Polarization independent conversion device of cascade mode conversion waveguide

Abstract

The invention relates to a polarization independent conversion device of a cascade mode conversion waveguide, and belongs to the field of semiconductor optical signal transmission. The device comprises a substrate of a wafer, a buried oxide layer of the wafer, a device layer and a SiO2 upper cladding layer of the device layer from bottom to top. The device layer comprises an input waveguide, a mode evolution waveguide, a multi-section conical mode conversion waveguide, a polarization beam splitting rotator and a light beam combiner assembly. The mode evolution waveguide realizes high-order conversion from a TM0 mode to a TE1 mode; the multi-section conical mode conversion waveguide converts a TM mode of an optical signal in the input waveguide into a TE mode, and the mode coupling ratio is improved by sequentially superposing the conversion ratio of the TM mode; the phase shifter is used for ensuring that the phase difference of two columns of combined waves is 0; and the light beam combining assembly is used for combining the two columns of TE mode light signals and finally outputting a single-mode waveguide TE mode. According to the invention, TE0 single-mode beam combination output irrelevant to any polarization state of an input optical signal is realized, the structure is simple and compact, and the device is suitable for large-scale integration.

Description

Technical Field

[0001] The invention relates to a polarization-independent conversion device of a cascaded mode conversion waveguide, belonging to the technical field of semiconductor optical signal transmission. Background Art

[0002] In the past three decades, the research on silicon-based optical interconnect has achieved the integration of various optical functional devices on-chip, such as on-chip lasers, edge couplers, electro-optic modulators, optical wavelength division multiplexers, photodetectors, etc. However, with the increase in integration and the reduction in device size, the birefringence effect of silicon waveguides has become stronger and stronger, making the same silicon-based device respond to signals with different polarization states differently. On the other hand, in addition to on-chip optical interconnection, communication with the outside world is necessary, and the polarization state in the optical fiber is random. On the basis that most devices are currently extremely sensitive to polarization states, further solving the problem of polarization sensitivity of device performance is the goal of replacing electrical interconnection with optical interconnection.

[0003] There are currently two effective solutions to the polarization sensitivity problem of silicon photonic devices and loop systems. One is to design polarization-independent silicon photonic devices so that they have the same performance for different input TE / TM polarization states. However, this design requires that the waveguide must be processed into a square waveguide and be completely symmetrical. This design has more complex and demanding requirements on the processing technology. The second is to use polarization diversity to decompose the input polarization state into polarization states supported by the current on-chip system, and then process them separately, and finally combine the two polarization signals for output. This solution requires the design of a more complex on-chip system. Summary of the invention

[0004] The technical problem to be solved by the present invention is: in view of the problems and shortcomings of the two effective solutions to the polarization sensitivity problem of silicon photonic devices and loop systems: 1. Designing polarization-independent silicon photonic devices requires that the waveguide must be processed into a square waveguide and be completely symmetrical. This design has more complex and demanding requirements on the processing technology; 2. Using polarization diversity requires the design of a more complex on-chip system. The present invention provides a polarization-independent conversion device of cascaded mode conversion waveguides to achieve high-efficiency TE mode output that is independent of the input polarization state.

[0005] The technical solution of the present invention is: a polarization-independent conversion device of a cascaded mode conversion waveguide, wherein the input end of the polarization-independent device is connected to an input optical fiber; from bottom to top, it includes a wafer substrate, a wafer buried oxide layer, a device layer, and a SiO2 upper cladding of the device layer, characterized in that: the device layer includes: an input waveguide, a mode evolution waveguide 100, a multi-section tapered mode conversion waveguide, a polarization beam splitter rotator, and a photosynthetic beam combiner component;

[0006] The input waveguide, the mode evolution waveguide 100, the multi-section tapered mode conversion waveguide, the polarization beam splitter rotator and the optical beam combiner component are connected in sequence; the multi-section tapered mode conversion waveguide is also connected to the optical beam combiner component.

[0007] As a further solution of the present invention, the multi-section tapered mode conversion waveguide includes a first horizontal directional coupler 210 and a second horizontal directional coupler 220;

[0008] The through port of the polarization beam splitter rotator is loaded with a phase shifter 300;

[0009] The optical combiner assembly includes a first optical combiner 410 and a second optical combiner 420; the optical signal phases at two input ends of each optical combiner are the same, and each optical combiner uses a Y branch, a multi-mode interference coupler, etc.;

[0010] The mode evolution waveguide 100, the first horizontal directional coupler 210, the second horizontal directional coupler 220, and the phase shifter 300 are connected in sequence. The output end of the first horizontal directional coupler 210 and the output end of the second horizontal directional coupler 220 are respectively connected to the input end of the first optical combiner 410, and the output end of the second horizontal directional coupler 220 is also connected to the input end of the phase shifter 300. The through port of the phase shifter 300 and the output end of the first optical combiner 410 are respectively connected to the input end of the second optical combiner 420, and the output end of the second optical combiner 420 is combined for output. The optical signal inputted by the input optical fiber passes through the input waveguide, the mode evolution waveguide 100, the first horizontal directional coupler 210, the second horizontal directional coupler 220, the phase shifter 300, and the second optical combiner 420 in sequence; the two optical signals outputted by the first horizontal directional coupler 210 and the second horizontal directional coupler 220 enter the first optical combiner 410, and the first optical combiner 410 combines the two optical signals of the first horizontal directional coupler 210 and the second horizontal directional coupler 220 and inputs them into the second optical combiner 420, and the optical signals outputted by the first horizontal directional coupler 210, the second horizontal directional coupler 220, and the phase shifter 300 are combined and outputted in the second optical combiner 420, so as to realize the TE polarization state conversion output based on silicon waveguide which is independent of the input polarization state. In addition, the cascaded horizontal directional couplers realize the high-efficiency conversion from TM mode to TE mode, which is conducive to large-scale on-chip inheritance and realizes the technical effect of TE mode output which is independent of the input polarization state.

[0011] As a further solution of the present invention, the multi-section tapered mode conversion waveguide includes a first horizontal directional coupler 210, a second horizontal directional coupler 220, and a third horizontal directional coupler 200;

[0012] The through port of the polarization beam splitter rotator is loaded with a phase shifter 300;

[0013] The optical combiner assembly includes a first optical combiner 410, a second optical combiner 420, and a third optical combiner 400; the mode evolution waveguide 100, the first horizontal directional coupler 210, the second horizontal directional coupler 220, the third horizontal directional coupler 200, and the phase shifter 300 are connected in sequence; the output end of the first horizontal directional coupler 210 and the output end of the second horizontal directional coupler 220 are respectively connected to the input end of the first optical combiner 410, the optical signal at the output end of the first optical combiner 410 and the output end of the third horizontal directional coupler 200 are respectively connected to the input end of the third optical combiner 400, the output end of the third horizontal directional coupler 200 is also connected to the input end of the phase shifter 300, the through port of the phase shifter 300 and the output end of the third optical combiner 400 are respectively connected to the input end of the second optical combiner 420, and the output end of the second optical combiner 420 is combined for output. The optical signal inputted by the input optical fiber passes through the input waveguide, the mode evolution waveguide 100, the first horizontal directional coupler 210, the second horizontal directional coupler 220, the third horizontal directional coupler 200, the phase shifter 300, and the second optical combiner 420 in sequence; the two optical signals outputted by the first horizontal directional coupler 210 and the second horizontal directional coupler 220 enter the first optical combiner 410, the first optical combiner 410 combines the two optical signals and the optical signal outputted by the third horizontal directional coupler 200 enters the third optical combiner 400, and the third optical combiner 400 combines the two optical signals into the third optical combiner 400. The two optical signals of the optical combiner 200 and the first optical combiner 410 are combined and input into the second optical combiner 420, and then combined with the optical signals outputted by the first horizontal directional coupler 210, the second horizontal directional coupler 220, the third horizontal directional coupler 200 and the phase shifter 300 in sequence for output, so as to realize the TE polarization state conversion output based on silicon waveguide which is independent of the input polarization state; and the cascaded horizontal directional couplers realize the high-efficiency conversion from TM mode to TE mode, which is conducive to large-scale on-chip inheritance and realizes the technical effect of TE mode output which is independent of the input polarization state.

[0014] As a further solution of the present invention, the first horizontal directional coupler 210 and the second horizontal directional coupler 220 are completely identical in structure, with only an x-axis shift in position, and the mode conversion efficiency is the same.

[0015] As a further solution of the present invention, the mode evolution waveguide 100 is used to achieve a high-order conversion from the TM0 mode to the TE1 mode;

[0016] The first horizontal directional coupler 210 converts the TE1 mode into the TE0 mode, and the second horizontal directional coupler 220 converts the incompletely converted TE1 mode into the TE0 mode again; the conversion and separation of the TE1 mode into the TE0 mode are realized by the first horizontal directional coupler 210 and the second horizontal directional coupler 220. The output ends of the first horizontal directional coupler 210 and the second horizontal directional coupler 220 are both in the TE0 mode, and since there is a specific optical path difference between the second horizontal directional coupler 220 and the first horizontal directional coupler 210, the output optical signals have the same phase.

[0017] As a further solution of the present invention, the phase shifter 300 is an electro-optic phase shifter or a thermo-optic phase shifter. The phase shifter 300 can change the effective refractive index of the silicon-based waveguide, thereby changing the phase of the optical signal, and changing the phase of the through-end optical signal in the form of electro-optical / thermo-optical, so that the phase of the optical signal when input into the second optical combiner 420 is consistent with the phase of the optical signal input from the output end of the first optical combiner 410 to the input end of the second optical combiner 420.

[0018] As a further solution of the present invention, the first optical combiner 410 is a multimode interference coupler or a Y-branch waveguide, which is used to combine two optical beams with the same phase and different intensities and input them to the input end of the second optical combiner 420.

[0019] As a further solution of the present invention, the through end of the polarization beam splitter rotator and the output end of the first photosynthesizer 410 have the same phase at the input end of the second photosynthesizer 420, but different light intensities, and are combined and output from the output end of the second photosynthesizer 420. The photosynthesizers are all 2×1 photosynthesizer components.

[0020] The beneficial effects of the present invention are:

[0021] 1. It can realize TE0 single-mode beam combining output which is independent of the arbitrary polarization state of the input optical signal;

[0022] 2. A high-efficiency mode conversion is achieved by cascading multiple horizontal directional couplers; multiple optical combiners are used to combine optical signals, and finally a single-mode TE0 optical signal is output; a high-efficiency polarization conversion device is realized that is independent of the input polarization state;

[0023] 3. It is compatible with traditional CMOS processing technology, has a simple and compact structure, and provides a polarization-independent solution suitable for large-scale integration. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a partial structural schematic diagram of a polarization-independent conversion device of a cascaded mode conversion waveguide provided in Embodiment 1 of the present invention;

[0025] Figure 2It is a partial structural schematic diagram of a polarization-independent conversion device of a cascaded mode conversion waveguide provided in Embodiment 2 of the present invention;

[0026] Figure 1-2 The numbers in the figure are: 100 - mode evolution waveguide, 210 - first horizontal directional coupler, 220 - second horizontal directional coupler, 200 - third horizontal directional coupler, 300 - phase shifter, 410 - first optical combiner, 420 - second optical combiner, 400 - third optical combiner. DETAILED DESCRIPTION

[0027] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0028] Example 1: Figure 1 As shown, a polarization-independent conversion device of a cascaded mode conversion waveguide, the input end of the polarization-independent device is connected to an input optical fiber; from bottom to top, it includes a wafer substrate, a wafer buried oxide layer, a device layer and a SiO2 upper cladding layer of the device layer, the device layer material is single crystal silicon, and the device layer includes: an input waveguide, a mode evolution waveguide 100, a multi-section tapered mode conversion waveguide, a polarization beam splitter rotator and a photosynthetic beam combiner component;

[0029] The present invention can be applied to the polarization modulation process of optical signals; the optical signal inputted from the input optical fiber in the polarization control device is processed in sequence by the mode evolution waveguide 100, the first horizontal directional coupler 210, the second horizontal directional coupler 220, the first optical combiner 410, the phase shifter 300 and the second optical combiner 420, wherein the phase shifter 300 can be a thermo-optical phase shifter 300 / electro-optical phase shifter 300, which can realize the conversion of any input polarization state to the TE0 mode, which is beneficial to on-chip integration, so that the polarization-independent conversion device of the cascaded mode conversion waveguide can realize the effect of arbitrary polarization state input and single polarization TE0 mode output.

[0030] See also Figure 1 , Figure 1 A schematic diagram of the structure of a polarization-independent conversion device provided in an embodiment of the present application;

[0031] Exemplarily, the mode evolution waveguide 100 is connected to an input optical fiber via an input waveguide.

[0032] The input waveguide, the mode evolution waveguide 100, the multi-section tapered mode conversion waveguide, the polarization beam splitter rotator and the optical beam combiner component are connected in sequence; the multi-section tapered mode conversion waveguide is also connected to the optical beam combiner component.

[0033] The multi-section tapered mode conversion waveguide includes a first horizontal directional coupler 210 and a second horizontal directional coupler 220;

[0034] The through port of the polarization beam splitter rotator is loaded with a phase shifter 300;

[0035] The optical combiner assembly includes a first optical combiner 410 and a second optical combiner 420; the optical signal phases at two input ends of each optical combiner are the same, and each optical combiner uses a Y branch, a multi-mode interference coupler, etc.;

[0036] The mode evolution waveguide 100, the first horizontal directional coupler 210, the second horizontal directional coupler 220, and the phase shifter 300 are connected in sequence, the output end of the first horizontal directional coupler 210 and the output end of the second horizontal directional coupler 220 are respectively connected to the input end of the first optical combiner 410, the output end of the second horizontal directional coupler 220 is also connected to the input end of the phase shifter 300, the through port of the phase shifter 300 and the output end of the first optical combiner 410 are respectively connected to the input end of the second optical combiner 420, and the output end of the second optical combiner 420 is combined and output. Through the control of the phase shifter 300, the optical signal phase of the input port of the second optical combiner 420 is consistent.

[0037] The optical signal input by the input optical fiber passes through the input waveguide, the mode evolution waveguide 100, the first horizontal directional coupler 210, the second horizontal directional coupler 220, the phase shifter 300, and the second optical combiner 420 in sequence; the two optical signals output by the first horizontal directional coupler 210 and the second horizontal directional coupler 220 enter the first optical combiner 410, and the optical signals of the first horizontal directional coupler 210 and the second horizontal directional coupler 220 have the same phase when entering the first optical combiner 410; the first optical combiner 410 combines the two optical signals of the first horizontal directional coupler 210 and the second horizontal directional coupler 220 and inputs them into the second optical combiner 420, and in the second optical combiner 420, the optical signals are combined with the optical signals output by the first horizontal directional coupler 210, the second horizontal directional coupler 220 and the phase shifter 300 in sequence for output, so as to realize the TE polarization state conversion output based on silicon waveguide which is independent of the input polarization state. Furthermore, the cascaded horizontal directional couplers realize high-efficiency conversion from TM mode to TE mode, which is beneficial to large-scale on-chip inheritance and realizes the technical effect of TE mode output that is independent of the input polarization state.

[0038] The mode evolution waveguide 100 is connected to the input optical fiber through the input waveguide, and the input optical fiber transmits an optical signal of any mode orthogonal polarization, such as TE mode, TM mode, TE mixed TM mode, to the mode evolution waveguide 100. Optionally, the polarization rotation beam splitter 100 converts the optical signal of the TM mode in the input optical fiber into a TE1 mode with the same phase and intensity.

[0039] The first horizontal directional coupler 210 and the second horizontal directional coupler 220 are completely identical in structure, with only an x-axis shift in position, and the mode conversion efficiency is the same; the second horizontal directional coupler 220 converts the TE1 mode that is not converted by the first horizontal directional coupler 210 into the TE0 mode again;

[0040] The mode evolution waveguide 100 is used to achieve high-order conversion from TM0 mode to TE1 mode;

[0041] The first horizontal directional coupler 210 converts the TE1 mode into the TE0 mode, and the second horizontal directional coupler 220 converts the incompletely converted TE1 mode into the TE0 mode again; the conversion and separation of the TE1 mode into the TE0 mode are realized by the first horizontal directional coupler 210 and the second horizontal directional coupler 220. The output ends of the first horizontal directional coupler 210 and the second horizontal directional coupler 220 are both in the TE0 mode, and since there is a specific optical path difference between the second horizontal directional coupler 220 and the first horizontal directional coupler 210, the output optical signals have the same phase.

[0042] The phase shifter 300 is an electro-optical phase shifter or a thermo-optical phase shifter. The phase shifter 300 changes the phase of the optical signal at the through end in an electro-optical / thermo-optical manner so that the phase of the optical signal when input into the second optical combiner 420 is consistent with the phase of the optical signal input from the output end of the first optical combiner 410 to the input end of the second optical combiner 420.

[0043] The first optical combiner 410 is a multimode interference coupler or a Y-branch waveguide, and is used to combine two optical beams with the same phase and different intensities and input them to the input end of the second optical combiner 420;

[0044] The through end of the polarization beam splitter rotator and the output end of the first optical combiner 410 have the same phase at the input end of the second optical combiner 420, but different light intensities, and are combined and output from the output end of the second optical combiner 420. The optical combiners are all 2×1 optical combiner components.

[0045] The present invention adjusts the phase by using multiple optical beam combiner components and phase shifters, and the TE mode optical signals at the through end and the cross end of the polarization beam splitter rotator are collected and combined for multiple outputs, thereby achieving high-efficiency polarization conversion output.

[0046] Embodiment 2, as Figure 2 As shown, a polarization-independent conversion device of cascaded mode conversion waveguides is shown. This embodiment is different from the embodiment 1 in that the number of cascaded horizontal directional couplers is 2, and the number of cascaded horizontal directional couplers in the embodiment 2 is 3. Also, the number of optical combiners is different from the embodiment 1 in that the number of optical combiners is 2, and the number of optical combiners in the embodiment 2 is 3, and other structures remain unchanged.

[0047] Exemplarily, three horizontal directional couplers are placed in sequence at the through end of the polarization beam splitter rotator, and the phase difference of the optical signal at the output end of each horizontal directional coupler is 2nπ.

[0048] Specifically, the multi-section tapered mode conversion waveguide includes a first horizontal directional coupler 210, a second horizontal directional coupler 220, and a third horizontal directional coupler 200;

[0049] The through port of the polarization beam splitter rotator is loaded with a phase shifter 300;

[0050] The optical beam combiner assembly includes a first optical beam combiner 410, a second optical beam combiner 420, and a third optical beam combiner 400;

[0051] The multi-section tapered mode conversion waveguide includes a first horizontal directional coupler 210, a second horizontal directional coupler 220, and a third horizontal directional coupler 200;

[0052] The through port of the polarization beam splitter rotator is loaded with a phase shifter 300;

[0053] The optical combiner assembly includes a first optical combiner 410, a second optical combiner 420, and a third optical combiner 400; the mode evolution waveguide 100, the first horizontal directional coupler 210, the second horizontal directional coupler 220, the third horizontal directional coupler 200, and the phase shifter 300 are connected in sequence; the output end of the first horizontal directional coupler 210 and the output end of the second horizontal directional coupler 220 are respectively connected to the input end of the first optical combiner 410, the optical signal at the output end of the first optical combiner 410 and the output end of the third horizontal directional coupler 200 are respectively connected to the input end of the third optical combiner 400, the output end of the third horizontal directional coupler 200 is also connected to the input end of the phase shifter 300, the through port of the phase shifter 300 and the output end of the third optical combiner 400 are respectively connected to the input end of the second optical combiner 420, and the output end of the second optical combiner 420 is combined for output. The optical signal inputted by the input optical fiber passes through the input waveguide, the mode evolution waveguide 100, the first horizontal directional coupler 210, the second horizontal directional coupler 220, the third horizontal directional coupler 200, the phase shifter 300, and the second optical combiner 420 in sequence; the two optical signals outputted by the first horizontal directional coupler 210 and the second horizontal directional coupler 220 enter the first optical combiner 410, and the first optical combiner 410 combines the two optical signals and then combines them with the optical signal outputted by the third horizontal directional coupler 200. The signal enters the third optical combiner 400, the third optical combiner 400 combines the two optical signals of the third horizontal directional coupler 200 and the first optical combiner 410 and inputs them into the second optical combiner 420, and in the second optical combiner 420, the optical signals are combined with the optical signals outputted by the first horizontal directional coupler 210, the second horizontal directional coupler 220, the third horizontal directional coupler 200 and the phase shifter 300 in sequence for output, so as to realize the TE polarization state conversion output based on silicon waveguide which is independent of the input polarization state.

[0054] Exemplarily, the phases of the optical signals at the two input ends of each optical combiner are the same.

[0055] Optionally, each optical beam combiner uses a Y-branch, a multimode interference coupler, etc.;

[0056] The preparation process of the device is as follows: a waveguide structure of the device of the present invention is manufactured on an SOI wafer through multiple photolithography / etching semiconductor processes. After the waveguide is formed, a 1.5μm thick SiO2 upper cladding layer is deposited through a PECVD process, and a flat and smooth surface is obtained through reverse etching and polishing processes. A 110nm thick layer of high-resistance material TiN is deposited on this smooth surface through a PVD technology, and a TiN heating electrode is formed through photolithography / etching. The TiN heating electrode is a folded distribution structure with a width of 5μm and a total length of 200μm. A 450nm thick SiO2 isolation layer is deposited above the TiN electrode material through a PECVD process; a heating electrode lead hole is formed above the TiN electrode through a photolithography / etching technology, and the lead hole etching stops on the TiN heating electrode; finally, a 2μm metal lead material Al is deposited through a PMI technology, the Al material is connected to the TiN heating electrode, and a 10μm wide Al metal lead is formed through a photolithography / etching technology. The terminal structure of the Al metal lead and the detection contact is a square with a side length of 70μm.

[0057] The specific embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A polarization-independent conversion device of a cascaded mode conversion waveguide, comprising, from bottom to top, a wafer substrate, a wafer buried oxide layer, a device layer, and a SiO2 upper cladding layer of the device layer, characterized in that: The device layer comprises: an input waveguide, a mode evolution waveguide (100), a multi-section tapered mode conversion waveguide, a polarization beam splitter rotator and an optical beam combiner component; The input waveguide, the mode evolution waveguide (100), the multi-section tapered mode conversion waveguide, the polarization beam splitter rotator and the optical beam combiner component are connected in sequence; the multi-section tapered mode conversion waveguide is also connected to the optical beam combiner component.

2. The polarization-independent conversion device of cascaded mode conversion waveguides according to claim 1, characterized in that: The multi-section tapered mode conversion waveguide comprises a first horizontal directional coupler (210) and a second horizontal directional coupler (220); The through port of the polarization beam splitter rotator is loaded with a phase shifter (300); The optical beam combiner assembly comprises a first optical beam combiner (410) and a second optical beam combiner (420); The mode evolution waveguide (100), the first horizontal directional coupler (210), the second horizontal directional coupler (220), and the phase shifter (300) are connected in sequence; the output end of the first horizontal directional coupler (210) and the output end of the second horizontal directional coupler (220) are respectively connected to the input end of the first optical combiner (410); the output end of the second horizontal directional coupler (220) is also connected to the input end of the phase shifter (300); the through port of the phase shifter (300) and the output end of the first optical combiner (410) are respectively connected to the input end of the second optical combiner (420); and the output end of the second optical combiner (420) combines the beams for output.

3. The polarization-independent conversion device of cascaded mode conversion waveguides according to claim 1, characterized in that: The multi-section tapered mode conversion waveguide comprises a first horizontal directional coupler (210), a second horizontal directional coupler (220), and a third horizontal directional coupler (200); The through port of the polarization beam splitter rotator is loaded with a phase shifter (300); The optical beam combiner assembly comprises a first optical beam combiner (410), a second optical beam combiner (420), and a third optical beam combiner (400); the mode evolution waveguide (100), the first horizontal directional coupler (210), the second horizontal directional coupler (220), the third horizontal directional coupler (200), and the phase shifter (300) are connected in sequence; the output end of the first horizontal directional coupler (210) and the output end of the second horizontal directional coupler (220) are respectively connected to the first optical beam combiner (410), and the output end of the second horizontal directional coupler (220) are respectively connected to the first optical beam combiner (410). 0) input end, the optical signal at the output end of the first optical combiner (410) and the output end of the third horizontal directional coupler (200) are respectively connected to the input end of the third optical combiner (400), the output end of the third horizontal directional coupler (200) is also connected to the input end of the phase shifter (300), the through port of the phase shifter (300) and the output end of the third optical combiner (400) are respectively connected to the input end of the second optical combiner (420), and the output end of the second optical combiner (420) is combined for output.

4. The polarization-independent conversion device of cascaded mode conversion waveguides according to claim 2, characterized in that: An optical signal inputted from an input optical fiber passes through an input waveguide, a mode evolution waveguide (100), a first horizontal directional coupler (210), a second horizontal directional coupler (220), a phase shifter (300), and a second optical combiner (420) in sequence; two optical signals outputted from the first horizontal directional coupler (210) and the second horizontal directional coupler (220) enter the first optical combiner (410); the first optical combiner (410) combines the two optical signals from the first horizontal directional coupler (210) and the second horizontal directional coupler (220) and inputs the combined optical signals into the second optical combiner (420); in the second optical combiner (420), the combined optical signals are combined with the optical signals outputted from the first horizontal directional coupler (210), the second horizontal directional coupler (220), and the phase shifter (300) in sequence and output, thereby realizing TE polarization state conversion output based on silicon waveguide that is independent of the input polarization state.

5. The polarization-independent conversion device of cascaded mode conversion waveguides according to claim 3, characterized in that: An optical signal input from an input optical fiber passes through an input waveguide, a mode evolution waveguide (100), a first horizontal directional coupler (210), a second horizontal directional coupler (220), a third horizontal directional coupler (200), a phase shifter (300), and a second optical combiner (420) in sequence; two optical signals output from the first horizontal directional coupler (210) and the second horizontal directional coupler (220) enter the first optical combiner (410), and the first optical combiner (410) combines the two optical signals with the optical signals output from the third horizontal directional coupler (200) to form a phase shifter (300). The signal enters the third optical combiner (400), and the third optical combiner (400) combines the two optical signals of the third horizontal directional coupler (200) and the first optical combiner (410) and inputs the combined optical signals into the second optical combiner (420). In the second optical combiner (420), the combined optical signals are combined with the optical signals outputted from the first horizontal directional coupler (210), the second horizontal directional coupler (220), the third horizontal directional coupler (200), and the phase shifter (300) in sequence and output, thereby realizing TE polarization state conversion output based on silicon waveguide that is independent of the input polarization state.

6. The polarization-independent conversion device of cascaded mode conversion waveguides according to claim 2, characterized in that: The first horizontal directional coupler (210) and the second horizontal directional coupler (220) are completely identical in structure, with only an x-axis shift in position, and the mode conversion efficiency is the same.

7. The polarization-independent conversion device of cascaded mode conversion waveguides according to claim 2, characterized in that: The mode evolution waveguide (100) is used to realize high-order conversion from TM0 mode to TE1 mode; The first horizontal directional coupler (210) converts the TE1 mode into the TE0 mode, and the second horizontal directional coupler (220) converts the incompletely converted TE1 mode into the TE0 mode again; the conversion and separation of the TE1 mode into the TE0 mode are achieved by the first horizontal directional coupler (210) and the second horizontal directional coupler (220).

8. The polarization-independent conversion device of cascaded mode conversion waveguides according to claim 2, characterized in that: The phase shifter (300) is an electro-optical phase shifter or a thermo-optical phase shifter. The phase shifter (300) changes the phase of the optical signal at the through-end in an electro-optical / thermo-optical manner, so that the phase of the optical signal when input into the second optical combiner (420) is consistent with the phase of the optical signal input from the output end of the first optical combiner (410) to the input end of the second optical combiner (420).

9. The polarization-independent conversion device of cascaded mode conversion waveguides according to claim 2 or 3, characterized in that: The first optical combiner (410) is a multimode interference coupler or a Y-branch waveguide, and is used to combine two optical beams with the same phase and different intensities and input them to the input end of the second optical combiner (420).

10. The polarization-independent conversion device of cascaded mode conversion waveguides according to claim 2, characterized in that: The through end of the polarization beam splitter rotator and the output end of the first optical combiner (410) have the same phase at the input end of the second optical combiner (420), but different light intensities, and are combined and output from the output end of the second optical combiner (420), and the optical combiners are all 2×1 optical combiner components.

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