End-face coupler, preparation method, and communication system

Abstract

Disclosed in embodiments of the present application are an end-face coupler, a preparation method, and a communication system. The end-face coupler comprises a substrate, a waveguide structure located on the substrate, and a cladding layer covering the waveguide structure; the waveguide structure comprises a gradient index lens, a first waveguide, and a second waveguide; a first side of the gradient index lens is used for being connected to an optical fiber; the first waveguide is in contact with a second side of the gradient index lens; the first waveguide is in contact with the second waveguide; and the second waveguide is used for being connected to an optical waveguide in an optoelectronic chip. On this basis, an end face of the optical fiber can be connected to an end face of the optical waveguide in the optoelectronic chip by means of the end-face coupler, and in a transmission process of an optical signal, the mode spot size of the optical signal can be gradually reduced by means of the gradient index lens, the first waveguide, and the second waveguide, so that the mode spot size of the optical signal outputted by the end-face coupler can be better matched with the mode spot size in the optical waveguide, and reduction of the coupling loss of the optical signal from the optical fiber to the optoelectronic chip is implemented.

Description

End coupler, preparation method and communication system

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office of the People's Republic of China on September 15, 2023, with application number 202311205718.X and application name "A kind of end face coupler, preparation method and communication system", the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present application relates to the technical field of optoelectronic devices, and in particular to an end coupler, a preparation method and a communication system. Background Art

[0004] With the rapid development of optical communication technology, the integration of optoelectronic devices is becoming increasingly higher. In optical communication systems, when light is transmitted through an optical fiber, the end face size of the fiber is often hundreds of microns, and the size of the mode spot in the fiber is often several to ten microns. When light is transmitted through the optical waveguide in an optoelectronic chip, the end face size of the optical waveguide is generally hundreds of nanometers, and the size of the mode spot in the waveguide is also often hundreds of nanometers. As a result, there is a significant size mismatch between the mode spot in the optical fiber and the mode spot in the optical waveguide. Directly connecting the optical fiber and the optical waveguide will result in a large mode field mismatch, resulting in significant coupling loss. Therefore, how to reduce the coupling loss between the optical fiber and the optoelectronic chip is a technical problem that needs to be solved urgently.

[0005] Summary of the Invention

[0006] Embodiments of the present application provide an end coupler, a preparation method, and a communication system for reducing coupling loss between an optical fiber and an optoelectronic chip.

[0007] In a first aspect, embodiments of the present application provide an end-face coupler comprising: a substrate, a waveguide structure located on the substrate, and a cladding covering the waveguide structure, wherein the waveguide structure comprises: a gradient index lens, a first waveguide, and a second waveguide. The refractive index of the first waveguide is lower than that of the second waveguide, enabling optical signals in the first waveguide to be coupled into the second waveguide and preventing light leakage through the cladding. Furthermore, the gradient index lens has a first side and a second side disposed opposite each other in a first direction, the first side of the gradient index lens being configured to connect to an optical fiber, and the first waveguide being located on the second side of the gradient index lens and in contact with the second side of the gradient index lens. Based on this, the gradient index lens can reduce the spot size of an optical signal input from the optical fiber in a vertical direction (i.e., perpendicular to the substrate) and couple it into the first waveguide. Since the second waveguide is located on the second side of the gradient index lens and in contact with the first waveguide, the first waveguide extends in the first direction, and the second waveguide also extends in the first direction. Furthermore, the cross-sectional area of ​​the first waveguide gradually decreases in the direction from the gradient index lens toward the first waveguide. Furthermore, since the side of the second waveguide facing away from the gradient refractive index lens is used to connect to the optical waveguide in the optoelectronic chip, and the cross-sectional area of ​​the second waveguide gradually increases in the direction along the gradient refractive index lens pointing to the first waveguide. Based on this, in combination with the first waveguide and the second waveguide, the optical signal is subjected to a reduction in the pattern size in the horizontal direction (the horizontal direction is perpendicular to the vertical direction, and the horizontal direction is perpendicular to the first direction) and is coupled to the optical waveguide through the second waveguide. In summary, by setting the first waveguide, the pattern size of the optical signal output by the gradient refractive index lens is first reduced by the first waveguide and then coupled to the second waveguide, which can reduce the coupling loss of the optical signal directly coupled to the second waveguide by the gradient refractive index lens. Therefore, during the transmission of the optical signal, the pattern size of the optical signal can be gradually reduced in the horizontal and vertical directions by the gradient refractive index lens, the first waveguide and the second waveguide, so that the pattern size of the optical signal output by the end coupler can be better matched with the pattern size in the optical waveguide, thereby reducing the coupling loss of the optical signal from the optical fiber to the optoelectronic chip.

[0008] In some examples, a first waveguide is wrapped around a second waveguide, and the length of the first waveguide in the first direction is the same as the length of the second waveguide in the vertical direction, that is, the orthographic projection of the first waveguide on the substrate covers the orthographic projection of the second waveguide on the substrate. This arrangement enables the first and second waveguides to be combined to reduce the optical signal's spot size in both the horizontal and vertical directions. For example, the first waveguide has first and second sides that are opposed to each other in the first direction, the first side of the first waveguide being in contact with the gradient index lens, and the second waveguide has first and second sides that are opposed to each other in the first direction. Furthermore, the first side of the second waveguide can be aligned with the first side of the first waveguide in the first direction, and the second side of the second waveguide can be aligned with the second side of the first waveguide in the first direction.

[0009] In some examples, the second waveguide is located on the side of the first waveguide facing away from the gradient-index lens, and the second waveguide contacts the side of the first waveguide facing away from the gradient-index lens. That is, the orthographic projection of the first waveguide on the substrate does not overlap with the orthographic projection of the second waveguide on the substrate, but the orthographic projection of the first waveguide on the substrate abuts the orthographic projection of the second waveguide on the substrate. This arrangement enables the first waveguide to reduce the optical signal's spot size horizontally before coupling it to the second waveguide. For example, the first side of the second waveguide can also be aligned in the first direction with the second side of the first waveguide.

[0010] To further direct light into the optical waveguide, the waveguide structure also includes a third waveguide extending along the first direction. The third waveguide contacts the side of the second waveguide facing away from the gradient index lens. The side of the third waveguide facing away from the gradient index lens is used to connect to the optical waveguide in the optoelectronic chip, so that the second waveguide is connected to the optical waveguide through the third waveguide. Furthermore, the cross-sectional area of ​​the third waveguide is made uniform along the direction of the gradient index lens toward the first waveguide, so that light output from the second waveguide is directionally transmitted into the optical waveguide through the third waveguide. Exemplarily, the refractive index of the third waveguide is the same as that of the second waveguide, and the cladding also covers the third waveguide to prevent light leakage from the third waveguide. Furthermore, the cross-sectional area of ​​the third waveguide can be made to match the dimensions of the optical waveguide in the optoelectronic chip, further improving the reliability of optical signal transmission.

[0011] To further reduce transmission loss, the third waveguide also has a first side and a second side disposed opposite each other in a first direction. The cross-section of the third waveguide is identical in shape from the first side to the second side. Furthermore, the cross-section of the first side of the third waveguide can be configured to have the same area and shape as the cross-section of the second side of the second waveguide, further reducing coupling loss between the second and third waveguides. Furthermore, the cross-section of the third waveguide has the same area and shape as the cross-section of the optical waveguide, further reducing coupling loss between the third waveguide and the optical waveguide.

[0012] In some examples, to further reduce light leakage, the waveguide structure also includes a fourth waveguide extending along the first direction. The fourth waveguide contacts the side of the first waveguide facing away from the gradient-index lens. While the first waveguide covers the second waveguide, the fourth waveguide covers the third waveguide. Specifically, the orthographic projection of the fourth waveguide on the substrate overlaps the orthographic projection of the third waveguide on the substrate, further reducing light leakage. Exemplarily, the refractive index of the fourth waveguide is the same as that of the first waveguide, and the cladding also covers the fourth waveguide. Thus, the fourth waveguide and the cladding confine light to the third waveguide, preventing light leakage.

[0013] In yet other examples, to further reduce light leakage, the waveguide structure also includes a fourth waveguide extending along the first direction, the fourth waveguide contacting the side of the first waveguide facing away from the gradient-index lens. When the second waveguide is located on the side of the first waveguide facing away from the gradient-index lens, the fourth waveguide clads the second and third waveguides. Specifically, the orthographic projection of the fourth waveguide on the substrate covers the orthographic projections of the second and third waveguides on the substrate, further reducing light leakage. Exemplarily, the refractive index of the fourth waveguide is the same as that of the first waveguide, and the cladding further clads the fourth waveguide. Thus, the fourth waveguide and cladding confine light to the third waveguide, preventing light leakage.

[0014] Exemplarily, in a direction along the gradient refractive index lens pointing toward the first waveguide, the cross-sectional areas of the fourth waveguide are made the same.

[0015] To reduce coupling loss between the second and third waveguides, the third waveguide can be made of the same material as the second waveguide and formed into an integral structure. This allows the second and third waveguides to be formed using the same patterning process, reducing the number of steps in the manufacturing process.

[0016] To reduce the number of steps in the manufacturing process, the fourth waveguide is made of the same material as the first waveguide and is integrally formed with the first waveguide. This allows the fourth waveguide and the first waveguide to be formed using the same patterning process, reducing the number of steps in the manufacturing process.

[0017] In some examples, the first waveguide includes, but is not limited to, being a tapered waveguide, ie, the first waveguide is a positive tapered waveguide.

[0018] In some examples, the second waveguide includes, but is not limited to, being a tapered waveguide, ie, the second waveguide is an inverted tapered waveguide.

[0019] In some examples, the third waveguide includes, but is not limited to, a rectangular waveguide.

[0020] In some examples, the fourth waveguide includes, but is not limited to, being a rectangular waveguide.

[0021] In some examples, a gradient-index lens comprises: multiple light-transmitting layers stacked on a substrate, with the refractive index of the layers decreasing in a direction from the substrate toward the gradient-index lens. Furthermore, a first side surface of the multiple light-transmitting layers in a first direction serves as the first side of the gradient-index lens, while a second side surface in the first direction serves as the second side of the gradient-index lens. This arrangement can vertically reduce the spot size of the optical signal at the optical fiber end face.

[0022] Furthermore, the first waveguide contacts the second side surface of the light-transmitting layer of the gradient index lens that contacts the substrate, and the refractive index of the first waveguide is the same as the refractive index of the light-transmitting layer of the gradient index lens that contacts the substrate. This configuration allows the gradient index lens to vertically reduce the spot size of the optical signal at the optical fiber end face, while coupling the optical signal into the first waveguide through the light-transmitting layer in contact with the substrate, thereby reducing coupling losses.

[0023] Exemplarily, the first waveguide and the light-transmitting layer in the gradient refractive index lens that is in contact with the substrate are an integrally formed structure and are made of the same material.

[0024] To reduce light leakage, the cladding further covers the gradient index lens, and the cladding exposes the first side of the gradient index lens so that the first side of the gradient index lens can be connected to the optical fiber.

[0025] Furthermore, the thicknesses of the plurality of light-transmitting layers in the vertical direction may be the same or different to meet process requirements.

[0026] In some examples, the material of the first waveguide includes but is not limited to oxynitride. For example, the material of the first waveguide is silicon oxynitride, so that the first waveguide is a forward-tapered silicon oxynitride waveguide.

[0027] In some examples, the material of the second waveguide includes, but is not limited to, silicon, so that the second waveguide is an inverted tapered silicon waveguide.

[0028] In some examples, the material of the light-transmitting layer in the gradient index lens includes but is not limited to oxynitride. For example, the material of the light-transmitting layer is silicon oxynitride, so that the gradient index lens is a silicon oxynitride gradient index lens.

[0029] In some examples, the material of the cladding layer includes but is not limited to oxide. For example, the material of the cladding layer is silicon dioxide, so that the cladding layer is a silicon dioxide cladding layer.

[0030] In a specific implementation, the substrate may include a stacked oxide layer and a semiconductor layer, with the waveguide structure and cladding located on the side of the oxide layer facing away from the semiconductor layer. Alternatively, the substrate may be an oxide layer, i.e., without a semiconductor layer. Furthermore, the oxide layer and the cladding may be made of the same material to prevent light leakage from the substrate side.

[0031] In a second aspect, the present invention also provides a method for preparing an end coupler, including the following contents:

[0032] forming a second waveguide on the substrate, wherein the second waveguide extends along a first direction and the cross-sectional area of ​​the second waveguide gradually increases in the first direction; the second waveguide is used to connect to the optical waveguide in the optoelectronic chip, and the first direction is parallel to the substrate;

[0033] forming a gradient refractive index lens and a first waveguide on the substrate, wherein the gradient refractive index lens has a first side and a second side opposite to each other in a first direction, the first side of the gradient refractive index lens being used for connection to an optical fiber, the second waveguide being in contact with the first waveguide, and the first waveguide being in contact with the second side of the gradient refractive index lens, the second waveguide extending along the first direction, and the cross-sectional area of ​​the second waveguide gradually decreasing in the first direction;

[0034] A cladding is deposited on the substrate, where the cladding covers the gradient refractive index lens, the first waveguide, and the second waveguide.

[0035] To further directionally transmit light into the optical waveguide, the device further includes: forming a third waveguide when forming the second waveguide, the third waveguide extending along the first direction, contacting a side of the second waveguide facing away from the gradient index lens, and the side of the third waveguide facing away from the gradient index lens being used to connect to an optical waveguide in an optoelectronic chip; the cross-sectional area of ​​the third waveguide in a direction along the gradient index lens toward the first waveguide is the same. Furthermore, the cladding layer also covers the third waveguide.

[0036] To further reduce light leakage, the manufacturing method further includes: forming a fourth waveguide when forming the first waveguide, the fourth waveguide extending along the first direction and contacting the side of the first waveguide facing away from the gradient index lens; wherein, when the first waveguide covers the second waveguide, the fourth waveguide covers the third waveguide; or, when the second waveguide is located on the side of the first waveguide facing away from the gradient index lens, the fourth waveguide covers both the second waveguide and the third waveguide. Furthermore, the cladding also covers the fourth waveguide.

[0037] In a specific implementation, a silicon-on-insulator (SOI) substrate is used to form an end-face coupler. Exemplarily, the preparation method includes the following process: providing an SOI substrate, the SOI substrate including a bottom silicon layer, a buried oxide layer, and a top silicon layer. Patterning the top silicon layer and etching to form a second waveguide. Furthermore, forming a gradient refractive index lens and a first waveguide on the substrate includes the following process: depositing multiple silicon oxynitride film layers on the buried oxide layer on which the second waveguide is formed, such that the refractive index of the multiple silicon oxynitride film layers decreases in sequence in the direction from the bottom silicon layer to the buried oxide layer. Thereafter, patterning the remaining silicon oxynitride film layers in the multiple silicon oxynitride film layers and etching to form the remaining light-transmitting layers in the gradient refractive index lens. The remaining silicon oxynitride film layers are the silicon oxynitride film layers in the multiple silicon oxynitride film layers excluding the silicon oxynitride film layers in contact with the buried oxide layer. Then, the silicon oxynitride film layer in contact with the buried oxide layer is patterned, and etched to form a light-transmitting layer and a first waveguide in contact with the buried oxide layer in the gradient refractive index lens.

[0038] On the third aspect, an embodiment of the present application further provides a communication system, which includes an optical fiber, an optoelectronic chip, and an end coupler. The end face of the optical fiber is connected to the first side of the gradient refractive index lens in the end coupler, and the second side of the second waveguide in the end coupler is connected to the end face of the optical waveguide in the optoelectronic chip, so that the mode spot size of the end face of the optical fiber is reduced by the end coupler and then coupled to the optical waveguide, thereby reducing the coupling loss. In addition, the end coupler is an end coupler as in the first aspect or various possible designs of the first aspect. Since the coupling loss of the end coupler is low, the coupling loss of the communication system including the end coupler is also low. In addition, the principle of solving the problem of the communication system is similar to the principle of solving the problem of the aforementioned end coupler. Therefore, the technical effect of the communication system can refer to the technical effect of the aforementioned end coupler, and the repeated parts will not be repeated. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] FIG1 is a schematic diagram of a three-dimensional structure of an end face coupler in one embodiment of the present application;

[0040] FIG2 is a schematic diagram of the top view of the end face coupler in FIG1 ;

[0041] FIG3 is a schematic cross-sectional view of the structure along the AA' dashed line in FIG2;

[0042] 4a to 4e are schematic diagrams of partial structures of an end face coupler in one embodiment of the present application;

[0043] 5a to 5c are schematic diagrams of simulation results in one embodiment of the present application;

[0044] FIG6 is a flow chart of a preparation method in one embodiment of the present application;

[0045] 7a to 7e are schematic structural diagrams of an end face coupler during the preparation process according to an embodiment of the present application;

[0046] FIG8 is a schematic diagram of a three-dimensional structure of an end face coupler in another embodiment of the present application;

[0047] FIG9 is a schematic top view of the end face coupler in FIG8 ;

[0048] FIG10 is a schematic cross-sectional view of the structure along the dotted line AA′ in FIG9 ;

[0049] FIG11 is a schematic diagram of a three-dimensional structure of an end face coupler in another embodiment of the present application;

[0050] FIG12 is a schematic top view of the end face coupler in FIG11;

[0051] FIG13 is a schematic cross-sectional view of the structure along the dotted line AA′ in FIG12 ;

[0052] 14a to 14c are schematic diagrams of simulation results in yet another embodiment of the present application;

[0053] FIG15 is a schematic diagram of a three-dimensional structure of an end face coupler in another embodiment of the present application;

[0054] FIG16 is a schematic top view of the end face coupler in FIG15 ;

[0055] FIG17 is a schematic cross-sectional view of the structure along the dotted line AA′ in FIG16 .

[0056] Figure markings: 100 - substrate; 110 - oxide layer; 120 - semiconductor layer; 200 - gradient refractive index lens; 210 / 220 / 230 / 240 / 250 - light-transmitting layer; 210a / 220a / 230a / 240a / 250a - silicon oxynitride film layer; 310 - second waveguide; 320 - first waveguide; 330 - third waveguide; 340 - fourth waveguide; 400 - cladding; 500 - optical fiber, X - first direction; Y - horizontal direction; Z - vertical direction; d1 / d2 / d3 / d4 - length; h0 / h1 / h2 / h3 / h4 - thickness; S01 / S11 / S21 / S31 / S41 - first side; S02 / S12 / S22 / S32 / S42 - second side; TW tip width. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings. References to "one embodiment" or "some embodiments" etc. described in this specification mean that one or more embodiments of the present application include specific features, structures or characteristics described in conjunction with the embodiment. Therefore, the sentences "in one embodiment", "in some other embodiments", "in some other embodiments" etc. that appear in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways. In addition, the words "first", "second", etc. involved in this specification are only used to distinguish the purpose of description, and cannot be understood as indicating or implying relative importance, nor can they be understood as indicating or implying order.

[0058] The terms used in the following embodiments are only for the purpose of describing specific embodiments and are not intended to limit the present application. As used in the specification and appended claims of this application, the singular expressions "a", "an", "said", "above", "the", and "this" are intended to also include expressions such as "one or more", unless the context clearly indicates otherwise.

[0059] The end coupler provided in the embodiment of the present application is connected between the end face of the optical fiber and the end face of the optical waveguide of the optoelectronic chip, and is used to reduce the mode spot size of the optical signal transmitted by the optical fiber and couple it into the optical waveguide. The end coupler provided in the embodiment of the present application can be widely used in communication systems based on the coupling of optoelectronic chips and optical fibers, such as access networks, transmission networks, data centers, routers and other communication systems that require the use of optical modules. In addition, the above-mentioned optical fibers include but are not limited to single-mode optical fibers, and the above-mentioned optoelectronic chips include but are not limited to silicon-based optoelectronic chips. It is understandable that the end couplers in the embodiments of the present application are intended to include but are not limited to applications in these and any other suitable types of equipment.

[0060] Figure 1 is a schematic diagram of the three-dimensional structure of an end coupler in one embodiment of the present application, Figure 2 is a schematic diagram of the top view of the end coupler in Figure 1, Figure 3 is a schematic diagram of the cross-sectional structure along the AA' dashed line in Figure 2, and Figures 4a to 4e are schematic diagrams of partial structures of an end coupler in one embodiment of the present application. Referring to Figures 1 to 4e, the end coupler may include: a substrate 100, a waveguide structure located on the substrate 100, and a cladding 400 covering the waveguide structure. The waveguide structure includes a gradient refractive index lens (GRIN lens) 200 formed on the substrate 100, a second waveguide 310, and a first waveguide 320. The first waveguide 320 is located on the side of the second waveguide 310 facing away from the substrate 100 and covers the second waveguide 310. That is, the orthographic projection of the first waveguide 320 on the substrate 100 covers the orthographic projection of the second waveguide 310 on the substrate 100. The cladding 400 is located on the side of the first waveguide 320 facing away from the substrate 100 and covers the first waveguide 320. That is, the orthographic projection of the cladding 400 on the substrate 100 covers the orthographic projection of the first waveguide 320 on the substrate 100. Furthermore, the refractive index of the first waveguide 320 is lower than that of the second waveguide 310, so that the optical signal in the first waveguide 320 can be coupled into the second waveguide 310. The refractive index of the cladding 400 is lower than that of the first waveguide 320, so as to prevent light leakage through the cladding 400. Furthermore, the gradient index lens 200 has a first side S01 and a second side S02 disposed opposite each other in a first direction X. The second waveguide 310 has a first side S11 and a second side S12 disposed opposite each other in the first direction X. The first waveguide 320 has a first side S21 and a second side S22 disposed in the first direction X. The first side S01 of the gradient index lens 200 is used to connect to an optical fiber, the first side S21 of the first waveguide 320 contacts the second side S02 of the gradient index lens 200, the first waveguide 320 contacts the second waveguide 310, and the second side S22 of the second waveguide 310 is used to connect to an optical waveguide in an optoelectronic chip. Based on this, the optical fiber 500 is connected to the end face of the optical waveguide in the optoelectronic chip via the aforementioned end face coupler. Specifically, the end face of the optical fiber 500 is connected to the first side S01 of the gradient index lens 200, and the second side S12 of the second waveguide 310 is connected to the end face of the optical waveguide. During the optical signal transmission process, the gradient index lens 200 reduces the spot size of the optical signal in the end face of the optical fiber 500 in the vertical direction Z and then couples the optical signal to the first waveguide 320 and the second waveguide 310 .With respect to the second waveguide 310 and the first waveguide 320, the cross-sectional area of ​​the first waveguide 320 in a direction perpendicular to the first direction X gradually decreases in the direction from the gradient index lens 200 to the first waveguide 320 (i.e., the direction indicated by the arrow in the first direction X), and the cross-sectional area of ​​the second waveguide 310 in a direction perpendicular to the first direction X gradually increases in the direction from the gradient index lens 200 to the first waveguide 320 (i.e., the direction indicated by the arrow in the first direction X). Based on this, the first waveguide 320 and the second waveguide 310 are combined with each other, and the optical signal coupled to the gradient index lens 200 is subjected to reduced pattern size in the horizontal direction Y and the vertical direction Z. The optical signal is then coupled to the optical waveguide via the second waveguide 310, thereby reducing the pattern size, and the optical signal with reduced pattern size is then coupled to the optical waveguide. In summary, by providing the first waveguide 320, the mode spot size of the optical signal output from the gradient index lens 200 is first reduced by the first waveguide 320 before being coupled into the second waveguide 310. This can reduce the coupling loss that would otherwise occur when the gradient index lens 200 directly couples the optical signal to the second waveguide 310. Therefore, during optical signal transmission, the mode spot size is gradually reduced by the gradient index lens 200, the first waveguide 320, and the second waveguide 310, enabling a better match between the mode spot size of the optical signal output from the end coupler and the mode spot size in the optical waveguide, thereby reducing the coupling loss of the optical signal from the optical fiber to the optoelectronic chip.

[0061] In addition, the first direction X and the horizontal direction Y are both parallel to the substrate 100 , and the first direction X is perpendicular to the horizontal direction Y. The vertical direction Z is also perpendicular to the first direction X. Furthermore, the vertical direction Z is perpendicular to the substrate 100 .

[0062] Continuing with Figures 1 to 4e, the orthographic projection of the first waveguide 320 on the substrate 100 can overlap the orthographic projection of the second waveguide 310 on the substrate 100. That is, the first waveguide 320 is located on the side of the second waveguide 310 facing away from the substrate 100, and the first waveguide 320 is arranged to cover the second waveguide 310. For example, the first side S11 of the second waveguide 310 can be aligned with the first side S21 of the first waveguide 320 in the first direction X, and the second side S12 of the second waveguide 310 can be aligned with the second side S22 of the first waveguide 320 in the first direction X. In this manner, the length d1 of the second waveguide 310 along the first direction X and the length d2 of the first waveguide 320 along the first direction X can be the same. Furthermore, the first side S11 and the second side S12 of the second waveguide 310 are arranged parallel to each other, and the first side S21 and the second side S22 of the first waveguide 320 are also arranged parallel to each other.

[0063] In order to further directionally transmit light into the optical waveguide, referring to Figures 1 to 3, 4b and 4d, the waveguide structure further includes a third waveguide 330 extending along the first direction X. The refractive index of the third waveguide 330 is the same as that of the second waveguide 310. The cladding 400 also covers the third waveguide 330, that is, the orthographic projection of the cladding 400 on the substrate 100 also covers the orthographic projection of the third waveguide 330 on the substrate 100, thereby preventing light from leaking from the third waveguide 330. Furthermore, the third waveguide 330 has a first side S31 and a second side S32 arranged opposite each other in the first direction X. The first side S31 of the third waveguide 330 contacts the second side S12 of the second waveguide 310, that is, the third waveguide 330 contacts the side of the second waveguide 310 facing away from the gradient index lens 200. The side of the third waveguide 330 facing away from the gradient index lens 200 is used to connect to an optical waveguide in the optoelectronic chip, that is, the second side S32 of the third waveguide 330 is used to connect to an optical waveguide in the optoelectronic chip. Furthermore, the cladding 400 exposes the second side S32 of the third waveguide 330, enabling connection to the optical waveguide. This configuration allows the second waveguide 310 to be connected to an optical waveguide through the third waveguide 330, thereby matching the dimensions of the optical waveguide in the optoelectronic chip. Furthermore, the area of ​​the cross section of the third waveguide 330 in the direction perpendicular to the first direction X is the same in the direction along the gradient refractive index lens 200 pointing to the first waveguide 320 (i.e., the direction indicated by the arrow in the first direction X), so that the light output from the second waveguide 310 is directionally transmitted into the optical waveguide through the third waveguide 330.

[0064] Furthermore, to reduce transmission loss, the cross-sectional shape of the third waveguide 330 perpendicular to the first direction X can be made uniform in the direction along the gradient index lens 200 pointing toward the first waveguide 320 (i.e., the direction indicated by the arrow in the first direction X). Furthermore, the cross-sectional area and shape of the first side S31 of the third waveguide 330 perpendicular to the first direction X can be made the same as the cross-sectional area and shape of the second side S12 of the second waveguide 310 perpendicular to the first direction X, further reducing coupling loss between the second waveguide 310 and the third waveguide 330. Furthermore, the cross-sectional area and shape of the third waveguide 330 perpendicular to the first direction X and the cross-sectional area and shape of the optical waveguide perpendicular to the first direction X can further reduce coupling loss between the third waveguide 330 and the optical waveguide. Furthermore, the first side S31 and the second side S32 of the third waveguide 330 are arranged parallel to each other.

[0065] To further reduce light leakage, referring to Figures 1 to 3 and 4b to 4e, the end coupler further includes a fourth waveguide 340 extending along the first direction X. The refractive index of the fourth waveguide 340 is the same as that of the first waveguide 320. The cladding 400 further covers the fourth waveguide 340, i.e., the orthographic projection of the cladding 400 on the substrate 100 also covers the orthographic projection of the fourth waveguide 340 on the substrate 100. The fourth waveguide 340 further covers the third waveguide 330, i.e., the orthographic projection of the fourth waveguide 340 on the substrate 100 covers the orthographic projection of the third waveguide 330 on the substrate 100. Furthermore, the fourth waveguide 340 contacts a side of the first waveguide 320 facing away from the gradient-index lens 200. For example, the fourth waveguide 340 has a first side S41 and a second side S42 oppositely disposed in the first direction X, and the first side S41 of the fourth waveguide 340 contacts the second side S22 of the first waveguide 320. The second side S42 of the fourth waveguide 340 and the second side S32 of the third waveguide 330 can be aligned in the first direction X. In the direction from the gradient index lens 200 to the first waveguide 320 (i.e., the direction indicated by the arrow in the first direction X), the cross-sectional area of ​​the fourth waveguide 340 perpendicular to the first direction X is the same. Therefore, the fourth waveguide 340 confines light within the third waveguide 330, preventing light leakage. Furthermore, the cross-sectional area of ​​the first side S41 of the fourth waveguide 340 and the cross-sectional area of ​​the second side S22 of the first waveguide 320 perpendicular to the first direction X are the same and have the same shape. Furthermore, the cross-sectional shape of the fourth waveguide 340 perpendicular to the first direction X can also be the same in the direction from the first side S41 of the fourth waveguide 340 to the second side S42 of the fourth waveguide 340 (i.e., the direction indicated by the arrow in the first direction X).

[0066] 1 and 2 , the second side S12 of the second waveguide 310, the second side S22 of the first waveguide 320, the first side S31 of the third waveguide 330, and the first side S41 of the fourth waveguide 340 are aligned in the first direction X, and the second side S32 of the third waveguide 330 and the second side S42 of the fourth waveguide 340 are aligned in the first direction X, so that a length d3 of the third waveguide 330 along the first direction X is the same as a length d4 of the fourth waveguide 340 along the first direction X, thereby further preventing light leakage.

[0067] Continuing with FIG1 and FIG2, the end face coupler has a center line extending along the first direction X (e.g., dashed line AA'), and the orthographic projection of the gradient index lens 200 on the substrate 100 can be symmetrically arranged about the dashed line AA'. Exemplarily, the gradient index lens 200 includes: light-transmitting layers 210 to 250 stacked on the substrate 100, and in the direction from the substrate 100 to the gradient index lens 200 (i.e., the direction indicated by the arrow perpendicular to the direction Z), the refractive index n of the light-transmitting layer 210 is210 , the refractive index n of the light-transmitting layer 220 220 , the refractive index n of the light-transmitting layer 230 230 , the refractive index n of the light-transmitting layer 240 240 , the refractive index n of the light-transmitting layer 250 250 becomes smaller in sequence, that is, n 210 >n 220 >n 230 >n 240 >n 250 . In addition, the first side surface of the light-transmitting layers 210 to 250 in the first direction X serves as the first side S01 of the gradient index lens 200, and the second side surface in the first direction X serves as the second side S02 of the gradient index lens 200. In addition, the first side S21 of the first waveguide 320 is in contact with the second side surface of the light-transmitting layer 210 in the gradient index lens 200 that is in contact with the substrate 100, and the refractive index of the first waveguide 320 is the same as the refractive index of the light-transmitting layer 210 in contact. With this arrangement, the light-transmitting layers 210 to 250 can reduce the mode spot size of the optical signal at the end face of the optical fiber in the vertical direction Z, and the light signal can be coupled to the first waveguide 320 through the light-transmitting layer 210, thereby reducing coupling loss.

[0068] Furthermore, the thickness of the light-transmitting layers 210 to 250 in the vertical direction Z can be made the same or different to meet process requirements. In addition, the present application does not limit the material of the light-transmitting layer. Optionally, the material of the light-transmitting layer includes nitride oxide, for example, the material of the light-transmitting layer is silicon oxynitride, so that the gradient refractive index lens is a silicon oxynitride gradient refractive index lens. It is understandable that the present application uses the gradient refractive index lens 200 having five light-transmitting layers as an example. In actual applications, the specific number of light-transmitting layers in the gradient refractive index lens 200 can be determined according to the needs of the actual application to meet process requirements.

[0069] Continuing with FIG. 1 and FIG. 2 , the orthographic projection of the second waveguide 310 on the substrate 100 can be symmetrically arranged about the dashed line AA'. For example, the second waveguide 310 includes, but is not limited to, a tapered waveguide. Furthermore, this application does not limit the material of the second waveguide 310. For example, the material of the second waveguide 310 can include silicon, such that the second waveguide 310 is an inverted tapered silicon waveguide.

[0070] Continuing with Figures 1 and 2 , the orthographic projection of the third waveguide 330 on the substrate 100 can be symmetrically arranged about the dashed line AA'. For example, the third waveguide 330 includes, but is not limited to, a rectangular waveguide. Furthermore, this application does not limit the material of the third waveguide 330. Furthermore, the second waveguide 310 and the third waveguide 330 can be made of the same material, that is, the third waveguide 330 can be made of silicon, such that the third waveguide 330 is a rectangular silicon waveguide.

[0071] For example, the third waveguide 330 and the second waveguide 310 are configured as an integrally molded structure, and the third waveguide 330 and the second waveguide 310 are made of the same material. This configuration allows the third waveguide 330 and the second waveguide 310 to be disposed in the same layer, so that the thickness h1 of the second waveguide 310 in the vertical direction Z is the same as the thickness h3 of the third waveguide 330 in the vertical direction Z. This further reduces the coupling loss of the optical signal from the second waveguide 310 to the third waveguide 330. Furthermore, the second waveguide 310 and the third waveguide 330 can be formed using the same patterning process, reducing the number of steps in the manufacturing process.

[0072] Continuing with FIG. 1 and FIG. 2 , the orthographic projection of the first waveguide 320 on the substrate 100 can be symmetrically arranged about the dashed line AA'. For example, the first waveguide 320 includes, but is not limited to, a tapered waveguide. Furthermore, this application does not limit the material of the first waveguide 320. For example, the material of the first waveguide 320 can include oxynitride, such as silicon oxynitride, so that the first waveguide 320 is a normal-tapered silicon oxynitride waveguide.

[0073] Furthermore, the material of the first waveguide 320 is the same as that of the light-transmitting layer in the gradient-index lens 200, thereby reducing coupling losses caused by light coupling from the light-transmitting layer to the first waveguide 320. Furthermore, the first waveguide 320 and the light-transmitting layer 210 in the gradient-index lens 200, which contacts the substrate 100, are integrally formed. This allows the first waveguide 320 and the light-transmitting layer 210 to be fabricated using the same patterning process, reducing the number of fabrication steps.

[0074] Continuing with FIG. 1 and FIG. 2 , the orthographic projection of the fourth waveguide 340 on the substrate 100 can be symmetrically arranged about the dashed line AA'. For example, the fourth waveguide 340 includes, but is not limited to, a rectangular waveguide. Furthermore, this application does not limit the material of the fourth waveguide 340. Optionally, the material of the fourth waveguide 340 includes oxynitride. For example, the material of the fourth waveguide 340 is silicon oxynitride, so that the fourth waveguide 340 is a rectangular silicon oxynitride waveguide.

[0075] Furthermore, the first waveguide 320, the fourth waveguide 340, and the light-transmitting layer 210 are made of the same material and are integrally formed. This allows the thickness h2 of the first waveguide 320 in the vertical direction Z, the thickness h4 of the fourth waveguide 340 in the vertical direction Z, and the thickness h0 of the light-transmitting layer 210 in the vertical direction Z to be the same. This allows the first waveguide 320, the fourth waveguide 340, and the light-transmitting layer 210 to be formed using the same patterning process, thereby reducing the number of steps in the manufacturing process.

[0076] It is understood that in Figures 1 and 2 of the present application, the cladding 400 covers the second side surface of the light-transmitting layers 220 to 250 in the gradient index lens 200 as an example. In actual applications, the orthographic projection of the cladding 400 on the substrate 100 can also cover the orthographic projection of the gradient index lens 200 on the substrate, that is, the cladding 400 also covers the upper surface of the gradient index lens 200 facing away from the substrate 100 and the two side surfaces of the gradient index lens 200 in the horizontal direction Y. In addition, the cladding 400 exposes the first side S01 of the gradient index lens 200 so that the first side S01 of the gradient index lens 200 can be connected to the optical fiber. In addition, the present application does not limit the material of the cladding 400. For example, the material of the cladding 400 includes but is not limited to oxides. For example, the material of the cladding is silica, so that the cladding is a silica cladding.

[0077] Continuing with Figures 1 and 2, substrate 100 includes a stacked oxide layer 110 and a semiconductor layer 120. Gradient-index lens 200, second waveguide 310, first waveguide 320, third waveguide 330, fourth waveguide 340, and cladding 400 are located on the side of oxide layer 110 facing away from semiconductor layer 120. Alternatively, substrate 100 may be an oxide layer, i.e., without a semiconductor layer. Furthermore, oxide layer 110 and cladding 400 may be made of the same material to prevent light leakage from one side of substrate 100.

[0078] This application uses the structure of the end coupler shown in FIG1 and a 10-micron optical signal spot size at the end face of optical fiber 500 as an example for simulation. The simulation demonstrates that the gradient index lens 200 can reduce the spot size from 10 microns to approximately a few microns (e.g., 3 microns) in the vertical direction Z, while maintaining the same size in the horizontal direction Y. The optical signal with the reduced spot size is then coupled to the first waveguide 320 and the second waveguide 310 via the light-transmitting layer 210. The combination of the first waveguide 320 and the second waveguide 310 can reduce the spot size of the optical signal to several hundred nanometers (e.g., 300 nanometers) in both the horizontal direction Y and the vertical direction Z, respectively. The optical signal is then transmitted to the optical waveguide via the third waveguide 330. This allows for a conversion process that reduces the spot size from 10 microns to several hundred nanometers.

[0079] This application also uses the structure of the end coupler shown in Figure 1, in which the second waveguide 310 and the third waveguide 330 are made of silicon, and the light-transmitting layer, the first waveguide 320, and the fourth waveguide 340 are made of silicon oxynitride, as an example to simulate the coupling loss of the end coupler. The coupling loss of the end coupler mainly includes: a first loss, Loss1, and a second loss, Loss2. The first loss, Loss1, represents the total loss of the optical signal from the optical fiber through the gradient index lens 200 to the first waveguide 320 (this total loss mainly includes: Fresnel reflection loss between the optical fiber and the gradient index lens 200, the mode conversion loss of the gradient index lens 200, and the Fresnel reflection loss between the gradient index lens 200, the first waveguide 320, and the cladding 400). The second loss, Loss2, represents the transmission loss of the optical signal from the first waveguide 320 to the third waveguide 330. As for the transmission losses inherent in each structure itself, these transmission losses include material absorption loss, scattering loss caused by side wall roughness, and radiation loss caused by waveguide bending. Due to the limitations of material properties and simulation, this transmission loss can be ignored. Among them, for the first loss Loss1: its key influencing factor is the performance of the gradient refractive index lens 200. Based on this, a physical model of the end coupler is established in the 2D FDTD module of the simulation software for simulation, and the influence curve of the refractive index change of the light-transmitting layer in contact with the substrate 100 in the gradient refractive index lens 200 on the first loss Loss1 is obtained, as shown in Figure 5a, wherein the horizontal axis IB represents the refractive index of the light-transmitting layer in contact with the substrate 100 in the gradient refractive index lens 200, the vertical axis Loss1 represents the first loss, and different line types represent the first loss Loss1 of the TE mode respectively. TE and the first loss of TM mode Loss1 TM . Referring to Figure 5a, when IB=1.5, Loss1 TE =-0.039dB, Loss 1 TM =-0.052dB. In addition, for the second loss Loss2: its key influencing factors are the length d1 of the second waveguide 310, the length d2 of the first waveguide 320 (d1=d2), and the tip width TW of the second waveguide 310. Based on this, a physical model of the end coupler is established in the MODE module of the simulation software for simulation, and the influence curve of the length d1 of the second waveguide 310 and the length d2 of the first waveguide 320 on the second loss Loss2 is obtained, as shown in Figure 5b, where the horizontal axis LE represents the length d1 of the second waveguide 310 and the length d2 of the first waveguide 320, the vertical axis Loss2 represents the second loss, and different line types represent the second loss Loss2 of the TE mode, respectively. TE and the second loss of TM mode Loss2 TM . Referring to Figure 5b, when d1 = d2 = 700 μm, Loss2TE =-0.014dB, Loss2 TM =-0.012dB. In addition, taking d1=d2=700μm as an example, the second loss Loss2 is optimized by changing the tip width TW of the second waveguide 310. As shown in FIG5c, the horizontal axis TW represents the tip width of the second waveguide 310, and the vertical axis Loss2 represents the second loss. Different line types represent the second loss Loss2 of the TE mode. TE and the second loss of TM mode Loss2 TM When the tip width TW of the second waveguide 310 is 40 nm, Loss2 TE and Loss2 TM Minimum, close to 0. In summary, the coupling loss Loss of the end coupler corresponding to the TE mode is obtained through simulation TE =Loss1 TE +Loss2 TE =-0.053dB, and the corresponding TM mode coupling loss Loss TM =Loss1 TM +Loss2 TM =-0.064dB. It can be understood that when IB=1.5, d1 (or d2)=700μm, and the tip width TW of the second waveguide 310=40nm, the corresponding coupling loss is the lowest loss of the current structure.

[0080] FIG6 is a flow chart of a preparation method in an embodiment of the present application. Referring to FIG6 , the preparation method may include the following steps:

[0081] S10, etching to form a second waveguide and a third waveguide on the substrate.

[0082] Taking the end coupler structure shown in FIG2 as an example, step S10 may include the following process: Referring to FIG7a , a silicon-on-insulator (SOI) substrate 100 may be used. The SOI substrate 100 includes a bottom silicon layer, a buried oxide layer, and a top silicon layer. The top silicon layer is patterned and etched to form the second waveguide 310 and the third waveguide 330. The buried oxide layer serves as the oxide layer 110 of the substrate 100 in the end coupler, and the bottom silicon layer serves as the semiconductor layer 120 of the substrate 100 in the end coupler. Alternatively, a semiconductor layer, an oxide layer, and a silicon layer may be epitaxially grown in sequence, and the silicon layer is patterned and etched to form the second and third waveguides.

[0083] S20, etching on the substrate to form a gradient refractive index lens, a first waveguide, and a fourth waveguide.

[0084] Taking the end coupler structure shown in FIG2 as an example, step S20 may include the following process: First, referring to FIG7b , five silicon oxynitride film layers 210a-250a are deposited on the oxide layer 110. The refractive index and thickness of these five silicon oxynitride film layers 210a-250a are adjusted to meet process requirements. Next, referring to FIG7c , the silicon oxynitride film layers 220a-250a are patterned and etched to form the light-transmitting layers 220-250 of the gradient index lens 200. Next, referring to FIG7d , the silicon oxynitride film layer 210a is patterned and etched to form the light-transmitting layer 210, the first waveguide 320, and the fourth waveguide 340 of the gradient index lens 200. The first waveguide 320 covers the second waveguide 310, and the fourth waveguide 340 covers the first waveguide 320.

[0085] S30, depositing a cladding layer on the substrate.

[0086] Taking the structure of the end coupler shown in FIG2 as an example, step S30 may include the following process: Referring to FIG7e , a silica cladding 400 is deposited on substrate 100, such that silica cladding 400 covers the side surfaces of first waveguide 320, fourth waveguide 340, and light-transmitting layers 220-250. For example, cladding 400 also contacts the second side surfaces of light-transmitting layers 220-250 in gradient index lens 200, further preventing light leakage. Furthermore, the orthographic projection of cladding 400 on substrate 100 also covers the orthographic projection of gradient index lens 200 on the substrate, that is, cladding 400 also covers the upper surface of gradient index lens 200 facing away from substrate 100 and both side surfaces of gradient index lens 200 in horizontal direction Y. Furthermore, cladding 400 exposes first side S01 of gradient index lens 200, enabling connection to an optical fiber. Furthermore, the present application does not limit the material of the cladding 400 . For example, the material of the cladding 400 includes but is not limited to oxides (eg, silicon dioxide).

[0087] FIG8 is a schematic diagram of the three-dimensional structure of an end coupler in another embodiment of the present application, FIG9 is a schematic diagram of the top view of the end coupler in FIG8 , and FIG10 is a schematic diagram of the cross-sectional structure along the dashed line AA' in FIG9 . Referring to FIG8 to FIG10 , the end coupler may include: a substrate 100 and a gradient index lens 200 located on the substrate 100, a second waveguide 310, a first waveguide 320, and a cladding 400. This embodiment differs from the embodiment shown in FIG1 in that the third waveguide 330 and the fourth waveguide 340 are not provided. In other words, the second side S12 of the second waveguide 310 is directly connected to the optical waveguide in the optoelectronic chip, so that light is directly coupled from the second waveguide 310 to the optical waveguide. The remaining details of this embodiment are substantially the same as those of the embodiment shown in FIG1 and are not further described here.

[0088] Taking the preparation of the end coupler structure shown in FIG8 as an example, the corresponding preparation method flowchart can be referred to FIG6 . In step S10, etching is not required for forming the third waveguide 330. In step S20, etching is not required for forming the fourth waveguide 340. The remaining preparation process can be referred to the description of the preparation method above and is not detailed here.

[0089] Figure 11 is a schematic diagram of the three-dimensional structure of an end coupler in another embodiment of the present application, Figure 12 is a schematic diagram of the top view of the end coupler in Figure 11, and Figure 13 is a schematic diagram of the cross-sectional structure taken along the dashed line AA' in Figure 12. Referring to Figures 11 to 13, the end coupler may include: a substrate 100, a gradient index lens 200 disposed on the substrate 100, a second waveguide 310, a first waveguide 320, a third waveguide 330, a fourth waveguide 340, and a cladding 400. The second waveguide 310 is located on the side of the first waveguide 320 facing away from the gradient index lens 200, and the second waveguide 310 contacts the side of the first waveguide 320 facing away from the gradient index lens 200. That is, the orthographic projection of the first waveguide 320 on the substrate 100 does not overlap with the orthographic projection of the second waveguide 310 on the substrate 100, and the first side S11 of the second waveguide 310 contacts the second side S22 of the first waveguide 320, so that the orthographic projection of the first waveguide 320 on the substrate 100 is located between the orthographic projection of the second waveguide 310 on the substrate 100 and the gradient index lens 200. With this arrangement, the optical signal can first pass through the first waveguide 320 to undergo spot reduction in the horizontal direction Y before being coupled to the second waveguide 310. Furthermore, the fourth waveguide 340 covers the second waveguide 310 and the third waveguide 330. That is, the orthographic projection of the fourth waveguide 340 on the substrate 100 covers the orthographic projections of the second waveguide 310 and the third waveguide 330 on the substrate 100. The fourth waveguide 340 prevents light leakage from the second waveguide 310 and the third waveguide 330. Furthermore, the first side S11 of the second waveguide 310, the second side S22 of the first waveguide 320, and the first side S41 of the fourth waveguide 340 are aligned in the first direction X, and the second side S32 of the third waveguide 330 and the second side S42 of the fourth waveguide 340 are aligned in the first direction X. Furthermore, the sum of the length d1 of the second waveguide 310 and the length d3 of the third waveguide 330 can be made equal to the length d4 of the fourth waveguide 340. The remaining details of this embodiment are substantially the same as those of the embodiment shown in FIG. 1 and are not further described here.

[0090] Taking the preparation of the end coupler structure shown in FIG11 as an example, the corresponding preparation method flowchart can be referred to FIG6 . In step S20 , the etched second waveguide 310 and first waveguide 320 need to be disposed between the oxide layer 110 and the fourth waveguide 340 , with the fourth waveguide 340 covering the second waveguide 310 and first waveguide 320 . The remaining preparation process can be referred to the description of the preparation method above and is not repeated here.

[0091] This application uses the structure of the end coupler shown in FIG11 and a 10-micron optical signal spot size at the end face of an optical fiber 500 as an example for simulation. The simulation shows that the gradient index lens 200 can reduce the spot size from 10 microns to approximately several microns (e.g., 3 microns) in the vertical direction Z, while maintaining the same size in the horizontal direction Y. The optical signal with the reduced spot size is then coupled to the first waveguide 320 via the light-transmitting layer 210. The first waveguide 320 can reduce the spot size of the optical signal from 10 microns to several microns (e.g., 3 microns) in the horizontal direction Y, while maintaining the same size in the vertical direction Z. The signal is then coupled to the second waveguide 310. Consequently, the spot size of the light coupled to the second waveguide 310 is approximately several microns (e.g., 3 microns) in the vertical direction Z and also approximately several microns (e.g., 3 microns) in the horizontal direction Y. The second waveguide 310 can reduce the spot size of the input light from several microns to several hundred nanometers (e.g., 300 nanometers) in the horizontal direction Y, and also from several microns to several hundred nanometers (e.g., 300 nanometers) in the vertical direction Z, and couples it to the optical waveguide. This allows for a conversion process that reduces the spot size from 10 microns to several hundred nanometers.

[0092] This application also uses the structure of the end coupler shown in Figure 11, and the second waveguide 310 and the third waveguide 330 are made of silicon, and the light-transmitting layer, the first waveguide 320 and the fourth waveguide 340 are made of silicon oxynitride as an example to simulate the coupling loss of the end coupler. For the first loss Loss1: refer to Figure 5a. When IB = 1.5, Loss1 TE =-0.039dB, Loss 1 TM =-0.052dB. Furthermore, regarding the second loss Loss2: a physical model of the end coupler was established in the MODE module of the simulation software for simulation, and a curve showing the effect of the length d2 of the first waveguide 320 on the transmission loss of the first waveguide was obtained, as shown in FIG14a , where the abscissa LE represents the length d2 of the first waveguide 320, the ordinate Loss2_1 represents the transmission loss of the first waveguide, and the different line shapes represent the transmission loss Loss2_1 of the first waveguide in the TE mode, respectively. TE and the transmission loss Loss2_1 of the first waveguide of the TM mode TMBased on Figure 14a, d2 can be set to 300μm, and the tip width TW = 40nm is given for simulation to obtain the influence curve of the length d1 of the second waveguide 310 on the second loss, as shown in Figure 14b, where the horizontal axis LE represents the length d1 of the second waveguide 310, the vertical axis Loss2 represents the second loss, and different line types represent the second loss Loss2 of the TE mode respectively. TE and the second loss of TM mode Loss2 TM . Referring to Figure 14b, when d1 = 400 μm, Loss2 TE =-0.038dB, Loss2 TM =-0.028dB. In addition, taking d1 = 400μm and d2 = 300μm as an example, the second loss Loss2 is optimized by changing the tip width TW of the second waveguide 310. As shown in FIG14c, the horizontal axis TW represents the tip width of the second waveguide 310, and the vertical axis Loss2 represents the second loss. Different line types represent the second loss Loss2 of the TE mode. TE and the second loss of TM mode Loss2 TM In summary, when d2 = 300 μm, the tip width TW of the second waveguide 310 = 40 nm, and d1 = 400 μm, the coupling loss Loss of the end coupler corresponding to the TE mode is obtained through simulation. TE =Loss1 TE +Loss2 TE =-0.077dB, and the corresponding TM mode coupling loss Loss TM =Loss1 TM +Loss2 TM =-0.080 dB. It can be understood that when IB=1.5, d1=400 μm, d2=300 μm, and the tip width TW of the second waveguide 310=40 nm, the corresponding coupling loss is the lowest loss of the current structure.

[0093] FIG15 is a schematic diagram of the three-dimensional structure of an end coupler in another embodiment of the present application, FIG16 is a schematic diagram of the top view of the end coupler in FIG15 , and FIG17 is a schematic diagram of the cross-sectional structure along the dashed line AA' in FIG16 . Referring to FIG15 to FIG17 , the end coupler may include: a substrate 100 and a gradient index lens 200 disposed on the substrate 100, a second waveguide 310, a first waveguide 320, and a cladding 400. This embodiment differs from the embodiment shown in FIG11 in that the third waveguide 330 and the fourth waveguide 340 are not provided. In other words, the second side S12 of the second waveguide 310 is directly connected to the optical waveguide in the optoelectronic chip, so that the optical signal is directly coupled from the second waveguide 310 to the optical waveguide. The remaining details of this embodiment are substantially the same as those of the embodiment shown in FIG11 and are not further described here.

[0094] Taking the preparation of the end coupler structure shown in FIG15 as an example, the corresponding preparation method flowchart can be referred to FIG6 . In step S10, the third waveguide 330 does not need to be etched. In step S20, the fourth waveguide 340 does not need to be etched. The remaining preparation process can be referred to the description of the preparation method above and will not be repeated here.

[0095] The embodiment of the present application also provides a communication system, which includes an optical fiber, an optoelectronic chip, and an end coupler provided by the embodiment of the present application. The end face of the optical fiber is connected to the first side of the gradient refractive index lens in the end coupler, and the second waveguide in the end coupler is connected to the end face of the optical waveguide in the optoelectronic chip, so that the mode spot size of the end face of the optical fiber is reduced by the end coupler and then coupled to the optical waveguide. Since the coupling loss of the above-mentioned end coupler is low, the coupling loss of the communication system including the above-mentioned end coupler is also low. In addition, the principle of solving the problem of this communication system is similar to the principle of solving the problem of the aforementioned end coupler, so the technical effect of the communication system can refer to the technical effect of the aforementioned end coupler, and the repeated parts will not be repeated.

[0096] The above content is only a specific implementation method of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with this technical field can easily think of changes or replacements within the technical scope disclosed in this application, and they should all be covered by the protection scope of the present application.

Claims

1. An end coupler, characterized in that: include: A substrate, a waveguide structure located on the substrate, and a cladding covering the waveguide structure, wherein the waveguide structure comprises: a gradient refractive index lens, a first waveguide, and a second waveguide; The gradient refractive index lens has a first side and a second side arranged opposite to each other in a first direction, the first side of the gradient refractive index lens is used to connect to the optical fiber, and the first direction is parallel to the substrate; The first waveguide is located at a second side of the gradient refractive index lens and contacts the second side of the gradient refractive index lens, the first waveguide extends along the first direction, and an area of ​​a cross section of the first waveguide gradually decreases in a direction along the gradient refractive index lens pointing to the first waveguide; The second waveguide is located at a second side of the gradient refractive index lens and contacts the first waveguide, the second waveguide extends along the first direction, and the cross-sectional area of ​​the second waveguide gradually increases in a direction along the gradient refractive index lens pointing to the first waveguide, the side of the second waveguide away from the gradient refractive index lens is used to connect with an optical waveguide in an optoelectronic chip, and the refractive index of the first waveguide is smaller than that of the second waveguide.

2. The end coupler according to claim 1, characterized in that: The first waveguide covers the second waveguide, and a length of the first waveguide in the first direction is the same as a length of the second waveguide in the perpendicular direction.

3. The end coupler according to claim 1, characterized in that: The second waveguide is located on a side of the first waveguide away from the gradient refractive index lens, and the second waveguide is in contact with a side of the first waveguide away from the gradient refractive index lens.

4. The end coupler according to claim 1 or 2, characterized in that: The waveguide structure further includes: a third waveguide extending along the first direction, the third waveguide being in contact with a side of the second waveguide away from the gradient refractive index lens, and the side of the third waveguide away from the gradient refractive index lens being used to connect with an optical waveguide in an optoelectronic chip; In a direction along the gradient refractive index lens pointing toward the first waveguide, the cross-sectional areas of the third waveguide are the same.

5. The end coupler according to claim 4, characterized in that: The waveguide structure further includes: a fourth waveguide extending along the first direction, the fourth waveguide being in contact with a side of the first waveguide facing away from the gradient refractive index lens; Wherein, when the first waveguide covers the second waveguide, the fourth waveguide covers the third waveguide; or, When the second waveguide is located on a side of the first waveguide away from the gradient refractive index lens, the fourth waveguide covers the second waveguide and the third waveguide.

6. The end coupler according to claim 5, characterized in that: In a direction along the gradient refractive index lens pointing toward the first waveguide, the cross-sectional areas of the fourth waveguide are the same.

7. The end coupler according to any one of claims 4 to 6, characterized in that: The third waveguide and the second waveguide are integrally formed and made of the same material; and / or, The fourth waveguide and the first waveguide are integrally formed and made of the same material.

8. The end coupler according to any one of claims 1 to 7, characterized in that: The first waveguide comprises: a tapered waveguide; and / or, The second waveguide comprises: a tapered waveguide; and / or, The third waveguide comprises: a rectangular waveguide; and / or, The fourth waveguide includes: a rectangular waveguide.

9. The end coupler according to any one of claims 1 to 8, characterized in that: The gradient refractive index lens comprises: a plurality of light-transmitting layers stacked on the substrate, wherein the refractive indexes of the plurality of light-transmitting layers decrease in sequence in a direction from the substrate to the gradient refractive index lens; The first side surfaces of the plurality of light-transmitting layers in the first direction serve as the first side of the gradient refractive index lens, and the second side surfaces of the plurality of light-transmitting layers in the first direction serve as the second side of the gradient refractive index lens.

10. The end coupler according to claim 9, characterized in that: The first waveguide is in contact with a light-transmitting layer in the gradient index lens that is in contact with the substrate, and a refractive index of the first waveguide is the same as a refractive index of the light-transmitting layer in the gradient index lens that is in contact with the substrate.

11. The end coupler according to claim 10, characterized in that: The first waveguide and the light-transmitting layer in the gradient refractive index lens that is in contact with the substrate are an integrally formed structure and are made of the same material.

12. The end coupler according to any one of claims 1 to 11, characterized in that: The material of the first waveguide includes oxynitride; The material of the second waveguide includes silicon; The material of the cladding layer includes oxide; The material of the light-transmitting layer in the gradient refractive index lens includes oxynitride.

13. A method for preparing an end coupler, characterized in that: include: A second waveguide is formed on the substrate, wherein the second waveguide extends along a first direction, and in the first direction, the cross-sectional area of ​​the second waveguide gradually increases; the second waveguide is used to connect with the optical waveguide in the optoelectronic chip, and the first direction is parallel to the substrate; A gradient refractive index lens and a first waveguide are formed on the substrate, wherein the gradient refractive index lens has a first side and a second side arranged opposite to each other in a first direction, the first side of the gradient refractive index lens is used to connect with an optical fiber, the second waveguide contacts the first waveguide, the first waveguide contacts the second side of the gradient refractive index lens, the second waveguide extends along the first direction, and the cross-sectional area of ​​the second waveguide gradually decreases in the first direction; A cladding is deposited on the substrate, wherein the cladding covers the gradient refractive index lens, the first waveguide, and the second waveguide.

14. The preparation method according to claim 13, characterized in that: Also includes: A third waveguide is formed when the second waveguide is formed, the third waveguide extends along the first direction, the third waveguide is in contact with a side of the second waveguide away from the gradient refractive index lens, and the side of the third waveguide away from the gradient refractive index lens is used to connect with an optical waveguide in an optoelectronic chip; in a direction along the gradient refractive index lens pointing to the first waveguide, the cross-sectional area of ​​the third waveguide is the same; The cladding also covers the third waveguide.

15. The preparation method according to claim 14, characterized in that: The preparation method further includes: forming a fourth waveguide when forming the first waveguide, the fourth waveguide extending along the first direction, and the fourth waveguide contacting a side of the first waveguide away from the gradient refractive index lens; wherein when the first waveguide covers the second waveguide, the fourth waveguide covers the third waveguide; or when the second waveguide is located on a side of the first waveguide away from the gradient refractive index lens, the fourth waveguide covers the second waveguide and the third waveguide; The cladding also covers the fourth waveguide.

16. The preparation method according to any one of claims 13 to 15, characterized in that: The preparation method comprises: Providing a silicon-on-insulator substrate, the silicon-on-insulator substrate comprising bottom silicon, a buried oxide layer and top silicon; Patterning the top silicon and etching to form the second waveguide; The step of forming a gradient refractive index lens and a first waveguide on the substrate comprises: Depositing a plurality of silicon oxynitride film layers on the buried oxide layer on which the second waveguide is formed, wherein the refractive indexes of the plurality of silicon oxynitride film layers gradually decrease in a direction from the bottom silicon to the buried oxide layer; Patterning the remaining silicon oxynitride film layers among the plurality of silicon oxynitride film layers, and etching to form the remaining light-transmitting layers in the gradient refractive index lens, wherein the remaining silicon oxynitride film layers are the silicon oxynitride film layers among the plurality of silicon oxynitride film layers except the silicon oxynitride film layers in contact with the buried oxide layer; The silicon oxynitride film layer in contact with the buried oxide layer is patterned, and is etched to form a light-transmitting layer in contact with the buried oxide layer and the first waveguide in the gradient refractive index lens.

17. A communication system, characterized in that: Comprising an optical fiber, an optoelectronic chip and an end coupler as claimed in any one of claims 1 to 12; The end face of the optical fiber is connected to the first side of the gradient refractive index lens in the end face coupler, and the second waveguide in the end face coupler is connected to the end face of the optical waveguide in the optoelectronic chip.

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