On-chip polarization-rotating beam splitting structure

Abstract

The application discloses a kind of on-chip polarization rotation beam splitting structures, input silicon nitride waveguide, mode converter, mode coupler and output silicon waveguide, input silicon nitride waveguide is coupled into TM and TE two polarization modes in optical fiber, TM base mode in silicon nitride waveguide layer is converted into TE1 mode in silicon waveguide layer after mode converter, TE base mode is still TE0 mode in silicon waveguide layer is coupled;TE1 mode and TE0 mode in silicon waveguide layer are converted into TE0 mode of two waveguide output ports again after mode coupler, and finally transmitted by output silicon waveguide respectively.The advantages of the application, the overall design of the structure is simple, only contains strip waveguide, only needs to be etched single time on production, and the process stability is higher;And design uses two kinds of materials to improve overall performance.

Description

Technical Field

[0001] This invention relates to an on-chip polarization rotation beam splitter structure. Background Technology

[0002] As photonic integrated circuits (PICs) develop towards higher density and multifunctionality, on-chip polarization control technology has become a core support for realizing polarization multiplexing systems. Polarization rotating beamsplitters (PRS), as key photonic devices capable of efficiently separating and rotating incident optical signals of arbitrary polarization states (typically TE and TM modes) to achieve co-polarized output, have significant application value in optical communication and optical computing.

[0003] Currently, on-chip polarization rotation beam splitters based on silicon-on-insulator (SOI) platforms are mainly implemented through asymmetric directional couplers (ADCs), subwavelength gratings, asymmetric waveguide structures, or mode evolution adiabatic conical structures. While these structures achieve polarization separation and rotation to some extent, they still face several technical bottlenecks in practical applications. One significant aspect is the complexity of the structure and the low tolerance of the manufacturing process. Specifically, some high-performance PRS designs require complex stacked structures, complex waveguide cross-section designs, or special doping processes. This not only increases the complexity of photolithography but also raises manufacturing costs and results in poor compatibility with standard CMOS-compatible processes. Furthermore, existing structures often require extremely high process precision to achieve accurate mode conversion and beam splitting. Even minor processing deviations (such as waveguide sidewall roughness or etching depth errors) can lead to a significant decrease in mode coupling efficiency, increased crosstalk, and deterioration of the extinction ratio, making it difficult to guarantee device yield in large-scale production. In addition, many PRS structures based on mode coupling or interference principles are sensitive to wavelength changes, resulting in narrow operating bandwidths. In broadband optical communication applications, these devices struggle to maintain stable extinction ratios and insertion losses across the entire communication band, limiting their practical application scenarios.

[0004] In summary, existing on-chip polarization rotation beam splitters struggle to achieve an ideal balance between compact size, wide operating bandwidth, high manufacturing tolerance, and low insertion loss. Therefore, there is an urgent need to design a novel on-chip polarization rotation beam splitter structure to realize a high-performance PRS structure with simple structure and high process tolerance, thereby further improving the overall performance of photonic integrated systems. Summary of the Invention

[0005] The purpose of this invention is to propose an on-chip polarization rotation beam splitter structure, and the technical solution adopted is as follows:

[0006] An on-chip polarization rotation beam splitter structure includes an input silicon nitride waveguide, a mode converter, a mode coupler, and an output silicon waveguide. One end of the mode converter is connected to the input silicon nitride waveguide, and the other end is connected to the mode coupler. The input silicon nitride waveguide couples the TM and TE polarization modes from the optical fiber into the input. The mode converter converts the TM fundamental mode in the silicon nitride waveguide layer into the TE1 mode in the silicon waveguide layer, while the TE fundamental mode, coupled into the silicon waveguide layer, remains the TE0 mode. The mode coupler then converts the TE1 and TE0 modes in the silicon waveguide layer into the TE0 modes at the two waveguide output ports, which are then transmitted separately by the output silicon waveguide.

[0007] In a further preferred embodiment of the technical solution of the present invention, the mode converter is a reverse tapered waveguide structure, including a silicon nitride tapered waveguide and a silicon tapered waveguide. The starting end of the silicon nitride tapered waveguide is connected to the input silicon nitride waveguide. The starting end of the silicon tapered waveguide overlaps with the silicon nitride tapered waveguide in the vertical direction, with the silicon nitride tapered waveguide located on top. The width of the silicon nitride tapered waveguide gradually decreases along the mode transmission direction, while the width of the silicon tapered waveguide gradually increases along the mode transmission direction.

[0008] In a further preferred embodiment of the technical solution of this invention, the waveguide edge variation function in the reverse tapered waveguide structure is any one of first, second, or third order. Specifically, a first-order function corresponds to the case where the waveguide width changes uniformly with the tapered length, while a second- or third-order function corresponds to the case where the waveguide width changes slowly with the length starting from the narrow end and then changes rapidly. A second- or third-order function at the waveguide edge allows for more complete coupling at the narrow end, thereby shortening the overall length of the structure, but it also places higher demands on the waveguide etching process.

[0009] In a further preferred embodiment of the technical solution of the present invention, the mode coupler includes a first coupling waveguide and a second coupling waveguide, which are arranged in parallel. The starting end of the first coupling waveguide is connected to the ending end of the silicon tapered waveguide. The waveguide width of the first coupling waveguide is equal to the waveguide width of the ending end of the silicon tapered waveguide. The TE1 mode and TE0 mode output by the mode converter enter the first coupling waveguide. The first coupling waveguide transmits the TE0 mode and couples the TE1 mode energy into the second coupling waveguide, transforming it into the TE0 mode in the second coupling waveguide.

[0010] In a further preferred embodiment of the technical solution of the present invention, the output silicon waveguide includes a first output silicon waveguide and a second output silicon waveguide. One end of the first output silicon waveguide is connected to the termination end of the first coupled waveguide, and outputs a first TEO mode. One end of the second output silicon waveguide is connected to the second coupled waveguide, and outputs a second TEO mode.

[0011] In a further preferred embodiment of the technical solution of the present invention, all waveguides are strip waveguides.

[0012] A further preferred embodiment of the technical solution of the present invention is an on-chip polarization rotation beam splitter structure, which, from bottom to top, comprises: a substrate layer, a silicon waveguide layer, and a silicon nitride waveguide layer, all surrounded by silicon oxide. The silicon waveguide layer has a trapezoidal cross-section and a sidewall tilt angle of θ. The thickness of the silicon nitride waveguide layer ranges from 100 nanometers to 500 nanometers, and the width of the silicon nitride waveguide layer ranges from 90 nanometers to 2 micrometers. The thickness of the silicon waveguide layer ranges from 200 nanometers to 1 micrometer, and the width of the silicon waveguide layer ranges from 90 nanometers to 2 micrometers.

[0013] In a further preferred embodiment of the technical solution of the present invention, the sidewall tilt angle θ of the silicon waveguide layer ranges from 50° to 85°. The smaller the waveguide sidewall tilt angle, the stronger the asymmetry in the vertical direction of the waveguide, the stronger the mode hybridization effect, the shorter the required length of the tapered waveguide, and the shorter the overall length of the polarization rotation beam splitter structure, which is more conducive to on-chip integration.

[0014] In a further preferred embodiment of the technical solution of the present invention, the thickness of silicon oxide between the silicon nitride waveguide layer and the silicon waveguide layer is 200 nanometers to 600 nanometers.

[0015] In a further preferred embodiment of the technical solution of the present invention, the thickness of the silicon oxide cladding layer above the silicon nitride waveguide layer is 1 micrometer to 6 micrometers.

[0016] The advantages of this invention compared to the prior art are as follows:

[0017] The on-chip polarization rotation beam splitter structure of the present invention utilizes the low refractive index waveguide design of silicon nitride waveguides in the input waveguide section to design the coupling and transmission structure. Compared with silicon waveguide couplers, it has a lower refractive index difference, which reduces the coupling loss from the mode in the optical fiber to the integrated chip.

[0018] The on-chip polarization rotation beam splitter structure of the present invention, in the mode converter section, couples the modes in the silicon nitride waveguide to the silicon waveguide through the interlayer reverse tapering structure of the silicon waveguide and the silicon waveguide. At the same time, it utilizes the mode hybridization effect in the silicon waveguide to complete the mode conversion during the slow tapering process. This section of the structure has both interlayer mode coupling and mode hybridization functions, reduces the overall length of the structure, and improves the device compactness and overall integration.

[0019] The on-chip polarization rotation beam splitter structure of the present invention is simple in design, consisting of basic strip waveguide device units. It only requires a single etching, which reduces the risk of parameter deviation introduced by multiple etching, reduces the complexity of the etching process, and makes the overall process more stable, thereby improving the device yield from the design level.

[0020] The on-chip polarization rotation beam splitter structure of this invention functionally balances coupling loss and overall device length, achieving optimization of insertion loss and integration density. In terms of fabrication, it reduces the complexity of the etching process, making manufacturing more stable and improving device yield from a design perspective. Attached Figure Description

[0021] Figure 1 This is a top view of the on-chip polarization rotation beam splitter structure of the present invention;

[0022] Figure 2 This is a side view of the on-chip polarization rotation beam splitter structure of the present invention.

[0023] Figure 3 This is a cross-sectional view of the on-chip polarization rotating beam splitter structure of the present invention;

[0024] Figure 4 This is a schematic diagram of the mode hybridization effect in the silicon waveguide of the mode converter obtained through simulation in an embodiment of the present invention;

[0025] Figure 5 The curves showing the variation of the mode energy of the TE and TM fundamental modes in the silicon tapered waveguide of the mode converter as a function of the length of the silicon tapered waveguide are obtained from simulation in the embodiments of the present invention.

[0026] Figure 6 These are the effective refractive index matching curves of the TE0 and TE1 modes in the mode coupler obtained through simulation in this embodiment of the invention, based on the change in silicon waveguide width.

[0027] Figure 7 The above are simulation results obtained in this embodiment of the invention, showing the coupling effect of TE1 mode in the first coupled waveguide and TE0 mode in the second coupled waveguide of the mode coupler, as well as the curve of insertion loss of the mode coupler as a function of wavelength.

[0028] Figure 8 This is a curve showing the splitting ratio of the two output ports of the first and second output silicon waveguides as a function of wavelength, obtained through simulation in this embodiment of the invention.

[0029] Wherein, 1-mode converter, 101-silicon nitride tapered waveguide, 102-silicon tapered waveguide, 2-mode coupler, 201-first coupling waveguide, 202-second coupling waveguide, 3-silicon nitride waveguide layer, 4-silicon waveguide layer, 5-substrate layer, 6-silicon waveguide layer cross-section, 7-input silicon nitride waveguide, 8-first output silicon waveguide, 9-second output silicon waveguide. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the following description is provided in conjunction with the appendix. Figures 1-8 The present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0031] Example 1

[0032] like Figure 1 , 2 As shown in Figure 3, this embodiment proposes an on-chip polarization rotation beam splitter structure. This structure has a simple overall design, containing only a strip waveguide, and requires only a single etching process, resulting in higher process stability. Furthermore, the design utilizes two materials to improve overall performance. Specifically, a silicon nitride waveguide layer with a lower refractive index is used to fabricate the coupling and input structures, reducing coupling loss; a silicon waveguide layer with a higher refractive index is used to fabricate the mode hybrid waveguide device, utilizing the higher refractive index difference with the cladding to shorten the overall length of the device and improve integration.

[0033] like Figure 2 As shown, the on-chip polarization rotation beam splitter structure includes, from bottom to top: a substrate layer 5, a silicon waveguide layer 4, and a silicon nitride waveguide layer 3, all surrounded by silicon oxide. The silicon waveguide layer 4 has a trapezoidal cross-section and a tilt angle θ on its sidewall, which ranges from 75° to 85°.

[0034] like Figure 1 , 2 As shown in Figure 3, this invention proposes an on-chip polarization rotation beam splitter structure for integrated chips, comprising an input silicon nitride waveguide 7, a mode converter 1, a mode coupler 2, and an output silicon waveguide, all of which are strip waveguides.

[0035] Input silicon nitride waveguide 7 is used to input the TE fundamental mode (i.e., TE0 mode) and the TM fundamental mode (i.e., TM0 mode).

[0036] The mode converter 1 is a reverse tapered waveguide structure with one end connected to the input silicon nitride waveguide 7. It is used to convert the TM0 mode in the silicon nitride waveguide layer 3 into the TE1 mode in the silicon waveguide layer 4 below, and to couple the TE0 mode in the silicon nitride waveguide layer 3 to the silicon waveguide layer 4 below, which is still the TE0 mode. The mode converter 1 includes a silicon nitride tapered waveguide 101 and a silicon tapered waveguide 102.

[0037] The mode coupler 2 includes a first coupling waveguide 201 and a second coupling waveguide 202. One end of the first coupling waveguide 201 is connected to the other end of the mode converter 1, and is used to transmit the TE0 mode and couple the TE1 mode energy into the second coupling waveguide 202, so as to become the TE0 mode in the second coupling waveguide 202.

[0038] The first output silicon waveguide 8 is connected at one end to the other end of the first coupling waveguide 201 and is used to output the first TE0 mode; the second output silicon waveguide 9 is connected at one end to the other end of the second coupling waveguide 202 and is used to output the second TE0 mode.

[0039] Within the integrated chip, the steps for implementing the polarization rotation beam splitting function in the on-chip polarization rotation beam splitting structure of this embodiment are as follows:

[0040] S1. First, the TM and TE polarization modes in the optical fiber are coupled into the chip through the input silicon nitride waveguide 7. At this time, the silicon nitride waveguide layer 3 contains the TE fundamental mode (i.e., TE0 mode) and the TM fundamental mode (i.e., TM0 mode). Figure 1 As shown.

[0041] S2. Next, the modes (including TE and TM fundamental modes) in the silicon nitride waveguide layer 3 are converted to the silicon waveguide layer 4 by mode converter 1. Mode converter 1 consists of a silicon nitride tapered waveguide 101 and a silicon tapered waveguide 102 overlapping vertically. Specifically, the width of the silicon nitride tapered waveguide 101 gradually decreases, reducing the confinement of the mode and coupling it to the underlying silicon waveguide layer 4 (silicon tapered waveguide 102). The width of the silicon waveguide layer 4 gradually widens, gradually increasing the confinement of the mode and enabling stable mode transmission. Figure 1 and 2 As shown. Furthermore, the cross-section of silicon waveguide layer 4 is trapezoidal, with a tilt angle θ on the sidewall. The presence of tilt angle θ disrupts the symmetry in the vertical direction; the modes in the waveguide generate intermode hybridization effects. Slowly pulling the width of the tapered silicon waveguide past the hybridization position causes the TM0 mode within the silicon waveguide to transform into the TE1 mode. At this point, both the TE0 and TE1 modes exist within the silicon waveguide.

[0042] S3. Next, by designing the widths of the first coupling waveguide 201 and the second coupling waveguide 202 in the mode coupler 2, the effective refractive indices of the corresponding modes are matched, enabling mode coupling between silicon waveguides of different widths. This converts the TE1 mode in the first coupling waveguide into the TE0 mode in the second coupling waveguide for transmission, while the TE0 mode in the first coupling waveguide continues to transmit without coupling. Figure 1 As shown.

[0043] S4. Finally, the TE polarization mode input from the fiber-coupled input is converted into the first TE0 mode in the first output silicon waveguide 8 for transmission, while the TM polarization mode input from the fiber-coupled input is converted into the second TE0 mode in the second output silicon waveguide 9 for transmission. The device completes the on-chip polarization rotation beam splitting function.

[0044] To better understand this invention, the following details an application example of an on-chip polarization rotation beam splitter structure for integrated chips proposed in this invention. Specific Implementation Example 1:

[0046] An embodiment of the present invention relates to an on-chip polarization rotation beam splitter structure, comprising an input silicon nitride waveguide 7, a mode converter 1, a mode coupler 2, a first output silicon waveguide 8, and a second output silicon waveguide 9, as shown below. Figure 1 , 2 As shown in Figure 3.

[0047] The on-chip polarization rotation beam splitting function of the entire structure can be described as follows: The TM and TE polarization modes in the optical fiber are coupled into the input silicon nitride waveguide 7. Mode converter 1 converts the TM fundamental mode in the silicon nitride waveguide layer 3 into the TE1 mode in the underlying silicon waveguide layer 4. The TE fundamental mode, coupled into the underlying silicon waveguide layer 4, remains in the TE0 mode. Mode coupler 2 then converts the TE1 mode in the silicon waveguide layer 4 into the TE0 mode in the second coupling waveguide 202 for transmission. The TE0 mode in the silicon waveguide layer 4 propagates along the first coupling waveguide 201. Finally, the TE polarization mode coupled from the optical fiber is converted into the first TE0 mode in the first output silicon waveguide 8 for transmission, while the TM polarization mode coupled from the optical fiber is converted into the second TE0 mode in the second output silicon waveguide 9 for transmission. The device thus completes the on-chip polarization rotation beam splitting function.

[0048] The material parameters, structural parameters, and simulation results set in this embodiment are as follows:

[0049] The refractive index of silicon nitride waveguide layer 3 is set to 1.96, and its thickness is 250 nm. The refractive index of silicon waveguide layer 4 is set to 3.47, and its thickness is 220 nm. The tilt angle θ of the silicon waveguide sidewall of silicon waveguide layer 4 is 82°. The thickness of the silicon oxide layer between silicon nitride waveguide layer 3 and silicon waveguide layer 4 is 400 nm, and the thickness of the covering silicon oxide layer is 3 μm, with a refractive index of 1.44. The effective refractive index of each mode within silicon waveguide layer 4 as a function of the silicon waveguide width is obtained through width scanning, as shown below. Figure 4 As shown in the figure, it can be seen that the hybridization position of the TM0 mode and TE1 mode in silicon waveguide layer 4 is near the silicon waveguide width of 0.7 micrometers.

[0050] First, the width of the input silicon nitride waveguide 7 is set to 1 micrometer.

[0051] Next, in the mode converter 1 section, the initial width of the silicon nitride tapered waveguide 101 is set to 1 micrometer, with its initial end connected to the input silicon nitride waveguide 7. The final width of the silicon nitride tapered waveguide 101 is set to 200 nanometers, and the tapered length is 150 micrometers. The initial width of the silicon tapered waveguide 102 is set to 100 nanometers, with its initial end overlapping the silicon nitride tapered waveguide 101 in the vertical direction. The final width is set to 0.8 micrometers, so that the width of the silicon tapered waveguide 102 slowly passes through the hybridization position within the tapered length. The waveguide widths of both silicon nitride tapered waveguides 101 and 102 change uniformly with the tapered length, i.e., the waveguide edge variation functions are both first-order functions. By scanning the slowly tapered length of the silicon waveguide in silicon waveguide layer 4, the mode energy changes of the TM and TE fundamental modes in the silicon nitride waveguide of silicon nitride waveguide layer 3 after passing through this mode converter 1 structure are obtained, such as... Figure 5 As shown. From Figure 5 It can be observed that as the length of the silicon tapered waveguide 102 increases, the energy of the TE fundamental mode within the silicon tapered waveguide 102 gradually increases to near 1 and then remains unchanged, while the energy of the TM fundamental mode gradually becomes 0. This indicates that the TM fundamental mode in the silicon nitride waveguide of the silicon nitride waveguide layer 3 is converted into the TE1 mode in the silicon waveguide of the silicon waveguide layer 4 after passing through this mode converter 1, and the TE fundamental mode in the silicon nitride waveguide is coupled downwards to become the TE0 mode in the silicon waveguide. Here, the length of the silicon tapered waveguide 102 is chosen to be 210 micrometers.

[0052] Then, in the mode coupler 2 section, such as Figure 6 As shown, curves of the effective refractive index for TE0 and TE1 modes were obtained by scanning the width of the silicon waveguide layer 4. When the two modes have the same effective refractive index, the waveguide width W1 (width of the first coupling waveguide 201) corresponding to the TE1 mode and the waveguide width W2 (width of the second coupling waveguide 202) corresponding to the TE0 mode can be obtained on the horizontal axis. Here, W1 is taken as 0.8 micrometers, which is consistent with the termination width value of the silicon tapered waveguide 102. Figure 6 W2 is found to be around 0.35 micrometers. The first coupled waveguide 201 is set to start at position 0 and end at position 10.8 micrometers. The second coupled waveguide 202 starts at position 3.5 micrometers and ends at position 16 micrometers. Both the first and second coupled waveguides 201 and 202 are silicon waveguides, and the two silicon waveguides (first coupled waveguide 201 and second coupled waveguide 202) are arranged in parallel with a spacing of 0.2 micrometers. The starting end of the first coupled waveguide 201 is connected to the ending end of the silicon tapered waveguide 102. Simulation of the mode coupler 2 shows that, through effective refractive index matching, the TE1 mode in the first coupled waveguide 201 will couple to the second coupled waveguide 202 and become the TE0 mode for transmission. The mode energy change is as follows... Figure 7 As shown in the figure. The insertion loss of section 2 of the mode coupler varies with wavelength as follows. Figure 7 As shown in the image.

[0053] Finally, the beam splitting curves at the two output ends of the on-chip polarization rotation beam splitter in this embodiment are as follows: Figure 8 As shown, this indicates that the TE polarization mode input from the fiber-coupled input is converted into the first TE0 mode in the first output silicon waveguide 8 for transmission, while the TM polarization mode input from the fiber-coupled input is converted into the second TE0 mode in the second output silicon waveguide 9 for transmission. The device completes the on-chip polarization rotation beam splitting function.

[0054] The on-chip polarization rotation beam splitter structure can be extended to integrated chips using other material systems. Based on the same principle, similar polarization rotation beam splitting functionality can also be achieved in integrated chips using other material systems, including silicon and thin-film lithium niobate, silicon nitride and thin-film lithium niobate, silicon and group III-V materials, and silicon nitride and group III-V materials. The higher the refractive index of the material, the stronger the asymmetry generated in the vertical direction at the same sidewall tilt angle, the stronger the mode hybridization within the waveguide, the shorter the required tapered waveguide length, and the shorter the overall length of the polarization rotation beam splitter structure.

[0055] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An on-chip polarization rotation beam splitter structure, characterized in that, The system includes an input silicon nitride waveguide (7), a mode converter (1), a mode coupler (2), and an output silicon waveguide. One end of the mode converter (1) is connected to the input silicon nitride waveguide (7), and the other end of the mode converter (1) is connected to the mode coupler (2). The input silicon nitride waveguide (7) couples the two polarization modes TM and TE in the optical fiber into the input. After passing through the mode converter (1), the TM fundamental mode in the silicon nitride waveguide layer (3) is converted into the TE1 mode in the silicon waveguide layer (4). The TE fundamental mode is coupled into the silicon waveguide layer (4) and remains as the TE0 mode. Then, through the mode coupler (2), the TE1 mode and TE0 mode in the silicon waveguide layer (4) are converted into the TE0 mode of the two waveguide output ports, and finally transmitted by the output silicon waveguide.

2. The on-chip polarization rotation beam splitter structure according to claim 1, characterized in that, The mode converter (1) is a reverse tapered waveguide structure, including a silicon nitride tapered waveguide (101) and a silicon tapered waveguide (102). The starting end of the silicon nitride tapered waveguide (101) is connected to the input silicon nitride waveguide (7). The starting end of the silicon tapered waveguide (102) overlaps with the silicon nitride tapered waveguide (101) in the vertical direction, and the silicon nitride tapered waveguide (101) is located above it. The width of the silicon nitride tapered waveguide (101) gradually decreases along the mode transmission direction, and the width of the silicon tapered waveguide (102) gradually increases along the mode transmission direction.

3. The on-chip polarization rotation beam splitter structure according to claim 2, characterized in that, The waveguide edge variation function in the reverse tapered waveguide structure can be any one of first, second, or third order.

4. The on-chip polarization rotation beam splitter structure according to claim 2, characterized in that, The mode coupler (2) includes a first coupling waveguide (201) and a second coupling waveguide (202). The first coupling waveguide (201) and the second coupling waveguide (202) are arranged in parallel. The starting end of the first coupling waveguide (201) is connected to the ending end of the silicon tapered waveguide (102). The waveguide width of the first coupling waveguide (201) is equal to the waveguide width of the ending end of the silicon tapered waveguide (102). The TE1 mode and TE0 mode output by the mode converter (1) enter the first coupling waveguide (201). The first coupling waveguide (201) transmits the TE0 mode and couples the TE1 mode energy into the second coupling waveguide (202), which becomes the TE0 mode in the second coupling waveguide (202).

5. The on-chip polarization rotation beam splitter structure according to claim 4, characterized in that, The output silicon waveguide includes a first output silicon waveguide (8) and a second output silicon waveguide (9). One end of the first output silicon waveguide (8) is connected to the termination end of the first coupling waveguide (201) and outputs the first TE0 mode. One end of the second output silicon waveguide (9) is connected to the second coupling waveguide (202) and outputs the second TE0 mode.

6. The on-chip polarization rotation beam splitter structure according to claim 5, characterized in that, All waveguides are strip waveguides.

7. The on-chip polarization rotation beam splitter structure according to claim 1, characterized in that, The on-chip polarization rotation beam splitter structure comprises, from bottom to top: a substrate layer (5), a silicon waveguide layer (4), and a silicon nitride waveguide layer (3), all surrounded by silicon oxide. The silicon waveguide layer (4) has a trapezoidal cross-section and a sidewall tilt angle of θ. The thickness of the silicon nitride waveguide layer (3) ranges from 100 nanometers to 500 nanometers, and the width of the silicon nitride waveguide layer (3) ranges from 90 nanometers to 2 micrometers. The thickness of the silicon waveguide layer (4) ranges from 200 nanometers to 1 micrometer, and the width of the silicon waveguide layer (4) ranges from 90 nanometers to 2 micrometers.

8. The on-chip polarization rotation beam splitter structure according to claim 7, characterized in that, The sidewall tilt angle θ of the silicon waveguide layer (4) ranges from 50° to 85°.

9. The on-chip polarization rotation beam splitter structure according to claim 7, characterized in that, The thickness of silicon oxide between the silicon nitride waveguide layer (3) and the silicon waveguide layer (4) is 200 nm to 600 nm.

10. The on-chip polarization rotation beam splitter structure according to claim 6, characterized in that, The thickness of the silicon oxide cladding above the silicon nitride waveguide layer (3) is 1 micrometer to 6 micrometers.

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