Fiber-optic gyroscope

Abstract

The application relates to an optical fiber gyroscope which comprises a broadband light source, a detector, a coupler, a phase modulator and a single polarization fiber ring; light emitted by the broadband light source enters the coupler, and is divided into a first light beam and a second light beam by the coupler; the first light beam enters the single polarization fiber ring via the phase modulator, and the second light beam directly enters the single polarization fiber ring; the first light beam and the second light beam are output after propagating clockwise and counterclockwise in the single polarization fiber ring respectively; the first light beam enters the coupler; the second light beam enters the coupler after passing through the phase modulator; the first light beam and the second light beam generate an interference signal in the coupler; and the interference signal emitted by the coupler enters the detector to determine the rotation state of the optical fiber gyroscope. The optical fiber gyroscope has simple structure and high detection precision.

Description

Technical Field

[0001] This application belongs to the field of gyroscope technology, and specifically relates to a fiber optic gyroscope. Background Technology

[0002] A fiber optic gyroscope is a high-precision sensor for measuring the angular velocity of an object's rotation. Its principle is based on the Sagnac effect: when the gyroscope rotates, a phase difference φs proportional to the rotational angular velocity Ω is generated between two light waves propagating clockwise and counterclockwise within the fiber optic coil. Ideally, by measuring this phase difference φs and performing real-time signal processing, the object's rotational angular velocity can be accurately obtained. The fiber optic gyroscope is a new type of all-solid-state inertial device with a simple structure, low cost, and potentially high accuracy, and will become a major instrument in inertial navigation and strategic applications.

[0003] Currently, most interferometric fiber optic gyroscopes are made of polarization-maintaining fiber. Traditional polarization-maintaining fibers introduce a stress structure to induce linear birefringence. As the temperature rises, the stress in the stress region gradually releases, and the birefringence value gradually decreases or even disappears, resulting in poor temperature stability of the polarization characteristics of traditional polarization-maintaining fibers. Therefore, fiber optic gyroscopes made of traditional polarization-maintaining fibers are susceptible to changes in the polarization-maintaining capability of the transmitted light, polarization coupling, and crosstalk due to temperature variations, leading to significant bias errors and affecting their accuracy. Photonic crystal fiber, on the other hand, is a new type of fiber whose cladding consists of periodically arranged air holes and silica along the axial direction. It is less affected by temperature, and through structural design, problems such as polarization crosstalk and polarization mode dispersion can be fundamentally solved, reducing zero-point drift and signal fading in fiber optic gyroscopes and improving their accuracy.

[0004] Currently, fiber optic gyroscopes on the market are generally very expensive, largely due to the high cost of optical components. For example, in the Chinese patent "A Fiber Optic Gyroscope Based on Single-Mode Single-Polarization Photonic Crystal Fiber" (Publication No. CN102914299A), this fiber optic gyroscope uses a lithium niobate modulator (Y-waveguide) to modulate two beams, simultaneously serving as polarizer and beam splitter. The Y-waveguide device used in this Chinese patent is a very expensive component. Therefore, designing novel fiber optic gyroscopes to simplify system structure and reduce manufacturing costs is one of the urgent problems that the industry needs to solve. Summary of the Invention

[0005] This application provides a fiber optic gyroscope to solve the problems of complex structure and large error in existing fiber optic gyroscopes.

[0006] To address the aforementioned technical problems, this application proposes a fiber optic gyroscope, comprising a broadband light source, a detector, a coupler, a phase modulator, and a single-polarization fiber ring. Light emitted from the broadband light source enters the coupler and is split into a first beam and a second beam. The first beam enters the single-polarization fiber ring via the phase modulator, while the second beam directly enters the single-polarization fiber ring. The first and second beams propagate clockwise and counterclockwise respectively within the single-polarization fiber ring before being output. The first beam enters the coupler, and the second beam enters the coupler via the phase modulator. The first and second beams generate an interference signal within the coupler. The interference signal emitted by the coupler enters the detector to determine the rotational state of the fiber optic gyroscope.

[0007] In one embodiment, the fiber ring is wound from a single-mode, single-polarization photonic crystal fiber.

[0008] In one embodiment, the inner diameter of the fiber optic ring is 15mm-20mm, and the outer diameter is 15mm-35mm.

[0009] In one embodiment, the broadband light source is a superluminescent diode light source or an amplified spontaneous emission light source.

[0010] In one embodiment, the coupler is a polarization-maintaining fiber coupler.

[0011] In one embodiment, the phase modulator is a piezoelectric ceramic phase modulator.

[0012] In one embodiment, the fiber optic gyroscope includes: a middle frame, an upper cover and a bottom cover disposed at both ends of the middle frame, and a middle cover disposed within the middle frame; a power board and a signal processing board, both disposed between the upper cover and the middle cover, with the power board disposed close to the upper cover and the signal processing board disposed close to the middle cover; wherein, the fiber optic ring is disposed between the middle cover and the bottom cover, and the detector, the coupler, and the phase modulator are all disposed on the power board or the signal processing board and connected to the power board and the signal processing board.

[0013] In one embodiment, the power board and the top cover are fixedly connected by studs at intervals, and the power board and the signal processing board are fixedly connected by studs at intervals.

[0014] In one embodiment, the middle frame, the top cover, and the bottom cover constitute a cubic shell with a side length of 44 mm.

[0015] In one embodiment, the signal processing board includes a field-programmable gate array (FPGA), a digital-to-analog converter (DAC), an analog-to-digital converter (ADC), and an output serial port connected to the FPGA; the DAC is connected to the detector, and the ADC is connected to the phase modulator.

[0016] Unlike existing technologies, the fiber optic gyroscope of this application includes a broadband light source, a detector, a coupler, a phase modulator, and a fiber optic ring. Light emitted from the broadband light source enters the coupler and is split into a first beam and a second beam. The first beam enters the fiber optic ring via the phase modulator, while the second beam directly enters the fiber optic ring. The first and second beams propagate clockwise and counterclockwise respectively within the single-polarization fiber optic ring before being output. The first beam enters the coupler, and the second beam enters the coupler via the phase modulator. The first and second beams generate an interference signal in the coupler. The interference signal emitted by the coupler enters the detector to determine the rotation state of the fiber optic gyroscope. The fiber optic gyroscope of this application eliminates the need for a polarizer and a Y-waveguide chip, resulting in a simple structure and high detection accuracy. Attached Figure Description

[0017] The above and other objects, features, and advantages of exemplary embodiments of the present disclosure will become readily apparent upon reading the following detailed description with reference to the accompanying drawings. In the drawings, several embodiments of the present disclosure are illustrated by way of example and not limitation, and like or corresponding reference numerals denote like or corresponding parts, wherein:

[0018] Figure 1 This is a schematic diagram of the optical path structure of the fiber optic gyroscope in this application;

[0019] Figure 2 This is a schematic diagram of the paths of the first beam and the second beam in the fiber optic gyroscope of this application;

[0020] Figure 3 This is a three-dimensional schematic diagram of the overall structure of the fiber optic gyroscope of this application;

[0021] Figure 4 This is an exploded three-dimensional structural diagram of the fiber optic gyroscope of this application;

[0022] Figure 5 This is a schematic diagram of the circuit structure of the fiber optic gyroscope in this application;

[0023] Figure 6 This is a schematic diagram of the optical fiber structure in the fiber optic gyroscope of this application. Detailed Implementation

[0024] The technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0025] The following is in conjunction with the accompanying drawings. Figures 1-6 To describe this application. First refer to Figure 1 , Figure 1 This is the optical path structure of the fiber optic gyroscope of this application. The fiber optic gyroscope 100 in this embodiment includes a broadband light source 11, a detector 12, a coupler 13, a phase modulator 14, and a single-polarization fiber loop 15.

[0026] Among them, the broadband light source 11 can be a superluminescent diode (SLD) light source or an amplified spontaneous emission (ASE) light source. The SLD light source provides output power equivalent to a laser diode and a wide oscillating spectral width equivalent to an LED (light-emitting diode), as well as low coherence. Because its emitted light has a narrow active layer equivalent to a laser diode, it is very suitable for insertion into optical fibers and has characteristics between SLD and LED. The ASE light source is specifically designed for production and laboratory experiments. The main body of the light source consists of erbium-doped fiber as the gain medium and a high-performance pump laser. Unique ATC and APC circuits ensure stable output power by controlling the output of the pump laser. The output power can be adjusted within a certain range by adjusting the APC. It features simple and intelligent operation and remote control.

[0027] Detector 12 is a photodetector. The working principle of a photodetector is based on the photoelectric effect. A thermal detector is based on the fact that the temperature of a material increases after absorbing light radiation energy, thereby changing its electrical properties. Its biggest difference from a photon detector is that it is non-selective in terms of the wavelength of light radiation. A photodetector can convert light signals into electrical signals.

[0028] Coupler 13 is a polarization-maintaining fiber coupler, which is a key device for realizing the coupling, splitting, and multiplexing of linearly polarized light. Its most significant feature is that it can stably transmit two orthogonal linearly polarized lights while maintaining their respective polarization states.

[0029] Phase modulator 14 is a piezoelectric ceramic phase modulator (PZT type phase modulator), specifically, an optical fiber wound on piezoelectric ceramic (PZT). Utilizing the piezoelectric effect of PZT, a phase modulator is constructed using a specific multi-layer winding method, resulting in high stability and high-speed modulation characteristics. In this embodiment, using a piezoelectric ceramic phase modulator allows for modulation of only one channel, without degrading gyroscope performance, and the use of only one phase modulator reduces the overall size.

[0030] The single-polarization fiber ring 15 is made of single-mode single-polarization photonic crystal fiber. In this embodiment, the fiber ring only retains a single polarization mode for transmission in the fiber, which can fundamentally solve problems such as polarization crosstalk and polarization mode dispersion, and reduce the zero-position drift and signal fading of the fiber optic gyroscope.

[0031] In this embodiment, the fiber optic gyroscope 100 does not require a polarizer or a Y-waveguide. The light emitted from the broadband light source 11 enters the coupler 13, which splits it into a first beam and a second beam. The paths of the first beam and the second beam can be found in [reference needed]. Figure 2 The first beam enters the single-polarization fiber ring 15 via the phase modulator 14, and the second beam directly enters the single-polarization fiber ring 15. The first beam and the second beam propagate clockwise and counterclockwise in the single-polarization fiber ring 15, respectively, and are then output. The first beam enters the coupler 13. The second beam enters the phase modulator 13 and then enters the coupler 13. The first beam and the second beam generate an interference signal in the coupler 13. The interference signal emitted by the coupler 13 enters the detector 12 to determine the rotation state of the fiber optic gyroscope.

[0032] Specifically, because the open-loop fiber optic gyroscope in this application uses a uniquely designed single-polarization fiber ring, it eliminates the need for Y-waveguide devices, simplifying the system structure and significantly reducing gyroscope costs while ensuring performance compliance. In this embodiment, the fiber optic gyroscope 100 is based on single-mode, single-polarization photonic crystal fiber. Light emitted from the SLD light source 11 is output through its single-mode pigtail and splits into two beams via the polarization-maintaining fiber coupler 13. One beam passes through the optical phase modulator (PZT) 14 and is output to one end of the single-polarization fiber ring 15, while the other beam is output to the other end. The single-polarization fiber ring 15 is wound with single-mode, single-polarization photonic crystal fiber. The two beams propagate clockwise and counterclockwise within the single-polarization fiber ring 15, respectively. The output light returns to the polarization-maintaining fiber coupler 13, generating an interference signal. The detector 12 detects the interference signal to obtain the rotation rate of the measurement system.

[0033] The inner diameter of the single-polarization fiber ring 15 is 15mm-20mm, and the outer diameter is 15-35mm, depending on the number of fiber winding layers. It uses bend-resistant photonic crystal fiber, is manufactured using a dedicated fiber drawing tower, and exhibits excellent single-polarization performance with an expected accuracy of 0.1 degrees / hour and high overall precision.

[0034] For the specific structure of the fiber optic gyroscope 100, please refer to [link / reference needed]. Figure 3 and Figure 4 The fiber optic gyroscope includes a middle frame 161, a top cover 162, a middle cover 163, a bottom cover 164, a power board 17, and a signal processing board 18.

[0035] The upper cover 162 and the bottom cover 164 are respectively installed on both ends of the middle frame 161, and the middle cover 163 is installed inside the middle frame 161, all connected by screws 20. The power board 17 and the signal processing board 18 are both installed between the upper cover 162 and the middle cover 163, with the power board 17 located closer to the upper cover 162 and the signal processing board 18 located closer to the middle cover.

[0036] The single-polarization fiber ring 15 is located between the middle cover 163 and the bottom cover 164. The broadband light source 11, detector 12, coupler 13 and phase modulator 14 are all located on the power board 17 or signal processing board 18 and are electrically connected to the power board and signal processing board.

[0037] To facilitate component placement, studs 19 are used for fixed connections between the power board 17 and the top cover 162, as well as between the power board 17 and the signal processing board 18.

[0038] In this embodiment, the middle frame 161, the upper cover 162, and the bottom cover 164 constitute a cubic shell with a height of 47 mm and a side length of 44 mm. The height of the middle cover 163 to the bottom cover 164 is 25 mm, which is used to adapt to the height of the single polarization fiber ring 15.

[0039] The fiber optic gyroscope 100 in this embodiment has a simplified structure, fewer components, lower cost, and smaller overall size.

[0040] The structure of the signal processing board 18 in this embodiment is as follows: Figure 5 Specifically, it includes a field-programmable gate array (FPGA), a digital-to-analog converter (DAC), an analog-to-digital converter (ADC), and an output serial port RS-422 connected to the FPGA. More specifically, the DAC is connected to the detector (PD), and the ADC is connected to the phase modulator (PZT).

[0041] The structure of the single-mode, single-polarization photonic crystal fiber in this embodiment can be found in [reference]. Figure 6 Firstly, in this embodiment, the single-polarization photonic crystal fiber is made of pure quartz material to form the photonic crystal fiber. Multiple circular air holes are formed within the single-polarization photonic crystal fiber, axially penetrating the fiber. These circular air holes include two large circular air holes, multiple medium circular air holes, and multiple small circular air holes.

[0042] The cross-section of a single-polarization photonic crystal fiber is circular. On the cross-section, two large circular air holes are symmetrically distributed about the center of the cross-section. Multiple small circular air holes are arranged around the two large circular air holes, forming a multi-layered polygonal air hole ring with increasing size from the inside to the outside. Multiple medium-sized circular air holes are distributed on the outermost layer of the multi-layered polygonal air hole ring.

[0043] Multiple small circular air holes are arranged in a regular hexagonal array. The distance between the centers of two adjacent small circular air holes and two adjacent medium circular air holes is a fixed pitch, and the distance between the centers of two large circular air holes is twice the pitch.

[0044] The centers of the two large circular air holes are on the same horizontal line as the centers of the medium circular air holes on their left and right.

[0045] The outermost layer of the regular hexagon formed by the central circular air holes does not have the central circular air holes at its six corners.

[0046] The diameter d1 of the two large circular air holes is 5.5um ± 0.5um, and the diameter d2 of the multiple medium circular air holes is 3.0um ± 0.5um. The diameter d3 of the multiple small circular air holes is 2.2um ± 0.5um. The spacing L between the medium holes is 4.4um ± 0.5um.

[0047] The size of the small circular air hole d3 and the spacing L between the two holes determine the single-mode properties and low confinement loss of the single-polarization photonic crystal fiber in this embodiment. The design of the large circular air hole d1 determines the polarization-maintaining characteristics of the fiber, affecting both the single-polarization effect and its single-polarization performance during bending. The size of the medium circular air hole d2 determines the low bending confinement loss of the fiber in this embodiment. When d1, d2, and d3 are within the parameter range of this embodiment, good single-polarization performance can be achieved within a bending diameter range of 15mm-30mm.

[0048] In this embodiment, only one layer of circular air holes is set. While achieving single-polarization optical fiber with bending resistance through parameter design, the structure is simplified to the greatest extent, reducing the difficulty of the manufacturing process. The parameter control technology for multiple central holes is relatively mature, resulting in a high production yield. Other single-polarization photonic crystal fiber structures, such as elliptical air holes, triangular air holes, and multiple nanoscale air holes, are currently difficult to achieve with existing technology.

[0049] The circular air hole arrangement in this embodiment is suitable for single-polarization photonic crystal fibers with a cross-sectional diameter D of 60µm, 80µm, or 125µm.

[0050] This fiber optic gyroscope includes a broadband light source, a detector, a coupler, a phase modulator, and a fiber optic ring. Light emitted from the broadband light source enters the coupler and is split into a first beam and a second beam. The first beam enters the fiber optic ring via the phase modulator, while the second beam directly enters the fiber optic ring. The first and second beams propagate clockwise and counterclockwise respectively within the single-polarization fiber optic ring before being output. The first beam enters the coupler, and the second beam enters the coupler via the phase modulator. The first and second beams generate an interference signal within the coupler. The interference signal emitted by the coupler enters the detector to determine the rotation state of the fiber optic gyroscope. This fiber optic gyroscope eliminates the need for a polarizer and a Y-waveguide chip, reduces the size of the fiber optic ring, simplifies the overall structure, and achieves high detection accuracy.

[0051] In the foregoing description of this specification, unless otherwise expressly specified and limited, the terms "fixed," "installed," "connected," or "linked" should be interpreted broadly. For example, the term "linked" can refer to a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; or it can refer to the internal communication of two components or the interaction between two components. Therefore, unless otherwise expressly limited in this specification, those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0052] Based on the above description in this specification, those skilled in the art will also understand that the following terms used, such as "upper," "lower," "front," "rear," "left," "right," "length," "width," "thickness," "vertical," "horizontal," "top," "bottom," "inner," "outer," "axial," "radial," "circumferential," "center," "longitudinal," "transverse," "clockwise," or "counterclockwise," are terms indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings of this specification. They are only for the purpose of facilitating the explanation of the present application and simplifying the description, and do not explicitly or implicitly suggest that the device or element involved must have the specific orientation, or be constructed and operated in a specific orientation. Therefore, the above-mentioned orientation or positional relationship terms should not be understood or interpreted as limitations on the present application.

[0053] Furthermore, the terms "first" or "second," etc., used in this specification to refer to numbers or ordinal numbers are for descriptive purposes only and should not be construed as indicating, explicitly or implicitly, relative importance or specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this specification, "a plurality of" means at least two, such as two, three, or more, unless otherwise explicitly specified.

[0054] While this specification has shown and described numerous embodiments of the present application, it will be apparent to those skilled in the art that such embodiments are provided by way of example only. Many modifications, alterations, and alternatives will occur to those skilled in the art without departing from the spirit and intent of the present application. It should be understood that various alternatives to the embodiments of the present application described herein may be employed in the practice of this application. The appended claims are intended to define the scope of protection of this application and therefore cover modular compositions, equivalents, or alternatives within the scope of these claims.

Claims

1. An optical fiber gyroscope, characterized by The fiber-optic gyroscope comprises a broadband light source, a detector, a coupler, a phase modulator and a single-polarization fiber ring; The light emitted by the broadband light source enters the coupler, and is divided into a first light beam and a second light beam by the coupler, the first light beam enters the single-polarization fiber ring via the phase modulator, and the second light beam directly enters the single-polarization fiber ring; The first light beam and the second light beam are output after propagating in the single-polarization fiber ring in clockwise and counterclockwise directions respectively, the first light beam enters the coupler, the second light beam enters the coupler via the phase modulator, and the first light beam and the second light beam generate an interference signal in the coupler, the interference signal emitted by the coupler enters the detector to determine the rotation state of the fiber-optic gyroscope; The single-polarization fiber ring is made of a single-mode single-polarization photonic crystal fiber; When the single-mode single-polarization photonic crystal fiber is bent, the light of the fast axis is coupled out of the core and is cut off, and the light of the slow axis continues to be transmitted in the core in the form of a guided mode, the bending diameter of the single-mode single-polarization photonic crystal fiber ranges from 5 mm to 30 mm, a plurality of circular air holes axially penetrating the single-mode single-polarization photonic crystal fiber are formed in the single-mode single-polarization photonic crystal fiber, and the plurality of circular air holes comprise two large circular air holes, a plurality of small circular air holes and a plurality of medium circular air holes; The cross section of the single-mode single-polarization photonic crystal fiber is circular, and on the cross section, the two large circular air holes are distributed symmetrically left and right about the center of the cross section, the plurality of small circular air holes are arranged around the two large circular air holes and form a plurality of layers of polygonal air hole rings with increasing sizes from inside to outside, and the plurality of medium circular air holes are distributed on the outermost layer of the plurality of layers of polygonal air hole rings formed by the small circular air holes; The two adjacent small circular air holes are arranged according to a regular hexagonal array, the center-to-center distance between the two adjacent small circular air holes is a fixed pitch, the center-to-center distance between the two adjacent medium circular air holes is also the same pitch, and the center-to-center distance between the two large circular air holes is twice the pitch.

2. The fiber optic gyroscope of claim 1, wherein, The inner diameter of the single-polarization fiber ring ranges from 15 mm to 20 mm, and the outer diameter ranges from 15 mm to 35 mm.

3. The fiber optic gyroscope of claim 1, wherein, The broadband light source is a superluminescent diode light source or an amplified spontaneous emission light source.

4. The fiber optic gyroscope of claim 1, wherein, The coupler is a polarization maintaining fiber coupler, and the phase modulator is a piezoelectric ceramic modulator.

5. The fiber optic gyroscope of claim 1, wherein, The phase modulator is a piezoelectric ceramic phase modulator.

6. The fiber optic gyroscope of claim 1, wherein, The fiber-optic gyroscope comprises: a middle frame, upper and bottom covers arranged at two ends of the middle frame, and a middle cover arranged in the middle frame; a power supply board and a signal processing board, both arranged between the upper cover and the middle cover, the power supply board being arranged close to the upper cover, and the signal processing board being arranged close to the middle cover; wherein the single-polarization fiber ring is arranged between the middle cover and the bottom cover, the detector, the coupler and the phase modulator are all arranged on the power supply board or the signal processing board, and are connected to the power supply board and the signal processing board.

7. The fiber optic gyroscope of claim 6, wherein, The power board and the upper cover are fixedly connected by studs, and the power board and the signal processing board are fixedly connected by studs.

8. The fiber optic gyroscope of claim 6, wherein, The middle frame, the upper cover and the bottom cover form a cubic shell, and the cubic shell has a side length of 44 mm.

9. The fiber optic gyroscope of claim 6, wherein, The signal processing board comprises a field programmable logic gate array, a digital-to-analog converter, an analog-to-digital converter and an output serial port connected to the field programmable logic gate array; the digital-to-analog converter is connected to the detector, and the analog-to-digital converter is connected to the phase modulator.

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