A high-sensitivity fiber optic gyroscope based on mode division multiplexing

Abstract

The present invention discloses a high-sensitivity fiber optic gyroscope based on mode division multiplexing, characterized in that the light emitted by the light source first enters the MIOC through an optical fiber circulator for modulation and is evenly divided into two paths and enters the first and second depolarizers respectively; the light passing through the first depolarizer enters the first mode division multiplexer through a few-mode fiber, and then enters the few-mode fiber ring; the light coming out of the few-mode fiber ring enters the second mode division multiplexer, and then enters the single-mode few-mode fiber connector through the few-mode fiber; the light coming out of the single-mode few-mode fiber connector enters the first mode division multiplexer through the single-mode fiber, enters the few-mode fiber ring again, and then enters the second mode division multiplexer again. The transmission path of the light entering the second depolarizer on the second path is similar to that of the above-mentioned light. The present invention doubles the length of the sensing fiber through mode division multiplexing of the few-mode fiber ring, greatly improves the sensitivity of the fiber optic gyroscope, helps to break through the sensitivity limit of existing fiber optic gyroscopes, and provides a new technical direction for the design of fiber optic gyroscopes.

Description

Technical Field

[0001] The present invention relates to the field of fiber optic gyroscopes, and in particular to a high-sensitivity fiber optic gyroscope based on mode division multiplexing. Background Art

[0002] Interferometric fiber optic gyroscopes (IFGs) are widely used in aerospace, automotive, and earthquake monitoring due to their high sensitivity, broadband response, strong environmental adaptability, and ease of mass production. Currently, IGFGs are continuously developing towards higher sensitivity, lower cost, and smaller size.

[0003] There are two common approaches to achieving high sensitivity in interferometric fiber gyros. One is to minimize system noise, for example by improving the optical path structure to suppress relative intensity noise from the light source or by using thin polarization-maintaining fiber to suppress polarization crosstalk noise. To date, noise suppression has significantly increased the sensitivity of fiber gyros, but further improvement through this approach has become difficult. This is because as fiber gyro sensitivity increases, noise begins to approach quantum noise, and traditional noise suppression methods are gradually becoming ineffective.

[0004] Another way to achieve high sensitivity is to increase the length of the sensing fiber or the closed area of the fiber ring. According to the fiber optic gyroscope demodulation principle, the angular velocity value Ω(t) can be expressed as:

[0005]

[0006] Where c is the angular acceleration, L is the length of the sensing fiber, R is the radius of the fiber ring, φ s (t) is the phase change. As the formula shows, the angular velocity can be demodulated from the phase shift caused by the Sagnac principle when the fiber ring rotates along the ring plane. The sensitivity of the sensing system directly corresponds to the length of the sensing fiber; the longer the length, the higher the sensitivity of the fiber optic gyroscope. However, increased length also means increased cost and size. Achieving higher sensitivity with shorter sensing fibers has always been a challenge in fiber optic gyroscope development. Summary of the Invention

[0007] In response to the problems existing in the prior art, the purpose of the present invention is to provide a high-sensitivity fiber optic gyroscope based on mode division multiplexing; the present invention performs mode division multiplexing of light based on few-mode fiber, thereby doubling the length of the sensing fiber and further improving the sensitivity of the fiber optic gyroscope.

[0008] Mode division multiplexing is a technology that allows multiple orthogonal modes with different paths and mode field distributions carrying different information to be propagated together in the same multimode optical waveguide. Currently, mode division multiplexing has been widely used in the field of communications, and the technology of high-capacity signal transmission using optical fiber for mode division multiplexing is very mature. However, in the production of fiber optic gyroscopes, no researchers have ever proposed a design to improve the sensitivity of fiber optic gyroscopes through mode division multiplexing. The inventors of this application have proposed for the first time the application of mode division multiplexing technology to the design of fiber optic gyroscopes. By using mode division multiplexing to transmit sensor signals in a few-mode optical fiber, the length of the sensing fiber in the fiber optic gyroscope can be increased exponentially, thereby significantly improving the sensitivity of the fiber optic gyroscope.

[0009] Furthermore, the high-sensitivity fiber optic gyroscope based on mode division multiplexing offers advantages such as wide frequency response, strong environmental adaptability, miniaturization, and low cost. The implementation of this invention will provide a theoretical basis and technical support for the development of new high-sensitivity fiber optic gyroscopes, promoting their application in various fields such as inertial navigation and seismic monitoring, and possesses enormous application value.

[0010] The technical solution of the present invention is:

[0011] A high-sensitivity fiber optic gyroscope based on mode division multiplexing is characterized by comprising a light source module 1, a fiber circulator 2, a photodetector 3, an integrated optical multifunctional optical waveguide modulator 5, a few-mode fiber ring 9, and a single-mode few-mode fiber connector 12; further comprising two depolarizers and two mode division multiplexers, which are respectively denoted as a first depolarizer 6, a second depolarizer 10, a first mode division multiplexer 8, and a second mode division multiplexer 11;

[0012] The ports of the mode division multiplexer include a few-mode fiber coupling input end, a single-mode fiber coupling input end, and a few-mode fiber coupling output end, and are used to couple the light input from the few-mode fiber coupling input end and the single-mode fiber coupling input end and output the light from the few-mode fiber coupling output end, thereby combining the two modes of light; and transmit the light of the few-mode fiber mode entering from the few-mode fiber coupling output end to the few-mode fiber coupling input end for output, and transmit the light of the single-mode fiber mode entering from the few-mode fiber coupling output end to the single-mode fiber coupling input end for output;

[0013] The first port of the optical fiber circulator 2 is connected to the light source module 1, and the second port of the optical fiber circulator 2 is connected to the integrated optical multifunctional optical waveguide modulator 5, so as to input the light emitted by the light source module 1 into the integrated optical multifunctional optical waveguide modulator 5;

[0014] The third port of the optical fiber circulator 2 is connected to the photodetector 3, and is used to receive the light returned from the integrated optical multifunctional optical waveguide modulator 5 and input the light into the photodetector 3;

[0015] The integrated optical multifunctional optical waveguide modulator 5 is used to modulate the light emitted by the light source module 1 and divide it into two output paths, wherein the first path sequentially passes through the first depolarizer 6 and the first few-mode fiber 7 to enter the few-mode fiber coupling input end of the first mode division multiplexer 8; the second path sequentially passes through the second depolarizer 10 and the single-mode fiber to enter the single-mode fiber coupling input end of the second mode division multiplexer 11;

[0016] The few-mode fiber coupling input end of the second mode division multiplexer 11 is connected to the single-mode fiber coupling input end of the first mode division multiplexer 8 via the single-mode few-mode fiber connector 12; the few-mode fiber coupling output end of the second mode division multiplexer 11 is connected to one end of the few-mode fiber ring 9, and the few-mode fiber coupling output end of the first mode division multiplexer 8 is connected to the other end of the few-mode fiber ring 9.

[0017] Furthermore, the structure of the mode division multiplexer includes a packaging shell 13 comprising two units assembled together; a groove is etched in the middle of the first unit for embedding a single-mode optical fiber with a partial thickness cladding removed; a groove is etched in the middle of the second unit for embedding a few-mode optical fiber with a partial thickness cladding removed; the end face of the single-mode optical fiber with a partial thickness cladding removed and the end face of the few-mode optical fiber with a partial thickness cladding removed are assembled relative to each other.

[0018] Furthermore, the packaging shell 13 is a glass fixture.

[0019] Furthermore, the few-mode fiber port of the single-mode few-mode fiber connector 12 is connected to the few-mode fiber coupling input end of the second mode division multiplexer 11 via the second few-mode fiber 17, and the single-mode fiber port of the single-mode few-mode fiber connector 12 is connected to the single-mode fiber coupling input end of the first mode division multiplexer 8 via the second single-mode fiber 16.

[0020] Furthermore, the photodetector 3 is connected to a signal processing unit, which is used to collect and digitally process the input detection signal and restore the angular velocity value using a demodulation algorithm.

[0021] The advantages of the present invention are as follows:

[0022] The present invention multiplies the length of the sensing fiber by mode multiplexing of the few-mode fiber, thereby greatly improving the high sensitivity of the fiber optic gyroscope and breaking through the technical bottleneck of the fiber optic gyroscope's sensitivity. In addition, the fiber optic gyroscope designed by the present invention also has the advantages of wide-band response, small size and strong environmental adaptability, providing a new technical direction for the design of fiber optic gyroscopes. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the structure principle of the fiber optic gyroscope of the present invention.

[0024] Figure 2This is a structural cross-sectional view of the mode division multiplexer of the present invention.

[0025] Figure 3 It is a longitudinal cross-sectional view of the mode division multiplexer of the present invention. DETAILED DESCRIPTION

[0026] The present invention will be described in further detail below with reference to the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0027] The present invention relates to a high-sensitivity fiber optic gyroscope based on fiber mode division multiplexing, and its principle diagram is as follows: Figure 1 As shown. The invention is based on an optical sensing system built with a few-mode fiber ring and a mode division multiplexer, including a light source module 1, a fiber circulator 2, a photodetector 3, an integrated optical multifunctional optical waveguide modulator (MIOC) 5, a first depolarizer 6 and a second depolarizer 10, a first mode division multiplexer 8 and a second mode division multiplexer 11, a few-mode fiber ring (FMF) 9, and a single-mode few-mode fiber connector 12. The optical path connection of the entire system is completed through the first single-mode fiber 4, the second single-mode fiber 16 and the first few-mode fiber 7, the second few-mode fiber 17. The specific working principle is as follows:

[0028] Light from the light source first enters the fiber circulator 2. Because the fiber circulator 2 is directional for the input light, the light enters the MIOC 5 and not the photodetector 3. The light entering the MIOC 5 is modulated and split into two equal paths, each of which enters the first depolarizer 6 and the second depolarizer 10. After depolarization by the first depolarizer 6, the light passes through the first few-mode fiber 7 and enters the first mode division multiplexer 8, and then enters the few-mode fiber ring 9. As the few-mode fiber ring 9 rotates along its plane, it modulates the light transmitted within, thus carrying angular motion information. Light exiting the few-mode fiber ring 9 enters the second mode division multiplexer 11 and then, via the second few-mode fiber 17, enters the single-mode few-mode fiber connector 12. At this point, due to the action of the first mode division multiplexer 8, the light does not enter the single-mode fiber 16. Light exiting the single-mode few-mode fiber connector 12 passes through the second single-mode fiber 16 and enters the first mode division multiplexer 8, again entering the few-mode fiber ring 9, and then the second mode division multiplexer 11. This time, due to the change in light mode, it will be transmitted from the single-mode fiber of the second mode division multiplexer 11, and then enter the MIOC 5 through the second depolarizer 10. Due to the different modes, the light passes through the few-mode fiber ring 9 twice, thus achieving two cycles of multiplexing in the clockwise direction of the few-mode fiber ring, and thus doubling the length of the sensing fiber.

[0029] The other light path from MIOC 5 to the second depolarizer 10 follows a similar transmission path as the aforementioned light. It passes through a single-mode fiber, the second mode division multiplexer 11, the few-mode fiber ring 9, and the first mode division multiplexer 8 before entering the single-mode few-mode fiber connector 12, completing one loop. After exiting the single-mode few-mode fiber connector 12, it passes through the second mode division multiplexer 11, the few-mode fiber ring 9, the first mode division multiplexer 8, and finally enters the first depolarizer 6 through the few-mode fiber, completing a second loop. This achieves two counterclockwise loops of the few-mode fiber ring and doubles the length of the sensing fiber. The unpolarized light exiting the depolarizer reenters MIOC 5, interfering with the clockwise sensing light. It then passes through the fiber circulator 2 and enters the photodetector 3. Finally, after signal acquisition and digitization, a demodulation algorithm can restore the original angular velocity value. The depolarizer converts polarized light into unpolarized light, minimizing polarization coupling errors during subsequent interference.

[0030] The key to high-sensitivity fiber optic gyroscope based on mode division multiplexing is the mode division multiplexer. Figure 2 This is a structural cross-sectional diagram of the mode division multiplexer in this patent, in which the encapsulation shell 13 is a glass fixture used, which is divided into two parts, an upper part and an lower part, with a fine groove etched in the middle of each part. Then, the first single-mode optical fiber 4 and the first few-mode optical fiber 7 are embedded in the upper and lower grooves, and then the single-mode optical fiber and the few-mode optical fiber in the grooves are polished. Finally, the two glass fixtures are combined together to form the final mode division multiplexer 8.

[0031] The mode division multiplexer has directional properties for light transmission in different modes. Light entering the first few-mode fiber 7 through port ① and light entering the first single-mode fiber 4 through port ② can achieve mode coupling at the connection point and be output from port ③, thus combining the two modes of light. If the light entering from port ③ is in the few-mode fiber mode, it will be transmitted to the first few-mode fiber 7 and then output from port ①. If the light entering from port ③ is in the single-mode fiber mode, it will enter the first single-mode fiber 4 and then output from port ②. This directional light transmission of the mode division multiplexer enables the sensing light signal to circulate twice in the few-mode fiber ring, thereby doubling the sensitivity of the fiber optic gyroscope.

[0032] Figure 3 This is a longitudinal cross-sectional view of the mode division multiplexer 8. It can be seen that the first few-mode fiber 7 and the first single-mode fiber 4 are partially polished and then aligned and fixed. In this patent, the output power of the mode division multiplexer 8 entering through port ① at port ③ is almost 100%, but the output power of the mode division multiplexer 8 entering through port ② at port ③ satisfies the formula:

[0033]

[0034] Among them, P in and P outare the input and output coupled optical powers, κ is the coupling constant, z is the interaction length between single-mode fiber and few-mode fiber, and δ is the propagation constant between single-mode fiber and few-mode mode. It can be seen from the formula that the maximum power coupling can be achieved when the propagation constant is minimum, and δ is less than 2.2×10 -4 The coupling efficiency can reach over 80%, which meets the requirements of this patent. Finally, the mode division multiplexer required by this patent can be manufactured by fixing the glass packaging shell 13.

[0035] While specific embodiments of the present invention have been disclosed for illustrative purposes, intended to facilitate understanding and implementation of the present invention, those skilled in the art will appreciate that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the disclosure of the preferred embodiments, and the scope of protection claimed in the present invention shall be determined by the scope of the claims.

Claims

1. A high-sensitivity fiber optic gyroscope based on mode division multiplexing, characterized in that: The invention comprises a light source module (1), an optical fiber circulator (2), a photodetector (3), an integrated optical multifunctional optical waveguide modulator (5), a few-mode optical fiber ring (9), and a single-mode few-mode optical fiber connector (12); and further comprises two depolarizers and two mode division multiplexers, which are respectively denoted as a first depolarizer (6), a second depolarizer (10), a first mode division multiplexer (8), and a second mode division multiplexer (11). The ports of the mode division multiplexer include a few-mode fiber coupling input end, a single-mode fiber coupling input end, and a few-mode fiber coupling output end, which are used to couple the light input from the few-mode fiber coupling input end and the single-mode fiber coupling input end and then output the light from the few-mode fiber coupling output end, thereby achieving beam combining of the two modes of light; and transmitting the light of the few-mode fiber mode entering from the few-mode fiber coupling output end to the few-mode fiber coupling input end for output, and transmitting the light of the single-mode fiber mode entering from the few-mode fiber coupling output end to the single-mode fiber coupling input end for output; The first port of the optical fiber circulator (2) is connected to the light source module (1), and the second port of the optical fiber circulator (2) is connected to the integrated optical multifunctional optical waveguide modulator (5), for inputting the light emitted by the light source module (1) into the integrated optical multifunctional optical waveguide modulator (5); The third port of the optical fiber circulator (2) is connected to the photodetector (3) and is used to receive light returned from the integrated optical multifunctional optical waveguide modulator (5) and input the light into the photodetector (3); The integrated optical multifunctional optical waveguide modulator (5) is used to modulate the light emitted by the light source module (1) and divide the light into two output paths, wherein the first path sequentially passes through a first depolarizer (6) and a first few-mode optical fiber (7) to enter the few-mode optical fiber coupling input end of a first mode division multiplexer (8); and the second path sequentially passes through a second depolarizer (10) and a single-mode optical fiber to enter the single-mode optical fiber coupling input end of a second mode division multiplexer (11); The few-mode fiber coupling input end of the second mode division multiplexer (11) is connected to the single-mode fiber coupling input end of the first mode division multiplexer (8) via the single-mode few-mode fiber connector (12); the few-mode fiber coupling output end of the second mode division multiplexer (11) is connected to one end of the few-mode fiber ring (9), and the few-mode fiber coupling output end of the first mode division multiplexer (8) is connected to the other end of the few-mode fiber ring (9).

2. The high-sensitivity fiber optic gyroscope according to claim 1, characterized in that: The structure of the mode division multiplexer includes a packaging shell (13) comprising two units assembled together; a groove is etched in the middle of the first unit for embedding a single-mode optical fiber with a partially removed cladding layer; A groove is etched in the middle of the second unit for embedding the few-mode optical fiber with partially removed cladding; the end face of the single-mode optical fiber with partially removed cladding is assembled relative to the end face of the few-mode optical fiber with partially removed cladding.

3. The high-sensitivity fiber optic gyroscope according to claim 2, characterized in that: The packaging shell (13) is a glass fixture.

4. The high-sensitivity fiber optic gyroscope according to claim 1, 2 or 3, characterized in that: The few-mode fiber port of the single-mode few-mode fiber connector (12) is connected to the few-mode fiber coupling input end of the second mode division multiplexer (11) via a second few-mode fiber (17), and the single-mode fiber port of the single-mode few-mode fiber connector (12) is connected to the single-mode fiber coupling input end of the first mode division multiplexer (8) via a second single-mode fiber (16).

5. The high-sensitivity fiber optic gyroscope according to claim 1, characterized in that: The photoelectric detector (3) is connected to a signal processing unit, and the signal processing unit is used to collect and digitally process the input detection signal and restore the angular velocity value using a demodulation algorithm.

Images