A differential fiber optic gyroscope based on polarization mode multiplexing

Abstract

This invention belongs to the field of fiber optic gyroscope technology, specifically relating to a differential fiber optic gyroscope based on polarization mode multiplexing, aiming to solve the problem of performance degradation in existing fiber optic gyroscopes caused by environmental factors such as temperature. The invention includes: a broadband light source, a first coupler, a second coupler, a third coupler, a polarization-maintaining fiber ring, a polarization mode multiplexing module, a first photodetector, a second photodetector, and a digital closed-loop detection module. The polarization mode multiplexing module includes a 3D multi-functional integrated optical modulator, a first polarization beamsplitter, and a second polarization beamsplitter. The 3D multi-functional integrated optical modulator integrates two mirror-image Y-waveguide modulators on its upper and lower surfaces. The digital closed-loop detection module receives the detection signals from the first and second photodetectors, performs detection and processing, and then outputs the results. This invention can effectively eliminate phase errors caused by fluctuations in environmental factors such as temperature, vibration, and magnetism, while simultaneously improving the sensitivity coefficient of the fiber optic gyroscope.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic gyroscope technology, specifically relating to a differential fiber optic gyroscope based on polarization mode multiplexing. Background Technology

[0002] Fiber Optic Gyroscopes (FOGs) achieve rotational motion sensing based on the Sagnac effect. Composed of optical fibers and optical wave devices, they have no moving parts, are lightweight, and highly reliable. They have wide applications in defense, aerospace, celestial motion observation, and unmanned vehicles, and are currently the mainstream gyroscope instrument in the field of inertial technology.

[0003] Interferometric fiber optic gyroscopes have achieved very high levels of performance in terms of zero drift and noise. Currently, the use of high-power broadband light sources can effectively suppress noise terms such as coherent backscattering, shot noise, and thermal noise. The remaining relative intensity noise (RIN) can also be reduced to extremely low levels using RIN noise cancellation circuits or optical path modifications, overmodulation, Wiener filters, and other techniques. In a stable, interference-free environment, the zero drift of a fiber optic gyroscope can reach less than 10. -5 At the ° / h level, the scaling factor stability can also reach 1ppm. However, the performance of a gyroscope is not only related to its own structure, but also closely related to the surrounding environment. Environmental factors such as temperature, radiation, and magnetic fields can all have an adverse effect on the performance of the gyroscope, ultimately introducing phase error in the detection phase and causing zero bias drift.

[0004] Under normal circumstances, fiber optic gyroscopes are affected by temperature, which changes over time. This time-varying temperature affects the fiber optic sensing loop, causing non-reciprocal phase errors. Traditional suppression methods such as symmetrical winding, thermal insulation structures, and model compensation have some effect, but residual temperature drift errors remain the main factor limiting the performance of fiber optic gyroscopes. In some applications, such as aerospace, fiber optic gyroscopes also face harsh environments such as space radiation, vibration, and magnetism, which severely affect the fiber optic sensing loop and significantly degrade the gyroscope's performance. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, specifically the performance degradation of existing fiber optic gyroscopes due to environmental factors such as temperature, this invention proposes a differential fiber optic gyroscope based on polarization mode multiplexing. The differential fiber optic gyroscope includes a broadband light source, a first coupler, a second coupler, a third coupler, and a polarization-maintaining fiber loop. Furthermore, the differential fiber optic gyroscope also includes a polarization mode multiplexing module, a first photodetector, a second photodetector, and a digital closed-loop detection module.

[0006] The polarization mode multiplexing module includes a 3D multi-functional integrated optical modulator, a first polarization beam splitter, and a second polarization beam splitter; the upper and lower surfaces of the 3D multi-functional integrated optical modulator are respectively integrated with a first Y-waveguide modulator and a second Y-waveguide modulator.

[0007] The first Y-waveguide modulator, the fast axis of the first polarization beamsplitter, the fast axis of the second polarization beamsplitter, and the fast axis of the polarization-maintaining fiber ring constitute the first fiber sensitive loop; the second Y-waveguide modulator, the slow axis of the first polarization beamsplitter, the slow axis of the second polarization beamsplitter, and the slow axis of the polarization-maintaining fiber ring constitute the second fiber sensitive loop.

[0008] A first fiber optic gyroscope is formed by the first beam of light split from the broadband light source by the first coupler, the second coupler, the first fiber optic sensitive loop, and the first photodetector; a second fiber optic gyroscope is formed by the second beam of light split from the broadband light source by the first coupler, the third coupler, the second fiber optic sensitive loop, and the second photodetector; the first fiber optic gyroscope and the second fiber optic gyroscope constitute a differential fiber optic gyroscope.

[0009] The digital closed-loop detection module is used to receive the detection signals from the first photodetector and the second photodetector, detect and process the detection signals and output them, and simultaneously apply two square wave modulation signals and a feedback step wave modulation signal to the polarization mode multiplexing module.

[0010] In some preferred embodiments, the first fiber optic gyroscope and the second fiber optic gyroscope are mirror images of each other, independent of each other, and have opposite directions of angular velocity sensitive surface vectors;

[0011] The angular velocity sensing loop of the first fiber optic gyroscope and the angular velocity sensing loop of the second fiber optic gyroscope output signals of the same input angular velocity with the same magnitude but opposite signs. However, the magnitude and sign of the common-mode phase error introduced by the set environmental conditions remain unchanged. The set environmental conditions include temperature.

[0012] In some preferred embodiments, the first Y-waveguide modulator and the second Y-waveguide modulator integrated on the upper and lower surfaces of the 3D multifunctional integrated optical modulator are in a mirror-reversed spatial position relationship.

[0013] In some preferred embodiments, the fast axes of the two polarization beamsplitters in the polarization mode multiplexing module are coupled to the optical axis of the first Y-waveguide modulator of the 3D multifunctional integrated optical modulator, and the slow axes of the two polarization beamsplitters are coupled to the optical axis of the second Y-waveguide modulator of the 3D multifunctional integrated optical modulator.

[0014] In some preferred embodiments, the digital closed-loop detection module comprises a pre-switching circuit, a first analog-to-digital converter, a second analog-to-digital converter, a digital logic circuit, a first digital-to-analog converter, and a second digital-to-analog converter;

[0015] The detection signals from the first photodetector and the second photodetector are synchronously acquired by the first analog-to-digital converter and the second analog-to-digital converter after the spike pulses are eliminated by the pre-switching circuit. After being processed by the digital logic circuit, the demodulation result is output and two digital modulation signals are generated. The two digital modulation signals are converted by the first digital-to-analog converter and the second digital-to-analog converter and output to the first Y-waveguide modulator and the second Y-waveguide modulator of the 3D multifunctional integrated optical modulator, respectively.

[0016] In some preferred embodiments, both digital modulation signals are superimposed square waves and feedback stepped waves; wherein the square wave modulation signals are in the same direction, and the feedback stepped wave modulation signals are in opposite directions.

[0017] In some preferred embodiments, the total phase detected by the first fiber optic gyroscope is expressed as:

[0018]

[0019] The total phase detected by the second fiber optic gyroscope is expressed as follows:

[0020]

[0021] The output of the differential fiber optic gyroscope is the difference in total phase between the outputs of the first fiber optic gyroscope and the second fiber optic gyroscope.

[0022]

[0023] in, The Sagnac phase shift caused by the fiber optic sensitive loop. The common-mode phase error caused by temperature, vibration, and magnetism in the first and second fiber-optic sensitive loops.

[0024] The beneficial effects of this invention are:

[0025] This invention can effectively eliminate phase errors caused by fluctuations in environmental factors such as temperature, vibration, and magnetism, while also improving the sensitivity coefficient of fiber optic gyroscopes.

[0026] This invention utilizes a polarization mode multiplexing module to achieve the multiplexing of two polarization modes in a polarization-maintaining fiber optic loop. Based on the fundamental principle of common-mode suppression, two independent fiber optic gyroscopes with opposite angular velocity sensing surface vector directions are constructed within the shared fiber optic loop. The two gyroscopes output signals of equal magnitude but opposite sign at the same input angular velocity. Since the fiber optic loop is subjected to the same environmental factors, the magnitude and sign of the common-mode phase error introduced by environmental factors such as ambient temperature remain unchanged for both gyroscopes. By performing differential phase analysis on the two independent fiber optic gyroscopes, phase errors caused by fluctuations in environmental factors such as temperature, vibration, and magnetism can be effectively eliminated, while simultaneously improving the sensitivity coefficient of the fiber optic gyroscopes. Attached Figure Description

[0027] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings.

[0028] Figure 1 This is a schematic diagram of the structure of a differential fiber optic gyroscope based on polarization mode multiplexing according to an embodiment of the present invention;

[0029] Figure 2 This is a schematic diagram of the polarization mode multiplexing module of a differential fiber optic gyroscope based on polarization mode multiplexing according to an embodiment of the present invention;

[0030] Figure 3 This is a schematic diagram of the fiber optic sensitive loop road surface vector of a differential fiber optic gyroscope based on polarization mode multiplexing according to an embodiment of the present invention;

[0031] Figure 4 This is a schematic diagram of the structure of a digital closed-loop detection module based on a differential fiber optic gyroscope with polarization mode multiplexing according to an embodiment of the present invention;

[0032] Figure 5 This is a schematic diagram of the zero-bias output curves of a first fiber optic gyroscope, a second fiber optic gyroscope, and a differential fiber optic gyroscope according to an embodiment of the present invention.

[0033] Explanation of reference numerals in the attached figures: 1 is a broadband light source; 2 is the first coupler; 3 is the second coupler; 4 is the third coupler; 5 is a polarization mode multiplexing module; 6 is a polarization-maintaining fiber loop; 7 is the first photodetector; 8 is the second photodetector; 9 is a digital closed-loop detection module; 10 is a 3D multi-functional integrated optical modulator; 11 is the first Y-waveguide modulator; 12 is the second Y-waveguide modulator; 13 is the first polarization beamsplitter; 14 is the second polarization beamsplitter; 15 is the first port of the first Y-waveguide; 16 is the second port of the first Y-waveguide; 17 is the first port of the second Y-waveguide; 18 is the second port of the second Y-waveguide; 19 is the first modulation signal; 20 is the second modulation signal; 21 is the first surface vector; 22 is the second surface vector; 23 is the pre-switching circuit; 24 is the first analog-to-digital converter; 25 is the second analog-to-digital converter; 26 is the digital logic circuit; 27 is the first digital-to-analog converter; 28 is the second digital-to-analog converter. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0036] A differential fiber optic gyroscope based on polarization mode multiplexing according to the first embodiment of the present invention, such as... Figure 1 As shown, the differential fiber optic gyroscope includes a broadband light source, a first coupler, a second coupler, a third coupler, and a polarization-maintaining fiber loop; the differential fiber optic gyroscope also includes a polarization mode multiplexing module, a first photodetector, a second photodetector, and a digital closed-loop detection module;

[0037] The polarization mode multiplexing module includes a 3D multi-functional integrated optical modulator, a first polarization beam splitter, and a second polarization beam splitter; the upper and lower surfaces of the 3D multi-functional integrated optical modulator are respectively integrated with a first Y-waveguide modulator and a second Y-waveguide modulator.

[0038] The first Y-waveguide modulator, the fast axis of the first polarization beamsplitter, the fast axis of the second polarization beamsplitter, and the fast axis of the polarization-maintaining fiber ring constitute the first fiber sensitive loop; the second Y-waveguide modulator, the slow axis of the first polarization beamsplitter, the slow axis of the second polarization beamsplitter, and the slow axis of the polarization-maintaining fiber ring constitute the second fiber sensitive loop.

[0039] A first fiber optic gyroscope is formed by the first beam of light split from the broadband light source by the first coupler, the second coupler, the first fiber optic sensitive loop, and the first photodetector; a second fiber optic gyroscope is formed by the second beam of light split from the broadband light source by the first coupler, the third coupler, the second fiber optic sensitive loop, and the second photodetector; the first fiber optic gyroscope and the second fiber optic gyroscope constitute a differential fiber optic gyroscope.

[0040] The digital closed-loop detection module is used to receive the detection signals from the first photodetector and the second photodetector, detect and process the detection signals and output them, and simultaneously apply two square wave modulation signals and a feedback step wave modulation signal to the polarization mode multiplexing module.

[0041] To more clearly illustrate the differential fiber optic gyroscope based on polarization mode multiplexing of the present invention, the modules of one embodiment of the device of the present invention will be described in detail below with reference to the accompanying drawings.

[0042] A schematic diagram of a differential fiber optic gyroscope embodiment based on polarization mode multiplexing according to the present invention is shown below. Figure 1 As shown, it includes a broadband light source 1, a first coupler 2, a second coupler 3, a third coupler 4, a polarization mode multiplexing module 5, a polarization-maintaining fiber loop 6, a first photodetector 7, a second photodetector 8, and a digital closed-loop detection module 9; a schematic diagram of the polarization mode multiplexing module is shown below. Figure 2 As shown, the system includes a 3D multifunctional integrated optical modulator 10, a first polarization beamsplitter 13, and a second polarization beamsplitter 14. A first Y-waveguide modulator 11 and a second Y-waveguide modulator 12 are integrated on the upper and lower surfaces of the 3D multifunctional integrated optical modulator 10, respectively. The fast axes of the two polarization beamsplitters are coupled to the optical transmission axis of the first Y-waveguide modulator 11, and the slow axes of the two polarization beamsplitters are coupled to the optical transmission axis of the second Y-waveguide modulator 12. This allows two polarization modes of light to operate independently and simultaneously within the same fiber optic sensitive loop, thereby enabling polarization mode multiplexing.

[0043] The light emitted by the broadband light source 1 is split by the first coupler 2 and then input to the second coupler 3 and the third coupler 4 respectively. After being output from the second coupler 3 and the third coupler 4, the light is incident on the fiber optic sensitive loop composed of the polarization mode multiplexing module 5 and the polarization-maintaining fiber loop 6. Two interference light signals are formed in the two polarization principal axes of the fiber optic sensitive loop. After the two interference light signals return, they pass through the second coupler 3 and the third coupler 4 again and are incident on the first photodetector 7 and the second photodetector 8 respectively, forming two independent fiber optic gyroscope optical paths that share a single polarization-maintaining fiber loop.

[0044] In this 3D multifunctional integrated optical modulator 10, the first Y-waveguide modulator 11, the fast axis of the first polarization beamsplitter 13, the fast axis of the second polarization beamsplitter 14, and the fast axis of the polarization-maintaining fiber ring 6 constitute the first fiber sensitive loop; the second Y-waveguide modulator 12, the slow axis of the first polarization beamsplitter 13, the slow axis of the second polarization beamsplitter 14, and the slow axis of the polarization-maintaining fiber ring 6 constitute the second fiber sensitive loop; the first Y-waveguide modulator 11 and the second Y-waveguide modulator 12 of the 3D multifunctional integrated optical modulator 10 are mirror images of each other in spatial position, and the two fiber sensitive loops formed therefrom are also mirror images of each other in spatial position, and they share the same polarization-maintaining fiber ring.

[0045] Figure 3 This diagram illustrates the surface vector of the fiber optic sensitive loop in a differential fiber optic gyroscope based on polarization mode multiplexing according to the present invention. The surface vector is a vector perpendicular to the plane containing the fiber optic sensitive loop, and its direction is indicated by the right-hand rule, representing the direction of the angular velocity sensed by the fiber optic sensitive loop. The direction indicated by the right-hand rule from the first port 15 to the second port 16 of the first Y-waveguide 11 is the direction of the first surface vector 21 of the first fiber optic sensitive loop, and the direction indicated by the right-hand rule from the second port 18 to the first port 17 of the second Y-waveguide 12 is the direction of the second surface vector 22 of the second fiber optic sensitive loop. The first and second fiber optic sensitive loops are mirror images of each other in spatial position; therefore, the directions of the first surface vector 21 and the second surface vector 22 are parallel and opposite. When experiencing the same input angular velocity, the phase magnitudes generated by the two fiber optic sensitive loops are equal, but their signs are opposite.

[0046] The first beam of light split from the broadband light source 1 by the first coupler 2, the second coupler 3, the first fiber optic sensitive loop, and the first photodetector 7 constitute the first fiber optic gyroscope. The second beam of light split from the broadband light source 1 by the first coupler 2, the third coupler 4, the second fiber optic sensitive loop, and the second photodetector 8 constitute the second fiber optic gyroscope. The resulting differential fiber optic gyroscope is composed of the first fiber optic gyroscope and the second fiber optic gyroscope, which are mirror images of each other.

[0047] Figure 4This diagram illustrates a digital closed-loop detection module structure for a differential fiber optic gyroscope based on polarization mode multiplexing according to the present invention. The digital closed-loop detection module consists of a pre-switching circuit 23, a first analog-to-digital converter 24, a second analog-to-digital converter 25, a digital logic circuit 26, a first digital-to-analog converter 27, and a second digital-to-analog converter 28. The detection signals from the first photodetector 7 and the second photodetector 8 are processed by the pre-switching circuit 23 to eliminate spike pulses, and then synchronously acquired by the first analog-to-digital converter 24 and the second analog-to-digital converter 25, respectively, and then transmitted via the digital logic circuit 26. After processing, the demodulation result is output and two digital modulation signals are generated. The two digital modulation signals are converted by the first digital-to-analog converter 27 and the second digital-to-analog converter 28, respectively, and output to the first Y-waveguide modulator 11 and the second Y-waveguide modulator 12 of the 3D multi-functional integrated optical modulator 10. The square wave modulation signals of the first modulation signal 19 and the second modulation signal 20 have the same direction, while the feedback step wave modulation signals have opposite directions (that is, both digital modulation signals are square wave and feedback step wave superimposed modulation signals; the square wave modulation signals have the same direction, while the feedback step wave modulation signals have opposite directions).

[0048] A differential fiber optic gyroscope consists of a first fiber optic gyroscope and a second fiber optic gyroscope that are mirror images of each other. These two gyroscopes are independent of each other, and the surface vectors of the fiber optic sensing loops are opposite in direction. Therefore, the sensitive angular velocities are in opposite directions, and the phases generated by the same angular velocity are of the same magnitude but opposite in sign. However, the magnitude and sign of the common-mode phase error caused by the set environmental conditions (including temperature, as well as vibration and magnetism) remain unchanged.

[0049] The total phase detected by the first fiber optic gyroscope is expressed as follows:

[0050]

[0051] The total phase detected by the second fiber optic gyroscope is expressed as follows:

[0052]

[0053] The output of the differential fiber optic gyroscope is the difference in total phase between the outputs of the first fiber optic gyroscope and the second fiber optic gyroscope.

[0054]

[0055] in, The Sagnac phase shift caused by the fiber optic sensitive loop. The common-mode phase error caused by temperature, vibration, and magnetism in the first and second fiber sensing loops was eliminated by differential operation, thus doubling the gyroscope sensitivity.

[0056] In addition, to verify the effectiveness of the technical solution of the present invention, an experiment was conducted to verify the technical solution of the present invention. The verification process is as follows:

[0057] A prototype differential fiber optic gyroscope based on polarization mode multiplexing was placed on a horizontal test platform with its reference axis parallel to the vertical. A heating element was attached to the polarization-maintaining fiber loop, and a temperature excitation was applied by passing a current through the heating element. The outputs of the two independent fiber optic gyroscopes and the differential fiber optic gyroscope were tested and recorded, yielding results as follows: Figure 5 The zero-bias output curves of the first fiber optic gyroscope, the second fiber optic gyroscope, and the differential fiber optic gyroscope are shown. The zero-bias drift in the curves is caused by temperature excitation. It can be seen that, except for the drift data segment, the average value of the zero-bias output of the two independent fiber optic gyroscopes is symmetrical about the zero-point line, and their magnitudes are both equal to the component of the Earth's rotational angular velocity perpendicular to the horizontal, but with opposite signs. The magnitude and sign of the zero-bias drift caused by temperature excitation are exactly the same. The first and second fiber optic gyroscopes share the same light source and fiber optic loop, and their scale factors, measured under synchronous closed-loop detection, are the same, both being 543081 (° / s). -1 After performing differential operations, the scaling factor of the differential fiber optic gyroscope becomes 1086162 (° / s). -1 The angular velocity sensitivity of the fiber optic gyroscope is doubled, the Earth's rotation angular velocity information is preserved, and the drift peak of ~2° / h caused by temperature excitation is effectively eliminated. Simultaneously, the minute fluctuations in the zero-bias curves of both the first and second fiber optic gyroscopes are also eliminated. Experiments show that the differential fiber optic gyroscope based on polarization mode multiplexing can not only improve the gyroscope sensitivity but also eliminate common-mode errors caused by environmental factors, significantly improving environmental adaptability.

[0058] It should be noted that the differential fiber optic gyroscope based on polarization mode multiplexing provided in the above embodiments is only an example of the division of the above functional modules. In practical applications, the above functions can be assigned to different functional modules as needed, that is, the modules or steps in the embodiments of the present invention can be further decomposed or combined. For example, the modules in the above embodiments can be merged into one module, or further divided into multiple sub-modules to complete all or part of the functions described above. The names of the modules and steps involved in the embodiments of the present invention are only for distinguishing the various modules or steps and are not considered as an improper limitation of the present invention.

[0059] Those skilled in the art will recognize that the modules of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. The programs corresponding to the software modules and method steps can be placed in random access memory (RAM), main memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disks, removable disks, CD-ROMs, or any other form of storage medium known in the art. To clearly illustrate the interchangeability of electronic hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in electronic hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the invention.

[0060] The terms “first”, “second”, etc., are used to distinguish similar objects, not to describe or indicate a specific order or sequence.

[0061] The term "comprising" or any other similar term is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus / device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent in such process, method, article, or apparatus / device.

[0062] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A differential fiber optic gyroscope based on polarization mode multiplexing, the differential fiber optic gyroscope comprising a broadband light source, a first coupler, a second coupler, a third coupler, and a polarization-maintaining fiber loop; characterized in that, The differential fiber optic gyroscope further includes: a polarization mode multiplexing module, a first photodetector, a second photodetector, and a digital closed-loop detection module; The polarization mode multiplexing module includes a 3D multi-functional integrated optical modulator, a first polarization beam splitter, and a second polarization beam splitter; the upper and lower surfaces of the 3D multi-functional integrated optical modulator are respectively integrated with a first Y-waveguide modulator and a second Y-waveguide modulator. The first Y-waveguide modulator, the fast axis of the first polarization beamsplitter, the fast axis of the second polarization beamsplitter, and the fast axis of the polarization-maintaining fiber ring constitute the first fiber sensitive loop; the second Y-waveguide modulator, the slow axis of the first polarization beamsplitter, the slow axis of the second polarization beamsplitter, and the slow axis of the polarization-maintaining fiber ring constitute the second fiber sensitive loop. A first fiber optic gyroscope is formed by the first beam of light split from the broadband light source by the first coupler, the second coupler, the first fiber optic sensitive loop, and the first photodetector; a second fiber optic gyroscope is formed by the second beam of light split from the broadband light source by the first coupler, the third coupler, the second fiber optic sensitive loop, and the second photodetector; the first fiber optic gyroscope and the second fiber optic gyroscope constitute a differential fiber optic gyroscope. The digital closed-loop detection module is used to receive the detection signals from the first photodetector and the second photodetector, detect and process the detection signals and output them, and simultaneously apply two square wave modulation signals and a feedback step wave modulation signal to the polarization mode multiplexing module, wherein the square wave modulation signals are in the same direction and the feedback step wave modulation signals are in opposite directions. The first Y-waveguide modulator and the second Y-waveguide modulator integrated on the upper and lower surfaces of the 3D multifunctional integrated optical modulator are in a mirror-reversed spatial position relationship. The first fiber optic gyroscope and the second fiber optic gyroscope are mirror images of each other, independent of each other, and have opposite directions of angular velocity sensitive surface vectors. The angular velocity sensing loop of the first fiber optic gyroscope and the angular velocity sensing loop of the second fiber optic gyroscope output signals of the same input angular velocity with the same magnitude but opposite signs. However, the magnitude and sign of the common-mode phase error introduced by the set environmental conditions remain unchanged. The set environmental conditions include temperature. The total phase detected by the first fiber optic gyroscope is expressed as follows: The total phase detected by the second fiber optic gyroscope is expressed as follows: The output of the differential fiber optic gyroscope is the difference in total phase between the outputs of the first fiber optic gyroscope and the second fiber optic gyroscope. in, The Sagnac phase shift caused by the fiber optic sensitive loop. The common-mode phase error caused by temperature, vibration, and magnetism in the first and second fiber-optic sensitive loops.

2. The differential fiber optic gyroscope based on polarization mode multiplexing according to claim 1, characterized in that, In the polarization mode multiplexing module, the fast axes of the two polarization beamsplitters are coupled to the optical axis of the first Y-waveguide modulator of the 3D multifunctional integrated optical modulator, and the slow axes of the two polarization beamsplitters are coupled to the optical axis of the second Y-waveguide modulator of the 3D multifunctional integrated optical modulator.

3. The differential fiber optic gyroscope based on polarization mode multiplexing according to claim 1, characterized in that, The digital closed-loop detection module consists of a pre-switching circuit, a first analog-to-digital converter, a second analog-to-digital converter, a digital logic circuit, a first digital-to-analog converter, and a second digital-to-analog converter. The detection signals from the first photodetector and the second photodetector are synchronously acquired by the first analog-to-digital converter and the second analog-to-digital converter after the spike pulses are eliminated by the pre-switching circuit. After being processed by the digital logic circuit, the demodulation result is output and two digital modulation signals are generated. The two digital modulation signals are converted by the first digital-to-analog converter and the second digital-to-analog converter and output to the first Y-waveguide modulator and the second Y-waveguide modulator of the 3D multifunctional integrated optical modulator, respectively.

4. The differential fiber optic gyroscope based on polarization mode multiplexing according to claim 3, characterized in that, Both digital modulation signals are square waves with feedback stepped waves superimposed on each other.

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