical switch and the phase-locked amplifier are provided with internal synchronous devices, so that the periodic optical switch can realize periodic on/off at the frequency of the reference signal, and in one period, only a part of time of the signal light A can pass through the periodic optical switch input system, thereby achieving the purpose of applying periodic amplitude modulation to the incident signal light A. Simultaneously, the reference signal and the output electric signal of the balanced differential detector are input into a phase-locked amplifier, the result of the phase-locked amplifier is the product of the reference signal and the electric signal (the frequencies of the two signals are the same) output by the balanced differential detector, and the result is nonzero and corresponds to the reading of the gyroscope; the jitter caused by the environmental noise has no obvious frequency characteristic, so that the jitter is eliminated by averaging to 0, and the purpose of increasing the signal-to-noise ratio is achieved.
For ease of understanding, the structure and principles of the gyroscope of the present invention are further described below with reference to the accompanying drawings.
1. A gyroscope structure.
As shown in fig. 1, it mainly includes: the device comprises a signal light A, a periodic optical switch 1, a first half wave plate 2, a second half wave plate 17, a first polarization beam splitter prism 3, a second polarization beam splitter prism 5, a conjugate superposition phase plate 4, a first dichroic mirror 6, a second dichroic mirror 10, a first high-reflectivity cavity mirror 7, a second high-reflectivity cavity mirror 8, piezoelectric ceramics 9, a reference laser light source 11, a piezoelectric ceramics server 12, a photoelectric detector 13, first to third reflectors 14-16, a dove prism 18, a first pattern matching lens 19, a second pattern matching lens 20, a balanced differential detector 21 and a lock-in amplifier 22.
The signal light a and the reference light are output by a two-color laser light source (not shown in fig. 1). The solid line passing through the element in fig. 1 represents the signal light, and the broken line represents the reference light. The signal light is modulated into linear polarized light through the half wave plate 2, and the vertical polarized light is directly reflected by the polarization beam splitter prism 3 and is collected by the upper path (i.e. the first optical signal input end) of the balanced differential detector 21. The horizontal polarization part passes through the polarization beam splitter prism 3, passes through the conjugate superposition phase plate 4 for the first time, and then passes through the polarization beam splitter prism 5 entirely. The first dichroic mirror 6 and the second dichroic mirror 10 are antireflective for signal light wavelengths and highly reflective for reference light wavelengths. The optical axes of the signal light and the reference light are completely overlapped on the first dichroic mirror 6, and the signal light and the reference light jointly enter a resonant cavity formed by the first high-reflectivity cavity mirror 7 and the second high-reflectivity cavity mirror 8. In the embodiment of the invention, the high-reflectivity cavity mirrors 7 and 8 are glass plane concave surface reflecting mirrors, and the two concave surfaces are oppositely arranged and the planes are oppositely arranged; the plane is not coated with a film, and the concave surface is coated with a dual-wavelength high-reflection film. The piezoelectric ceramic 9 is hollowed in the center, and is glued on the plane of the cavity mirror 8 by using 502 strong glue, and the voltage is controlled by the server 12, so that the relative position is adjusted.
The reference laser source 11 is frequency tunable to a frequency at which it has the same resonance point in the cavity as the signal laser carrying the higher order orbital angular momentum. The reference light emitted by the reference laser source 11 and passing through the cavity carries a frequency modulation sideband, which is reflected off the subsequent optical path by the dichroic mirror 10 and received by the photodetector 13. Using the mount-Drewer-Hall technique, the server 12 can control the extension and retraction of the piezoelectric ceramic 9 with the optical signal received by the photodetector 13, so that the resonant cavity length is maintained at the resonance point of the signal light.
The first to third reflectors 14 to 16 guide the signal light mode carrying the conjugated superimposed state orbital angular momentum, the signal light mode is firstly converted into vertical polarization through the second half wave plate 17, then is turned by a certain angle through the dove prism 18, and after the best matching is achieved through the mode matching lens 19 again, only about half of the power on the conjugated superimposed state phase plate 4 is restored to the Gaussian mode, and is focused by the second mode matching lens 20, enters a single mode fiber, is collected by the lower path of the balanced differential detector 21, and the mode corresponding to the other half of the power carries the orbital angular momentum and cannot be focused to one point, and finally is filtered by the single mode fiber.
The periodic optical switch 1 and the lock-in amplifier 22 can average the rotational speed over a longer period. The periodic optical switch is a circular rotary table with a through window, the rotary table is driven by a motor and is locked with a reference signal source in frequency and phase, and meanwhile, the reference signal source is input into a phase-locked amplifier, so that the digitized electric signal output by the differential detector can be read in the phase-locked amplifier, and the electric signal output by the differential detector is balanced evenly in a certain period.
In addition, the periodic optical switch 1 and the phase-locked amplifier 22 are used, and the power of the part with the same frequency as the reference signal source in the signal is extracted at the phase-locked amplifier side, so that the noise with the frequency different from the reference signal source after the periodic optical switch 1 in the optical path is restrained.
In the embodiment of the invention, the periodic optical switch 1 can be an electrical switch or a mechanical switch, preferably an electrical switch is used, and the polarity of the signal input by the balanced differential detector to the lock-in amplifier is reversed every half of the period of the reference signal, so that the error can be further reduced, and the detection precision is improved.
2. Principle of operation
1. A bi-color laser light source.
The bicolor laser light source outputs laser with two wavelengths, one is used for generating signal light carrying high-order orbital angular momentum, and the other is used as reference light for locking the resonant cavity after electro-optical modulation. Both wavelengths of laser light remain locked to the ultra-stable reference cavity outside the device, ensuring that both have a stable frequency.
2. Conjugated superimposed phase plates.
The conjugated superimposed phase plate is a circular optical element, and the surface of the conjugated superimposed phase plate is uniformly divided into 2l sectors with the apex angle of pi/l, wherein l is the order of the conjugated superimposed phase plate. Each sector in turn having a relative phaseGaussian mode laser light generated by light source (0)>Beam expansion, after transmission through the centre of the phase plate, is converted into a conjugate superimposed Laguerre-Gaussian (Laguerre-Gaussian) mode |l>+|-l>。
The conjugate superimposed phase plate can pass normal incidence through |l of its own center>+exp(2iθ)|-l>Mode with η=cos 2 The efficiency of θ translates back to gaussian mode. Wherein l>+exp(2iθ)|-l>Is a rotated conjugate superimposed orbital angular momentum pattern, which can be represented by |l>+|-l>The pattern is rotated by θ/m about its own center.
The beam may carry intrinsic angular momentum in two parts, one spin angular momentum from polarization and the other orbital angular momentum from the shape of the helical wavefront. A single continuous beam of lager-gaussian mode light has a well-defined orbital angular momentum of the magnitude of each photonWherein l is an integer parameter describing the Laguerre-Gaussian mode, +.>Is about the planck constant. The use of a conjugated superimposed phase plate allows for the interconversion between the gaussian mode directly output by the laser and the lagrangian-gaussian mode described above.
3. A dichroic mirror.
The two-color mirror is used to completely combine and separate the spatial positions of the two wavelength lasers in the optical path. At 45 degree incidence, the surface of the dichroic mirror is antireflective to the wavelength of the signal light, while it is nearly fully reflective to the wavelength of the reference light.
4. An optical resonator.
An optical resonator is a structure that uses several high reflectivity mirrors to limit the propagation of light so that the light can internally reflect the superposition. For a passive cavity without amplification medium inside, a beam of laser light containing multiple modes is coupled in from outside, and only specific modes meeting the resonance condition are overlapped and constructive in the laser light, and can leave the cavity from the output end, and the modes are called as eigenmodes of the cavity. The other modes are returned to the input. The mirror shape is a stable cavity with a circular shape and the transverse eigenmode is the Laguerre-Gaussian (Laguerre-Gaussian) mode. When continuous light is input into the resonant cavity, the output mode is coherent superposition of signals reflected for different times from different previous moments. By using the round-tailer-Hall technique, the length and resonant mode of the optical resonant cavity can be kept stable in an unstable environment by means of negative feedback of the reference light source. In the cavity, the light is equivalent to propagating in free space or air medium, and the loss is smaller than propagating in optical fiber medium.
In the embodiment of the invention, each cavity mirror of the optical resonant cavity has high reflectivity to the signal light and the reference light, wherein the transmission coefficient of the signal light intensity is T < 1 (the magnitude of T is 10 -2 Left-right), the cavity having a free spectral range v FSR Input |l>+|-l>The mode delays the output after multiple reflections therein. When the conjugate superimposed phase plate rotates at an angular velocity Ω with the input light as an axis, the incident modes from different times are mixed, and the mode of actual output becomes:
5. piezoelectric ceramic servo system.
The piezoelectric ceramic servo system uses a reference light source to emit an error signal from the cavity, and uses the Pound-Drewer-Hall technology to control the position of a cavity mirror, so as to stabilize the length of the resonant cavity at |psi 1 >At the corresponding longitudinal mode resonance point.
6. Pattern matching lens-prism assembly
The pattern matching lens-prism assembly includes a Dove (Dove) prism and a pair of pattern matching convex lenses. Wherein, the conjugated superposition incident mode can be rotated by a certain angle by using the dove prism, in the device, the rotation angle of the dove prism is pi/8 l, so that the output mode is changed to pi/4 l along the central axis, and the output mode is evolved into:
the pattern matching convex lens group is composed of |psi 2 >Converting the mode matched with the resonant cavity into a near-parallel mode, and enabling the near-parallel mode to pass through the conjugated superposition phase plate againMode conversion occurs. The efficiency of the conversion to gaussian mode is:
7. balanced differential detectors.
The balanced differential detector has two optical signal inputs and an electrical signal output. The two optical signals are respectively input into a signal obtained by splitting before the phase plate for the first time and a signal collected by an optical fiber after being reconverted into a Gaussian mode for the second time. The electric signal outputs the result of the amplified difference between the light intensities of the two optical signals.
When the first optical signal (i.e., the signal obtained by splitting the beam before the phase plate) is adjusted so that the gyroscope is stationary, the intensities of the two optical signals are equal, and when the gyroscope rotates, the magnitude B of the electrical signal output by the balanced differential detector is a simple function of the rotation angle of the system:
when the balanced differential detector is used for solving the differential signal, possible errors caused by the total input laser intensity jitter are subtracted, so that the zero point position of the rotation speed measurement is insensitive to the deviation of the total light intensity.
Fig. 2 gives an example of the evolution of the optical mode for carrying orbital angular momentum.
As shown in fig. 2, a conjugated superimposed phase plate with l=3 is used. An observer always observes the system in the direction of the input light and keeps the conjugate superimposed phase plate stationary relative to himself, now he tries to judge the overall rotational speed of the system and himself. In fig. 2, all dashed lines represent the angle of the reference point in the mode when the system is stationary, and the solid lines represent the true angle of the reference point in the rotating system.
The input signal beam is initially in a gaussian mode (e.g., a in fig. 2), denoted as |0>First pass through a commonAfter the yoke is overlapped with the phase plate, an orbital angular momentum mode |3 is obtained>+|-3>The appearance is a six-lobed petal shape (e.g., b in fig. 2). If this pattern is rotated counter-clockwise by θ along the symmetry axis, the new pattern will be 3>+e i(12)θ |-3>. Considering now the results of the output cavity, assuming that the system has a stable total angular velocity Ω in the direction perpendicular to the surface of the phase plate, the output pattern comprises portions that pass directly through the cavity, portions that are reflected twice in total by two cavity mirrors, portions that are reflected four times, … … each portion being 1/v earlier than the last portion FSR Into the cavity so that the angle of the phase plate is behind omega/v from the current moment FSR . The mode of the output obtained by the superposition and summation of the amplitudes for all modes is as follows:
i.e. rotated clockwise by omega/v compared to the mode prior to the input chamber FSR The angle of T (e.g., c in fig. 2).
Next |ψ 1 >By turning the reflecting surface through a 7.5 ° dove prism from horizontal, a 15 degree counter-clockwise rotation (e.g. d in fig. 2) evolves as:
|ψ 2 >projection measurements (e.g. e in fig. 2) are made to gaussian mode, again through the conjugate superimposed phase plate.
In fig. 2, four typical measurements are shown. Firstly, a Gaussian mode is evolved into a conjugated superposition state through a phase plate, and is collected by using a single-mode fiber, which is equivalent to measurement in the Gaussian mode, the result is 0, and the position of the single-mode fiber is fixed; secondly, a |3> ++ | -3> mode is completely converted into a Gaussian mode by a phase plate, and all power is obtained through collection of single-mode fibers; thirdly, a mode of |3> +i| -3> is evolved into a Gaussian mode by a phase plate with the efficiency of 1/2, and a single-mode fiber collects half of the power; fourth, one |3> - | -3> mode is completely evolved by the phase plate to a |6> - | -6> mode, and the single mode fiber does not collect power, resulting in 0. The power of the first and fourth measurements is 0 and is therefore not shown in fig. 2.
In the experiment, the power collected by the single mode fiber is:
next, the observer can determine the rotational angular velocity of the system in which he is located in the above-described direction by using the method of balance detection as long as he is described in the above-described scheme.
The foregoing is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions easily contemplated by those skilled in the art within the scope of the present invention should be included in the scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.
Claims (2)
1. A continuous optical orbital angular momentum cavity gyroscope, comprising: the system comprises a bicolor laser light source, a conjugated superposition phase plate, a first dichroic mirror, a second dichroic mirror, an optical resonant cavity, a photoelectric detector, a mode matching lens-prism group, a piezoelectric ceramic servo system and a balance differential detector; wherein:
the bicolor laser light source outputs signal light and reference light; a part of signal light A1 is received by a first optical signal input end of the balanced differential detector before passing through the conjugate superposition phase plate; the other part of the signal light A2 carries out mode conversion through a conjugate superposition state phase plate, carries conjugate superposition state orbital angular momentum and is injected into the first dichroic mirror; meanwhile, reference light is also emitted into the first dichroic mirror, the optical axes of the signal light A2 and the reference light are completely overlapped on the first dichroic mirror, the signal light and the reference light enter the optical resonant cavity together, the reference light is reflected by the second dichroic mirror and enters the photoelectric detector, and the piezoelectric ceramic servo system stabilizes the length of the resonant cavity at a resonant point according to an error signal emitted from the optical resonant cavity by the reference light detected by the photoelectric detector; the signal light A2 is transmitted from the second dichroic mirror, then is rotated by a certain angle through a mode matching lens-prism group and a conjugated superposition phase plate, is received by a second optical signal input end of a balanced differential detector after mode matching and mode conversion, and is amplified to obtain a result of the difference of the light intensities of two optical signals by the balanced differential detector, so that the rotation angle of the gyroscope is determined;
the pattern matching lens-prism group includes: the device comprises a dove prism, a first mode matching lens and a second mode matching lens which are sequentially arranged; the signal light A2 passes through the dove prism and the first mode matching lens and then enters the second mode matching lens through the conjugated superposition phase plate;
the gyroscope further includes: the first half wave plate, the second half wave plate, the first polarization beam splitting prism, the second polarization beam splitting prism, the single mode fiber, the first reflecting mirror, the second reflecting mirror and the third reflecting mirror;
the signal light is modulated into linearly polarized light through a first half wave plate, and a vertically polarized part, namely the signal light A1, is received by a first optical signal input end of the balanced differential detector after being reflected by a first polarization beam splitter prism; the horizontal polarization part, namely the signal light A2, is transmitted by the first polarization beam splitter prism, after entering the conjugated superposition phase plate, the signal light A2 is converted into a conjugated superposition Laguerre-Gaussian mode from the Gaussian mode, and then all the signal light A2 is transmitted out of the second polarization beam splitter prism to enter the first dichroic mirror;
the signal light A2 which is transmitted from the second double color is sequentially transmitted through the first reflecting mirror, the second half wave plate and the second reflecting mirror and then enters the dove prism, the dove prism is rotated by a certain angle, then is reflected to the first mode matching lens through the third reflecting mirror to achieve optimal matching, then enters the conjugated superposition phase plate again through the reflection of the second polarization beam splitting prism to restore to the Gaussian mode, and then is reflected by the first polarization beam splitting prism to be focused by the second mode matching lens, wherein only part of the signal light is restored to the Gaussian mode when entering the conjugated superposition phase plate again, and is received by the second optical signal input end of the balanced differential detector through the single mode fiber; the other part is not restored to the Gaussian mode, cannot be focused by the second mode matching lens, and is finally filtered by the single-mode fiber;
the optical resonant cavity is used for delaying the propagation of signal light A2 carrying orbital angular momentum and comprises two cavity mirrors; the two cavity mirrors are glass plane-concave reflecting mirrors, the two concave surfaces are oppositely arranged, the planes are not coated with films, and the concave surfaces are coated with double-wavelength high-reflection films; the piezoelectric ceramic center part is hollowed out and glued on a cavity mirror plane close to the second dichroic mirror;
the gyroscope further includes: a periodic optical switch and a lock-in amplifier; the periodic optical switch and the phase-locked amplifier are connected to the same reference signal source, and the phase-locked amplifier is also connected with the electric signal output end of the balanced differential detector;
the periodic optical switch is a circular turntable with a through window, the turntable is driven by a motor and is locked with a reference signal in frequency and phase, and the periodic optical switch and the phase-locked amplifier are provided with internal synchronous devices, so that the periodic optical switch can realize periodic on/off at the frequency of the reference signal, and in one period, only a part of time of signal light A passes through the periodic optical switch input system;
the result of the lock-in amplifier is the product of the reference signal and the electrical signal output by the balanced differential detector, with a non-zero result, corresponding to the gyroscope reading.
2. A continuous optical orbital angular momentum cavity gyroscope according to claim 1, wherein,
the piezoelectric ceramic servo system comprises: piezoelectric ceramics and piezoelectric ceramics servo; the piezoelectric ceramic servo uses the Pound-Drewer-Hall technology, and utilizes error signals emitted by reference light from the optical resonant cavity to control the expansion and contraction of the piezoelectric ceramic.
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| CN114322851B (en) * | 2021-12-01 | 2023-12-08 | 东莞理工学院 | Micro rotation angle measuring system based on orbital angular momentum light beam |
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