Grating Coupler Based on Double-Layer Silicon Nitride Structure and Its Fabrication Method

Abstract

This invention provides a grating coupler based on a double-layer silicon nitride structure and its fabrication method, comprising a substrate, a first silicon dioxide layer, a lower silicon nitride grating, a lower silicon nitride waveguide, a second silicon dioxide layer, an upper silicon nitride grating, an upper silicon nitride waveguide, and a third silicon dioxide layer. The upper silicon nitride grating couples a portion of the input light into the upper silicon nitride waveguide, while the other portion of the input light passes through the upper silicon nitride grating and is incident on the substrate as transmitted light. The lower silicon nitride grating reflects a portion of the transmitted light back to the upper silicon nitride grating and couples it into the upper silicon nitride waveguide. The other portion of the transmitted light enters the lower silicon nitride grating and couples into the lower silicon nitride waveguide, and then couples into the upper silicon nitride waveguide. The grating coupler of this invention has a coupling efficiency of over 60% for input light with wavelengths of 1530 nm to 1565 nm, and a 1 dB bandwidth greater than 100 nm.

Description

Technical Field

[0001] This invention belongs to the field of photonic device design and manufacturing, and in particular relates to a grating coupler based on a double-layer silicon nitride structure and its fabrication method. Background Technology

[0002] The development of silicon-based optoelectronics compatible with CMOS technology has integrated low-cost silicon chip manufacturing technologies with optical technologies, breaking down the traditional boundaries between electronic computing and fiber optic communication. Simultaneously, the development of high-speed electronic circuits based on silicon CMOS technology has made it possible to integrate high-performance optical paths and circuits into single-chip devices with specific functions. SOI is an abbreviation for Silicon-On-Insulator. An SOI substrate consists of a silicon substrate layer, a silicon dioxide intermediate layer, and a top silicon layer stacked from bottom to top, with the silicon substrate layer, silicon dioxide intermediate layer, and top silicon layer parallel to each other. Currently, silicon-based optoelectronic devices compatible with CMOS technology are fabricated on SOI (silicon-on-insulator) substrates.

[0003] Over the years, numerous silicon-based optoelectronic devices have emerged, including optical switches, polarization mode splitters, wavelength division multiplexers / demultiplexers, optical filters, and optical modems. Grating couplers play a crucial role in these devices, forming the foundation of their design and providing a highly effective method for beam coupling between photonic integrated circuits and external optical fibers. Therefore, the development of silicon-based grating couplers has significant practical value and real-world implications. A grating coupler uses the diffraction effect of a grating to couple incident light into an optical waveguide for propagation. Gratings, used to implement coupler functions, offer advantages such as flexible placement and ease of wafer-level testing, leading to their widespread use in silicon-based optical integrated chips.

[0004] Optical couplers act as bridges for light transmission between optical waveguides and optical fibers. Depending on the coupling method, couplers can be classified into grating couplers and inverted conical waveguide couplers. Grating couplers use the diffraction effect of gratings to couple light waves from the optical fiber into the waveguide. Grating couplers offer advantages such as high spatial freedom, simple fabrication, and ease of wafer-level testing; however, their coupling efficiency is low. Silicon nitride (SiN) materials, on the other hand, possess advantages such as lower nonlinearity, low loss, and the ability to allow for larger energy inputs, giving them a natural advantage in applications requiring higher energy inputs. Single-layer uniform grating couplers based on SiN materials have relatively large bandwidths, reaching 68nm per dB, but their coupling efficiency is only 38%. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a grating coupler based on a double-layer silicon nitride structure and its fabrication method, so as to solve the problem of low coupling efficiency of single-layer uniform grating couplers based on silicon nitride (SiN) material in the prior art.

[0006] To achieve the above and other related objectives, the present invention provides a grating coupler based on a double-layer silicon nitride structure. The grating coupler includes: a substrate; a first silicon dioxide layer disposed on the substrate; a lower silicon nitride grating disposed on the first silicon dioxide layer; a lower silicon nitride waveguide disposed on the first silicon dioxide layer and connected to the lower silicon nitride grating; a second silicon dioxide layer disposed on the lower silicon nitride grating and the lower silicon nitride waveguide; an upper silicon nitride grating disposed on the second silicon dioxide layer; an upper silicon nitride waveguide disposed on the second silicon dioxide layer and connected to the upper silicon nitride grating; and a third silicon dioxide layer disposed on the upper silicon nitride grating and the lower silicon nitride waveguide. The upper silicon nitride waveguide is described above; wherein, when input light enters the grating coupler, the upper silicon nitride grating couples a portion of the input light into the upper silicon nitride waveguide, and the other portion of the input light passes through the upper silicon nitride grating and is incident on the substrate to form transmitted light. The lower silicon nitride grating reflects a portion of the transmitted light back to the upper silicon nitride grating, and is coupled into the upper silicon nitride waveguide by the upper silicon nitride grating. The other portion of the transmitted light enters the lower silicon nitride grating, and is coupled into the lower silicon nitride waveguide by the lower silicon nitride grating, and then coupled into the upper silicon nitride waveguide by the lower silicon nitride waveguide, and finally outputs from the upper silicon nitride waveguide.

[0007] Optionally, the lower silicon nitride grating includes multiple parallel and spaced first silicon nitride grating strips, and the upper silicon nitride grating includes multiple parallel and spaced second silicon nitride grating strips.

[0008] Optionally, the lower silicon nitride grating may further include a first silicon nitride connection portion between adjacent first silicon nitride grating strips, wherein the thickness of the first silicon nitride connection portion is less than the thickness of the first silicon nitride grating strip.

[0009] Optionally, the upper silicon nitride grating may further include a second silicon nitride connection between adjacent second silicon nitride grating bars, wherein the thickness of the silicon nitride connection is less than the thickness of the second silicon nitride grating bar.

[0010] Optionally, the lower silicon nitride grating further includes a first silicon nitride connection portion between adjacent first silicon nitride gate strips, the thickness of the first silicon nitride connection portion being less than the thickness of the first silicon nitride gate strip; and the upper silicon nitride grating further includes a second silicon nitride connection portion between adjacent second silicon nitride gate strips, the thickness of the second silicon nitride connection portion being less than the thickness of the second silicon nitride gate strip.

[0011] Optionally, the grating coupler based on the double-layer silicon nitride structure has a coupling efficiency of over 60% for input light with wavelengths of 1530nm to 1565nm.

[0012] Optionally, the 1dB bandwidth of the grating coupler based on the double-layer silicon nitride structure is greater than 100nm.

[0013] This invention also provides a method for fabricating a grating coupler based on a double-layer silicon nitride structure. The method includes the following steps: providing a substrate and forming a first silicon dioxide layer on the substrate; forming a first silicon nitride layer on the first silicon dioxide layer and etching the first silicon nitride layer to form a lower silicon nitride grating and a lower silicon nitride waveguide connected to the lower silicon nitride grating on the first silicon dioxide layer; forming a second silicon dioxide layer on the lower silicon nitride grating and the lower silicon nitride waveguide; forming a second silicon nitride layer on the second silicon dioxide layer and etching the second silicon nitride layer to form an upper silicon nitride grating and an upper silicon nitride waveguide connected to the upper silicon nitride grating on the second silicon dioxide layer. A third silicon dioxide layer is formed on the upper silicon nitride grating and the upper silicon nitride waveguide; wherein, when input light enters the grating coupler, the upper silicon nitride grating couples part of the input light into the upper silicon nitride waveguide, and the other part of the input light passes through the upper silicon nitride grating and is incident on the substrate to form transmitted light, the lower silicon nitride grating reflects part of the transmitted light back to the upper silicon nitride grating, and is coupled into the upper silicon nitride waveguide by the upper silicon nitride grating, the other part of the transmitted light enters the lower silicon nitride grating, and is coupled into the lower silicon nitride waveguide by the lower silicon nitride grating, and then coupled into the upper silicon nitride waveguide by the lower silicon nitride waveguide.

[0014] Optionally, the lower silicon nitride grating formed by etching includes multiple parallel and spaced-apart first silicon nitride gratings, and the upper silicon nitride grating formed by etching includes multiple parallel and spaced-apart second silicon nitride gratings.

[0015] Optionally, during the etching process of the first silicon nitride layer, a portion of the first silicon nitride layer between adjacent first silicon nitride gate strips is retained to form a first silicon nitride connection portion, wherein the thickness of the first silicon nitride connection portion is less than the thickness of the first silicon nitride gate strip.

[0016] Optionally, during the etching process of the second silicon nitride layer, a portion of the second silicon nitride layer between adjacent second silicon nitride gate strips is retained to form a second silicon nitride connection portion, wherein the thickness of the second silicon nitride connection portion is less than the thickness of the second silicon nitride gate strip.

[0017] Optionally, during the etching of the first silicon nitride layer, a portion of the first silicon nitride layer between adjacent first silicon nitride gate strips is retained to form a first silicon nitride connection portion, the thickness of the first silicon nitride connection portion being less than the thickness of the first silicon nitride gate strip; during the etching of the second silicon nitride layer, a portion of the second silicon nitride layer between adjacent second silicon nitride gate strips is retained to form a second silicon nitride connection portion, the thickness of the second silicon nitride connection portion being less than the thickness of the second silicon nitride gate strip.

[0018] Optionally, the fabricated grating coupler based on the double-layer silicon nitride structure has a coupling efficiency of over 60% for input light with wavelengths of 1530nm to 1565nm, and the 1dB bandwidth of the fabricated grating coupler based on the double-layer silicon nitride structure is greater than 100nm.

[0019] As described above, the grating coupler based on a double-layer silicon nitride structure and its fabrication method of the present invention have the following beneficial effects:

[0020] In this invention, when input light enters the grating coupler, the upper silicon nitride grating couples a portion of the input light into the upper silicon nitride waveguide, while the other portion passes through the upper silicon nitride grating and is incident on the substrate, forming transmitted light. The lower silicon nitride grating reflects a portion of the transmitted light back to the upper silicon nitride grating, and then couples it into the upper silicon nitride waveguide. The other portion of the transmitted light enters the lower silicon nitride grating and is coupled into the lower silicon nitride waveguide, and then from the lower silicon nitride waveguide into the upper silicon nitride waveguide. Through this double-layer silicon nitride structure, the energy of light transmitted through the upper silicon nitride grating can be reused, thereby improving the coupling efficiency and 1dB bandwidth of the grating coupler.

[0021] The grating coupler based on the double-layer silicon nitride structure of the present invention has a coupling efficiency of over 60% for input light with wavelengths of 1530nm to 1565nm, and especially for input light with a wavelength of 1550nm, the coupling efficiency can reach 62%, which is significantly higher than the coupling efficiency of traditional single-layer uniform silicon nitride gratings. At the same time, the 1dB bandwidth of the grating coupler based on the double-layer silicon nitride structure of the present invention is greater than 100nm. Attached Figure Description

[0022] Figures 1 to 8The diagram shows the structural schematics of each step in the fabrication method of the grating coupler based on a double-layer silicon nitride structure according to Embodiment 1 of the present invention. Figure 8 The diagram shown is a schematic diagram of a grating coupler based on a double-layer silicon nitride structure according to Embodiment 1 of the present invention.

[0023] Figure 9 The diagram shown is a schematic diagram of the principle of the grating coupler based on the double-layer silicon nitride structure in Embodiment 1 of the present invention.

[0024] Figure 10 The graph shown is a wavelength-coupling efficiency curve of a grating coupler based on a double-layer silicon nitride structure according to Embodiment 1 of the present invention.

[0025] Figure 11 The diagram shown is a schematic diagram of a grating coupler based on a double-layer silicon nitride structure according to Embodiment 2 of the present invention.

[0026] Figure 12 The diagram shown is a schematic diagram of a grating coupler based on a double-layer silicon nitride structure according to Embodiment 3 of the present invention.

[0027] Figure 13 The diagram shown is a schematic diagram of a grating coupler based on a double-layer silicon nitride structure according to Embodiment 4 of the present invention.

[0028] Component designation explanation

[0029] 101 substrate

[0030] 102 First silicon dioxide layer

[0031] 103 First silicon nitride layer

[0032] 104 Lower silicon nitride grating

[0033] 105 Lower layer silicon nitride waveguide

[0034] 106 Second silicon dioxide layer

[0035] 107 Second silicon nitride layer

[0036] 108 Upper silicon nitride grating

[0037] 109 Upper silicon nitride waveguide

[0038] 110 Third silicon dioxide layer

[0039] 111 First silicon nitride connector

[0040] 112 Second silicon nitride connector Detailed Implementation

[0041] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0042] In the detailed description of embodiments of the present invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged and not to scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. In actual fabrication, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0043] For ease of description, spatial relation terms such as “below,” “under,” “lower than,” “below,” “above,” and “upper” may be used herein to describe the relationship between one element or feature shown in the accompanying drawings and other elements or features. It will be understood that these spatial relation terms are intended to include directions other than those depicted in the drawings for devices in use or operation. Furthermore, when a layer is referred to as being “between” two layers, it may be the only layer between the two layers, or there may be one or more layers in between.

[0044] In the context of this application, the structure described above the first feature may include embodiments in which the first and second features are formed in direct contact, or embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

[0045] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0046] Example 1

[0047] like Figure 8 As shown, this embodiment provides a grating coupler based on a double-layer silicon nitride structure. The grating coupler includes: a substrate 101, a first silicon dioxide layer 102, a lower silicon nitride grating 104, a lower silicon nitride waveguide 105, a second silicon dioxide layer 106, an upper silicon nitride grating 108, an upper silicon nitride waveguide 109, and a third silicon dioxide layer 110.

[0048] The substrate 101 can be an SOI wafer or a Si substrate.

[0049] like Figure 8 As shown, the first silicon dioxide layer 102 is disposed on the substrate 101. For SOI wafers, the original Si top layer on the SOI wafer can be etched away by processes such as photolithography and etching, leaving the Si substrate and the first silicon dioxide layer 102 thereon. For Si substrates, the first silicon dioxide layer 102 of a certain thickness can be directly grown on the surface of the Si substrate by thermal oxidation.

[0050] like Figure 8 As shown, the lower silicon nitride grating 104 is disposed on the first silicon dioxide layer 102. In this embodiment, the lower silicon nitride grating 104 includes a plurality of parallel and spaced-apart first silicon nitride grating strips.

[0051] like Figure 8 As shown, the lower silicon nitride waveguide 105 is disposed on the first silicon dioxide layer 102 and connected to the lower silicon nitride grating 104.

[0052] like Figure 8 As shown, the second silicon dioxide layer 106 is disposed on the lower silicon nitride grating 104 and the lower silicon nitride waveguide 105.

[0053] like Figure 8 As shown, the upper silicon nitride grating 108 is disposed on the second silicon dioxide layer 106. The upper silicon nitride grating 108 includes a plurality of parallel and spaced-apart second silicon nitride grating strips. In this embodiment, the lower silicon nitride grating 104 is displaced from the upper silicon nitride grating 108 to enhance the coupling efficiency of light reflected from the lower silicon nitride grating 104 back to the upper silicon nitride grating 108.

[0054] like Figure 8 As shown, the upper silicon nitride waveguide 109 is disposed on the second silicon dioxide layer 106 and connected to the upper silicon nitride grating 108. For example, the upper silicon nitride waveguide 109 can be configured as a tapered waveguide, the width of which is equal to or close to the width of the upper silicon nitride grating 108 to improve the coupling efficiency between the upper silicon nitride waveguide 109 and the upper silicon nitride grating 108, and the width of which is equal to or close to the width of the front waveguide to be coupled to improve the coupling efficiency of the output light from the upper silicon nitride waveguide 109. In this embodiment, the upper silicon nitride waveguide 109 and the lower silicon nitride waveguide 105 have an overlapping portion, so that the light from the lower silicon nitride waveguide 105 can be coupled into the upper silicon nitride waveguide 109 and the coupling efficiency is guaranteed.

[0055] like Figure 8 As shown, the third silicon dioxide layer 110 is disposed on the upper silicon nitride grating 108 and the upper silicon nitride waveguide 109.

[0056] Figure 9 This is a schematic diagram of the grating coupler based on a double-layer silicon nitride structure in this embodiment. Figure 9 As shown, when the input light 20 enters the grating coupler, the upper silicon nitride grating 108 couples a portion 201 of the input light into the upper silicon nitride waveguide 109, while the other portion 202 of the input light passes through the upper silicon nitride grating 108 and is directed toward the substrate 101 to form transmitted light. The lower silicon nitride grating 104 reflects a portion 203 of the transmitted light back to the upper silicon nitride grating 108, and then couples it into the upper silicon nitride waveguide 109. The other portion 204 of the transmitted light enters the lower silicon nitride grating 104, and then couples it into the lower silicon nitride waveguide 105, which in turn couples it into the upper silicon nitride waveguide 109, and finally outputs the light from the upper silicon nitride waveguide 109. In addition, by designing the length of the silicon nitride waveguide and the relative displacement of the upper and lower silicon nitride gratings, the present invention can make the light in the lower silicon nitride waveguide 105 almost completely coupled into the upper silicon nitride waveguide 109 and output from the upper silicon nitride waveguide 109, thereby achieving a high coupling efficiency.

[0057] Figure 10 The image shown is a wavelength-coupling efficiency curve of the grating coupler based on a double-layer silicon nitride structure in this embodiment. Figure 10 As shown, in this embodiment, the grating coupler based on the double-layer silicon nitride structure has a coupling efficiency of over 60% for input light with wavelengths of 1530nm to 1565nm, and particularly achieves a coupling efficiency of up to 62% for input light with a wavelength of 1550nm. The 1dB bandwidth of the grating coupler based on the double-layer silicon nitride structure is greater than 100nm.

[0058] like Figures 1 to 8 As shown, the present invention also provides a method for fabricating a grating coupler based on a double-layer silicon nitride structure, the method comprising the following steps:

[0059] like Figures 1-2 As shown, step 1) is performed first, a substrate 101 is provided, and a first silicon dioxide layer 102 is formed on the substrate 101.

[0060] The substrate 101 can be an SOI wafer or a Si substrate. For an SOI wafer, the original Si top layer on the SOI wafer can be etched away using processes such as photolithography and etching, leaving the Si substrate and its first silicon dioxide layer 102. For a Si substrate, a first silicon dioxide layer 102 of a certain thickness can be directly grown on the surface of the Si substrate using thermal oxidation. In this embodiment, the substrate 101 is selected as a Si substrate.

[0061] like Figures 3-4 As shown, step 2) is then performed, where a first silicon nitride layer 103 is formed on the first silicon dioxide layer 102 using low-pressure chemical vapor deposition (LPCVD) or plasma-enhanced chemical vapor deposition (PECVD). The first silicon nitride layer 103 is then etched using photolithography and etching processes to form a lower silicon nitride grating 104 and a lower silicon nitride waveguide 105 connected to the lower silicon nitride waveguide 105 on the first silicon dioxide layer 102. In this embodiment, the lower silicon nitride grating 104 formed by etching includes multiple parallel and spaced-apart first silicon nitride grating strips.

[0062] like Figure 5 As shown, then step 3) is performed, in which a second silicon dioxide layer 106 is formed on the lower silicon nitride grating 104 and the lower silicon nitride waveguide 105 using plasma enhanced chemical vapor deposition (PECVD), and the second silicon dioxide layer 106 is polished by chemical mechanical polishing (CMP) to obtain a flat surface.

[0063] like Figures 6-7 As shown, step 4) is then performed, where a second silicon nitride layer 107 is formed on the second silicon dioxide layer 106 using low-pressure chemical vapor deposition (LPCVD) or plasma-enhanced chemical vapor deposition (PECVD). The second silicon nitride layer 107 is then etched using photolithography and etching processes to form an upper silicon nitride grating 108 and an upper silicon nitride waveguide 109 connected to the upper silicon nitride waveguide 109 on the second silicon dioxide layer 106. In this embodiment, the upper silicon nitride grating 108 formed by etching includes multiple parallel and spaced-apart second silicon nitride grating strips.

[0064] For example, the upper silicon nitride waveguide 109 can be configured as a tapered waveguide, the width of which is equal to or close to the width of the upper silicon nitride grating 108, to improve the coupling efficiency between the upper silicon nitride waveguide 109 and the upper silicon nitride grating 108. The narrow portion of the tapered waveguide is equal to or close to the width of the front waveguide to be coupled, to improve the coupling efficiency of the output light from the upper silicon nitride waveguide 109. In this embodiment, the upper silicon nitride waveguide 109 and the lower silicon nitride waveguide 105 have an overlapping portion, so that the light from the lower silicon nitride waveguide 105 can be coupled into the upper silicon nitride waveguide 109, ensuring coupling efficiency.

[0065] like Figure 8 As shown, in step 5), a third silicon dioxide layer 110 is formed on the upper silicon nitride grating 108 and the upper silicon nitride waveguide 109 using plasma-enhanced chemical vapor deposition (PECVD), and the third silicon dioxide layer 110 is polished by chemical mechanical polishing (CMP) to obtain a flat surface.

[0066] like Figure 9 As shown, when the input light enters the grating coupler, the upper silicon nitride grating 108 couples a portion of the input light into the upper silicon nitride waveguide 109, while the other portion of the input light passes through the upper silicon nitride grating 108 and is incident on the substrate 101 to form transmitted light. The lower silicon nitride grating 104 reflects a portion of the transmitted light back to the upper silicon nitride grating 108, and then couples it into the upper silicon nitride waveguide 109. The other portion of the transmitted light enters the lower silicon nitride grating 104, and then couples it into the lower silicon nitride waveguide 105, which in turn couples it into the upper silicon nitride waveguide 109, and finally outputs the light from the upper silicon nitride waveguide 109.

[0067] like Figure 10 As shown, the fabricated grating coupler based on the double-layer silicon nitride structure has a coupling efficiency of over 60% for input light with wavelengths of 1530nm to 1565nm, and the 1dB bandwidth of the fabricated grating coupler based on the double-layer silicon nitride structure is greater than 100nm.

[0068] Example 2

[0069] like Figure 11As shown, this embodiment provides a grating coupler based on a double-layer silicon nitride structure, with the basic structure as described in Embodiment 1. The difference from Embodiment 1 is that the lower silicon nitride grating 104 has a first silicon nitride connection portion 111 between adjacent first silicon nitride grating strips. The thickness of the first silicon nitride connection portion 111 is less than the thickness of the first silicon nitride grating strip. The first silicon nitride connection portion 111 can optimize the coupling performance of the lower silicon nitride grating, thereby improving the coupling efficiency of the lower silicon nitride grating.

[0070] like Figure 11 As shown, this embodiment also provides a method for fabricating a grating coupler based on a double-layer silicon nitride structure. The basic steps are as in Embodiment 1, except that: during the etching process of the first silicon nitride layer 103, a portion of the first silicon nitride layer 103 between adjacent first silicon nitride gate strips is retained to form a first silicon nitride connection portion 111. The thickness of the first silicon nitride connection portion 111 is less than the thickness of the first silicon nitride gate strip.

[0071] Example 3

[0072] like Figure 12 As shown, this embodiment provides a grating coupler based on a double-layer silicon nitride structure, with the basic structure as described in Embodiment 1. The difference from Embodiment 1 is that during the etching process of the second silicon nitride layer 107, a portion of the second silicon nitride layer 107 between adjacent second silicon nitride grating strips is retained to form a second silicon nitride connection portion 112. The thickness of the second silicon nitride connection portion 112 is less than the thickness of the second silicon nitride grating strips. The second silicon nitride connection portion 112 can reduce the reflection of input light by the upper silicon nitride grating, which is beneficial to the coupling efficiency of the upper silicon nitride grating 108 for the input light.

[0073] like Figure 12 As shown, this embodiment also provides a method for fabricating a grating coupler based on a double-layer silicon nitride structure. The basic steps are as in Embodiment 1, except that the upper silicon nitride grating 108 has a second silicon nitride connection portion 112 between adjacent second silicon nitride grating strips. The thickness of the second silicon nitride connection portion is less than the thickness of the second silicon nitride grating strip.

[0074] Example 4

[0075] like Figure 13As shown, this embodiment provides a grating coupler based on a double-layer silicon nitride structure. Its basic structure is as described in Embodiment 1, except that: during the etching of the first silicon nitride layer 103, a portion of the first silicon nitride layer 103 between adjacent first silicon nitride gate strips is retained to form a first silicon nitride connection portion 111. The thickness of the first silicon nitride connection portion 111 is less than the thickness of the first silicon nitride gate strips. During the etching of the second silicon nitride layer 107, a portion of the second silicon nitride layer 107 between adjacent second silicon nitride gate strips is retained to form a second silicon nitride connection portion 112. The thickness of the second silicon nitride connection portion 112 is less than the thickness of the second silicon nitride gate strips. The first silicon nitride connection portion 111 can optimize the coupling performance of the lower silicon nitride grating, thereby improving the coupling efficiency of the lower silicon nitride grating. The second silicon nitride connection portion 112 can improve the coupling efficiency of the upper silicon nitride grating 108 for input light and reduce transmitted light. By combining the first silicon nitride connector 111 and the second silicon nitride connector 112, the light coupling efficiency of the grating coupler can be comprehensively improved by enhancing the coupling efficiency of the single-layer grating, reducing the reflection of light on the device surface, and enhancing light transmission.

[0076] like Figure 13 As shown, this embodiment also provides a method for fabricating a grating coupler based on a double-layer silicon nitride structure. The basic steps are as in Embodiment 1, except that the lower silicon nitride grating 104 has a first silicon nitride connection portion 111 between adjacent first silicon nitride grating strips, the thickness of the first silicon nitride connection portion 111 being less than the thickness of the first silicon nitride grating strip; and the upper silicon nitride grating 108 has a second silicon nitride connection portion 112 between adjacent second silicon nitride grating strips, the thickness of the second silicon nitride connection portion 112 being less than the thickness of the second silicon nitride grating strip.

[0077] As described above, the grating coupler based on a double-layer silicon nitride structure and its fabrication method of the present invention have the following beneficial effects:

[0078] In this invention, when input light enters the grating coupler, the upper silicon nitride grating 108 couples a portion of the input light into the upper silicon nitride waveguide 109, while the other portion of the input light passes through the upper silicon nitride grating 108 and is incident on the substrate, forming transmitted light. The lower silicon nitride grating 104 reflects a portion of the transmitted light back to the upper silicon nitride grating 108, and then couples it into the upper silicon nitride waveguide 109. The other portion of the transmitted light enters the lower silicon nitride grating 104, and then couples it into the lower silicon nitride waveguide 105, which in turn couples it into the upper silicon nitride waveguide 109. Through this double-layer silicon nitride structure, the energy of the light transmitted through the upper silicon nitride grating 108 can be reused, thereby improving the coupling efficiency and 1dB bandwidth of the grating coupler.

[0079] The grating coupler based on the double-layer silicon nitride structure of the present invention has a coupling efficiency of over 60% for input light with wavelengths of 1530nm to 1565nm, and especially for input light with a wavelength of 1550nm, the coupling efficiency can reach 62%, which is significantly higher than the coupling efficiency of traditional single-layer uniform silicon nitride gratings. At the same time, the 1dB bandwidth of the grating coupler based on the double-layer silicon nitride structure of the present invention is greater than 100nm.

[0080] Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0081] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A grating coupler based on a double-layer silicon nitride structure, characterized in that, The grating coupler includes: Substrate; A first silicon dioxide layer is disposed on the substrate; The lower silicon nitride grating is disposed on the first silicon dioxide layer; A lower silicon nitride waveguide is disposed on the first silicon dioxide layer and connected to the lower silicon nitride grating; A second silicon dioxide layer is disposed on the lower silicon nitride grating and the lower silicon nitride waveguide; The upper silicon nitride grating is disposed on the second silicon dioxide layer; An upper silicon nitride waveguide is disposed on the second silicon dioxide layer and connected to the upper silicon nitride grating; A third silicon dioxide layer is disposed on the upper silicon nitride grating and the upper silicon nitride waveguide; When input light enters the grating coupler, the upper silicon nitride grating couples a portion of the input light into the upper silicon nitride waveguide, while the other portion of the input light passes through the upper silicon nitride grating and is incident on the substrate to form transmitted light. The lower silicon nitride grating reflects a portion of the transmitted light back to the upper silicon nitride grating, and then couples it into the upper silicon nitride waveguide. The other portion of the transmitted light enters the lower silicon nitride grating, and then couples it into the lower silicon nitride waveguide, and then couples it into the upper silicon nitride waveguide, finally outputting from the upper silicon nitride waveguide.

2. The grating coupler based on a double-layer silicon nitride structure according to claim 1, characterized in that: The lower silicon nitride grating includes multiple parallel and spaced first silicon nitride grating strips, and the upper silicon nitride grating includes multiple parallel and spaced second silicon nitride grating strips.

3. The grating coupler based on a double-layer silicon nitride structure according to claim 2, characterized in that: The lower silicon nitride grating also has a first silicon nitride connection portion between adjacent first silicon nitride grating strips, and the thickness of the first silicon nitride connection portion is less than the thickness of the first silicon nitride grating strip.

4. The grating coupler based on a double-layer silicon nitride structure according to claim 2, characterized in that: The upper silicon nitride grating also has a second silicon nitride connection between adjacent second silicon nitride grating strips, and the thickness of the silicon nitride connection is less than the thickness of the second silicon nitride grating strip.

5. The grating coupler based on a double-layer silicon nitride structure according to claim 2, characterized in that: The lower silicon nitride grating also has a first silicon nitride connection between adjacent first silicon nitride grating bars, the thickness of the first silicon nitride connection being less than the thickness of the first silicon nitride grating bar; the upper silicon nitride grating also has a second silicon nitride connection between adjacent second silicon nitride grating bars, the thickness of the second silicon nitride connection being less than the thickness of the second silicon nitride grating bar.

6. The grating coupler based on a double-layer silicon nitride structure according to claim 1, characterized in that: The grating coupler based on the double-layer silicon nitride structure has a coupling efficiency of over 60% for input light with wavelengths of 1530nm to 1565nm.

7. The grating coupler based on a double-layer silicon nitride structure according to claim 1, characterized in that: The grating coupler based on the double-layer silicon nitride structure has a 1dB bandwidth greater than 100nm.

8. A method for fabricating a grating coupler based on a double-layer silicon nitride structure, characterized in that, Including the following steps: A substrate is provided, and a first silicon dioxide layer is formed on the substrate; A first silicon nitride layer is formed on the first silicon dioxide layer, and the first silicon nitride layer is etched to form a lower silicon nitride grating and a lower silicon nitride waveguide connected to the lower silicon nitride grating on the first silicon dioxide layer. A second silicon dioxide layer is formed on the lower silicon nitride grating and the lower silicon nitride waveguide; A second silicon nitride layer is formed on the second silicon dioxide layer, and the second silicon nitride layer is etched to form an upper silicon nitride grating and an upper silicon nitride waveguide connected to the upper silicon nitride grating on the second silicon dioxide layer. A third silicon dioxide layer is formed on the upper silicon nitride grating and the upper silicon nitride waveguide; When input light enters the grating coupler, the upper silicon nitride grating couples a portion of the input light into the upper silicon nitride waveguide, while the other portion of the input light passes through the upper silicon nitride grating and is incident on the substrate to form transmitted light. The lower silicon nitride grating reflects a portion of the transmitted light back to the upper silicon nitride grating, and then couples it into the upper silicon nitride waveguide. The other portion of the transmitted light enters the lower silicon nitride grating, and then couples it into the lower silicon nitride waveguide, and then couples it into the upper silicon nitride waveguide, finally outputting from the upper silicon nitride waveguide.

9. The method for fabricating a grating coupler based on a double-layer silicon nitride structure according to claim 8, characterized in that: The lower silicon nitride grating formed by etching includes multiple parallel and spaced-apart first silicon nitride gratings, and the upper silicon nitride grating formed by etching includes multiple parallel and spaced-apart second silicon nitride gratings.

10. The method for fabricating a grating coupler based on a double-layer silicon nitride structure according to claim 9, characterized in that: During the etching process of the first silicon nitride layer, a portion of the first silicon nitride layer between adjacent first silicon nitride gate strips is retained to form a first silicon nitride connection portion, the thickness of which is less than the thickness of the first silicon nitride gate strip.

11. The method for fabricating a grating coupler based on a double-layer silicon nitride structure according to claim 9, characterized in that: During the etching process of the second silicon nitride layer, a portion of the second silicon nitride layer between adjacent second silicon nitride gate strips is retained to form a second silicon nitride connection portion, the thickness of which is less than the thickness of the second silicon nitride gate strip.

12. The method for fabricating a grating coupler based on a double-layer silicon nitride structure according to claim 9, characterized in that: During the etching of the first silicon nitride layer, a portion of the first silicon nitride layer between adjacent first silicon nitride gate strips is retained to form a first silicon nitride connection portion, the thickness of which is less than the thickness of the first silicon nitride gate strip; during the etching of the second silicon nitride layer, a portion of the second silicon nitride layer between adjacent second silicon nitride gate strips is retained to form a second silicon nitride connection portion, the thickness of which is less than the thickness of the second silicon nitride gate strip.

13. The method for fabricating a grating coupler based on a double-layer silicon nitride structure according to claim 8, characterized in that: The fabricated grating coupler based on a double-layer silicon nitride structure has a coupling efficiency of over 60% for input light with wavelengths of 1530nm to 1565nm, and a 1dB bandwidth greater than 100nm.

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