Inertial Measurement Unit, Navigation System and Mobile Device

Abstract

The present application relates to an inertial measurement unit, a navigation system and a mobile device. The inertial measurement unit includes a one-axis fiber optic gyroscope, a two-axis MEMS gyroscope and a three-axis fiber optic accelerometer. The three-axis fiber optic accelerometer includes a narrowband light source, a first coupler, three second couplers, three first phase modulators, three first detectors and six compliant bodies. Every two of the compliant bodies are coaxially arranged, and each is wound with an optical fiber, and a high-reflection structure is arranged at the end of the optical fiber. The light beam emitted by the narrowband light source enters the first coupler and is divided into three light beams, which respectively enter the second couplers and are divided into two light beams. One of the light beams enters a coaxial compliant body via the first phase modulator, and the other directly enters the other coaxial compliant body. The light beam is reflected by the high-reflection structure and returns to the second coupler along the original path to generate a first interference signal, which enters the first detector to determine the acceleration state of the three-axis fiber optic accelerometer. The inertial measurement unit of the present application has high precision and small volume.

Description

Technical Field

[0001] This application belongs to the field of detection technology, and particularly relates to an inertial measurement unit, a navigation system, and a mobile device. Background Art

[0002] An inertial measurement unit is a device for measuring the three-axis angular velocity and linear acceleration of an object, mainly including gyroscopes and accelerometers. Existing inertial measurement units generally use three MEMS gyroscopes and three accelerometers, with low accuracy, and the overall structure is relatively complex and the volume is relatively large.

[0003] For the specific existing inertial measurement unit, reference can be made to the Chinese patent "Inertial Measurement System Based on a Highly Integrated Accelerometer" (Publication No. CN102305629A), where the inertial measurement system includes an X-axis fiber optic inertial measurement unit, a Y-axis fiber optic inertial measurement unit, and a Z-axis fiber optic inertial measurement unit. Each fiber optic inertial measurement unit is composed of an accelerometer and a closed-loop fiber optic gyro. The accelerometer and the fiber optic gyro in the inertial measurement system are both independently set components, and the structure is complex. In addition, the "Integrated Two-Dimensional Fiber Optic Micro Accelerometer Based on Four-Core Fiber" (Publication No. CN101858926A) discloses a single fiber optic accelerometer structure, but does not disclose how to design the structure of a three-axis fiber optic accelerometer to simplify the structure. Summary of the Invention

[0004] This application provides an inertial measurement unit, a navigation system, and a mobile device to solve the problems of complex structure and large volume of the existing inertial measurement unit.

[0005] To solve the above technical problems, the present application proposes an inertial measurement unit, which includes a one-axis fiber optic gyroscope, a two-axis MEMS gyroscope, and a three-axis fiber optic accelerometer. The three-axis fiber optic accelerometer includes a narrowband light source, a first coupler, three second couplers, three first phase modulators, three first detectors, and six compliant bodies. Every two of the six compliant bodies are coaxially arranged, and optical fibers are wound around each compliant body. A high-reflection structure is provided at the end of the optical fiber. The light emitted by the narrowband light source enters the first coupler and is divided into three beams of light by the first coupler. The three beams of light respectively enter the three second couplers and are respectively divided into two beams of light by the second couplers. One of the two beams of light enters the optical fiber on a coaxially arranged compliant body via the first phase modulator, and the other directly enters the optical fiber on another coaxially arranged compliant body. The light beam entering the optical fiber on the compliant body is reflected by the high-reflection structure and returns to the second coupler along the original path, generating a first interference signal in the second coupler. The first interference signal emitted by the second coupler enters the first detector to determine the acceleration states of the three-axis fiber optic accelerometer in three axes. The three-axis fiber optic accelerometer further includes a mass block in the shape of a cube, and the six compliant bodies are symmetrically arranged on six surfaces of the mass block.

[0006] In one embodiment, the one-axis fiber optic gyroscope includes a broadband light source, a second detector, a third coupler, a second phase modulator, and an optical fiber loop. The light emitted by the broadband light source enters the third coupler and is divided into two beams of light by the third coupler. One beam enters the optical fiber loop via the second phase modulator, and the other directly enters the optical fiber loop. The two beams of light respectively propagate clockwise and counterclockwise in the optical fiber loop and then output, and respectively return to the third coupler along the original path, generating a second interference signal in the third coupler. The second interference signal emitted by the third coupler enters the second detector to determine the rotation state of the one-axis fiber optic gyroscope.

[0007] In one embodiment, both the optical fiber loop and the optical fiber are wound by single-mode single-polarization photonic crystal fibers.

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

[0009] In one embodiment, the first coupler, the second coupler, and the third coupler are all polarization-maintaining fiber couplers.

[0010] In one embodiment, the first phase modulator and the second phase modulator are both piezoelectric ceramic type phase modulators.

[0011] In one embodiment, the inertial measurement unit further includes: an inner cavity body and an inner cover body, the inner cover body covers the inner cavity body to form a cube, and openings are provided on all six surfaces of the formed cube; the mass blocks are arranged in the inner cavity body, and the compliant bodies connected to the mass blocks are correspondingly arranged with respect to the openings; an outer cavity body and an outer cover body, the outer cover body covers the outer cavity body, and a slot is formed on the side surface of the outer cover body; the inner cavity body and the optical fiber ring are arranged side by side in the outer cavity body; a light source circuit board, including the broadband light source and the narrowband light source; is arranged in the outer cavity body and the outer cover body; a main board, which is arranged in the outer cavity body and the outer cover body and is connected to the light source circuit board; is used to carry the first coupler, the second coupler, the third coupler, the first phase modulator, the second phase modulator, the first detector and the second detector; a signal board, which is arranged in the outer cavity body and the outer cover body and is connected to the main board.

[0012] In one embodiment, the signal board is connected to a communication interface, and the communication interface is exposed in the slot.

[0013] To solve the above technical problems, the present application proposes a navigation system, and the navigation system includes the above inertial measurement unit.

[0014] To solve the above technical problems, the present application proposes a mobile device, and the mobile device includes the above navigation system.

[0015] Different from the prior art, the inertial measurement unit of the present application includes a one-axis fiber optic gyroscope, a two-axis MEMS gyroscope and a three-axis fiber optic accelerometer. The three-axis fiber optic accelerometer includes a narrowband light source, a first coupler, three second couplers, three first phase modulators, three first detectors, and six compliant bodies. Every two of the six compliant bodies are coaxially arranged, and optical fibers are wound on each compliant body, and a high-reflection structure is arranged at the end of the optical fiber; the light emitted by the narrowband light source enters the first coupler, and is divided into three beams of light by the first coupler. The three beams of light respectively enter the three second couplers, and are respectively divided into two beams of light by the second couplers. One of the two beams of light enters the optical fiber on a coaxially arranged compliant body via the first phase modulator, and the other beam directly enters the optical fiber on another coaxially arranged compliant body; the beam of light entering the optical fiber on the compliant body is reflected by the high-reflection structure and returns to the second coupler along the original path, and a first interference signal is generated in the second coupler. The first interference signal emitted by the second coupler enters the first detector to determine the acceleration states of the three-axis fiber optic accelerometer on the three axes. Description of the Drawings

[0016] By reading the following detailed description with reference to the accompanying drawings, the above and other objects, features and advantages of the exemplary embodiments of the present disclosure will become readily understood. In the drawings, several embodiments of the present disclosure are shown in an exemplary rather than restrictive manner, and the same or corresponding reference numerals represent the same or corresponding parts, wherein:

[0017] Figure 1 It is a schematic optical path structure diagram of the fiber optic gyroscope in the inertial measurement unit of the present application;

[0018] Figure 2 It is a schematic optical path structure diagram of the fiber optic accelerometer in the inertial measurement unit of the present application;

[0019] Figure 3 It is a three-dimensional overall schematic diagram of the mechanical structure of the inertial measurement unit of the present application;

[0020] Figure 4 It is a three-dimensional exploded schematic diagram of the mechanical structure of the inertial measurement unit of the present application;

[0021] Figure 5 It is a schematic circuit structure diagram of the inertial measurement unit of the present application;

[0022] Figure 6 It is a schematic structure diagram of the optical fiber in the inertial measurement unit of the present application. Detailed implementation manners

[0023] Next, the technical solutions in the embodiments of the present disclosure will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present disclosure. Obviously, the described embodiments are part of the embodiments of the present disclosure, rather than all of the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by those skilled in the art without creative efforts fall within the protection scope of the present disclosure.

[0024] Next, in conjunction with the accompanying drawings Figures 1-6 to describe the present application. The inertial measurement unit 400 in this embodiment includes a one-axis fiber optic gyroscope 100, a two-axis MEMS gyroscope 300, and a three-axis fiber optic accelerometer 200. The fiber optic gyroscope 100 is responsible for judging the rotation angle of one axis, the two-axis MEMS gyroscope 300 is responsible for judging the rotation angles of two axes, and the three-axis fiber optic accelerometer 200 is responsible for judging the linear accelerations of three axes. As Figure 5 shown is a schematic connection principle diagram of the one-axis fiber optic gyroscope 100, the two-axis MEMS gyroscope 300, and the three-axis fiber optic accelerometer 200.

[0025] First, refer to Figure 1 , Figure 1 , which is a schematic optical path structure diagram of the fiber optic gyroscope in the inertial measurement unit of the present 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 optic loop 15.

[0026] Among them, the broadband light source 11 can be a superluminescent light-emitting diode light source (SLD light source) or an amplified spontaneous emission light source (ASE light source). The SLD light source provides an output power equivalent to that of a laser diode, a wide oscillation spectral width equivalent to that of an LED (light-emitting diode), and a low coherence. Since the light it emits has a narrow active layer equivalent to that of a laser diode, it is very suitable for entering an optical fiber and has characteristics between those of an SLD and an LED. The ASE light source is designed for production and laboratory experiments. The main part of the light source is a gain medium, erbium-doped fiber, and a high-performance pump laser. The unique atc and apc circuits ensure the stability of the output power by controlling the output of the pump laser. By adjusting the apc, the output power can be adjusted within a certain range. Simple and intelligent operation and remote control.

[0027] The detector 12 is a photodetector. The working principle of the photodetector is based on the photoelectric effect. The thermal detector is based on the fact that the temperature of the material increases after absorbing the light radiation energy, thereby changing its electrical properties. The biggest feature that distinguishes it from the photon detector is that it has no selectivity for the wavelength of the light radiation. The photodetector can convert the optical signal into an electrical signal.

[0028] The coupler 13 is a polarization-maintaining fiber coupler. The polarization-maintaining fiber coupler is a key device for realizing the coupling, splitting, and multiplexing of linearly polarized light. Its biggest feature is that it can stably transmit two orthogonal linearly polarized lights and can maintain their respective polarization states unchanged. Specifically, it can maintain the polarization states of two orthogonal linearly polarized lights parallel to the axis basically.

[0029] The phase modulator 14 is a piezoelectric ceramic type phase modulator (PZT type phase modulator). Specifically, the optical fiber is wound around a piezoelectric ceramic (PZT), and the phase modulator is formed by using the piezoelectric effect of the PZT. Specifically, a specific multi-layer winding method is adopted to make the fragrance modulator have high stability and high-speed modulation characteristics.

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

[0031] In this embodiment, the fiber optic gyroscope 100 does not require a polarizer and a Y waveguide. The light emitted by the broadband light source 11 enters the coupler 13 and is divided by the coupler 13 into a first light beam and a second light beam. The first light beam enters the single-polarization fiber loop 15 via the phase modulator 14, and the second light beam directly enters the single-polarization fiber loop 15. The first light beam and the second light beam are output after propagating clockwise and counterclockwise respectively in the single-polarization fiber loop 15. The first light beam returns to the phase modulator 14 and enters the coupler 13. The second light beam directly returns to the coupler 13. The first light beam and the second light 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, the fiber optic gyroscope 100 in this embodiment is based on a single-mode single-polarization photonic crystal fiber. The light emitted by the SLD light source 11 is output through its single-mode pigtail, and through the polarization-maintaining pigtail of the polarization-maintaining fiber coupler 13, the light is divided into two beams. One beam of light is output to one end of the single-polarization fiber loop 15 after passing through the optical phase modulator (PZT) 14, and the other beam of light is output to the other end of the single-polarization fiber loop 15. The single-polarization fiber loop 15 is wound with a single-mode single-polarization photonic crystal fiber. The two beams of light propagate clockwise and counterclockwise respectively in the single-polarization fiber loop 15, and the output light returns to enter the polarization-maintaining fiber coupler 13 to obtain an interference signal. The photodetector (PD) 12 detects the interference signal to obtain the rotation rate of the measurement system.

[0033] The inner diameter of the single-polarization fiber loop 15 is 15 mm - 20 mm, and the outer diameter is 15 - 35 mm, which is specifically determined by the number of fiber winding layers. The anti-bending photonic crystal fiber is used and produced by a special fiber drawing tower, which has a good single-polarization effect, an expected accuracy of 0.1 degree / hour, and a high overall accuracy.

[0034] Please refer to Figure 2 , Figure 2 which is a schematic optical path structure diagram of the fiber optic accelerometer in the inertial measurement unit of this application. The fiber optic accelerometer 200 includes a narrowband light source 21, a first coupler 22, a second coupler 23, a first phase modulator 24, a first detector 25, and a compliant body 26.

[0035] Among them, there are three second couplers 23, three first phase modulators 24, three first detectors 25, and six compliant bodies 26. Two of the six compliant bodies 26 are coaxially arranged, and optical fibers are wound on each compliant body 26, and high-reflection structures are arranged at the ends of the optical fibers.

[0036] The light emitted by the narrowband light source 21 enters the first coupler 22, and is divided into three beams by the first coupler 22. The three beams respectively enter three second couplers 23, and are respectively divided into two beams by the second couplers 23. One of the two beams enters the optical fiber on a coaxial compliant body 26 via the first phase modulator 24, and the other beam directly enters the optical fiber on another coaxial compliant body 26.

[0037] The beam entering the optical fiber on the compliant body 26 is reflected by the high-reflection structure and returns to the second coupler 23 along the original path. The first interference signal is generated in the second coupler 23, and the first interference signal emitted by the second coupler 23 enters the first detector 25 to determine the acceleration states of the three-axis fiber optic accelerometer 200 in three axes.

[0038] The three-axis fiber optic accelerometer 200 further includes a cube-shaped mass block 27, and six compliant bodies 26 are symmetrically arranged on six surfaces of the mass block 27.

[0039] The compliant body 26 is an elastic deformation body. When the structure has an acceleration in a certain direction, the compliant body undergoes elastic deformation under the action of the inertial force of the mass block, and then the optical fiber wound on the compliant body 26 changes. Therefore, the detection of acceleration can be realized by demodulating the optical fiber signal. The wound optical fiber is similar to the optical fiber in the above optical fiber loop, and will not be elaborated here. This structure can realize the detection of acceleration in three axes as much as possible in a small volume.

[0040] The high-reflection structure is located at the end of the optical fiber, and can be a high-reflection thin film plated on the end face of the optical fiber end, such as gold, silver, aluminum; it can also be a reflection device such as a mirror or a Faraday rotator mirror connected to the optical fiber end.

[0041] In this embodiment, the first phase modulator (PZT) 24 and the first detector (PD) 25 are similar to the phase modulator and detector in the fiber optic gyroscope 100, and will not be elaborated here.

[0042] For the mechanical structure of the inertial measurement unit 400, please refer to Figure 3 and Figure 4 , where the inertial measurement unit 400 further includes an outer cavity 411 and an outer cover 412, an inner cavity 421 and an inner cover 422, a light source circuit board 43, a main board 44 and a signal board 45, and a communication interface 46 connected to the signal board 45.

[0043] The inner cover body 422 is covered on the inner cavity body 421 to form a cube, and openings are provided on all six surfaces of the formed cube; the mass block 27 is arranged in the inner cavity body 421, and the compliant bodies 26 connected to the mass block 27 are correspondingly arranged with respect to the openings, and a cover body 263 is provided at the openings. The compliant bodies 26 can be a silica gel cap 261 and a silica gel pad 262. When the silica gel cap undergoes elastic deformation under the action of the inertial force of the mass block 27, the optical signal changes immediately.

[0044] An outer cavity body 411 and an outer cover body 412, the outer cover body 412 is covered on the outer cavity body 411, and a slotted opening is formed on the side surface of the outer cover body 412; the inner cavity body 421 and the single-polarization optical fiber loop 15 are arranged side by side in the outer cavity body 411.

[0045] A light source circuit board 43, including a broadband light source and a narrowband light source; is arranged in the outer cavity body 411 and the outer cover body 412.

[0046] A main board 44, is arranged in the outer cavity body 411 and the outer cover body 412 and is connected to the light source circuit board 43; is used for carrying the first coupler, the second coupler, the first phase modulator, the first detector in the fiber optic accelerometer 200, and the third coupler, the second phase modulator and the second detector in the fiber optic gyroscope 100.

[0047] A signal board 45, is arranged in the outer cavity body 411 and the outer cover body 412 and is connected to the main board 44. The communication interface 46 connected to the signal board 45 is exposed in the slotted opening.

[0048] The structure of the single-mode single-polarization photonic crystal fiber in this embodiment can be referred to Figure 6 , first of all, the single-polarization photonic crystal fiber in this embodiment is made of pure quartz material to form a photonic crystal fiber. Multiple circular air holes axially penetrating the single-polarization photonic crystal fiber are formed in the single-polarization photonic crystal fiber. The multiple circular air holes include two large circular air holes, multiple medium circular air holes and multiple small circular air holes.

[0049] The cross-section of the single-polarization photonic crystal fiber is circular. On the cross-section, the two large circular air holes are symmetrically distributed about the center of the cross-section; the multiple small circular air holes are arranged around the two large circular air holes, forming multiple layers of polygonal air hole rings with increasing sizes from the inside to the outside; the multiple medium circular air holes are distributed in the outermost layer of the multiple layers of polygonal air hole rings.

[0050] The multiple small circular air holes are arranged according to a regular hexagon array. The center distances between two adjacent small circular air holes and between two adjacent medium circular air holes are both fixed pitch, and the center distance between the two large circular air holes is twice the pitch.

[0051] The centers of the two large circular air holes and the centers of the medium circular air holes on their left and right are on the same horizontal line.

[0052] The regular hexagon formed by the outermost medium circular air holes has no medium circular air holes at the six corners of the regular hexagon.

[0053] The diameters d of the two large circular air holes 1 are both 5.5um ± 0.5um, and the diameters d of multiple medium circular air holes 2 are both 3.0um ± 0.5um. The diameters d of multiple small circular air holes 3 are 2.2um ± 0.5um. The medium hole spacing L is 4.4um ± 0.5um.

[0054] Among them, the sizes of the small circular air holes d 3 and the medium hole spacing L determine the single-mode characteristics and low confinement loss of the single-polarization photonic crystal fiber in this embodiment. The design of the large circular air holes d 1 determines the polarization-maintaining characteristics of the fiber. It affects both the effect of single polarization and the single-polarization performance when the fiber is bent. The size of the medium circular air holes d 2 determines the low bending confinement loss of the fiber in this embodiment. When d 1 , d 2 , d 3 are within the parameter range of this embodiment, good single-polarization effects can be achieved within the range of bending diameters from 15mm to 30mm.

[0055] In this embodiment, only one layer of medium circular air holes is provided. On the basis of being able to achieve fiber bending-resistant single polarization through parameter design, the structure is maximally simplified, the difficulty of the manufacturing process is reduced, the parameter control technology for multiple medium holes is relatively mature, and the production yield is relatively high. Other single-polarization photonic crystal fiber structures such as elliptical air holes, triangular air holes, and multiple nano-scale air holes are currently difficult to achieve with existing technologies.

[0056] The arrangement structure of the circular air holes in this embodiment is applicable to single-polarization photonic crystal fibers with cross-sectional diameters D of 60um, 80um, or 125um.

[0057] The inertial measurement unit of the present application includes a one-axis fiber optic gyroscope, a two-axis MEMS gyroscope, and a three-axis fiber optic accelerometer. The three-axis fiber optic accelerometer includes a narrowband light source, a first coupler, three second couplers, three first phase modulators, three first detectors, and six compliant bodies. Every two of the six compliant bodies are coaxially arranged, and optical fibers are wound around each compliant body, and a high-reflection structure is arranged at the end of the optical fiber. The light beam emitted by the narrowband light source enters the first coupler and is divided into three beams by the first coupler. The three beams respectively enter the three second couplers and are respectively divided into two beams by the second couplers. One of the two beams enters the optical fiber on a coaxially arranged compliant body via the first phase modulator, and the other beam directly enters the optical fiber on another coaxially arranged compliant body. The light beam entering the optical fiber on the compliant body is reflected by the high-reflection structure and returns along the original path to the second coupler, and a first interference signal is generated in the second coupler. The first interference signal emitted by the second coupler enters the first detector to determine the acceleration states of the three-axis fiber optic accelerometer in three axes.

[0058] The present application also proposes a navigation system. While realizing inertial measurement by using the above inertial measurement unit, it can also fuse lidar, visual sensing, high-precision maps, etc. to realize the measurement of environmental information. It can be applied to the navigation of mobile devices such as automobiles and aircraft. Correspondingly, the present application also proposes a mobile device including the above navigation system.

[0059] In the above description of this specification, unless otherwise clearly specified and limited, terms such as "fixed", "installed", "connected" or "coupled" should be understood in a broad sense. For example, for the term "connected", it can be a fixed connection, a detachable connection, or an integral body; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, or it can be the internal connection of two components or the interaction relationship between two components. Therefore, unless otherwise clearly limited in this specification, those skilled in the art can understand the specific meanings of the above terms in the present application according to specific situations.

[0060] Based on the above description of this specification, those skilled in the art can also understand 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", etc. The terms indicating orientation or positional relationship are based on the orientation or positional relationship shown in the drawings of this specification. It is only for the purpose of facilitating the description of the solution of this application and simplifying the description, rather than explicitly or implicitly indicating that the device or component involved must have the specific orientation, be constructed and operated in the specific orientation. Therefore, the above terms of orientation or positional relationship cannot be understood or interpreted as a limitation to the solution of this application.

[0061] In addition, the terms "first" or "second", etc. used in this specification to refer to numbers or ordinals are only for descriptive purposes and cannot be understood as explicitly or implicitly indicating relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" or "second" may explicitly or implicitly include at least one such feature. In the description of this specification, the meaning of "a plurality" is at least two, such as two, three or more, etc., unless otherwise specifically defined.

[0062] Although this specification has shown and described multiple embodiments of this application, it is obvious to those skilled in the art that such embodiments are provided only by way of example. Those skilled in the art will think of many changes, alterations and alternative ways without departing from the spirit and idea of this application. It should be understood that various alternative solutions to the embodiments of this application described herein can be adopted in the process of practicing this application. The appended claims are intended to define the protection scope of this application and thus cover the module compositions, equivalents or alternative solutions within the scope of these claims.

Claims

1. An inertial measurement unit, characterized in that, the inertial measurement unit includes a one-axis fiber optic gyroscope, a two-axis MEMS gyroscope, and a three-axis fiber optic accelerometer, the three-axis fiber optic accelerometer includes a narrowband light source, a first coupler, three second couplers, three first phase modulators, three first detectors, and six compliant bodies. Every two of the six compliant bodies are coaxially arranged, and optical fibers are wound on each compliant body, and a high-reflection structure is arranged at the end of the optical fiber; the compliant body is an elastic deformation body. When there is an acceleration in a certain direction, the compliant body undergoes elastic deformation under the action of the inertial force of the mass block, and the optical fiber wound on the compliant body changes, and the detection of acceleration is realized by demodulating the optical fiber signal; the light emitted by the narrowband light source enters the first coupler, and is divided into three beams of light by the first coupler. The three beams of light respectively enter the three second couplers, and are respectively divided into two beams of light by the second couplers. One of the two beams of light enters the optical fiber on a coaxial compliant body via the first phase modulator, and the other directly enters the optical fiber on another coaxial compliant body; the light beam entering the optical fiber on the compliant body is reflected by the high-reflection structure and returns along the original path to the second coupler, and a first interference signal is generated in the second coupler. The first interference signal emitted by the second coupler enters the first detector to determine the acceleration states of the three-axis fiber optic accelerometer in three axes; the three-axis fiber optic accelerometer further includes a mass block in the shape of a cube, and the six compliant bodies are symmetrically arranged on six surfaces of the mass block.

2. The inertial measurement unit according to claim 1, characterized in that, the one-axis fiber optic gyroscope includes a broadband light source, a second detector, a third coupler, a second phase modulator, and an optical fiber loop; the light emitted by the broadband light source enters the third coupler, and is divided into two beams of light by the third coupler. One beam enters the optical fiber loop via the second phase modulator, and the other directly enters the optical fiber loop; the two beams of light propagate clockwise and counterclockwise respectively in the optical fiber loop and then output, and return along the original path to the third coupler respectively, and a second interference signal is generated in the third coupler; the second interference signal emitted by the third coupler enters the second detector to determine the rotation state of the one-axis fiber optic gyroscope.

3. The inertial measurement unit according to claim 2, characterized in that, both the optical fiber loop and the optical fiber are wound by single-mode single-polarization photonic crystal fiber.

4. The inertial measurement unit according to claim 3, characterized in that, the inner diameter of the optical fiber loop is 15 mm - 20 mm, and the outer diameter is 15 mm - 35 mm.

5. The inertial measurement unit according to claim 2, characterized in that, the first coupler, the second coupler, and the third coupler are all polarization-maintaining fiber couplers.

6. The inertial measurement unit according to claim 2, characterized in that, the first phase modulator and the second phase modulator are both piezoelectric ceramic type phase modulators.

7. The inertial measurement unit according to claim 2, characterized in that, The inertial measurement unit further includes: An inner cavity body and an inner cover body, the inner cover body is covered on the inner cavity body to form a cube, and openings are provided on all six surfaces of the formed cube; the mass block is arranged in the inner cavity body, and the compliant bodies connected to the mass block are correspondingly arranged with respect to the openings; An outer cavity body and an outer cover body, the outer cover body is covered on the outer cavity body, and a slotted opening is formed on the side surface of the outer cover body; the inner cavity body and the optical fiber ring are arranged side by side in the outer cavity body; A light source circuit board, including the broadband light source and the narrowband light source; arranged in the outer cavity body and the outer cover body; A main board, arranged in the outer cavity body and the outer cover body, connecting the light source circuit board; used for carrying the first coupler, the second coupler, the third coupler, the first phase modulator, the second phase modulator, the first detector and the second detector; A signal board, arranged in the outer cavity body and the outer cover body, connecting the main board.

8. The inertial measurement unit according to claim 7, wherein, the signal board is connected to a communication interface, and the communication interface is exposed in the slotted opening.

9. A navigation system, wherein, the navigation system includes the inertial measurement unit according to any one of claims 1-8.

10. A mobile device, wherein, the mobile device includes the navigation system according to claim 9.

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