End face coupler and preparation method thereof

Abstract

The invention provides an end face coupler and a preparation method thereof, and relates to the technical field of semiconductor devices, and the end face coupler comprises a silicon substrate layer, a silicon dioxide cladding layer and a waveguide layer. The silicon substrate layer comprises a silicon layer and a buried oxide layer arranged on the silicon layer; the silicon dioxide cladding is arranged on the buried oxide layer; the waveguide layer is provided with an end face coupler at the horizontal center of the silicon dioxide cladding; the waveguide layer further comprises a waveguide and a two-section type reverse conical end face coupling structure. The two-section type reverse conical end face coupling structure comprises a first-section reverse conical structure and a second-section reverse conical structure. The wide end of the first-section reverse conical structure is connected with the waveguide, and the tip end of the first-section reverse conical structure is connected with the wide end of the second-section reverse conical structure. Through the method provided by the invention, efficient coupling of the waveguide and the optical fiber is realized, and the feasibility of the waveguide and the optical fiber in large-scale preparation is ensured at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor devices, and in particular to an end face coupler and a preparation method thereof. Background Art

[0002] End couplers are key components for solving the problem of interconnecting optical signals on optoelectronic chips with external optical signals. They are widely used in optical communications, optical computing, and sensing. End couplers are located at the edge of optical chips. Their function is to expand the optical waveguide mode field diameter to match the optical fiber mode field diameter, thereby achieving low-loss, high-performance optical signal transmission. Compared with vertical coupling, end coupling has the advantages of large working bandwidth and low packaging difficulty, and plays an important role in realizing information transmission inside and outside optoelectronic chips.

[0003] The performance indicators of the end coupler mainly include mode field conversion efficiency, mode field matching efficiency, coupling bandwidth, size, etc., among which mode field conversion efficiency and mode field matching efficiency jointly measure the matching degree between the optical waveguide mode field and the optical fiber mode field. The design scheme of the existing technology is to design a reverse cone structure at the waveguide end, and the outer layer is covered with a cladding material with a lower refractive index, so that the mode field localized in the waveguide is diffused into the outer cladding.

[0004] How to achieve efficient coupling between waveguide and optical fiber is a technical problem that needs to be solved at present. Summary of the invention

[0005] The present invention provides an end face coupler and a preparation method thereof, which are used to solve the defects existing in the prior art.

[0006] The present invention provides an end face coupler, comprising: a silicon substrate layer, a silicon dioxide cladding layer and a waveguide layer; The silicon substrate layer comprises: a silicon layer and a buried oxide layer arranged on the silicon layer; The silicon dioxide cladding layer is disposed on the buried oxide layer; The waveguide layer is provided with an end face coupler at the horizontal center of the silicon dioxide cladding; the waveguide layer further comprises: a waveguide and a two-stage reverse tapered end face coupling structure; The two-section reverse cone end face coupling structure comprises: a first section reverse cone structure and a second section reverse cone structure; the wide end of the first section reverse cone structure is connected to the waveguide, and the tip is connected to the wide end of the second section reverse cone structure.

[0007] According to an end face coupler provided by the present invention, the width and height of the connection between the first section of the reverse conical structure and the second section of the reverse conical structure are the same.

[0008] According to an end face coupler provided by the present invention, the side edge slope of the first section of the reverse cone structure is greater than the side edge slope of the second section of the reverse cone structure.

[0009] According to an end face coupler provided by the present invention, the tip of the second section of the reverse tapered structure is used for inputting optical fiber optical signals.

[0010] According to an end face coupler provided by the present invention, the waveguide is a thin film lithium niobate straight waveguide.

[0011] The present invention also provides an optical chip, which includes the structure of the end face coupler as described in any one of the above.

[0012] The present invention also provides a method for preparing an end face coupler, wherein the end face coupler comprises: a silicon substrate layer, a silicon dioxide cladding layer and a waveguide layer; The method comprises: Providing a silicon layer, forming a buried oxide layer on the silicon layer, wherein the silicon layer and the buried oxide layer constitute the silicon substrate layer; forming a waveguide and a two-stage reverse tapered end face coupling structure on the buried oxide layer, wherein the waveguide and the two-stage reverse tapered end face coupling structure constitute the waveguide layer; forming the silicon dioxide cladding layer on the buried oxide layer so that the waveguide and the two-stage reverse tapered end face coupling structure are located at the horizontal center of the silicon dioxide cladding layer; The two-section reverse cone end face coupling structure comprises: a first section reverse cone structure and a second section reverse cone structure; the wide end of the first section reverse cone structure is connected to the waveguide, and the tip is connected to the wide end of the second section reverse cone structure.

[0013] According to a method for preparing an end face coupler provided by the present invention, the side wall inclination angle of the waveguide is set to 70 degrees.

[0014] According to a method for preparing an end face coupler provided by the present invention, a two-stage reverse tapered end face coupling structure is formed on the buried oxide layer, comprising: Determining target parameter values ​​corresponding to a plurality of target parameters of the two-stage reverse tapered end face coupling structure respectively by a time-domain finite difference simulation method; The multiple target parameters include: the tip width of the first section of the reverse cone structure, the tip width of the second section of the reverse cone structure, the cone length, the height of the silicon dioxide cladding, and the width of the silicon dioxide cladding.

[0015] According to a method for preparing an end coupler provided by the present invention, the silicon dioxide cladding is formed on the buried oxide layer so that the waveguide and the two-stage reverse tapered end coupling structure are located behind the horizontal center of the silicon dioxide cladding, and the method further includes: Prepare the end coupler based on a preset processing flow; Among them, the preset processing flow includes, in order of execution: chromium deposition, electron beam exposure, etching of chromium mask, removal of photoresist, inductively coupled plasma ICP dry etching, removal of chromium mask, chemical polishing, deposition of silicon dioxide, ultraviolet exposure, reactive ion RIE etching and end face polishing.

[0016] The present invention provides an end coupler and a preparation method thereof, comprising: a silicon substrate layer, a silicon dioxide cladding layer and a waveguide layer; the silicon substrate layer comprises: a silicon layer and a buried oxide layer arranged on the silicon layer; the silicon dioxide cladding layer is arranged on the buried oxide layer; the waveguide layer is arranged at the horizontal center of the silicon dioxide cladding layer; the waveguide layer also comprises: a waveguide and a two-stage reverse cone end face coupling structure; wherein the two-stage reverse cone end face coupling structure comprises: a first-stage reverse cone structure and a second-stage reverse cone structure; the wide end of the first-stage reverse cone structure is connected to the waveguide, and the tip is connected to the wide end of the second-stage reverse cone structure. It can be seen from this that the present invention realizes efficient coupling of waveguide and optical fiber through a two-stage reverse cone end face coupling structure, while ensuring its feasibility in mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 This is one of the structural schematic diagrams of the end face coupler provided by the present invention.

[0019] Figure 2 This is the second structural schematic diagram of the end face coupler provided by the present invention.

[0020] Figure 3 It is a schematic flow chart of the method for preparing the end face coupler provided by the present invention.

[0021] Figure 4 It is a schematic diagram of TE and TM mode field distribution of the waveguide cross section provided by the present invention.

[0022] Figure 5It is a schematic diagram of the relationship between the output end light field transmittance and the input wavelength provided by the present invention.

[0023] Figure 6 It is a schematic diagram of the light field distribution of the two-stage reverse conical end face coupling structure provided by the present invention.

[0024] Figure 7 It is a schematic diagram of conversion modes at different positions in the waveguide provided by the present invention.

[0025] Figure 8 It is a schematic diagram of the processing flow of the end face coupler provided by the present invention.

[0026] Fig. 9 It is a schematic diagram of the Mach-Zehnder modulator provided by the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] Combine the following Figure 1-Figure 9 An end face coupler and a method for preparing the same are described.

[0029] It should be noted that the performance indicators of the end coupler mainly include mode field conversion efficiency, mode field matching efficiency, coupling bandwidth, size, etc., among which mode field conversion efficiency and mode field matching efficiency jointly measure the matching degree between the optical waveguide mode field and the optical fiber mode field. The design scheme of the prior art is to design a section of reverse cone structure at the end of the waveguide, and the outer layer is covered with a cladding material with a lower refractive index, so that the mode field localized in the waveguide is diffused into the outer cladding. On this basis, in order to further improve the degree of mode field matching, a design scheme of multi-section reverse cone structure and layered etching is proposed, but due to the limitation of the material processing technology level, this design scheme has great difficulties in device preparation and large-scale application. Based on this, the present invention proposes an end coupler to solve at least one of the above problems.

[0030] Figure 1 is one of the structural schematic diagrams of the end face coupler provided by the present invention, such as Figure 1 As shown, the end face coupler comprises: a silicon substrate layer, a silicon dioxide cladding layer and a waveguide layer; The silicon substrate layer comprises: a silicon layer 101 and a buried oxide layer 102 disposed on the silicon layer; The silicon dioxide cladding layer 103 is disposed on the buried oxide layer 102; The waveguide layer 104 is arranged at the horizontal center of the silicon dioxide cladding layer; the waveguide layer further comprises: a waveguide and a two-stage reverse tapered end face coupling structure; The two-section reverse cone end face coupling structure comprises: a first section reverse cone structure and a second section reverse cone structure; the wide end of the first section reverse cone structure is connected to the waveguide, and the tip is connected to the wide end of the second section reverse cone structure.

[0031] It should be noted that the thin-film lithium niobate waveguide is a structure that uses optical waveguide technology to confine and conduct light waves. The light wave is totally reflected at the waveguide interface and is thus confined to an area whose cross-sectional size is only at the wavelength level, which enables the light beam to be effectively conducted. Ultra-high numerical aperture fiber (UHNA7) is a single-mode optical fiber with an ultra-high numerical aperture, whose operating wavelength is usually in the range of 1500-2000nm and whose core diameter is 2.4μm. The embodiment of the present invention realizes efficient coupling of the thin-film lithium niobate waveguide with the ultra-high numerical aperture fiber (UHNA7) by designing a two-stage reverse tapered structure of thin-film lithium niobate.

[0032] Specifically, Figure 2 This is the second structural schematic diagram of the end coupler provided by the present invention, including a three-dimensional overall diagram (a), a top view (b) and a cross-sectional view (c). The orange part is the thin-film lithium niobate straight waveguide and the two-stage reverse tapered end coupling structure, and the blue part is the SiO 2 The buried oxide layer in the cladding and substrate. The gray part is the silicon in the substrate. The left side of the top view is the optical fiber optical signal input port, and the right side is connected to the thin film lithium niobate waveguide. The reverse tapered layer is located in the SiO 2 The horizontal center of the cladding includes two transition structures with different side edge slopes. The wide end of the first reverse tapered structure (Taper1) is connected to the straight waveguide, and the tip is connected to the wide end of the second reverse tapered structure (Taper2). The width and height of the connection structure are the same to ensure the continuity of mode field conversion and reduce transmission loss. The side edges of Taper1 change rapidly, so that the mode field in the waveguide can be fully diffused to the SiO 2 In the cladding, the mode field matching efficiency can be improved; the side edge of Taper2 changes more gently, and on the basis of the effect of Taper1, the mode field confined in the waveguide is further diffused to the cladding, without introducing additional reflection loss, while compensating for the mode field energy lost in Taper1. Compared with the single-stage reverse tapered structure, the design of this embodiment introduces the idea of ​​complementary advantages, and utilizes the different degrees of smoothness of the side edge changes to improve the mode field matching degree between the thin-film lithium niobate waveguide and the UHNA7 optical fiber without introducing additional reflection loss as much as possible.

[0033] The above is a structural description of the end face coupler provided by the present invention. From the description of the above structure, it can be seen that the end face coupler provided by the present invention includes: a silicon substrate layer, a silica cladding and a waveguide layer; the silicon substrate layer includes: a silicon layer and a buried oxide layer arranged on the silicon layer; the silica cladding is arranged on the buried oxide layer; the waveguide layer is arranged at the horizontal center of the silica cladding; the waveguide layer also includes: a waveguide and a two-stage reverse cone end face coupling structure; wherein the two-stage reverse cone end face coupling structure includes: a first section reverse cone structure and a second section reverse cone structure; the wide end of the first section reverse cone structure is connected to the waveguide, and the tip is connected to the wide end of the second section reverse cone structure. It can be seen that the present invention realizes efficient coupling of waveguide and optical fiber through a two-stage reverse cone end face coupling structure, while ensuring its feasibility in mass production.

[0034] The present invention also provides an optical chip, which includes the structure of the end face coupler as described in any one of the above.

[0035] The following is a description of a method for preparing the end face coupler provided by the present invention. The method for preparing the end face coupler described below and the end face coupler described above can be referred to each other.

[0036] Figure 3 is a schematic flow chart of a method for preparing an end face coupler provided by the present invention, such as Figure 3 As shown, the method for preparing an end face coupler provided by the present invention comprises: a silicon substrate layer, a silicon dioxide cladding layer and a waveguide layer; The method comprises: Step 310: Provide a silicon layer, and form a buried oxide layer on the silicon layer. The silicon layer and the buried oxide layer constitute the silicon substrate layer.

[0037] Step 320: forming a waveguide and a two-stage reverse tapered end face coupling structure on the buried oxide layer, wherein the waveguide and the two-stage reverse tapered end face coupling structure constitute the waveguide layer.

[0038] Step 330, forming the silicon dioxide cladding layer on the buried oxide layer so that the waveguide and the two-stage reverse tapered end face coupling structure are located at the horizontal center of the silicon dioxide cladding layer; The two-section reverse cone end face coupling structure comprises: a first section reverse cone structure and a second section reverse cone structure; the wide end of the first section reverse cone structure is connected to the waveguide, and the tip is connected to the wide end of the second section reverse cone structure.

[0039] It should be noted that the embodiment of the present invention designs the two-stage reverse tapered end face coupling structure and the waveguide size respectively. Among them, the waveguide structure is mainly designed for its cutoff condition, and the two-stage reverse tapered end face coupling structure of the main body is optimized by the simulation method of finite difference time domain (FDTD) for structural parameters.

[0040] Specifically, the design of the thin-film lithium niobate waveguide structure is mainly achieved by adjusting the width of the waveguide, taking into account two factors: one is the transmission loss, and the other is the single-mode condition. If the waveguide width is too small, the ability to support guided mode transmission is weak, resulting in excessive transmission loss and low mode field conversion efficiency; if the waveguide width is too large, high-order modes will appear, and multiple modes will propagate in the waveguide at the same time, making it impossible to achieve efficient coupling with the optical fiber. During the design, the side wall inclination angle was set to 70°, taking into account the inclination of the waveguide side wall caused by the process. After parameter scanning, single-mode transmission can be achieved within a certain range of waveguide dimensions. Taking a width of 800nm ​​and a height of 400nm as an example, Figure 4 TE and TM mode field distribution diagram of the waveguide cross section provided by the present invention. The TE and TM mode field distribution diagram of the waveguide cross section is shown in FIG. Figure 4 As shown in the figure, it can be seen that the structure has a good confinement effect on the TE mode, and the effective refractive index is 1.703 at this time.

[0041] Furthermore, step 320 forms a two-stage reverse tapered end face coupling structure on the buried oxide layer, including: Determining target parameter values ​​corresponding to a plurality of target parameters of the two-stage reverse tapered end face coupling structure respectively by a time-domain finite difference simulation method; The multiple target parameters include: the tip width of the first section of the reverse cone structure, the tip width of the second section of the reverse cone structure, the cone length, the height of the silicon dioxide cladding, and the width of the silicon dioxide cladding.

[0042] Specifically, the design of the two-stage reverse tapered end face coupling structure is mainly realized by the time-domain finite difference simulation method. The designable parameters in the structure are: Taper1 tip width W 1 、Taper2 tip width W 2 , taper length L and SiO 2 The height H and width W of the cladding are scanned during design, and the light field transmittance T is used as the evaluation index. Figure 5 The relationship between the output light field transmittance and the input wavelength provided by the present invention is shown in FIG. Figure 5 As shown in the figure, at the working wavelength of 1550nm, the light field transmittance is 0.940, corresponding to the mode field conversion efficiency It is 94.0%, and the 0.5dB bandwidth of transmission loss is ~300nm (1500nm~1800nm). Figure 6 Schematic diagram of the light field distribution of the two-stage reverse conical end face coupling structure provided by the present invention. The light field distribution of the two-stage reverse conical end face coupling structure is as follows Figure 6 As shown, the light field can be seen to gradually leak into the cladding. Figure 7 is a schematic diagram of conversion modes at different positions in the waveguide provided by the present invention, Figure 2 The conversion patterns at positions ①, ②, and ③ in (a) are as follows: Figure 7 As shown in the figure, it can be seen that during the propagation process, the reverse cone structure gradually narrows, and the binding ability of the light field decreases. The mode field in the structure moves toward the SiO2 coated outside the reverse cone. 2 The mode field size gradually expands as it diffuses in the cladding, achieving matching with the UHNA7 fiber mode field. The overlap integral of the UHNA7 fiber eigenmode and the mode at the tip is calculated. The mode field overlap integral is 0.934 at a wavelength of 1550nm, corresponding to the mode field matching efficiency is 93.4%, and the total coupling efficiency is , Multiplying them together, it is 87.8%, corresponding to a coupling loss of 0.57dB / face; the light field transmittance at 1800nm ​​wavelength is about 0.850, the mode field overlap integral is 0.918, the total coupling efficiency is 78.1%, and the corresponding coupling loss is 1.07dB / face, and the 0.5dB coupling bandwidth of the end face coupler is about 250nm (1550nm~1800nm). Compared with the traditional single-stage reverse cone structure and the complex multi-stage gradient structure, the design in the embodiment of the present invention has made a trade-off in improving the coupling efficiency and reducing the process difficulty, so as to achieve better results, and the simulated coupling loss can be as low as 0.57dB / face.

[0043] The present invention provides a method for preparing an end face coupler, wherein the end face coupler comprises: a silicon substrate layer, a silicon dioxide cladding layer and a waveguide layer; the method comprises: providing a silicon layer, forming a buried oxide layer on the silicon layer, wherein the silicon layer and the buried oxide layer constitute the silicon substrate layer; forming a waveguide and a two-stage reverse cone end face coupling structure on the buried oxide layer, wherein the waveguide and the two-stage reverse cone end face coupling structure constitute the waveguide layer; forming the silicon dioxide cladding layer on the buried oxide layer so that the waveguide and the two-stage reverse cone end face coupling structure are located at the horizontal center of the silicon dioxide cladding; wherein the two-stage reverse cone end face coupling structure comprises: a first-stage reverse cone structure and a second-stage reverse cone structure; the wide end of the first-stage reverse cone structure is connected to the waveguide, and the tip is connected to the wide end of the second-stage reverse cone structure. It can be seen from this that the present invention realizes efficient coupling of waveguide and optical fiber through a two-stage reverse cone end face coupling structure, while ensuring its feasibility in mass production.

[0044] Based on the above embodiment, in this embodiment, after forming the silicon dioxide cladding on the buried oxide layer in step 330 so that the waveguide and the two-stage reverse tapered end face coupling structure are located at the horizontal center of the silicon dioxide cladding, the method further includes: Prepare the end coupler based on a preset processing flow; Among them, the preset processing flow includes, in order of execution: chromium deposition, electron beam exposure, etching of chromium mask, removal of photoresist, inductively coupled plasma ICP dry etching, removal of chromium mask, chemical polishing, deposition of silicon dioxide, ultraviolet exposure, reactive ion RIE etching and end face polishing.

[0045] It should be noted that LNOI, the full name of which is Lithium Niobate on Insulator, is a material widely used in integrated optoelectronic technology.

[0046] Specifically, the substrate for preparing the device is LNOI, wherein the device layer is a thin film lithium niobate. Figure 8 FIG. 1 is a schematic diagram of the processing flow of the end face coupler provided by the present invention. Figure 8 As shown in the figure, the processing flow of the device includes: Cr deposition, depositing a layer of chromium (Cr) on the LNOI substrate as a mask for subsequent processing; EB exposure, using electron beam (EB) for exposure to define the pattern to be etched; etching the chromium mask, completely etching the Cr mask part without photoresist coverage to facilitate the subsequent thin-film lithium niobate waveguide etching step; ICP dry etching, using inductively coupled plasma (ICP) for dry etching to remove the unnecessary lithium niobate thin film part; removing the Cr mask, removing the remaining Cr mask to expose the final device structure; chemical polishing, chemically polishing the device to improve its surface quality; depositing silicon dioxide, depositing a layer of silicon dioxide on the device to protect the device or as a dielectric layer for other functions; UV exposure and RIE etching, using UV light for exposure, and using reactive ion etching (RIE) technology to further process the device; end face polishing is completed, and the end face of the device is polished to complete the processing flow of the entire device.

[0047] Based on the above embodiments, in this embodiment, Fig. 9 Schematic diagram of the Mach-Zehnder modulator provided by the present invention, such as Fig. 9 As shown in FIG. 1 , the structure can be used for a Mach-Zehnder modulator. The green part in the figure is a thin-film lithium niobate layer, and the two-stage reverse tapered end face coupling structure is located at both ends. The blue part in the figure is a silicon dioxide cladding layer covering the end face coupling structure.

[0048] The embodiment of the present invention provides an end face coupler and a method for preparing the same, and proposes a design method and structure for a low insertion loss end face coupler on a thin-film lithium niobate platform, which can effectively improve the coupling efficiency and reduce the difficulty of process manufacturing compared to the traditional end face coupling structure. The embodiment of the present invention performs corresponding verification simulations and proposes feasible process steps, which makes it possible to prepare the structure.

[0049] The device embodiments described above are merely illustrative, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Those of ordinary skill in the art may understand and implement it without creative work.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An end coupler, characterized in that: include: silicon substrate layer, silicon dioxide cladding layer and waveguide layer; The silicon substrate layer comprises: a silicon layer and a buried oxide layer arranged on the silicon layer; The silicon dioxide cladding layer is disposed on the buried oxide layer; The waveguide layer is provided with an end face coupler at the horizontal center of the silicon dioxide cladding; the waveguide layer further comprises: a waveguide and a two-stage reverse tapered end face coupling structure; The two-section reverse cone end face coupling structure comprises: a first section reverse cone structure and a second section reverse cone structure; the wide end of the first section reverse cone structure is connected to the waveguide, and the tip is connected to the wide end of the second section reverse cone structure.

2. The end coupler according to claim 1, characterized in that: The width and height of the connection between the first section of the reverse conical structure and the second section of the reverse conical structure are the same.

3. The end coupler according to claim 1, characterized in that: The side edge slope of the first section of the reverse cone structure is greater than the side edge slope of the second section of the reverse cone structure.

4. The end coupler according to claim 1, characterized in that: The tip of the second section of the reverse tapered structure is used for inputting optical fiber optical signals.

5. The end coupler according to any one of claims 1 to 4, characterized in that: The waveguide is a thin film lithium niobate straight waveguide.

6. An optical chip, characterized in that: The optical chip comprises the structure of the end face coupler as described in any one of claims 1-5.

7. A method for preparing an end coupler, characterized in that: The end face coupler comprises: a silicon substrate layer, a silicon dioxide cladding layer and a waveguide layer; The method comprises: Providing a silicon layer, forming a buried oxide layer on the silicon layer, wherein the silicon layer and the buried oxide layer constitute the silicon substrate layer; forming a waveguide and a two-stage reverse tapered end face coupling structure on the buried oxide layer, wherein the waveguide and the two-stage reverse tapered end face coupling structure constitute the waveguide layer; forming the silicon dioxide cladding layer on the buried oxide layer so that the waveguide and the two-stage reverse tapered end face coupling structure are located at the horizontal center of the silicon dioxide cladding layer; The two-section reverse cone end face coupling structure comprises: a first section reverse cone structure and a second section reverse cone structure; the wide end of the first section reverse cone structure is connected to the waveguide, and the tip is connected to the wide end of the second section reverse cone structure.

8. The method for preparing an end coupler according to claim 7, characterized in that: The side wall inclination angle of the waveguide was set to 70 degrees.

9. The method for preparing an end coupler according to claim 7, characterized in that: The two-stage reverse tapered end face coupling structure is formed on the buried oxide layer, comprising: Determining target parameter values ​​corresponding to a plurality of target parameters of the two-stage reverse tapered end face coupling structure respectively by a time-domain finite difference simulation method; The multiple target parameters include: the tip width of the first section of the reverse cone structure, the tip width of the second section of the reverse cone structure, the cone length, the height of the silicon dioxide cladding, and the width of the silicon dioxide cladding.

10. The method for preparing an end coupler according to claim 7, characterized in that: The silicon dioxide cladding is formed on the buried oxide layer so that the waveguide and the two-stage reverse tapered end face coupling structure are located behind the horizontal center of the silicon dioxide cladding, and the method further includes: Prepare the end coupler based on a preset processing flow; Among them, the preset processing flow includes, in order of execution: chromium deposition, electron beam exposure, etching of chromium mask, removal of photoresist, inductively coupled plasma ICP dry etching, removal of chromium mask, chemical polishing, deposition of silicon dioxide, ultraviolet exposure, reactive ion RIE etching and end face polishing.

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