CN112066970A - Optical fiber gyroscope structure with double independent polarization states - Google Patents
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- 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
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Abstract
The application provides a fiber optic gyroscope structure of two independent polarization states, includes: the polarization maintaining optical fiber comprises a light source, a polarization splitting module, a first polarized light channel, a second polarized light channel and a polarization maintaining optical fiber ring; the light source is connected with the input end of the polarization splitting module, the output end of the polarization splitting module is respectively connected with the input ends of the first polarized light channel and the second polarized light channel which are connected in parallel, and the output ends of the first polarized light channel and the second polarized light channel are connected with the polarization-maintaining optical fiber ring. The invention changes the structure of the existing dual-polarization fiber-optic gyroscope, utilizes the polarization light splitting module to perform coherent elimination processing on the optical signal output by the light source, so that the first polarized light and the second polarized light do not have interference, the coupled light cannot interfere with the main shaft light, and the first polarized light and the second polarized light are matched to perform reverse modulation, thereby effectively reducing the polarization cross-coupling noise in the optical fiber and having very important significance for improving the wandering and zero-polarization performance of the fiber-optic gyroscope.
Description
Technical Field
The application relates to the technical field of fiber-optic gyroscopes, in particular to a fiber-optic gyroscope structure with double independent polarization states.
Background
The optical fiber gyroscope is a sensor for measuring the angular velocity of the inertial motion of an object. The high-precision high-reliability high-anti-interference high-precision high-reliability high-durability high-precision.
The fiber optic gyroscope is a directional device manufactured based on Sagnac effect (Sagnac effect), and the basic working principle of the optical gyroscope is as follows: when two beams of light with the same characteristics in a closed optical path are transmitted along a Clockwise (CW) direction and a counterclockwise (CCW) direction respectively, if the optical path rotates, the two beams of light can generate a phase difference related to the rotation angular velocity, so that the rotation angular velocity of the closed optical path can be obtained according to interference signals of the two beams of light. The above phase difference is called the Sagnac phase shift φsIts relationship to the rotational angular velocity Ω can be expressed as:
where λ is the source wavelength, c represents the speed of light in vacuum, and L and D represent the length and diameter of the polarization-maintaining fiber ring.
Since Sagnac phase shift is much smaller than that of light waves, the structural design of the fiber optic gyroscope should consider suppressing other nonreciprocal phase shifts and reducing noise as much as possible. A basic structural design prototype is to use the "least reciprocal structure" as the basic structure of the fiber-optic gyroscope, as shown in fig. 1. The design of the minimum reciprocity structure aims to ensure that the optical paths of clockwise CW and counterclockwise CCW optical waves are completely consistent, namely, the requirement of reciprocity is met. Since the Sagnac signal is a very small phase signal, much smaller than the optical wave transmission phase shift, it can only be clearly detected if reciprocity is guaranteed. The elements in the minimum reciprocity structure are the guarantee of reciprocity in two aspects: one is polarization reciprocity, that is, the polarization modes experienced by CW and CCW light waves are ensured to be the same; the other is coupler reciprocity, that is, the mode of ensuring that CW and CCW light waves pass through the coupler is the same. Polarization reciprocity is one of the most important aspects, and if polarization reciprocity is not well guaranteed, polarization non-reciprocity (PN) errors can occur. The polarization nonreciprocal error causes serious deterioration of the performance of the fiber-optic gyroscope, which is concentrated in causing deterioration of zero-bias stability, and determines the limit of noise reduction effect in the fiber-optic gyroscope. Therefore, in the structural design of the gyroscope, the polarization reciprocity is placed at a very preferential position, and the polarization non-reciprocity error is also a key problem for improving the accuracy of the gyroscope.
The dual-polarization fiber optic gyroscope is a novel fiber optic gyroscope structure proposed in recent years, and is different from the traditional fiber optic gyroscope in that the structure utilizes the optical compensation effect of two polarization states in the fiber optic ring to measure, and has the advantages of simple structure and strong environmental adaptability. However, the dual-polarization fiber-optic gyroscope structure is to measure by detecting optical compensation effects of two polarization directions of light in a closed optical path, and the two polarization directions of light are cross-coupled with each other in polarization maintaining optical fiber loop, that is, light transmitted on one main axis (e.g. fast axis) may enter the other main axis (e.g. slow axis) due to stress coupling, and light entering the other main axis is coupled light.
Therefore, it is desirable to provide a dual independent polarization state fiber optic gyroscope structure that reduces polarization cross-coupling noise.
Disclosure of Invention
The application aims to provide a fiber-optic gyroscope structure with double independent polarization states.
The application provides a fiber optic gyroscope structure of two independent polarization states, includes: the polarization maintaining optical fiber comprises a light source, a polarization splitting module, a first polarized light channel, a second polarized light channel and a polarization maintaining optical fiber ring; wherein the content of the first and second substances,
the light source is connected with the input end of the polarization splitting module, the output end of the polarization splitting module is respectively connected with the input ends of the first polarization light channel and the second polarization light channel which are connected in parallel, and the output ends of the first polarization light channel and the second polarization light channel are connected with the polarization-maintaining optical fiber ring.
In some embodiments of the present application, the first polarized light path includes a first Y waveguide and a first polarizing beam splitter and combiner; the single end of the first Y waveguide is connected with the input end of the first polarized light channel, one of the two branch ends of the first Y waveguide is connected with the first beam splitting end of the first polarized beam splitting and combining device, and the other one is connected with the first beam splitting end of the second polarized beam splitting and combining device; the beam combining end of the first polarization beam splitting and combining device is the output end of the first polarization light path;
the second polarized light path comprises a second Y waveguide and a second polarization beam splitting and combining device; the single end of the second Y waveguide is connected to the input end of the second polarized light path, one of the two branch ends of the second Y waveguide is connected to the second splitting end of the first polarized beam splitting and combining device, and the other is connected to the second splitting end of the second polarized beam splitting and combining device; and the beam combining end of the second polarization beam splitting and combining device is the output end of the second polarization light channel.
In some embodiments of the present application, the first polarized light path further comprises a first circulator and a first photodetector, a first end of the first circulator is an input end of the first polarized light path, and a second end of the first circulator is connected to an input end of the first Y waveguide; the input end of the first photoelectric detector is connected with the third end of the first circulator;
the second polarized light path further comprises a second circulator and a second photodetector, a first end of the second circulator is an input end of the second polarized light path, and a second end of the second circulator is connected with an input end of the second Y waveguide; and the input end of the second photoelectric detector is connected with the third end of the second circulator.
In some embodiments of the present application, an output end of the signal generator is connected to electrical signal input ends of the first Y waveguide and the second Y waveguide, the signal generator applies a first modulation signal and a second modulation signal to a first splitting end and a second splitting end of the first polarization beam splitter and combiner, respectively, and applies a first modulation signal and a second modulation signal to a first splitting end and a second splitting end of the second polarization beam splitter and combiner, respectively, wherein phases of the first modulation signal and the second modulation signal are opposite.
In some embodiments of the present application, the first and second modulation signals have a frequency that is an odd multiple of the eigenfrequency of the polarization-maintaining fiber loop or the eigenfrequency of the polarization-maintaining fiber loop.
In some embodiments of the present application, the extinction ratios of the first Y waveguide and the second Y waveguide are not less than 85 dB.
In some embodiments of the present application, the polarization splitting module separates a first polarized light and a second polarized light from an optical signal output by the optical source, and outputs the first polarized light and the second polarized light to the first Y waveguide and the second Y waveguide, respectively, where polarization states of the first polarized light and the second polarized light are orthogonal;
the first Y waveguide modulates two beams of first polarized light, one of the two beams of first polarized light is output to a first beam splitting end of the first polarization beam splitter, and the other beam of first polarized light is output to a first beam splitting end of the second polarization beam splitting and combining device;
the second Y waveguide modulates two beams of second polarized light, one of the two beams of second polarized light is output to the second beam splitting end of the first polarization beam splitter, and the other beam of second polarized light is output to the second beam splitting end of the second polarization beam splitting and combining device;
the first polarization beam splitting and combining device correspondingly outputs the first polarized light and the second polarized light which are input through a beam combining end of the first polarization beam splitting and combining device to the first Y waveguide and the second Y waveguide respectively;
the second polarization beam splitting and combining device correspondingly outputs the first polarized light and the second polarized light which are input through the beam combining end to the first Y waveguide and the second Y waveguide respectively.
In some embodiments of the present application, the polarization beam splitter further comprises an adjustable optical attenuator connected in series between the output end of the polarization beam splitting module and the input end of the first polarized light path.
In some embodiments of the present application, the polarization splitting module is a polarization beam splitter or a polarization beam splitter and combiner.
In some embodiments of the present application, a polarizer and a depolarizer are further connected in series between the light source and the input end of the polarization beam splitting module, and the optical signal output by the light source is input to the polarization beam splitting module through the polarizer and the depolarizer in sequence.
Compared with the prior art, the fiber-optic gyroscope structure with the double independent polarization states provided by the application has the advantages that the polarization splitting module carries out coherent elimination on the optical signal output by the light source, and the first polarized light and the second polarized light with orthogonal polarization directions are obtained, so that the first polarized light and the second polarized light do not have coherence, and therefore, in the transmission process of the spindle light (the first polarized light and the second polarized light) in the fiber-optic gyroscope structure, the coupling light cannot interfere with the spindle light. Therefore, the acquired detection signal only contains two partial signals of the interference of the main axis light (the clockwise polarized light and the anticlockwise polarized light) and the interference of the coupling light (the clockwise coupling light and the anticlockwise coupling light), so that the polarization cross coupling error in the polarization maintaining optical fiber ring is reduced, and then the two polarization states of the dual-polarization optical fiber gyroscope are better used, and the detection precision of the optical fiber gyroscope structure is improved.
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Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the application. Also, like reference numerals are used to refer to like parts throughout the drawings. In the drawings:
FIG. 1 shows a schematic diagram of a minimum reciprocity structure of a fiber optic gyroscope structure;
FIG. 2 is a schematic diagram of a dual independent polarization state fiber optic gyroscope structure according to some embodiments of the present application;
FIG. 3 is a birefringence diagram of a polarization splitting module of a dual independent polarization state fiber optic gyroscope structure according to some embodiments of the present application;
FIG. 4 illustrates an equivalent diagram of the Y-waveguide of a dual independent polarization state fiber optic gyroscope structure provided by some embodiments of the present application;
wherein the reference numerals are: 21. a light source; 211. an optical signal; 2111. a first polarized light; 2112. a second polarized light; 22. a polarization splitting module; 23a, a first polarized light path; 23b, a second polarized light path; 24. a polarization maintaining fiber ring; 251. a first circulator; 252. a second circulator; 261. a first Y waveguide; 262. a second Y waveguide; 2601. a single terminal; 2602. a branch end; 2603. an electrical signal input; 271. a first polarization beam splitting and combining device; 272. a second polarization beam splitting and combining device; 281. a first photodetector; 282. a second photodetector; 29. a signal generator.
Detailed Description
Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.
It is to be noted that, unless otherwise specified, technical or scientific terms used herein shall have the ordinary meaning as understood by those skilled in the art to which this application belongs.
In addition, the terms "first" and "second", etc. are used to distinguish different objects, rather than to describe a particular order. Furthermore, the terms "include" and "have," as well as any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, article, or apparatus that comprises a list of steps or elements is not limited to only those steps or elements listed, but may alternatively include other steps or elements not listed, or inherent to such process, method, article, or apparatus.
The embodiment of the present application provides a fiber-optic gyroscope structure with dual independent polarization states, which is described below with reference to the embodiments and accompanying drawings.
As shown in fig. 2 to 4, the dual independent polarization state fiber optic gyroscope structure of the present application may include: a light source 21, a polarization beam splitting module 22, a first polarized light path 23a, a second polarized light path 23b and a polarization-maintaining optical fiber ring 24; wherein the content of the first and second substances,
the light source 21 is connected to the input end of the polarization splitting module 22, the output end of the polarization splitting module 22 is respectively connected to the input ends of the first polarization path 23a and the second polarization path 23b which are connected in parallel, and the output ends of the first polarization path 23a and the second polarization path 23b are connected to the polarization-maintaining fiber ring 24. The light source is preferably a broad spectrum light source.
As shown in fig. 3, the polarization beam splitting module 22 (e.g., a polarization beam splitter/combiner) is configured to separate a first polarized light 2111 and a second polarized light 2112 with orthogonal polarization states from an optical signal 211 output by the light source 21 (e.g., an ASE light source), and output the first polarized light 2111 to the first polarized light path 23a and the second polarized light 2112 to the second polarized light path.
The output ends of the first polarized light path 23a and the second polarized light path 23b are connected to two ends of the polarization-maintaining fiber ring 24, that is, the polarization-maintaining fiber ring 24 has two ports, a first end and a second end, the output end of the first polarized light path 23a is connected to the first end of the polarization-maintaining fiber ring 24, and the output end of the second polarized light path 23b is connected to the second end of the polarization-maintaining fiber ring 24.
The detection signal output by the first polarized light path 2a and the detection signal output by the second polarized light path 2b are weighted and averaged to obtain the detection signal of the optical fiber gyroscope.
The fiber optic gyroscope structure of this embodiment is during operation: two beams of first polarized light are modulated, one of the two beams of first polarized light is output to the first end of the polarization-maintaining optical fiber ring 24 from the output end of the first polarized light channel 23a, and is output from the second end of the polarization-maintaining optical fiber ring 24, so that the first polarized light is transmitted clockwise in the optical fiber gyroscope structure; the other of the two first polarized lights is input to the second end of the polarization-maintaining fiber ring 24 from the output end of the second polarized light path 23b and is output from the first end of the polarization-maintaining fiber, so as to realize the counterclockwise transmission of the first polarized light in the fiber-optic gyroscope structure. Similarly, two beams of second polarized light are modulated, and one of the two beams of second polarized light is output to the first end of the polarization-maintaining optical fiber ring 24 from the output end of the first polarized light path 23a and is output from the second end of the polarization-maintaining optical fiber ring 24, so that the second polarized light is transmitted clockwise in the optical fiber gyroscope structure; the other of the two second polarized lights is input to the second end of the polarization-maintaining fiber ring 24 from the output end of the second polarized light path 23b and is output from the first end of the polarization-maintaining fiber, so as to realize the counterclockwise transmission of the second polarized light in the fiber-optic gyroscope structure. And then, acquiring detection signals generated when the first polarized light and the second polarized light are transmitted in the optical fiber gyroscope structure, and demodulating the detection signals to obtain the rotation angular velocity of the optical fiber gyroscope structure.
Compared with the prior art, in the fiber-optic gyroscope structure with two independent polarization states provided in the embodiment of the present application, the polarization splitting module performs coherent elimination on the optical signal output by the light source, and obtains the first polarized light and the second polarized light with orthogonal polarization directions, so that the first polarized light and the second polarized light do not have coherence, and thus, in the transmission process of the spindle light (the first polarized light and the second polarized light) in the fiber-optic gyroscope structure, the coupling light cannot interfere with the spindle light. Therefore, the acquired detection signal only contains two partial signals of the interference of the main axis light (the clockwise polarized light and the anticlockwise polarized light) and the interference of the coupling light (the clockwise coupling light and the anticlockwise coupling light), so that the polarization cross coupling error in the polarization maintaining optical fiber ring is reduced, and then, two polarization states of the dual-polarization optical fiber gyroscope are better used, and the detection precision of the optical fiber gyroscope structure is improved.
Further, the polarization splitting module 22 may be a polarization beam splitter or a polarization beam splitter/combiner, but may also be other optical elements in principle as long as it can separate two polarized lights with orthogonal polarization states from the optical signal output by the light source.
Further, the bandwidth, wavelength stability, output power, lifetime, etc. of the light source 21 have a very important influence on the performance of the fiber-optic gyroscope. The fiber-optic gyroscope has to adopt a wide-spectrum light source, and the wider the spectrum width, the better the performance, because the wider spectrum width means shorter coherence length, and the noise caused by the interference of the backward Rayleigh scattering light wave and the main light wave can be reduced.
Therefore, in this embodiment, the light source 21 may adopt a broadband erbium-doped superfluorescent fiber light source (ASE), and the light source theory of the broadband erbium-doped superfluorescent fiber light source (ASE) is mainly based on the light amplification principle of the erbium-doped fiber, and after the erbium-doped fiber is pumped by a semiconductor laser with a specific wavelength, erbium ions with different energy levels in the fiber will exhibit population inversion, and when the spontaneous emission light generated by atoms with high energy levels is transmitted in the fiber, the spontaneous emission light is continuously excited and amplified to form amplified spontaneous emission, thereby realizing superfluorescent output required by the fiber gyroscope. Spontaneous emission is characterized in that the phases of all light wave fields are not interfered, and the transmission directions and polarization states of the light wave fields are also randomly distributed.
In some variations of the present embodiment, the first polarized light path 23a includes a first Y waveguide 261 and a first polarization beam splitter and combiner 271; the single end 2601 of the first Y waveguide 261 is connected to the input end of the second polarized light path, one of the two branch ends 2602 of the first Y waveguide 261 is connected to the first splitting end of the first polarization beam splitting and combining device 271, and the other is connected to the first splitting end of the second polarization beam splitting and combining device 272; the beam combining end of the first polarization beam splitting and combining device 271 is connected with the output end of the first polarization light path 23 a;
the second polarized light path 23b includes a second Y waveguide 262 and a second polarization beam splitter and combiner 272; the single end 2601 of the second Y waveguide 262 is connected to the input end of the second polarized light path, one of the two branch ends 2602 of the second Y waveguide 262 is connected to the second splitting end of the first polarization beam splitting and combining device 271, and the other is connected to the second splitting end of the second polarization beam splitting and combining device 272; the beam combining end of the second polarization beam splitter and combiner 272 is connected to the output end of the second polarization optical path 23 b.
In this embodiment, the transmission process of the optical signal output by the light source 21 specifically includes:
first, an optical signal (e.g., a broadband light) emitted by the light source 21 passes through the polarization beam splitting module and then outputs a first polarized light and a second polarized light with orthogonal polarization directions, and the first polarized light and the second polarized light are respectively input into the first Y waveguide 261 and the second Y waveguide 262 through the output end of the polarization beam splitting module.
Then, the first polarized light is modulated into two first polarized lights by the first Y waveguide 261, one of the two first polarized lights is input to the first end of the polarization maintaining fiber ring 24 through the first polarization beam splitting and combining device 271, and is output to the combining end of the second polarization beam splitting and combining device 272 from the second end of the polarization maintaining fiber ring 24, that is, the first polarized light is transmitted clockwise in the polarization maintaining fiber ring 24; the other of the two first polarized lights is input to the second end of the polarization maintaining fiber ring 24 through the second polarization beam splitter/combiner 272, and is output to the first polarization beam splitter/combiner 271 through the first end of the polarization maintaining fiber ring 24, that is, the first polarized light is transmitted counterclockwise in the polarization maintaining fiber ring 24. Similarly, the second polarized light is modulated by the second Y waveguide 262 into two second polarized lights, one of the two second polarized lights is input to the second end of the polarization maintaining fiber ring 24 through the second polarization beam splitter/combiner 272 and is output to the first polarization beam splitter/combiner 271 through the first end of the polarization maintaining fiber ring 24, that is, the second polarized light is transmitted counterclockwise in the polarization maintaining fiber ring 24; the other of the two second polarized lights is input to the first end of the polarization-maintaining fiber ring 24 through the first polarization beam splitter/combiner 271, and is output to the second polarization beam splitter/combiner 272 through the second end of the polarization-maintaining fiber ring 24, that is, the second polarized light is transmitted clockwise in the polarization-maintaining fiber ring 24.
Finally, the first polarization beam splitter and combiner 271 outputs the first polarized light to the first Y waveguide 261, and the second polarized light to the second Y waveguide 262; similarly, the second polarization beam splitter and combiner 272 outputs the first polarized light to the first Y waveguide 261, and the second polarized light to the second Y waveguide 262.
In this embodiment, the main axis light (i.e., the first polarized light and the second polarized light) transmitted in each polarization direction passes through the processes of entering the polarization-maintaining fiber ring 24 and exiting from the polarization-maintaining fiber ring twice, and the Y waveguide through which any main axis light (the first polarized light or the second polarized light) enters the polarization-maintaining fiber ring 24 and the Y waveguide through which any main axis light exits the polarization-maintaining fiber ring 24 are the same Y waveguide, so that on one hand, the polarization modes of the clockwise transmitted main axis light and the counterclockwise transmitted main axis light are the same, that is, the polarization reciprocity is ensured; on the other hand, the way that the clockwise transmitted main axis light and the counterclockwise transmitted main axis light pass through the coupler (Y waveguide) is the same, i.e. the coupler reciprocity is ensured. That is, the optical path experienced by the clockwise transmitted main axis light and the counterclockwise transmitted main axis light is completely consistent, that is, the requirement of reciprocity is satisfied.
In some modified embodiments of the embodiment of the present application, the first polarized light path 23a further includes a first circulator 251 and a first photodetector, a first end of the first circulator 251 is an input end of the first polarized light path 23a, and a second end of the first circulator 251 is connected to an input end of the first Y waveguide 261; the input end of the first photodetector is connected with the third end of the first circulator 251;
the second polarized light path 23b further includes a second circulator 252 and a second photodetector, a first end of the second circulator 252 is an input end of the second polarized light path 23b, and a second end of the circulator is connected to an input end of the second Y waveguide 262; the input of the second photodetector is connected to the third terminal of the second circulator 252.
The circulator is a multi-terminal device, and optical signals can only circulate in a single direction when being transmitted in the circulator.
In this embodiment, on the premise of realizing transmission of optical signals according to a predetermined path, the hardware structure of the fiber-optic gyroscope structure is simplified.
Further, the output end of the first polarization beam splitting and combining device 271 is the output end of the first polarization optical path 23 a; the output of the second polarization beam splitter and combiner 272 is the output of the second polarized light path 23 b.
In some modified embodiments of the embodiment of the present application, the fiber-optic gyroscope structure further includes a signal generator 29, an output end of the signal generator 29 is connected to the electrical signal input end 2603 of the first Y waveguide 261 and the second Y waveguide 262, the signal generator 29 can apply the first modulation signal and the second modulation signal to the first beam splitting end and the second beam splitting end of the first polarization beam splitter and combiner 271, respectively, and can apply the first modulation signal and the second modulation signal to the first beam splitting end and the second beam splitting end of the second polarization beam splitter and combiner 272, respectively, where phases of the first modulation signal and the second modulation signal are opposite.
Normally, Sagnac phase-shifted signals of the gyroscope (i.e., the phase difference between the first polarization light transmitted clockwise and the first polarization light transmitted counterclockwise, and the phase difference between the second polarization light transmitted clockwise and the second polarization light transmitted counterclockwise) are very small, and in order to extract a weak useful signal from strong noise, a fixed offset phase is generated by adding a modulation signal to improve the sensitivity.
In some variations of the embodiments of the present application, the difference between the phases of the first modulated signal and the second modulated signal is pi.
Further, the modulation signal may be a sinusoidal signal or a square wave modulation signal.
Specifically, the optical field of the first polarized light input to the first Y waveguide 261 and the second polarized light of the second Y waveguide 262 may be expressed as:
wherein, theta1And a starting phase.
Here, as shown in fig. 4, the Y waveguides (the first Y waveguide 261 and the second Y waveguide 262) of the fiber-optic gyroscope structure may be equivalent to optical path structures of one polarizer, one coupler, and two modulators. The jones matrix of polarizers and couplers can be expressed as:
in the formula (I), the compound is shown in the specification,
the transmission coefficients of the first Y waveguide 261 and the second Y waveguide 262 are represented.
After entering the first Y waveguide 261 and the second Y waveguide 262, the first polarized light and the second polarized light are coupled into the polarization-maintaining fiber ring 24 through two polarization beam splitting and combining devices, respectively. There are 4 fusion points A, B, C, D between the Y waveguide and the polarization beam splitter/combiner (PBS/C), and there are some off-axis errors that cause large polarization cross-coupling, so the jones matrices of these points cannot be ignored in the analysis, and they can be expressed as:
θmrepresenting the off-axis angle of these several points.
In this embodiment, the shaft offset angles of the 4 points are substantially the same for the same shaft welder, and can be expressed as: thetaA≈θB≈θC≈θD≈θmis。
Polarization maintaining fiber ring 24 can be a polarization maintaining fiber ring 24, and polarization maintaining fiber ring 24 can be equivalently an M-section polarization maintaining fiber, using K (K)n) The transmission matrix for each section of polarization-maintaining fiber is represented such that the transmission matrix for the polarization-maintaining fiber loop 24 for Clockwise (CW) and counterclockwise (CCW) can be represented as:
in this embodiment, the interference signal reaching the first Y waveguide 261 is detected by the first photodetector (PD1), the interference signal reaching the second Y waveguide 262 is detected by the second photodetector (PD2), and the optical fields reaching the first photodetector and the second photodetector can be expressed as:
as can be seen from the above formula, each photodetector receives 8 types of light according to the polarization state of the light, and the polarization state of the light emitted from two ends i (i ═ 1, 2) of the beam splitting end of the PBS/C1 can be m, and the light reaches the PDjWhen (j is 1, 2), the light with polarization state n is written as Eimjn。
In the present embodiment, the first polarized light and the second polarized light do not have coherence, and the first Y waveguide 261 and the second Y waveguide 262 have a high extinction ratio, so that only the principal axis light (E) needs to be considered1x1x，E2y2y) And dual polarization coupled light (E)2y1x，E1x2y). The light fields reaching the first photodetector and the second photodetector can thus be reduced to a respective one
The intensity of light detected on the first photodetector and the second photodetector may be expressed as:
IPD1(t)≈D.C.+Ip1+Idi1
IPD2(t)≈D.C.+Ip2+Idi2
wherein: d.c. represents a direct current term; i isp1And Ip2Indicating principal axis light (E)1x1x，E2y2y) The interference term of (1), carrying the Sagnac phase shift; i isdi1And Idi2Representing dual polarized coupled light (E)2y1x，E1x2y) The interference term of (2) is the main source of the dual polarization intensity type error.
In this embodiment, Idi1And Idi2Can be expressed as:
wherein: k1And K2Respectively represent Idi1And Idi2The interference intensity coefficient of (a); phi is aerr1And phierr2Is a dual-polarization intensity type polarization nonreciprocal error caused by dual-polarization coupled light, which has opposite signs on two PDsmod1(t) and phimod2(t) is the offset phase brought by the sinusoidal modulation signal, which can be expressed as:
wherein, Delta thetam＝θ1θ 2, representing the difference between the initial phases of the sinusoidal modulation signals of the first Y waveguide 261 and the second Y waveguide 262.
When the two beams have good consistency and balanced power, K can be considered as1＝K2At this time Idi1And Idi2AddingThe following can be obtained:
Idi＝Idi1(t)+Idi2(t)＝2K1cosφerr1cos[φs+φmod1]
by adding the signals of the first and second photodetectors, the dual polarization intensity type error is completely compensated.
By adding the signals of the two PDs, the dual polarization type error is completely compensated.
However, in the actual operation of the fiber-optic gyroscope structure, due to the disturbance of the external environment, the two beams are difficult to maintain good consistency and power balance, which greatly reduces the compensation effect and affects the precision of the fiber-optic gyroscope structure. Taking the harmonic demodulation commonly used in the open-loop demodulation as an example, the error caused by the dual-polarization-intensity type error on the demodulation result can be expressed as:
wherein J1Is a first order bessel function.
It can be seen that: when Δ θmWhen pi, phidem0. This indicates that: when the difference between the initial phases of the sinusoidal modulation signals of the two Y waveguides is pi, i.e., the phases are opposite, the dual polarization intensity type phase error can be completely eliminated.
In some variations of the embodiments of the present application, the frequencies of the first and second modulation signals are odd multiples of the polarization maintaining fiber loop 24 eigenfrequency or the polarization maintaining fiber loop 24 eigenfrequency.
In principle, as the length of the polarization-maintaining fiber ring 24 increases, the eigenfrequency thereof will be lower and lower, and after collecting the signal of the polarization-maintaining fiber ring 24 and performing spectrum analysis, it is found that the signal spectrum is not flat, and the low-frequency noise is significantly higher than the high-frequency part, and for a large polarization-maintaining fiber ring 24 (for example, the fiber length is greater than 2 km), the modulation frequency thereof will be much lower than that of the small polarization-maintaining fiber ring 24, and will fall into the low-frequency part with higher 1/f noise (the eigenfrequency of the 30km polarization-maintaining fiber ring 24 is 3.3kHz), which will greatly affect the short-time wandering performance of the gyroscope, degrade the detection sensitivity, and the influence of the thermal phase noise cannot be ignored in the ultra-large high precision fiber gyroscope.
In the embodiment, odd-order frequency multiplication of the eigenfrequency is used as the modulation frequency, and the modulation frequency is moved to the broadband noise frequency band, so that the noise floor can be greatly reduced, and the short-time walking performance of the fiber-optic gyroscope is improved.
In some modified embodiments of the embodiment of the present application, the dual independent polarized fiber optic gyroscope structure further includes an adjustable optical attenuator serially connected between the splitting end of the polarization splitting module and the input end of the first polarized light path 23 a.
In principle, the ideal operating conditions for a fiber optic gyroscope structure with dual independent polarization states include: the power of the two beams of orthogonal polarized light is completely balanced.
In this embodiment, the first polarized light first passes through the polarizer and the depolarizer to perform dual-polarized light power equalization.
In some variations of the examples of the present application, the extinction ratios of the first Y waveguide 261 and the second Y waveguide 262 are not less than 85 dB.
In this embodiment, a polarization beam splitter/combiner with a high extinction ratio is used to perform coherent elimination on light in two polarization states, so that a non-reciprocal error caused by high-order polarized light can be effectively eliminated, and an effect of inverse modulation (i.e., the phases of the first modulation signal and the second modulation signal are opposite) is improved.
More preferably, the first Y waveguide 261 and the second Y waveguide 262 are similar in performance.
Further, in the present embodiment, the method used for demodulation by the photodetector may be harmonic demodulation commonly used in open-loop gyroscopes, and the rotation signal is obtained by extracting 1, 2, 3, and 4 harmonics of the interference signal. Since the interference result of the polarization components of the polarization cross-coupling is shifted to the low frequency part, this part of the noise is eliminated.
It should be noted that the flowchart and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present application. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems which perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.
It is clear to those skilled in the art that, for convenience and brevity of description, the specific working processes of the above-described systems, apparatuses and units may refer to the corresponding processes in the foregoing method embodiments, and are not described herein again.
In the several embodiments provided in the present application, it should be understood that the disclosed apparatus and method may be implemented in other ways. The above-described embodiments of the apparatus are merely illustrative, and for example, the division of the units is only one logical division, and there may be other divisions when actually implemented, and for example, a plurality of units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection of devices or units through some communication interfaces, and may be in an electrical, mechanical or other form.
The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.
In addition, functional units in the embodiments of the present application may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit.
The functions, if implemented in the form of software functional units and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, the technical solution of the present application or portions thereof that substantially contribute to the prior art may be embodied in the form of a software product stored in a storage medium and including instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present application. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk or an optical disk, and other various media capable of storing program codes.
Finally, it should be noted that: the above embodiments are only used for illustrating the technical solutions of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; such modifications and substitutions do not depart from the spirit and scope of the present disclosure, and the present disclosure should be construed as being covered by the claims and the specification.
Claims (9)
1. A fiber optic gyroscope structure having dual independent states of polarization, comprising:
the polarization maintaining optical fiber comprises a light source, a polarization splitting module, a first polarized light channel, a second polarized light channel and a polarization maintaining optical fiber ring; wherein the content of the first and second substances,
the light source is connected with the input end of the polarization splitting module, the output end of the polarization splitting module is respectively connected with the input ends of the first polarization light channel and the second polarization light channel which are connected in parallel, and the output ends of the first polarization light channel and the second polarization light channel are connected with the polarization-maintaining optical fiber ring.
2. The dual independent polarization state fiber optic gyroscope structure of claim 1,
the first polarized light path comprises a first Y waveguide and a first polarization beam splitting and combining device; the single end of the first Y waveguide is connected with the input end of the first polarized light channel, one of the two branch ends of the first Y waveguide is connected with the first beam splitting end of the first polarized beam splitting and combining device, and the other one is connected with the first beam splitting end of the second polarized beam splitting and combining device; the beam combining end of the first polarization beam splitting and combining device is the output end of the first polarization light path;
the second polarized light path comprises a second Y waveguide and a second polarization beam splitting and combining device; the single end of the second Y waveguide is connected to the input end of the second polarized light path, one of the two branch ends of the second Y waveguide is connected to the second splitting end of the first polarized beam splitting and combining device, and the other is connected to the second splitting end of the second polarized beam splitting and combining device; and the beam combining end of the second polarization beam splitting and combining device is the output end of the second polarization light channel.
3. The dual independent polarization state fiber optic gyroscope structure of claim 2,
the first polarized light path further comprises a first circulator and a first photodetector, wherein a first end of the first circulator is an input end of the first polarized light path, and a second end of the first circulator is connected with an input end of the first Y waveguide; the input end of the first photoelectric detector is connected with the third end of the first circulator;
the second polarized light path further comprises a second circulator and a second photodetector, a first end of the second circulator is an input end of the second polarized light path, and a second end of the second circulator is connected with an input end of the second Y waveguide; and the input end of the second photoelectric detector is connected with the third end of the second circulator.
4. The structure of claim 2, further comprising a signal generator, wherein an output end of the signal generator is connected to electrical signal input ends of the first Y waveguide and the second Y waveguide, the signal generator applies a first modulation signal and a second modulation signal to the first splitting end and the second splitting end of the first polarization beam splitter and combiner, respectively, and applies a first modulation signal and a second modulation signal to the first splitting end and the second splitting end of the second polarization beam splitter and combiner, respectively, wherein phases of the first modulation signal and the second modulation signal are opposite.
5. The dual independent polarization state fiber optic gyroscope structure of claim 4, wherein the frequencies of the first and second modulation signals are the eigenfrequencies of the polarization maintaining fiber ring or odd multiples of the eigenfrequencies of the polarization maintaining fiber ring.
6. The structure of claim 2, wherein the extinction ratios of the first Y waveguide and the second Y waveguide are not less than 85 dB.
7. The structure of a dual independent polarization state fiber-optic gyroscope of any of claims 2 to 6,
the polarization splitting module separates first polarized light and second polarized light from an optical signal output by the light source, and outputs the first polarized light and the second polarized light to the first Y waveguide and the second Y waveguide respectively, wherein polarization states of the first polarized light and the second polarized light are orthogonal;
the first Y waveguide modulates two beams of first polarized light, one of the two beams of first polarized light is output to a first beam splitting end of the first polarization beam splitter, and the other beam of first polarized light is output to a first beam splitting end of the second polarization beam splitting and combining device;
the second Y waveguide modulates two beams of second polarized light, one of the two beams of second polarized light is output to the second beam splitting end of the first polarization beam splitter, and the other beam of second polarized light is output to the second beam splitting end of the second polarization beam splitting and combining device;
the first polarization beam splitting and combining device correspondingly outputs the first polarized light and the second polarized light which are input through a beam combining end of the first polarization beam splitting and combining device to the first Y waveguide and the second Y waveguide respectively;
the second polarization beam splitting and combining device correspondingly outputs the first polarized light and the second polarized light which are input through the beam combining end to the first Y waveguide and the second Y waveguide respectively.
8. The structure of claim 1, further comprising an adjustable optical attenuator coupled in series between the output of the polarization beam splitting module and the input of the first polarized light path.
9. The structure of claim 1, wherein the polarization splitting module is a polarization splitter or a polarization splitter/combiner.
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