Film lithium niobate chip based on mode rotation multiplexing, application and application method

Abstract

The invention discloses a thin-film lithium niobate chip based on mode rotation multiplexing, application and an application method, and belongs to the field of integrated optical devices, and the thin-film lithium niobate chip comprises a grating coupler, a beam splitter, a mode rotation multiplexer and a phase modulator which are sequentially integrated on an LNOI platform in the light propagation direction, the grating coupler, the beam splitter, the mode rotary multiplexer and the phase modulator are all composed of thin-film lithium niobate waveguides, and optical interconnection is achieved among the grating coupler, the beam splitter, the mode rotary multiplexer and the phase modulator through the thin-film lithium niobate waveguides. According to the thin-film lithium niobate chip based on mode rotation multiplexing, the application and the application method, the originally lost TM0 mode is converted into the TE0 mode, and the TM0 mode is combined with the original TE0 mode, so that the intrinsic mode loss of 3dB can be reduced, and the insertion loss of the whole device is reduced by about 30%.

Description

Technical Field

[0001] The present invention relates to the field of integrated optical devices, and in particular to a thin-film lithium niobate chip based on mode rotation multiplexing, and its application and application method. Background Art

[0002] Fiber optic gyroscope is a product with wide application and mature development in the field of optical sensing. As the core component of inertial measurement unit, it has the characteristics of high precision, high stability, fast response speed, etc. In recent years, with the continuous development of technology, its application field has gradually shifted from military to civilian use, and cost reduction has become the main pursuit of the development of this field. At present, common solutions include low cost of various discrete functional devices, chip integration of various functional components of gyroscopes, etc.

[0003] Integrated optical chips are one of the current research hotspots in the optoelectronics field. Through micro-nano processing methods, they can realize on-chip integration of various optical functional devices, and use on-chip optical waveguides instead of optical fibers to achieve on-chip optical interconnection, which can replace traditional optical functional devices. The structural size is only a few millimeters or even tens of microns. As a result, the development direction of fiber optic gyroscopes has been derived, namely integrated optical gyroscopes. The technology of integrating the optical devices of fiber optic gyroscopes on a chip using micro-nano processing technology can greatly reduce the size, weight, number of devices and connection complexity of fiber optic gyroscopes, thereby reducing the cost and power consumption of fiber optic gyroscopes.

[0004] The integrated optical gyroscope requires a special design in the optical path, that is, the light needs to have a certain degree of polarization before entering the phase modulator, that is, the TE0 component needs to be much larger than the TM0 component, quantified as the polarization extinction ratio, which needs to be at least greater than 30dB. If the polarization extinction ratio is too small, it will have a great impact on the accuracy and may even fail to constitute the detection system of the optical gyroscope. However, in the process of polarization, the TM0 component is dissipated, which is equivalent to the direct loss of this part of the optical power, which is not conducive to the improvement of the detection sensitivity and dynamic range. Summary of the invention

[0005] To solve the above problems, the present invention provides a thin-film lithium niobate chip, application and application method based on mode rotation multiplexing, which converts the originally lost TM0 mode into TE0 mode and combines it with the original TE0 mode, thereby reducing the intrinsic mode loss by 3dB and reducing the overall device insertion loss by about 30%.

[0006] To achieve the above-mentioned purpose, the present invention provides a thin-film lithium niobate chip based on mode rotation multiplexing, including a grating coupler, a beam splitter, a mode rotation multiplexer and a phase modulator which are sequentially integrated on the LNOI platform along the direction of light propagation, the grating coupler, the beam splitter, the mode rotation multiplexer and the phase modulator are all composed of a thin-film lithium niobate waveguide, and the grating coupler, the beam splitter, the mode rotation multiplexer and the phase modulator are optically interconnected via a thin-film lithium niobate-based waveguide.

[0007] Preferably, the grating coupler is a two-dimensional waveguide grating structure, and the grating coupler includes an upper cladding, a grating region, and a thin-film lithium niobate-based waveguide arranged in sequence from top to bottom, wherein a coupling mark window is opened on the upper cladding, and the upper cladding is covered with a metal layer for absorbing stray light generated in the grating coupling process;

[0008] The grating region is covered with a fan-shaped covering layer for reducing the loss caused by scattering of light emitted from the grating region. The length and width of the fan-shaped covering layer are respectively greater than the length and width of the grating region, and the material of the fan-shaped covering layer is Al or Ti.

[0009] Preferably, an electrode layer is grown on the thin-film lithium niobate-based waveguide of the phase modulator, and a SiO2 layer is filled between the electrode layer and the thin-film lithium niobate-based waveguide of the phase modulator.

[0010] Preferably, the electrode layer of the phase modulator is a push-pull structure, the distance between the electrode layer and the thin film lithium niobate-based waveguide is 1 μm-2 μm, and the thickness of the SiO2 layer is 1 μm-2 μm.

[0011] Preferably, the mode rotation multiplexer comprises an input and output interface, a thin film lithium niobate-based waveguide, a first mode coupling region, a widening structure, a second mode coupling region and a multimode interference coupling region, which are sequentially arranged along the direction of light transmission;

[0012] The mode rotation multiplexer achieves conversion between modes by widening the thin-film lithium niobate-based waveguide and coupling the mode evanescent waves.

[0013] Preferably, the mode rotation multiplexer comprises an input and output interface, a thin-film lithium niobate-based waveguide, a tapered structure, a third mode coupling region and a multimode interference coupling region, which are sequentially arranged along the direction of light transmission;

[0014] The mode rotation multiplexer achieves conversion between modes by tapering the thin-film lithium niobate-based waveguide and coupling the mode evanescent waves.

[0015] The application of the thin-film lithium niobate chip based on mode rotation multiplexing in an integrated fiber optic gyroscope, the input end of the grating coupler is coupled with a wide-spectrum light source and a photodetector respectively, and the output end of the phase modulator is coupled with the fiber optic gyroscope;

[0016] The coupling region where the grating coupler is coupled to the wide-spectrum light source is used to simultaneously transmit light in the TE0 mode and the TM0 mode, and the coupling region where the grating coupler is coupled to the photodetector is used to transmit light in the TE0 mode.

[0017] The method for applying the thin-film lithium niobate chip based on mode rotation multiplexing in an integrated fiber optic gyroscope comprises the following steps:

[0018] First, the laser emitted by the wide-spectrum light source is coupled into one of the ports of the grating coupler, and the light of the TE0 mode and the TM0 mode is transmitted simultaneously in the grating coupler. After passing through the beam splitter, it enters the mode rotation multiplexer. In the mode rotation multiplexer, the TM0 mode in the upper waveguide in the first mode coupling region is coupled to the lower waveguide in the first mode coupling region by mode evanescent wave coupling, and excited to become the TE1 mode. The TE1 mode passes through the widening structure and the second mode coupling region, and the TE1 in the upper waveguide of the second mode coupling region is coupled to the lower waveguide in the second mode coupling region by mode evanescent wave coupling, and converted into the TE0 mode. The two TE0 modes are combined through the multi-mode interference coupling region to realize mode rotation multiplexing, and then the light beam phase is modulated by the phase modulator, and finally enters the fiber gyroscope, and the returned light is transmitted to the photodetector through another port of the grating coupler.

[0019] The application of the thin-film lithium niobate chip based on mode rotation multiplexing in an integrated fiber optic gyroscope, the input end of the grating coupler is coupled with a wide-spectrum light source and an optoelectronic beam splitter respectively, and the output end of the phase modulator is coupled with the fiber optic gyroscope;

[0020] The coupling region where the grating coupler is coupled to the wide-spectrum light source is used to simultaneously transmit light in the TE0 mode and the TM0 mode, and the coupling region where the grating coupler is coupled to the photodetector is used to transmit light in the TE0 mode.

[0021] The method for applying the thin-film lithium niobate chip based on mode rotation multiplexing in an integrated optical fiber gyroscope comprises the following steps: first, the laser emitted by a wide-spectrum light source is coupled into one of the ports of a grating coupler, and the light of TE0 mode and TM0 mode is simultaneously transmitted in the grating coupler, and enters a mode rotation multiplexer after passing through a beam splitter, and in the mode rotation multiplexer, the transmitted TM0 mode is converted into a TE1 mode through a taper structure, and then mode evanescent wave coupling is performed through a third mode coupling region, and the TE1 mode is coupled to a waveguide under the third mode coupling and converted into a TE0 mode, and two TE0 modes are combined through a multimode interference coupling region to realize mode rotation multiplexing, and then the light beam phase is modulated through a phase modulator, and finally enters the optical fiber gyroscope, and the returned light is transmitted to a photodetector through another port of the grating coupler.

[0022] The present invention has the following beneficial effects:

[0023] 1. The on-chip integration of lithium niobate functional devices has been realized, thereby achieving miniaturization while ensuring the performance of each integrated optical device and completing the hybrid integration of multi-material chips;

[0024] 2. The on-chip integration of grating couplers, mode rotation multiplexers, and phase modulators has been realized, and they are applied in integrated optical chips for gyroscopes. The coupling efficiency of the grating coupler can reach more than 60%, and it has good mode selection characteristics. The overall polarization effect of the chip can reach 35dB, which can reduce the intrinsic mode loss by about 3dB compared with the traditional polarization structure, that is, the overall insertion loss of the device can be reduced by about 3dB, and the overall device insertion loss can be reduced by about 30%;

[0025] 3. By setting up a phase modulator filled with a SiO2 layer, the overall modulation efficiency of the chip can be guaranteed to reach 1V·cm;

[0026] 4. It can be adapted to the existing thin-film lithium niobate-based processing technology and mass production technology, and the relevant devices can be processed into PDK (process design kit), which has the prospect of large-scale and mass production, and can then form various products in various related fields.

[0027] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the structure of the thin-film lithium niobate chip based on mode rotation multiplexing according to the present invention;

[0029] Figure 2 A filling diagram of the grating coupler of the thin-film lithium niobate chip based on mode rotation multiplexing according to the present invention;

[0030] Figure 3 A coupling schematic diagram of a grating coupler of a thin-film lithium niobate chip based on mode rotation multiplexing according to the present invention;

[0031] Figure 4 This is a schematic diagram of the interface structure of the phase modulator of the thin-film lithium niobate chip based on mode rotation multiplexing according to the present invention;

[0032] Figure 5 This is a schematic diagram of the working process of Example 1 of the thin-film lithium niobate chip based on mode rotation multiplexing according to the present invention;

[0033] Figure 6 This is a schematic diagram of the working process of Example 2 of the thin-film lithium niobate chip based on mode rotation multiplexing described in the present invention.

[0034] Among them: 1. grating coupler; 11. grating region; 111. fan-shaped covering layer; 12. upper cladding layer; 121. coupling mark window; 2. beam splitter; 3. mode rotation multiplexer; 4. phase modulator; 41. electrode layer; 42. SiO2 layer; 43. thin film lithium niobate-based waveguide. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and advantages disclosed in the embodiments of the present invention clearer, the embodiments of the present invention are further described in detail in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the embodiments of the present invention and are not intended to limit the embodiments of the present invention. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions.

[0036] It should be noted that the terms "include", "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or server comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or devices.

[0037] Like reference numerals and letters denote similar items in the following drawings, and thus, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0038] In the description of the present invention, it should be noted that the terms "upper", "lower", "inside", "outside", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, or are directions or positional relationships in which the product of the invention is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present invention.

[0039] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "setting", "installation" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0040] like Figure 1-Figure 4 As shown, a thin-film lithium niobate chip based on mode rotation multiplexing includes a grating coupler 1, a beam splitter 2, a mode rotation multiplexer 3 and a phase modulator 4 which are sequentially integrated on a LNOI (lithium niobate on insulator) platform along the direction of light propagation. The grating coupler 1, the beam splitter, the mode rotation multiplexer 3 and the phase modulator 4 are all composed of a thin-film lithium niobate waveguide, and the grating coupler 1, the beam splitter 2, the mode rotation multiplexer 3 and the phase modulator 4 are optically interconnected via a thin-film lithium niobate-based waveguide. The mode rotation multiplexer 3 described in this embodiment has only a unidirectional mode conversion characteristic, and will not cause mode changes for light transmitted back from a subsequent system, and will not introduce large losses.

[0041] Among them, the grating coupler 1 is a two-dimensional waveguide grating structure, and the grating coupler 1 includes an upper cladding 12, a grating region 11 and a thin film lithium niobate-based waveguide arranged in sequence from top to bottom, wherein a coupling mark window 121 is opened on the upper cladding 12 to facilitate vertical coupling alignment with the tube core of the wide-spectrum light source and the photodetector, and the upper cladding 12 is covered with a metal layer for absorbing stray light generated in the grating coupling process; the grating region 11 is covered with a fan-shaped covering layer 111 for reducing the loss caused by light scattering of the grating region 11, and the length and width of the fan-shaped covering layer 111 are respectively greater than the length and width of the grating region 11. In this embodiment, the length and width of the fan-shaped covering layer 111 are both 20μm, and the thickness is 5μm, and its material is Al or Ti.

[0042] An electrode layer 41 is grown on the thin-film lithium niobate-based waveguide of the phase modulator 4, and a SiO2 layer 42 is filled between the electrode layer 41 and the thin-film lithium niobate-based waveguide 43 of the phase modulator 4 to reduce the absorption loss of the electrode to the transmission light in the waveguide, thereby improving the modulation efficiency of the phase modulator 4. The electrode layer 41 of the phase modulator 4 is a push-pull structure, the distance between the electrode layer 41 and the thin-film lithium niobate-based waveguide 43 is 1μm-2μm, and the thickness of the SiO2 layer is 1μm-2μm to reduce the absorption loss of the electrode to the light, and higher modulation efficiency can be achieved when the electrode spacing is the same.

[0043] The mode rotation multiplexer 3 includes an input and output interface, a thin film lithium niobate-based waveguide, a first mode coupling region, a widening structure, a second mode coupling region and a multimode interference coupling region which are sequentially arranged along the direction of light transmission; the mode rotation multiplexer 3 realizes conversion between modes by widening the thin film lithium niobate-based waveguide and mode evanescent wave coupling.

[0044] Example 1

[0045] like Figure 5As shown, in the application of the thin-film lithium niobate chip based on mode rotation multiplexing in the integrated fiber gyroscope, the input end of the grating coupler 1 is coupled with the wide-spectrum light source and the photodetector respectively, and the output end of the phase modulator 4 is coupled with the fiber gyroscope; the coupling region of the grating coupler 1 coupled with the wide-spectrum light source is used to simultaneously transmit the light of TE0 mode and TM0 mode, and the coupling region of the grating coupler 1 with the photodetector is used to transmit the light of TE0 mode.

[0046] The method for applying the thin-film lithium niobate chip based on mode rotation multiplexing in an integrated fiber optic gyroscope comprises the following steps:

[0047] First, the laser emitted by the wide-spectrum light source is coupled into one of the ports of the grating coupler 1, and the light of the TE0 mode and the TM0 mode is transmitted simultaneously in the grating coupler 1, and enters the mode rotation multiplexer 3 after passing through the beam splitter 2. In the mode rotation multiplexer 3, the TM0 mode in the upper waveguide in the first mode coupling region is coupled to the lower waveguide in the first mode coupling region by mode evanescent wave coupling, and is excited to become the TE1 mode. The TE1 mode passes through the widening structure and the second mode coupling region, and the TE1 in the upper waveguide of the second mode coupling region is coupled to the lower waveguide in the second mode coupling region by mode evanescent wave coupling, and is converted into the TE0 mode. The two TE0 modes are combined through the multi-mode interference coupling region to realize mode rotation multiplexing, and then the light beam phase is modulated by the phase modulator 4, and finally enters the fiber gyroscope, and the returned light is transmitted to the photodetector through another port of the grating coupler 1.

[0048] Example 2

[0049] like Figure 6 As shown, the mode rotation multiplexer 3 includes an input and output interface, a thin-film lithium niobate-based waveguide, a tapered structure, a third mode coupling region and a multi-mode interference coupling region which are sequentially arranged along the direction of light transmission; the mode rotation multiplexer 3 realizes conversion between modes by tapering the thin-film lithium niobate-based waveguide and mode evanescent wave coupling.

[0050] The application of the thin-film lithium niobate chip based on mode rotation multiplexing in the integrated fiber gyroscope, the input end of the grating coupler 1 is coupled with the wide-spectrum light source and the photoelectric beam splitter 2 respectively, and the output end of the phase modulator 4 is coupled with the fiber gyroscope;

[0051] The coupling region where the grating coupler 1 is coupled with the broadband light source is used to simultaneously transmit light in the TE0 mode and the TM0 mode, and the coupling region where the grating coupler 1 is coupled with the photodetector is used to transmit light in the TE0 mode.

[0052] The method for applying the thin-film lithium niobate chip based on mode rotation multiplexing in an integrated optical fiber gyroscope comprises the following steps: first, the laser emitted by a wide-spectrum light source is coupled into one of the ports of a grating coupler 1, and the light of the TE0 mode and the TM0 mode is simultaneously transmitted in the grating coupler 1, and enters the mode rotation multiplexer 3 after passing through a beam splitter 2, and in the mode rotation multiplexer 3, the transmitted TM0 mode is converted into a TE1 mode through a taper structure, and then mode evanescent wave coupling is performed through a third mode coupling region, and the TE1 mode is coupled to a waveguide under the third mode coupling and converted into a TE0 mode, and two TE0 modes are combined through a multimode interference coupling region to realize mode rotation multiplexing, and then the light beam phase is modulated through a phase modulator 4, and finally enters the optical fiber gyroscope, and the returned light is transmitted to a photodetector through another port of the grating coupler 1.

[0053] Therefore, the present invention adopts the above-mentioned thin-film lithium niobate chip, application and application method based on mode rotation multiplexing, by converting the originally lost TM0 mode into TE0 mode, and combining it with the original TE0 mode, thereby reducing the intrinsic mode loss by 3dB and reducing the overall device insertion loss by about 30%.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A thin-film lithium niobate chip based on mode rotation multiplexing, characterized in that: It includes a grating coupler, a beam splitter, a mode rotation multiplexer and a phase modulator which are sequentially integrated on the LNOI platform along the direction of light propagation. The grating coupler, the beam splitter, the mode rotation multiplexer and the phase modulator are all composed of thin-film lithium niobate waveguides, and the grating coupler, the beam splitter, the mode rotation multiplexer and the phase modulator are optically interconnected via thin-film lithium niobate-based waveguides.

2. The thin-film lithium niobate chip based on mode rotation multiplexing according to claim 1, characterized in that: The grating coupler is a two-dimensional waveguide grating structure, and the grating coupler includes an upper cladding layer, a grating region, and a thin-film lithium niobate-based waveguide arranged in sequence from top to bottom, wherein a coupling mark window is opened on the upper cladding layer, and the upper cladding layer is covered with a metal layer for absorbing stray light generated in the grating coupling process; The grating region is covered with a fan-shaped covering layer for reducing the loss caused by scattering of light emitted from the grating region. The length and width of the fan-shaped covering layer are respectively greater than the length and width of the grating region, and the material of the fan-shaped covering layer is Al or Ti.

3. The thin-film lithium niobate chip based on mode rotation multiplexing according to claim 2, characterized in that: An electrode layer is grown on the thin-film lithium niobate-based waveguide of the phase modulator, and a SiO2 layer is filled between the electrode layer and the thin-film lithium niobate-based waveguide of the phase modulator.

4. The thin-film lithium niobate chip based on mode rotation multiplexing according to claim 3 is characterized in that: The electrode layer of the phase modulator is a push-pull structure, the distance between the electrode layer and the thin-film lithium niobate-based waveguide is 1 μm-2 μm, and the thickness of the SiO2 layer is 1 μm-2 μm.

5. The thin-film lithium niobate chip based on mode rotation multiplexing according to claim 4, characterized in that: The mode rotation multiplexer includes an input and output interface, a thin-film lithium niobate-based waveguide, a first mode coupling region, a widening structure, a second mode coupling region and a multimode interference coupling region, which are sequentially arranged along the direction of light transmission; The mode rotation multiplexer achieves conversion between modes by widening the thin-film lithium niobate-based waveguide and coupling the mode evanescent waves.

6. The thin-film lithium niobate chip based on mode rotation multiplexing according to claim 4, characterized in that: The mode rotation multiplexer includes an input and output interface, a thin-film lithium niobate-based waveguide, a tapered structure, a third mode coupling region and a multimode interference coupling region which are sequentially arranged along the direction of light transmission; The mode rotation multiplexer achieves conversion between modes by tapering the thin-film lithium niobate-based waveguide and coupling the mode evanescent waves.

7. Application of the thin-film lithium niobate chip based on mode rotation multiplexing in an integrated fiber gyroscope as claimed in claim 5, characterized in that: The input end of the grating coupler is coupled with the wide-spectrum light source and the photodetector respectively, and the output end of the phase modulator is coupled with the fiber gyroscope; The coupling region where the grating coupler is coupled to the wide-spectrum light source is used to simultaneously transmit light in the TE0 mode and the TM0 mode, and the coupling region where the grating coupler is coupled to the photodetector is used to transmit light in the TE0 mode.

8. The method for applying the thin-film lithium niobate chip based on mode rotation multiplexing in an integrated fiber optic gyroscope as claimed in claim 7, characterized in that: The following steps are involved: First, the laser emitted by the wide-spectrum light source is coupled into one of the ports of the grating coupler, and the light of the TE0 mode and the TM0 mode is transmitted simultaneously in the grating coupler. After passing through the beam splitter, it enters the mode rotation multiplexer. In the mode rotation multiplexer, the TM0 mode in the upper waveguide in the first mode coupling region is coupled to the lower waveguide in the first mode coupling region by mode evanescent wave coupling, and excited to become the TE1 mode. The TE1 mode passes through the widening structure and the second mode coupling region, and the TE1 in the upper waveguide of the second mode coupling region is coupled to the lower waveguide in the second mode coupling region by mode evanescent wave coupling, and converted into the TE0 mode. The two TE0 modes are combined through the multi-mode interference coupling region to realize mode rotation multiplexing, and then the light beam phase is modulated by the phase modulator, and finally enters the fiber gyroscope, and the returned light is transmitted to the photodetector through another port of the grating coupler.

9. Application of the thin-film lithium niobate chip based on mode rotation multiplexing in an integrated fiber gyroscope as claimed in claim 6, characterized in that: The input end of the grating coupler is coupled with the wide-spectrum light source and the photoelectric beam splitter respectively, and the output end of the phase modulator is coupled with the fiber gyroscope; The coupling region where the grating coupler is coupled to the wide-spectrum light source is used to simultaneously transmit light in the TE0 mode and the TM0 mode, and the coupling region where the grating coupler is coupled to the photodetector is used to transmit light in the TE0 mode.

10. The method for applying the thin-film lithium niobate chip based on mode rotation multiplexing in an integrated fiber optic gyroscope as claimed in claim 9, characterized in that: The following steps are involved: First, the laser emitted by the wide-spectrum light source is coupled into one of the ports of the grating coupler, and the TE0 mode and TM0 mode light are transmitted simultaneously in the grating coupler. After passing through the beam splitter, it enters the mode rotation multiplexer. In the mode rotation multiplexer, the transmitted TM0 mode is converted into the TE1 mode through the taper structure, and then the mode evanescent wave coupling is performed through the third mode coupling region, and the TE1 mode is coupled to the waveguide under the third mode coupling and converted into the TE0 mode. The two TE0 modes are combined through the multi-mode interference coupling region to realize mode rotation multiplexing, and then the light beam phase is modulated by the phase modulator, and finally enters the fiber gyroscope, and the returned light is transmitted to the photodetector through another port of the grating coupler.

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