CN111089578B - Interference type optical fiber gyroscope - Google Patents
Interference type optical fiber gyroscope Download PDFInfo
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- CN111089578B CN111089578B CN202010071804.6A CN202010071804A CN111089578B CN 111089578 B CN111089578 B CN 111089578B CN 202010071804 A CN202010071804 A CN 202010071804A CN 111089578 B CN111089578 B CN 111089578B
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- optical fiber
- phase modulator
- fiber coupler
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- gyroscope
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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
Abstract
An interference type optical fiber gyroscope comprises a light source, a first optical fiber coupler, a second optical fiber coupler, an optical fiber ring, a phase modulator, a photoelectric detector and a signal processing module. The phase modulator is formed by placing a lithium niobate dual-polarization mode strip waveguide in the middle of a pair of Faraday optical rotators with opposite rotation directions and 45-degree rotation angles, and adopts a modulation mode of z-axis cutting, z-axis light transmission and y-axis voltage application; the phase modulator is arranged in the middle of the optical fiber ring in the gyroscope light path, so that two beams of light transmitted clockwise and anticlockwise in the gyroscope loop reach the phase modulator for modulation. In the invention, the phase modulator which is not based on time delay is used, and the modulator is placed in the middle of the optical fiber loop, so that the back reflection and the back scattering in the optical path and the parasitic interference between the back reflection and the main wave are reduced, the measurement precision of the system can be effectively improved, and the method has an ideal technical effect.
Description
Technical Field
The invention relates to the technical field of fiber optic gyroscopes, in particular to an interference type fiber optic gyroscope.
Background
The fiber optic gyroscope is an inertial angular velocity measuring device based on the Sagnac interferometer principle, and compared with a traditional mechanical gyroscope, the fiber optic gyroscope has the advantages of being full-solid in structure, long in service life, large in dynamic range, simple in structure, small in size, light in weight and the like. The research of the fiber optic gyroscope focuses on proposing different gyroscope schemes to improve the detection sensitivity and analyzing the influence of various noise sources in the fiber optic gyroscope on the gyroscope. The fiber-optic gyroscope has relatively large noise unlike the traditional gyroscope, and the generated noise comprises optical signal noise, noise after interference and noise generated by signal detection from a sensitive input to the signal detection. The main reasons for generating interference noise in the interference type fiber optic gyroscope are as follows: polarization effects, back reflection or scattering within the fiber coil, non-linear refractive index changes related to light intensity, time-dependent temperature along the fiber, magnetic fields, electronic drift errors, and the like. In order to eliminate gyro errors caused by back reflection, back scattering and the like and improve measurement accuracy, most of interference type fiber optic gyroscopes generally adopt a broadband light source at present, and most of parasitic interference is eliminated by utilizing weak coherence of the broadband light source.
Fiber optic gyroscopes or tacho sensors have enjoyed an appreciable performance over the past decades, with the fiber optic loop mostly using active biasing, i.e. piezoelectric phase modulators (PZT) or integrated optical block modulators (Y waveguide devices). The principle of both phase modulators is based on the time delay between two beams of light with opposite transmission directions of the optical fiber ring, and the implementation of the modulation phase is limited by the delay time of the optical fiber ring. For phase modulation purposes, the modulator must modulate on one side of the fiber loop, which introduces additional back-reflection, parasitic interference from back-scattering. For high precision gyroscopes, phase modulation at the eigenfrequency is used to reduce the phase error due to back-scattering in order to further reduce the phase error. In practical application, there are many methods for measuring eigenfrequency, but most of them have low precision and cannot meet the requirements of fiber optic gyroscopes.
Disclosure of Invention
In view of the above problems, an object of the present invention is to provide an interference-type optical fiber gyro that improves the measurement accuracy of the interference-type optical fiber gyro and reduces the cost thereof by reducing the back reflection and back scattering of the optical fiber gyro and the interference noise generated thereby.
The technical scheme adopted by the invention is as follows:
the invention provides an interference type optical fiber gyroscope which comprises a light source, a first optical fiber coupler, a second optical fiber coupler, an optical fiber ring, a phase modulator, a photoelectric detector and a signal processing module. One side of the first optical fiber coupler is respectively connected with the light source and the photoelectric detector through two tail fibers, the other side of the first optical fiber coupler is in shaft-to-shaft connection with a port at one side of the second optical fiber coupler through one tail fiber, and the other side of the second optical fiber coupler is in shaft-to-shaft connection with the optical fiber ring through two tail fibers; two tail fibers led out from the optical fiber ring are connected with the phase modulator in a counter shaft manner; the signal processing module is connected between the photoelectric detector and the phase modulator.
Further, the phase modulator includes a pair of faraday rotators having opposite optical rotation directions and a rotation angle of 45 ° and a dual polarization mode strip waveguide disposed between the pair of faraday rotators.
Furthermore, the dual-polarization mode strip waveguide is made of a lithium niobate optical waveguide and adopts a modulation mode of z-axis cutting, z-axis light transmission and y-axis modulated voltage addition.
Furthermore, the polarization direction of incident linearly polarized light of the phase modulator is consistent with the angular bisector directions of the x axis and the y axis of the incident waveguide surface of the lithium niobate optical waveguide.
Furthermore, the phase modulator is placed in the middle of the optical fiber ring, so that two beams of light transmitted clockwise and anticlockwise in the gyroscope loop reach the phase modulator to be modulated.
Further, the first optical fiber coupler and the second optical fiber coupler are polarization maintaining optical fiber couplers of 2x2 or 2x1, and a polarizer is connected between the first optical fiber coupler and the second optical fiber coupler and used for enabling optical signals transmitted in the optical fiber loop to be linearly polarized light.
Further, the light source is a linearly polarized light source with a narrow line width.
Compared with the prior art, the invention has the following beneficial effects:
1. the phase modulator enables two light beams which move in opposite directions to be superposed with different phase changes after passing through the phase modulator, which means that extra delay coils are not needed to be added to increase the modulation time interval needed by phase offset, and simultaneously, polarization unstable factors such as linear birefringence and the like caused by long delay coils are reduced.
2. The optical path structure of the invention is a minimum nonreciprocal structure, thereby reducing the nonreciprocal error of the fiber-optic gyroscope to the maximum extent and improving the measurement precision of the gyroscope.
3. The phase modulator is placed in the middle of the optical fiber loop, interference errors between back reflection and back scattering between symmetrical points in an optical path are eliminated, parasitic interference between the back scattering and the main wave is inhibited, and the measurement accuracy of the gyroscope is improved.
Drawings
FIG. 1 is a schematic diagram of an overall optical path structure of an embodiment of an interference-type optical fiber gyroscope according to the present invention;
fig. 2 is a schematic diagram of the structure of the phase modulator in fig. 1.
Detailed Description
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
It should be noted that in the description of the present invention, the terms "upper", "lower", "top", "bottom", "one side", "the other side", "left", "right", and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of describing the present invention and simplifying the description, but do not mean that a device or an element must have a specific orientation, be configured and operated in a specific orientation.
Referring to fig. 1, a specific structure of an embodiment of an interference-type optical fiber gyroscope according to the present invention is shown. The optical fiber coupler comprises a light source 1, a first optical fiber coupler 2, a polarizer 3, a second optical fiber coupler 4, an optical fiber ring 5, a phase modulator 6, a signal processing module 7 and a photoelectric detector 8.
The left side of the first optical fiber coupler 2 is respectively connected with the light source 1 and the photoelectric detector 8 through two tail fibers, the right side of the first optical fiber coupler 2 is in shaft connection with the left side port of the second optical fiber coupler 4 through one tail fiber via a polarizer 3, the right side of the second optical fiber coupler 4 is in shaft connection with an optical fiber ring 5 through two tail fibers, two tail fibers led out from the optical fiber ring 5 are in shaft connection with a phase modulator 6, the phase modulator 6 is located in the middle of the optical fiber ring 5, two beams of light transmitted clockwise and anticlockwise in a gyroscope loop simultaneously reach the phase modulator 6 to be modulated, and the signal processing module 7 is connected between the photoelectric detector 8 and the phase modulator 6; in this embodiment, the light source 1 is a linearly polarized light source with a narrow line width, and is driven by a light source driving circuit; the first optical fiber coupler 2 and the second optical fiber coupler 4 are both polarization-maintaining optical fiber couplers of 2x2 or 2x 1.
Referring to fig. 2, the phase modulator 6 includes a first faraday rotator 61 and a second faraday rotator 62, and a dual polarization mode strip waveguide 63 connected between the first faraday rotator 61 and the second faraday rotator 62; the optical rotation direction of the first Faraday optical rotator 61 is right rotation, the optical rotation direction of the second Faraday optical rotator 62 is left rotation, the rotation angles of the first Faraday optical rotator 61 and the second Faraday optical rotator 62 are both 45 degrees, the polarization direction of incident linearly polarized light of the phase modulator 6 is consistent with the angular bisector directions of the x axis and the y axis of the incident waveguide surface of the lithium niobate optical waveguide, and the first Faraday optical rotator 61 and the second Faraday optical rotator 62 adopt diamagnetic Faraday optical rotation elements for reducing the influence of temperature on the optical rotation performance; the dual-polarization mode strip waveguide 63 is a lithium niobate optical waveguide, and adopts a modulation mode of z-axis cutting, z-axis light transmission and y-axis modulated voltage, when the phase modulator 6 is connected into an optical fiber loop, the incident light polarization direction of the phase modulator 6 forms an included angle of 45 degrees with the incident waveguide of the z-axis cut lithium niobate optical waveguide; wherein E is 1 For the forward direction of transmission, E 2 For reversing the direction of transmission, E 3 In the direction of linearly polarized light, E 4 Is the direction of rotation of the first Faraday rotator 61, E 5 The direction of rotation of the second Faraday rotator 62, E 6 To modulate voltage, E 7 Is a lithium niobate crystal substrate y-axis, E 8 X-axis and E of lithium niobate crystal substrate 9 And a z-axis of the lithium niobate crystal substrate.
In the invention, a light source 1 is used for providing an optical signal of an optical fiber gyroscope light path, a first optical fiber coupler 2 is used for connecting the light source 1, a photoelectric detector 8 and a second optical fiber coupler 4, the light source 1 and the photoelectric detector 8 are respectively connected with two ends of the same side of the first optical fiber coupler 2, the other side of the first optical fiber coupler 2 is connected with the second optical fiber coupler 4 through a polarizer 3, and the polarizer 3 can ensure that a transmission optical signal in an optical fiber loop is linearly polarized light; two output ends of the second optical fiber coupler 4 are used for connecting an optical fiber ring 5 to form a Sagnac interferometer, and the optical fiber ring 5 is used as a sensing unit for detecting the rotation angular velocity of the optical fiber gyroscope; the phase modulator 6 is connected to the middle position of the optical path of the optical fiber ring 5 and used for generating fixed phase delay, so that the optical fiber gyroscope works at a point with the maximum sensitivity, and the rotating direction can be distinguished; the photoelectric detector 8 is used for converting the detected light intensity signal into an electric signal; the signal processing module 7 has two functions, namely, demodulating the electric signal converted by the photoelectric detector 8, acquiring Sagnac phase shift in an interference optical signal, and calculating the rotation angular velocity of the optical fiber gyroscope; secondly, a modulation signal is applied to the phase modulator 6 to generate a pi/2 offset phase shift, so that the gyroscope works at the point with the maximum sensitivity, and simultaneously, the measured Sagnac phase shift is used as a feedback signal to apply a signal with opposite phase shift to the phase modulator 6, so that the optical fiber gyroscope is always kept at the point with the maximum sensitivity, and the effect of closed-loop feedback is realized.
The working principle of the invention is as follows: the light emitted by the light source 1 is divided into two beams of linearly polarized light after passing through the first optical fiber coupler 2, the polarizer 3 and the second optical fiber coupler 4, wherein one beam of linearly polarized light enters the optical fiber ring 5 in the clockwise direction, and rotates 45 degrees to the right after passing through the first Faraday optical rotator 61, and the polarized light enters the second Faraday optical rotator 62 after passing through the double-polarization mode strip waveguide 63, and the polarization direction of the polarized light is recovered to the original polarization direction after passing through the reverse optical rotation 45 degrees of the second Faraday optical rotator 62; the other beam of linearly polarized light enters the optical fiber ring 5 in the counterclockwise direction, rotates 45 degrees leftwards through the second Faraday optical rotator 62, then is recovered to the previous polarization direction through the first Faraday optical rotator 61 after passing through the double-polarization mode strip waveguide 63, and the non-reciprocal structure enables the modulation phase to be generated between the linearly polarized light which moves in the two directions; two beams of linearly polarized light which are transmitted clockwise and anticlockwise interfere with each other through the coupler to enter the detector, and the output optical signals are demodulated to obtain the rotation angular velocity information of the carrier.
The phase modulator 6 is located in the loop of the polarization-maintaining optical fiber ring 5, and has the function of generating a bias phase and a feedback phase for polarized light entering from two ends of the polarization-maintaining optical fiber ring, so that the sensitivity of the high-optical-fiber gyroscope is maximized, the feedback phase is used for offsetting Sagnac phase change caused by inertia change, and simultaneously compensating the interference of temperature, light source intensity change and the like on the system phase, so that the system is always kept at the point of the maximum detection sensitivity. The phase modulator 6 is placed in the middle of the loop of the optical fiber ring 5, so that interference errors between back reflection and back scattering between symmetrical points in the loop are eliminated, and parasitic interference between back scattering light waves and main waves is suppressed.
The building method is that each device is respectively added into the system, and the collimation of the device is calibrated by taking the maximum point of luminous flux as a standard in a mode of detecting the luminous flux so as to obtain the accurate building of the device. The first optical fiber coupler 2 and the second optical fiber coupler 4 adopt fast-axis polarization-maintaining optical fiber couplers, the polarizer 3 also adopts a fast-axis polarization-maintaining optical fiber polarizer, the optical fiber ring 5 is a polarization-maintaining optical fiber ring, various polarization-maintaining devices are subjected to fusion splicing after being determined to be axial by a polarization-maintaining fusion splicer, the fusion splicer is used for evaluation after the fusion splicing of tail fibers, and the axial angle difference between the tail fibers is preferably smaller than 3 degrees.
The above-mentioned embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solution of the present invention by those skilled in the art should fall within the protection scope defined by the claims of the present invention without departing from the spirit of the present invention.
Claims (4)
1. An interference type optical fiber gyro characterized in that: the gyroscope comprises a light source, a first optical fiber coupler, a second optical fiber coupler, an optical fiber ring, a phase modulator, a photoelectric detector and a signal processing module, wherein one side of the first optical fiber coupler is respectively connected with the light source and the photoelectric detector through two tail fibers, the other side of the first optical fiber coupler is in counter-shaft connection with a port on one side of the second optical fiber coupler through one tail fiber, and the other side of the second optical fiber coupler is in counter-shaft connection with the optical fiber ring through two tail fibers; two tail fibers led out from the optical fiber ring are connected with the phase modulator in a counter shaft manner; the signal processing module is connected between the photoelectric detector and the phase modulator;
the phase modulator comprises a pair of Faraday rotators with opposite rotation directions and a rotation angle of 45 degrees and a dual-polarization mode strip waveguide arranged between the pair of Faraday rotators;
the dual-polarization mode strip waveguide is made of a lithium niobate optical waveguide and adopts a modulation mode of z-axis cutting, z-axis light transmission and y-axis modulated voltage addition;
the phase modulator is placed in the middle of the optical fiber ring, so that two beams of light transmitted clockwise and anticlockwise in the gyroscope loop simultaneously reach the phase modulator for modulation.
2. An interferometric optical fiber gyroscope according to claim 1, characterized in that: the polarization direction of incident linearly polarized light of the phase modulator is consistent with the angular bisector directions of the x axis and the y axis of the incident waveguide surface of the lithium niobate optical waveguide.
3. An interferometric optical fiber gyroscope according to claim 1, characterized in that: the first optical fiber coupler and the second optical fiber coupler are polarization maintaining optical fiber couplers of 2x2 or 2x1, and a polarizer is connected between the first optical fiber coupler and the second optical fiber coupler and used for enabling optical signals transmitted in an optical fiber loop to be linearly polarized light.
4. An interferometric optical fiber gyroscope according to claim 1, characterized in that: the light source is a linearly polarized light source with narrow line width.
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| CN111811495B (en) * | 2020-07-03 | 2022-04-08 | 浙江大学 | Optical multiple multiplication device and method of polarization maintaining optical fiber ring |
| CN112083476A (en) * | 2020-09-10 | 2020-12-15 | 北京大学 | Rotary seismograph based on dual-polarization light path structure |
| CN112595307B (en) * | 2020-10-30 | 2022-09-16 | 西安航天精密机电研究所 | Optical path error calculation method for interference type fiber-optic gyroscope |
| CN112484752B (en) * | 2020-11-10 | 2023-07-21 | 广东工业大学 | Device and method for testing reflection characteristics of large dynamic range fiber optic gyroscope |
| CN114234954A (en) * | 2022-02-28 | 2022-03-25 | 深圳奥斯诺导航科技有限公司 | Double sensitization optical path integrated optical fiber gyroscope |
| CN114485907B (en) * | 2022-03-21 | 2022-08-23 | 中国人民解放军国防科技大学 | Device and method for eliminating parasitic interference signals in fiber grating hydrophone array |
| CN115077511B (en) * | 2022-08-23 | 2022-11-01 | 中国船舶重工集团公司第七0七研究所 | Hollow-core microstructure fiber-optic gyroscope capable of switching polarization modes |
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