Polarization separation end face coupler and linear design method thereof

Abstract

The application provides a polarization separation end face coupler and a linear design method thereof. The coupler comprises a bottom silicon substrate, a silicon oxide under-buried layer, a waveguide structure and an upper cladding layer. The waveguide structure is composed of two groups of waveguides in the same horizontal plane. One group of waveguides has two thicknesses and is used for coupling with an optical fiber and transmitting a transverse electric mode (TE) mode optical signal. The other group of waveguides has a constant thickness and is used for coupling with the former group of waveguides and transmitting a transverse magnetic mode (TM) mode optical signal. Based on the planar waveguide coupling structure, a waveguide linear design method is provided. The linear design of the coupling waveguide is optimized for different wavelengths, and the high-efficiency, large-bandwidth mode field coupling and polarization separation function of the optical fiber to the optical chip optical field are realized.

Description

Technical Field

[0001] This invention relates to the field of silicon-based optoelectronic chip design and packaging, and in particular to a polarization separation end-face coupler and its linear design method. Background Technology

[0002] Over the past few decades, optical communication technology has been widely used. In recent years, however, with the development of the AI ​​industry, the large-scale construction of data centers, and the booming development of cloud computing and intelligent computing, more demands and higher requirements have been placed on data transmission and interconnection. High integration and high transmission rates are two important indicators. Silicon-based optoelectronic chips have been widely used in these fields.

[0003] With the development of silicon-based optoelectronic integration platforms and their CMOS compatibility, the fabrication and packaging of silicon photonic chips have also made significant progress. The coupling between optical fibers and silicon photonic chips is a crucial step in improving interconnect performance and transmission efficiency, making the development of CMOS-compatible coupling devices extremely important. Furthermore, many silicon photonic devices are polarization-sensitive and wavelength-sensitive, thus requiring polarization separation of the input signal light to achieve better performance. Therefore, polarization-separated broadband couplers have a very broad application prospect and demand.

[0004] Currently, there are two types of silicon optical couplers: vertical grating couplers (VFRs) and end-face couplers. VFRs offer advantages such as high coupling tolerance and on-chip detection, but also suffer from significant drawbacks including high polarization sensitivity, small bandwidth, and high loss. End-face couplers, on the other hand, exhibit ultra-low loss and polarization insensitivity. There are two types of end-face couplers: conical and inverted conical. In the inverted conical structure, the cross-sectional area near the fiber is smaller to achieve a mode field that matches the fiber's mode field as closely as possible. This cross-sectional area gradually increases, confining the optical mode field within the waveguide before transmission to the subsequent optical chip. Traditional single-mode fibers have a mode field diameter of around 10µm. To match the fiber's mode field, the cross-sectional area of ​​the coupling section needs to be very small to obtain a large waveguide mode field. This typically requires reducing the waveguide radius or thickness at the coupling end face. However, the top layer Si thickness of the substrate used in standard SOI-fabricated optical chips is usually 220nm. To ensure compatibility with such devices, the width of the waveguide at the coupling end face must be reduced (typically less than 100nm), but this requires higher fabrication costs. Therefore, devices with interlayer coupling structures were proposed, which use thinner or lower refractive index waveguides to couple the optical fiber and the waveguide, and then couple the coupled light field into a 220nm thick silicon waveguide. However, the thickness between the two waveguides in interlayer coupling cannot be flexibly adjusted, reducing the degree of design freedom.

[0005] Therefore, this invention proposes a novel planar end-face coupler. First, a thin waveguide (less than 220 nm) is used to couple the chip waveguide and optical fiber within a relatively large waveguide width. Then, the coupled optical field is divided into TE and TM modes and coupled separately to a thicker (220 nm) waveguide fabricated using standard SOI technology on the same horizontal plane, achieving polarization separation coupling with a silicon photonic chip fabricated using standard CMOS technology. Because the coupling is on the same horizontal plane, in addition to the width of the coupling waveguide itself, the spacing between the two coupling waveguides can also be freely adjusted, thereby improving the coupling bandwidth and efficiency. Summary of the Invention

[0006] The purpose of this invention is to provide a polarization-separated end-face coupler and its linear design method. Through a novel device structure and linear design method, the optical field separation and coupling of TE and TM modes from the optical fiber to the optical chip waveguide is achieved. This solves the problem of mode field mismatch between the optical fiber and the chip waveguide in the optical chip, and also satisfies the problem of polarization-sensitive devices being sensitive to the polarization of the input optical signal.

[0007] A first aspect of the present invention provides a polarization separation end-face coupler, which is composed of a first waveguide and a second waveguide located on the same horizontal plane xy. The first waveguide includes an optical fiber coupling waveguide, a first coupling waveguide, and a TE coupling transmission waveguide. The transverse electric mode (TE) polarization of the optical field coupled in via the optical fiber is output to the optical chip by the TE coupling transmission waveguide, and the transverse magnetic mode (TM) polarization is coupled to the optical chip by the second coupling waveguide, the third coupling waveguide, and the TM transmission waveguide, thereby realizing the polarization separation and coupling of the optical mode field between the optical fiber and the optical chip.

[0008] Specifically, the first waveguide has a sudden change in thickness along the x-direction. The fiber-coupled waveguide and the first coupled waveguide have the same thickness and are both smaller than the TE coupled transmission waveguide. The fiber-coupled waveguide and the first coupled waveguide can be flexibly selected according to the process and actual thickness, and can be realized by a dual etching process.

[0009] Specifically, in the first waveguide, the fiber coupling waveguide is a width-gradient waveguide, whose width gradually increases from the fiber coupling end towards the first coupling waveguide and finally connects to the first coupling waveguide; the thickness and width of the first coupling waveguide remain unchanged, and its height and width are consistent with the end of the fiber coupling waveguide.

[0010] Specifically, the TE-coupled transmission waveguide in the first waveguide is located above the first coupled waveguide and includes a wedge-shaped waveguide and a straight waveguide. The width of the wedge-shaped waveguide tip is smaller than that of the first coupled waveguide, and the width gradually changes linearly until it is consistent with the first coupled waveguide. The first coupled waveguide and the TE-coupled transmission waveguide are closely connected vertically, and their thicknesses match those of the standard SOI substrate.

[0011] Specifically, the waveguide thickness of the second waveguide remains constant, while the spacing and width between it and the first waveguide vary. The spacing between the two waveguides is the distance between their edges. The waveguide spacing and width can be designed according to different operating wavelengths to improve coupling efficiency and increase operating bandwidth. The second and third coupling waveguides are used for coupling TM modes. The initial width of the third coupling waveguide is consistent with the end width of the second coupling waveguide, and the end width is consistent with the initial width of the TM transmission waveguide, while the width of the TM transmission waveguide remains constant. The spacing between the third coupling waveguide and the TM transmission waveguide and the first waveguide, as well as the spacing between the end of the second coupling waveguide and the first waveguide, remains consistent and unchanged. The function of the third coupling waveguide is to prevent the TM modes in the TM transmission waveguide from being recoupled.

[0012] Specifically, the waveguide spacing and waveguide width use a planar structure to enable the coupling of the TM mode between different waveguides. The TE mode generates low loss when propagating in the first waveguide. Therefore, the TM mode is coupled from the first waveguide to the second waveguide, while the TE mode is kept propagating in the first waveguide, thus achieving polarization separation coupling of TM and TE.

[0013] A second aspect of the present invention: a linear design method for a polarization separation end-face coupler, the design method comprising the following steps:

[0014] (1) After determining the width w1 and height h1 of the first coupled waveguide 102, simulation and calculation are performed to obtain the effective refractive index n1,λ of the first waveguide alone at wavelength λ.

[0015] (2) The height of the second waveguide is set to h2. The effective refractive index n2,λ of the second waveguide at wavelength λ is obtained by simulation and calculation. The width of the second waveguide w2 is obtained by interpolation fitting when n1,λ=n2,λ.

[0016] (3) The effective refractive index neff of the two waveguides is obtained by simulation calculation with w1, w2, and two waveguide spacings Gap, h1, and h2 fixed.

[0017] (4) Subtract n1,λ(n2,λ) from neff to obtain the coupling strength g of the two waveguides when the working wavelength is λ;

[0018] (5) Repeat steps (3) and (4) to change the gap, simulate the coupling strength g under different gaps, and then obtain the relationship between the gap and the coupling strength g through interpolation fitting.

[0019] (6) For a set of wavelengths {λ1, λ2, λ3……λi}, given a set of initial coupling strengths {g1, g2, g3……gi}, a set of waveguide spacings {Gap1, Gap2, Gap3……Gapi} is obtained according to the relationship between coupling strength g and Gap; repeat steps (1) and (2) to obtain the widths {w21, w22, w23……w2i} of a set of second waveguides (2) corresponding to this set of wavelengths;

[0020] (7) Perform linear interpolation fitting on {Gap1, Gap2, Gap3……Gapi} and {w21, w22, w23……w2i}, and connect the fitting results. Then take a set of waveguide spacing and waveguide width at linear equal intervals, denoted as {(Gap1, w1), (Gap2, w2), (Gap3, w3),……(Gapn, wn)}, where n is an integer greater than or equal to i, and the number and range of n are taken in the line segment of the connection.

[0021] (8) Obtain the relative y-axis coordinates of the first waveguide and the second waveguide based on a set of equally spaced points (Gapn,wn);

[0022] (9) Distribute n sets of relative coordinates evenly along the x-axis, with a total length of L;

[0023] (10) The length of the fixed coupled waveguide is modeled and simulated using the finite-difference time-domain method (FDTD), and the gap value is optimized through several iterations until the coupling efficiency of each working wavelength λ under the specified coupled waveguide length reaches the maximum or near maximum value, thereby obtaining the required working bandwidth, which is the linear shape of the second coupled waveguide in the second waveguide.

[0024] (11) Add a third coupled waveguide after the second coupled waveguide. The width of the third coupled waveguide is the same as the width of the end of the second coupled waveguide. Then, adjust the coupling length L through simulation to obtain the desired coupled waveguide structure. The coupling length L is the sum of the lengths of the second coupled waveguide and the third coupled waveguide.

[0025] Furthermore, the sum of the thicknesses of the TE-coupled transmission waveguide and the first coupled waveguide is the same as the thickness of the second waveguide. This thickness is compatible with standard SOI optical chips based on CMOS technology, and the width and thickness of the waveguide do not constitute a limitation on the design method.

[0026] A third aspect of the present invention: provides an electronic device comprising:

[0027] One or more processors;

[0028] Memory, used to store one or more programs;

[0029] When the one or more programs are executed by the one or more processors, the one or more processors implement the linear design method of a polarization separation end-face coupler.

[0030] A fourth aspect of the present invention provides a computer-readable storage medium having computer instructions stored thereon, which, when executed by a processor, implement the steps of the linear design method for a polarization separation end-face coupler.

[0031] The beneficial effects of this invention are as follows:

[0032] 1. A planar end-face coupler structure is provided, which uses a thinner waveguide to achieve coupling with optical fiber. The thinner the waveguide, the lower the requirement for photolithography linewidth, thus reducing the fabrication cost. Then, the light is coupled into a standard SOI process silicon waveguide with a thickness of 220nm.

[0033] 2. Based on the characteristics of planar coupled structures, namely that the spacing between waveguides is easy to adjust, a waveguide shape design method is proposed. Different spacings are designed according to the coupling strength at different wavelengths, so that the coupling strength at different working wavelengths can reach the optimal or near-optimal value under a certain coupling length, thereby improving the overall operating bandwidth of the device.

[0034] 3. The entire device and linear design requires only a simple dual-etching process and is compatible with standard CMOS processes. Attached Figure Description

[0035] Figure 1 This is a three-dimensional schematic diagram of a polarization separation end-face coupler in one embodiment of the present invention;

[0036] Figure 2 This is a top view schematic diagram of a polarization separation end-face coupler in one embodiment of the present invention;

[0037] Figure 3 This is an embodiment of the invention showing the variation of coupling strength with waveguide spacing at different wavelengths;

[0038] Figure 4 This is a schematic diagram of the TM coupling segment in one embodiment of the present invention;

[0039] Figure 5 This is a mode field distribution diagram of the TM coupling region in one embodiment of the present invention;

[0040] Figure 6 This is a mode field distribution diagram of the TE coupling region in one embodiment of the present invention.

[0041] Reference numerals: 1-First waveguide; 2-Second waveguide; 3-Upper cladding; 4-Silicon oxide buried layer; 5-Substrate; 6-Fiber coupling end face; 7-Output end face; 8-TM mode coupling region; 9-TE transmission region; 10-Incident fiber; 11-Optical chip system; 101-Fiber coupling waveguide; 102-First coupling waveguide; 103-TE coupling transmission waveguide; 201-Second coupling waveguide; 202-Third coupling waveguide; 203-TM transmission waveguide. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.

[0043] Obviously, the accompanying drawings described below are merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios based on these drawings without any creative effort. Furthermore, it is understood that although the efforts made in this development process may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, any changes to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of this application.

[0044] In this application, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this application may be combined with other embodiments without conflict.

[0045] This embodiment provides a polarization-separating end-face coupler. Figure 1 and Figure 2 This is a schematic diagram of the polarization separation end-face coupler in this embodiment. The specific line shape of the TM mode coupling region 8 can be found in the following diagram. Figure 4 The optical signal is input from the optical fiber, passes through the optical fiber coupling end face 6 and enters the end face coupler, and then enters the optical chip system 11 from the output end face 7 after polarization separation and coupling.

[0046] In this embodiment, the length, thickness, and other parameters of each waveguide are as follows:

[0047] The device consists of a first waveguide 1 and a second waveguide 2 located on the same horizontal plane (xy). The first waveguide 1 includes an optical fiber coupling waveguide 101, a first coupling waveguide 102, and a TE coupling transmission waveguide 103. The optical fiber coupling waveguide 101 is used to couple with an optical fiber and transmit light to the first coupling waveguide 102. The first coupling waveguide 102 couples the coupled TM mode light to another waveguide on the same plane. The optical fiber coupling waveguide 101 has a tip thickness of 150 nm and a width of 160 nm, which then linearly transitions to a tip width of 1100 nm and a height of 150 nm. The x-direction length of the optical fiber coupling waveguide 101 is 120 μm. Following this is the TM mode coupling region 8. The width and thickness of the first coupling waveguide 102 are 1100 nm and 150 nm, respectively. The TM mode is coupled into the second waveguide 2 in this region. The total length of the TM mode coupling region 8 is 160 μm. The TE transmission region 9 is composed of part of the first coupling waveguide 102 and the TE coupling transmission waveguide 103, which is used to transmit the TE mode optical field. The TE coupling transmission waveguide 103 has a thickness of 70nm and a tip width of 180nm. After passing through a gradient region (30um), the width is consistent with the first coupling waveguide 102 at 1100nm. Then, the TE mode optical field is output to the polarization-sensitive optical chip system.

[0048] The width and spacing between the second waveguide 2 and the first waveguide 1 are determined by the operating wavelength. In this embodiment, the operating wavelength is selected as 1260nm-1360nm. The transverse magnetic mode (TM) polarization is output from the second waveguide 2 to the optical chip, thereby realizing the polarization separation and coupling of the optical mode field between the optical fiber and the optical chip. The second waveguide 2 consists of three parts: a second coupling waveguide 201 and a third coupling waveguide 202 for coupling the TM mode, and a TM transmission waveguide 203 for outputting the TM mode light. The initial width of the second coupling waveguide 201 is selected as 0.19µm, the end width is 0.213µm, and its length is 150µm. Specifically, in this embodiment, the initial width of waveguide 202 is 0.213µm, and the end width is linearly varied to 0.5µm. The width of the TM transmission waveguide 203 is the same as that of the third coupling waveguide 202, both being 0.5µm and remaining unchanged. The length of the third coupling waveguide 202 is 10µm.

[0049] Because it is planar coupling (the two coupled waveguides are on the same horizontal plane), unlike traditional vertical coupling (the two waveguides are distributed vertically), the spacing between the two waveguides can be freely adjusted, thus allowing for more flexible design of the waveguide shape and spacing in the coupling region. Based on this, this invention proposes a linear design method for a polarization-separating end-face coupler, specifically for the linear design of the second coupled waveguide 201 and the third coupled waveguide 202, including the width and other parameters of each waveguide mentioned above. The design method is as follows:

[0050] 1) After determining the width (w1) and height h1 of the first coupled waveguide 102, the effective refractive index n1,λ of the first coupled waveguide 101 alone at wavelength λ is calculated by simulation.

[0051] 2) The height of the second waveguide 2 is set to 220nm. The effective refractive index n2,λ of the second waveguide 2 at wavelength λ is obtained by simulation and calculation as a function of the width of the second waveguide 2. The width (w2) of the second waveguide 2 when n1,λ=n2,λ is obtained by interpolation fitting.

[0052] 3) Fix w1, w2, the two waveguide spacing (Gap), h1, h2 and calculate the system effective refractive index neff of the two waveguides by simulation;

[0053] 4) Subtract n1,λ (or n2,λ) from neff to obtain the coupling strength g of the two waveguides when the working wavelength is λ;

[0054] 5) Repeat steps 3) and 4) by changing the gap, and simulate to obtain the coupling strength g under different gaps. Then, obtain the relationship between gap and coupling strength g through interpolation and fitting.

[0055] 6) For a set of wavelengths {λ1, λ2, λ3...λi}, given a set of initial coupling strengths {g1, g2, g3...gi}, a set of waveguide spacings {Gap1, Gap2, Gap3...Gapi} can be obtained based on the relationship between coupling strength and gap; repeat step 2) to obtain a set of widths of the second waveguide 2 {w21, w22, w23...w2i}.

[0056] 7) Perform linear interpolation fitting on {Gap1, Gap2, Gap3...Gap1} and {w21, w22, w23...w2i}, and linearly select a set of waveguide spacing and waveguide width from the fitting results, denoted as {(Gap1, w1), (Gap2, w2), (Gap3, w3), ... (Gapn, wn)}, where n is an integer greater than or equal to i, and the number and range of n are taken from the line segments; for example, n can be 1, 2, 3, 4, ..., 2000, that is, take 2000 pairs of values;

[0057] 8) The relative y-axis coordinates of the first waveguide 1 and the second waveguide 2 can be obtained from (Gapn, wn) (see coordinate axes). Figure 1 )

[0058] 9) Distribute n sets of relative coordinates evenly along the x-axis, with a total length of L1;

[0059] 10) With a fixed waveguide length, modeling and simulation are performed using the finite-difference time-domain method (FDTD), and the gap value is optimized through multiple iterations until the coupling efficiency of each working wavelength λ reaches the maximum or near maximum value under the specified coupled waveguide length, thereby obtaining the required working bandwidth.

[0060] 11) This yields the linear shape of the second coupled waveguide 201 in the second waveguide 2. Then, a third coupled waveguide 202 with a length of L2 is added after the second coupled waveguide 201. The coupling length L2 is fine-tuned through simulation to obtain the desired coupled waveguide structure. The sum of the length L1 of the second coupled waveguide 201 and the length L2 of the third coupled waveguide 202 is the total length of the TM mode coupling region 8.

[0061] In steps 1)-6), the width w1 of the first waveguide 1 is 1100 μm, and h1 is 150 nm. The operating wavelength is selected every 10 nm within the range of 1250 nm to 1370 nm. It should be noted that the selected wavelengths can be any range, and the more the better. However, the larger the wavelength range and the more wavelengths selected, the greater the computational and simulation workload. Considering all factors, this embodiment selects a wavelength every 10 nm within the 1250 nm to 1370 nm band to obtain a better bandwidth in the O-band (1260 nm-1360 nm). The finite-difference time-domain (FDTD) method is used for simulation calculations. The refractive index of silicon, the waveguide material and substrate material, is set to 3.503, and the refractive index of the silicon oxide buried layer 4 and the upper cladding layer 3 is set to 1.4579.

[0062] In this invention, the TM mode is coupled from the first waveguide 1 to the second waveguide 2. Therefore, the effective refractive index calculated in this embodiment is the effective refractive index of the TM mode. However, this linear design method can also be applied to the TE mode. The data obtained from the simulation calculations according to steps 1)-2) are shown in Table 1, which represents the simulation data of effective refractive index, waveguide width, and coupling strength at different wavelengths:

[0063] Table 1

[0064]

[0065] Therefore, the initial width of the second coupling waveguide 201 is selected as 0.19 μm, and the end width is 0.213 μm. In particular, in this embodiment, the initial width of the third coupling waveguide 202 is 0.213 μm, and the end width is linearly changed to 0.5 μm. The width of the TM transmission waveguide 203 is consistent with that of the third coupling waveguide 202, which is 0.5 μm and remains unchanged.

[0066] The relationship between coupling strength and gap at different wavelengths obtained from steps 3)-6) is as follows: Figure 3As shown; according to steps 1)-10) of a linear design method for a polarization separation end-face coupler, a schematic diagram of the 8-wavelength guide shape of the TM coupling region is obtained as follows. Figure 4 As shown.

[0067] Through the above steps, we obtained the structure and parameters of the device in the embodiment. Using the finite-difference time-domain (FDTD) method for modeling and simulation, we determined that the length L1 of the second coupled waveguide 201 is 150 μm, and the length L2 of the third coupled waveguide 202 is 10 μm, meaning the total length of the TM mode coupling region 8 is 160 μm. Simultaneously, we obtained the field distributions for both TE and TM modes, as shown below. Figure 5 and Figure 6 As shown, simulation results indicate that the mode field input from the optical fiber is separated into TE and TM modes and transmitted to the subsequent waveguide, achieving polarization-separated end-face coupling.

[0068] Furthermore, the present invention provides an electronic device comprising:

[0069] One or more processors;

[0070] Memory, used to store one or more programs;

[0071] When the one or more programs are executed by the one or more processors, the one or more processors implement the linear design method of a polarization separation end-face coupler.

[0072] The present invention also provides a computer-readable storage medium storing computer instructions thereon, which, when executed by a processor, implement the steps of the linear design method for a polarization separation end-face coupler.

[0073] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein.

[0074] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope.

Claims

1. A polarization separation end-face coupler, characterized in that, The coupler consists of a first waveguide (1) and a second waveguide (2) located on the same horizontal plane xy. The first waveguide (1) includes an optical fiber coupling waveguide (101), a first coupling waveguide (102), and a TE coupling transmission waveguide (103). The transverse electric mode (TE) polarization of the optical field coupled in through the optical fiber is output to the optical chip through the TE coupling transmission waveguide (103), and the transverse magnetic mode (TM) polarization is coupled and transmitted to the optical chip through the second coupling waveguide (201), the third coupling waveguide (202), and the TM transmission waveguide (203), thereby realizing the polarization separation and coupling of the optical mode field between the optical fiber and the optical chip. The first waveguide (1) has a sudden change in thickness along the x direction. The fiber-coupled waveguide (101) and the first coupled waveguide (102) have the same thickness. The fiber-coupled waveguide (101) and the first coupled waveguide (102) are flexibly selected according to the process and actual thickness, and are realized by a dual etching process. In the first waveguide (1), the TE-coupled transmission waveguide (103) is located above the first coupled waveguide (102), and includes a wedge-shaped waveguide and a straight waveguide. The width of the wedge-shaped waveguide tip is smaller than that of the first coupled waveguide (102), and the width gradually changes linearly, eventually matching the first coupled waveguide (102). The first coupled waveguide (102) and the TE-coupled transmission waveguide (103) are closely connected vertically, and the sum of their thicknesses matches that of a standard SOI substrate. The waveguide thickness of the second waveguide (2) remains constant, while the spacing and width between it and the first waveguide (1) vary. The spacing between the two waveguides is the distance between the two waveguide edges. The waveguide spacing and width can be designed according to different operating wavelengths to improve coupling efficiency and increase operating bandwidth. The second coupling waveguide (201) and the third coupling waveguide (202) are used for coupling in TM mode. The initial width of the third coupling waveguide (202) is consistent with the end width of the second coupling waveguide (201), and the end width is consistent with the initial width of the TM transmission waveguide (203). The width of the TM transmission waveguide (203) remains constant. The spacing between the third coupling waveguide (202) and the TM transmission waveguide (203) and the first waveguide (1) is consistent with and remains constant with the spacing between the end of the second coupling waveguide (201) and the first waveguide (1). The function of its third coupling waveguide (202) is to prevent the TM mode in the TM transmission waveguide (203) from being coupled again.

2. The polarization separation end-face coupler according to claim 1, characterized in that, In the first waveguide (1), the fiber-coupled waveguide (101) is a width-gradient waveguide, whose width gradually increases from the fiber-coupled end face (6) toward the first coupled waveguide (102) and finally connects to the first coupled waveguide (102); the thickness and width of the first coupled waveguide (102) remain unchanged, and its height and width are consistent with the end of the fiber-coupled waveguide (101).

3. A linear design method for a polarization separation end-face coupler as described in any one of claims 1-2, characterized in that, This design method includes the following steps: (1) After determining the width w1 and height h1 of the first coupled waveguide (102), simulation and calculation are performed to obtain the effective refractive index n of the first waveguide (1) at wavelength λ. 1, λ ; (2) The height of the second waveguide is set to h2. The effective refractive index n of the second waveguide at wavelength λ is obtained by simulation and calculation. 2,λ As the width of the second waveguide (2) changes, interpolation fitting is used to obtain the result when n1, λ=n 2,λ The width w2 of the second waveguide (2) is; (3) The effective refractive index n of the two waveguides is obtained by simulation calculation with w1, w2, and the two waveguide spacings Gap, h1, and h2 fixed. eff ; (4) Using n eff Subtract n 1,λ or n 2,λ The coupling strength g between the two waveguides is obtained when the operating wavelength is λ; (5) Repeat steps (3) and (4) to change the gap, simulate the coupling strength g under different gaps, and then obtain the relationship between the gap and the coupling strength g through interpolation fitting. (6) For a set of wavelengths {λ1, λ2, λ3……λ i Given a set of initial coupling strengths {g1, g2, g3...g}, i Based on the relationship between coupling strength g and gap, a set of waveguide spacings {Gap1, Gap2, Gap3...Gap} is obtained. i Repeat steps (1) and (2) to obtain the width {w} of a set of second waveguides (2) corresponding to this set of wavelengths. 21 w 22 w 23 ...w 2i }; (7) For {Gap1, Gap2, Gap3...Gap i } and {w 21 w 22 w 23 ...w 2i Linear interpolation fitting is performed, and the fitting results are connected. Then, a set of waveguide spacings and widths are taken at linear equal intervals, denoted as {(Gap1, w1), (Gap2, w2), (Gap3, w3), ..., (Gap... n w n )}, where n is an integer greater than or equal to i, and the quantity and range of n are taken from the line segments; (8) Based on a set of points taken at equal intervals (Gap) n ,w n The relative y-axis coordinates of the first waveguide (1) and the second waveguide (2) are obtained. (9) Distribute n sets of relative coordinates evenly along the x-axis, with a total length of L; (10) The fixed coupling waveguide length value is modeled and simulated using the finite-difference time-domain method (FDTD), and the gap value is optimized through several iterations until the coupling efficiency of each working wavelength λ under the specified coupling waveguide length reaches the maximum or near maximum value, thereby obtaining the working bandwidth that meets the requirements, that is, the linear shape of the second coupling waveguide (201) in the second waveguide (2); (11) Add a third coupling waveguide (202) after the second coupling waveguide (201). The initial width of the third coupling waveguide (202) is consistent with the width of the end of the second coupling waveguide (201). Then, adjust the coupling length L through simulation to obtain the desired coupling waveguide structure. The coupling length L is the sum of the lengths of the second coupling waveguide (201) and the third coupling waveguide (202).

4. The linear design method for a polarization separation end-face coupler according to claim 3, characterized in that, The sum of the thicknesses of the TE coupled transmission waveguide (103) and the first coupled waveguide (102) is the same as the thickness of the second waveguide (2). This thickness is compatible with standard SOI optical chips based on CMOS technology, and the width and thickness of the waveguides do not constitute a limitation on the design method.

5. An electronic device, characterized in that, include: One or more processors; Memory, used to store one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement the method as described in any one of claims 3-4.

6. A computer-readable storage medium storing computer instructions thereon, characterized in that, When executed by the processor, this instruction implements the steps of the method as described in any one of claims 3-4.

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