End face coupler and preparation method thereof

Abstract

The present invention discloses an end face coupler and a preparation method thereof, and relates to the field of optical communication technology. The end face coupler of the present invention comprises a silicon substrate and a lower cladding and an upper cladding stacked on the silicon substrate, a first waveguide and a second waveguide for co-directional light transmission are arranged between the lower cladding and the upper cladding, the second waveguide is symmetrically arranged on opposite sides of the first waveguide, the first waveguide comprises a first cone waveguide and a first straight waveguide connected along the light propagation direction, the cone tail of the first cone waveguide is connected to the first straight waveguide, the second waveguide comprises a double-layer cone waveguide with a gradually increasing width along the light propagation direction, a second straight waveguide and a second cone waveguide with a gradually decreasing width along the light propagation direction, the cone tip of the first cone waveguide is flush with the cone tail of the second cone waveguide, and the double-layer cone waveguide comprises a second cone and a first cone stacked on the second cone. The end face coupler provided by the present invention can reduce the limitation of the cone tip width on the coupling loss and improve the conversion efficiency of the end face coupler.

Description

Technical Field

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

[0002] The end coupler is a type of silicon-based mode spot converter. It uses the principle of mode field diffusion or mode field compression to match two mode spots of different sizes. The coupling efficiency is relatively high, the wavelength correlation is not high, and the polarization sensitivity is relatively small. Conical structures are common in various end couplers, including two-dimensional inverted cones, cantilever cone couplers, etc. The two-dimensional inverted cone coupler has very high requirements for etching accuracy, and the alignment tolerance of the coupling is very small; the cantilever cone coupler has certain requirements for the process of etching away the substrate silicon, and the mechanical stability of the cantilever structure also needs to be considered.

[0003] The coupling loss of the end coupler based on the tapered silicon waveguide is extremely sensitive to the width of the cone tip. At present, the minimum process line width achieved in my country is 180nm. Taking the coupling of the two-dimensional inverted cone coupler and the single-mode optical fiber as an example, the relationship between the coupling loss and the width of the cone tip is that the larger the width of the cone tip, the lower the efficiency of the end coupling. Compared with the etching process of the foreign 80nm silicon photonic platform, the coupling of the two-dimensional inverted cone coupler and the single-mode optical fiber using the 180nm process of the domestic silicon photonic platform will increase the coupling loss by about 4.7dB. This makes the link budget of silicon-based optoelectronic devices tight and cannot reduce the cost of large-scale applications. Summary of the invention

[0004] The object of the present invention is to provide an end face coupler and a preparation method thereof, which can reduce the limitation of the cone tip width on the coupling loss and improve the conversion efficiency of the end face coupler.

[0005] The embodiment of the present invention is achieved as follows:

[0006] An end face coupler comprises a silicon substrate and a lower cladding and an upper cladding stacked on the silicon substrate, a first waveguide and a second waveguide for co-directional light transmission are arranged between the lower cladding and the upper cladding, the second waveguide is symmetrically arranged on two opposite sides of the first waveguide, the first waveguide comprises a first cone waveguide and a first straight waveguide connected along the light propagation direction, the cone tail of the first cone waveguide is connected to the first straight waveguide, the second waveguide comprises a double-layer cone waveguide with a gradually increasing width along the light propagation direction, a second straight waveguide and a second cone waveguide with a gradually decreasing width along the light propagation direction, the first cone is flush with the cone tail of the second cone, the double-layer cone waveguide comprises a second cone and a first cone stacked on the second cone, and incident light is incident from the double-layer cone waveguide.

[0007] Optionally, as an implementable manner, the distance between the cone tip of the first cone and the cone tip of the second cone is between 5-50 μm, and the cone tail widths of the first cone and the second cone are the same.

[0008] Optionally, as an implementable manner, the width of the cone tip of the second cone is between 180-350 nm.

[0009] Optionally, as an implementable manner, the ratio of the height of the first cone to the height of the second cone is between 1:1 and 1:2.2.

[0010] Optionally, as an implementable manner, the distance between the cone tip of the first cone waveguide and the light incident end face is between 50-120 μm, and the ratio of the cone tip width of the first cone waveguide to the width of the first straight waveguide is between 1:2-1:3.

[0011] Optionally, as an implementable manner, the width of the second straight waveguide is between 200-350 nm.

[0012] Optionally, as an implementable manner, the distance between the two second waveguides is between 0.9-1.2 μm.

[0013] A method for preparing an end coupler, comprising:

[0014] Providing an SOI wafer, the SOI wafer comprising a silicon substrate, a lower cladding layer and a silicon material layer sequentially arranged on the silicon substrate, wherein the lower cladding layer is silicon dioxide;

[0015] Etching the silicon material layer to form a first waveguide and a second waveguide on the lower cladding layer, wherein the second waveguide includes two symmetrically arranged on opposite sides of the first waveguide, the first waveguide includes a first tapered waveguide and a first straight waveguide connected along a light propagation direction, the tapered tail of the first tapered waveguide is connected to the first straight waveguide, the second waveguide includes a double-layer tapered waveguide with a gradually increasing width along the light propagation direction, a second straight waveguide, and a second tapered waveguide with a gradually decreasing width along the light propagation direction, the double-layer tapered waveguide includes a second cone and a first cone stacked on the second cone, and the first cone is flush with the second cone tail;

[0016] An upper cladding layer is deposited on the lower cladding layer, and the upper cladding layer covers the first waveguide and the second waveguide.

[0017] Optionally, as an implementable manner, etching the silicon material layer to form a first waveguide and a second waveguide on the lower cladding layer includes:

[0018] Performing a first etching on the silicon material layer through a first photomask to form a preformed structure of a first waveguide and a second waveguide on the lower cladding layer, wherein the preformed structure is a second straight waveguide, a second cone waveguide and a preformed body of a double-layer cone, and the preformed body of the double-layer cone is a cone having a bottom area that is the same as the bottom area of ​​the second cone and a height that is the sum of the heights of the first cone and the second cone;

[0019] The preformed structure is etched a second time through a second photomask to form a second waveguide.

[0020] Optionally, as an practicable manner, after depositing the upper cladding layer on the lower cladding layer, the method further includes:

[0021] Polishing and grinding the light emitting end face and light incident end face of the upper cladding and the lower cladding respectively;

[0022] The top surface of the upper cladding is polished and ground.

[0023] The beneficial effects of the embodiments of the present invention include:

[0024] The end face coupler provided by the present invention comprises a silicon substrate and a lower cladding and an upper cladding stacked on the silicon substrate, a first waveguide and a second waveguide for co-directional light transmission are arranged between the lower cladding and the upper cladding, the second waveguides are symmetrically arranged on opposite sides of the first waveguide, after the light transmitted from the laser is transmitted into the end face coupler, the light leaks between the two second waveguides and is distributed in the mode field along the second waveguide, the second waveguide is used to limit the quasi-coupled wave within a mode field of a predetermined size, the mode field of the predetermined size is consistent with the mode field of the laser, and then the light is secondary coupled by the first waveguide and passes through the end face coupler, the first waveguide comprises a first tapered waveguide and a first straight waveguide connected along the light propagation direction, so that when the silicon-based photonic chip is coupled with the end face coupler, the mode spot of the silicon-based photonic chip is close to the mode spot size of the quasi-coupled wave outgoing side of the end face coupler, thereby improving the silicon-based photonic chip. The coupling efficiency between the laser and the end coupler is improved. The second waveguide includes a double-layer cone waveguide with a gradually increasing width along the light propagation direction, a second straight waveguide and a second cone waveguide with a gradually decreasing width along the light propagation direction. The second waveguide is arranged so that when the laser is coupled to the end coupler, the mode spot of the laser is close to the mode spot size on the pseudo-coupled wave input side of the end coupler, thereby improving the coupling efficiency between the laser and the end coupler. The double-layer cone waveguide includes a second cone and a first cone stacked on the second cone, and the cone tails of the first cone and the second cone are flush. The incident light is incident from the double-layer cone waveguide. The width tolerance of the first cone and the second cone is large, so that the mode spot size of the double-layer cone waveguide and the laser is close, thereby improving the coupling efficiency between the laser and the end coupler, and then improving the coupling efficiency between the laser and the silicon-based photonic chip, and reducing the coupling loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0026] Figure 1 is a schematic diagram of an end coupler according to an embodiment of the present invention;

[0027] Figure 2 It is a schematic diagram of another viewing angle of the end face coupler according to an embodiment of the present invention;

[0028] Figure 3 This is a flow chart of a method for preparing an end coupler according to an embodiment of the present invention;

[0029] Figure 4 This is the second flow chart of the method for preparing the end coupler according to the embodiment of the present invention;

[0030] Figure 5 It is a structural flow chart of a method for preparing an end face coupler according to an embodiment of the present invention.

[0031] Icon: 111 - substrate; 112 - lower cladding; 113 - upper cladding; 120 - first waveguide; 121 - first tapered waveguide; 122 - first straight waveguide; 130 - second waveguide; 131 - double-layer tapered waveguide; 132 - second straight waveguide; 133 - second tapered waveguide. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0033] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0035] In the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "center", "vertical", "horizontal", "inside", "outside", etc. are based on the directions or positional relationships shown in the drawings and cannot be understood as limiting the present invention. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0036] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection or a detachable connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0037] With the rapid development of CMOS technology, the number of electronic devices that can be accommodated per unit area is increasing rapidly. SOI has excellent optical properties, and silicon and silicon dioxide have a very large refractive index difference, which has become an important choice for compatibility with high-performance chips and reducing device power consumption. Silicon-based photonic chips made of SOI materials are considered to have great potential in the direction of high-speed, miniaturization, and low cost of optoelectronic communication devices. However, the low-loss optical interconnection of silicon-based optoelectronic chips is a big problem for channel link budget. If directly docked and coupled, the single-ended insertion loss of the waveguide interface of the silicon-based photonic chip and the single-mode optical fiber is about 18dB, and even the insertion loss of the coupling with a 3μm laser with a slightly smaller mode spot exceeds 10.4dB. Therefore, it is necessary to design a special coupling structure on the chip to achieve efficient matching of the mode field between the end face of the silicon-based photonic chip and the external optical interface.

[0038] The present invention provides an end coupler, such as Figure 1 , Figure 2 As shown, the present invention comprises a silicon substrate 111 and a lower cladding layer 112 and an upper cladding layer 113 stacked on the silicon substrate 111, a first waveguide 120 and a second waveguide 130 for co-directional light transmission are arranged between the lower cladding layer 112 and the upper cladding layer 113, the second waveguide 130 is symmetrically arranged on opposite sides of the first waveguide 120, the first waveguide 120 comprises a first tapered waveguide 121 and a first straight waveguide 122 connected along the light propagation direction, the tapered tail of the first tapered waveguide 121 is connected to the first straight waveguide 122 The first cone waveguide 121 is connected to the second cone waveguide 132, the second waveguide 130 includes a double-layer cone waveguide 131 whose width gradually increases along the light propagation direction, a second straight waveguide 132 and a second cone waveguide 133 whose width gradually decreases along the light propagation direction, the cone tip of the first cone waveguide 121 is flush with the cone tail of the second cone waveguide 133, the double-layer cone waveguide 131 includes a second cone and a first cone stacked on the second cone, the first cone is flush with the cone tail of the second cone, and the incident light is incident from the double-layer cone waveguide 131.

[0039] Among them, the material of the upper cladding 113 and the lower cladding 112 is silicon dioxide, the first waveguide 120 and the second waveguide 130 are silicon waveguides, when the wavelength of the incident light is 1550nm, the refractive index of silicon is 3.45, and the refractive index of silicon dioxide is 1.45. The refractive index difference between silicon and silicon dioxide is very large. The silicon-based waveguide has a strong ability to limit light, and the cross-sectional area of ​​the strip silicon waveguide working in single mode is generally less than lum.

[0040] It should be noted that Figure 2 The A direction is the light propagation direction of the laser, the B surface is the light input end surface, and the C surface is the light output end surface.

[0041] The end face coupler provided by the present invention includes a silicon substrate 111 and a lower cladding 112 and an upper cladding 113 stacked on the silicon substrate 111. A first waveguide 120 and a second waveguide 130 for co-directional light transmission are arranged between the lower cladding 112 and the upper cladding 113. The second waveguide 130 is symmetrically arranged on opposite sides of the first waveguide 120. After the light transmitted from the laser is transmitted into the end face coupler, the light leaks between the two second waveguides 130 and is distributed in the mode field along the second waveguide 130. The second waveguide 130 is used to limit the quasi-coupled wave within a mode field of a predetermined size, which is consistent with the mode field of the laser. Then, the light is secondary coupled by the first waveguide 120 and passes through the end face coupler. The first waveguide 120 includes a first tapered waveguide 121 and a first straight waveguide 122 connected along the light propagation direction, so that when the silicon-based photonic chip is coupled with the end face coupler, the mode spot of the silicon-based photonic chip and the mode spot size of the quasi-coupled wave outgoing side of the end face coupler are equal. The second waveguide 130 includes a double-layer cone waveguide 131 whose width gradually increases along the light propagation direction, a second straight waveguide 132, and a second cone waveguide 133 whose width gradually decreases along the light propagation direction. The second waveguide 130 is arranged so that when the laser is coupled with the end face coupler, the mode spot of the laser is close to the mode spot size on the light incident side of the end face coupler, thereby improving the coupling efficiency between the laser and the end face coupler. The double-layer cone waveguide 131 includes a second cone and a first cone stacked on the second cone, and the cone tails of the first cone and the second cone are flush. The incident light is incident from the double-layer cone waveguide 131. The width tolerance of the first cone and the second cone is large, so that the mode spot size of the double-layer cone waveguide 131 and the laser is close, thereby improving the coupling efficiency between the laser and the end face coupler, and further improving the coupling efficiency between the laser and the silicon-based photonic chip, and reducing the coupling loss.

[0042] Optional, such as Figure 1 , Figure 2 As shown, the distance between the cone tip of the first cone and the cone tip of the second cone is between 5-50 μm, and the cone tail widths of the first cone and the second cone are the same.

[0043] The first cone and the second cone have flush cone tails and the same cone tail width, and the distance between the cone tips is between 5-50μm, so that the cone widths of the first cone and the second cone have a certain tolerance, and the first cone is stacked on the second cone, so that the heights of the first cone and the second cone have a certain tolerance, thereby making the double-layer cone waveguide 131 and the laser mode spot size close, thereby improving the coupling efficiency between the laser and the end face coupler, and then improving the coupling efficiency between the laser and the silicon-based photonic chip, and reducing coupling loss.

[0044] The sum of the heights of the cone tail of the first cone and the cone tail of the second cone is the same as the height of the second straight waveguide 132, and the cone tail widths of the first cone and the second cone are the same, so that the cone tail end face of the double-layer cone waveguide 131 is equal to the end face area of ​​the second straight waveguide 132. When light is transmitted in the second waveguide 130, it can be smoothly transmitted from the double-layer cone waveguide 131 to the second straight waveguide 132.

[0045] In one possible implementation of the embodiment of the present invention, Figure 1 , Figure 2 As shown, the width of the cone tip of the second cone is between 180-350 nm.

[0046] Those skilled in the art should know that the narrower the width of the cone tip, the smaller the restriction on the light field, and the light can leak into the upper cladding 113 and the lower cladding 112 to increase the light mode spot. In other words, the smaller the width of the second cone tip, the more conducive it is to increase the mode spot, and the increase in the mode spot will be more effective in making the mode spot close to the size of the mode spot of the silicon-based photonic chip, thereby improving the coupling efficiency. For the current etching process in my country, only etching with a line width of 180nm can be achieved. Based on the current etching process in my country, the width of the second cone tip can be set to 180nm. In actual production, due to the matching requirements of incident light spots of different sizes and some manufacturing errors, the etching width is usually greater than 180nm. Based on the line width process of the current etching process in my country and the requirements for improving coupling efficiency, the width of the cone tip of the second cone is set between 180-350nm.

[0047] Optional, such as Figure 1 , Figure 2 As shown, the ratio of the height of the first cone to the height of the second cone is between 1:1 and 1:2.2.

[0048] The height difference between the first cone and the second cone can better match the laser mode spot, and the laser mode spot is close to the mode spot on the light-incoming side of the end coupler, thereby improving the coupling efficiency between the laser and the end coupler. For example, the height of the first cone in the embodiment of the present invention is 70nm, the height of the second cone is 150nm, and the height of the double-layer cone waveguide 131 is the sum of the height of the first cone and the height of the second cone, that is, 220nm, which is the same as the height of the second straight waveguide 132 and the second cone waveguide 133.

[0049] In one possible implementation of the embodiment of the present invention, Figure 1 , Figure 2 As shown, the distance between the cone tip of the first cone waveguide 121 and the light incident end faces of the upper cladding 113 and the lower cladding 112 is between 50-120 μm, and the ratio of the width of the cone tip of the first cone waveguide 121 to the width of the first straight waveguide 122 is between 1:2-1:3.

[0050] The double-layer tapered waveguide 131 of the two second waveguides 130 confines the laser mode field emitted by the laser to the area between them and propagates forward to the two second straight waveguides 132 respectively, and is steadily transmitted forward to the second tapered waveguide 133 in the second straight waveguide 132. Because the width of the second tapered waveguide 133 gradually decreases along the light propagation direction, the laser mode field confined in the center of the waveguide will leak out from the silicon waveguide and enter the upper cladding 113 and the lower cladding 112 with low refractive index, and the size of the mode spot increases. The distance between the cone tip of the first tapered waveguide 121 and the light incident end face of the upper cladding 113 and the lower cladding 112 is 50-120 μm, the lengths of the double-layer cone waveguide 131 and the second straight waveguide 132 are also within this range. When the width of the second cone waveguide 133 gradually decreases, the first cone waveguide 121 appears and its width along the light propagation direction gradually increases. At this time, the laser mode field is gradually coupled to the first cone waveguide 121, transmitted to the first straight waveguide 122 and emitted from the end of the first straight waveguide 122, and the width of the first cone waveguide 121 gradually increases along the light propagation direction until it is the same as the first straight waveguide 122, so that the light field between the upper cladding 113 and the lower cladding 112 is gradually coupled to the first waveguide 120, thereby improving the conversion efficiency of the end coupler.

[0051] Optional, such as Figure 1 , Figure 2 As shown, the width of the second straight waveguide 132 is between 200-350 nm.

[0052] After the laser is incident from the double-layer tapered waveguide 131, it is transmitted to the second straight waveguide 132 and is steadily transmitted forward in the second straight waveguide 132. In order to enable the laser to be steadily transmitted in the second straight waveguide 132, the width of the second straight waveguide 132 is set to be between 200-350nm.

[0053] In one possible implementation of the embodiment of the present invention, Figure 1 , Figure 2 As shown, the distance between the two second straight waveguides 132 is between 0.9 μm and 1.2 μm.

[0054] The two second waveguides 130 confine the incident laser mode field between them, and then propagate forward to the first waveguide 120. Here, the distance between the two second straight waveguides 132 is limited to 0.9-1.2μm, because when the distance between the two second straight waveguides 132 is less than 0.9μm, it is easy to cause etching errors, or it does not meet the process standards of some silicon photonic platforms; when the distance between the two second waveguides 130 is greater than 1.2μm, the end face mode spot formed is multi-mode, and the coupling loss will increase rapidly. It should be noted that the distance between the straight waveguides here is the distance between the geometric centers of the two second straight waveguides 132.

[0055] It should be noted that the end face coupler of the embodiment of the present invention performs mode spot conversion on a laser with a mode spot size of 2.7 μm×1.7 μm. The mode spot size after coupling by the end face coupler of the present invention is about 0.4 μm.

[0056] A method for preparing an end coupler, such as Figure 3 , Figure 5 As shown, including:

[0057] S110: providing an SOI wafer, wherein the SOI wafer comprises a silicon substrate 111, a lower cladding layer 112 and a silicon material layer sequentially arranged on the silicon substrate 111, wherein the lower cladding layer 112 is silicon dioxide;

[0058] S120: etching the silicon material layer to form a first waveguide 120 and a second waveguide 130 on the lower cladding layer 112, wherein the second waveguide 130 includes two symmetrically arranged on opposite sides of the first waveguide 120, the first waveguide 120 includes a first cone waveguide 121 and a first straight waveguide 122 connected along a light propagation direction, the cone tail of the first cone waveguide 121 is connected to the first straight waveguide 122, the second waveguide 130 includes a double-layer cone waveguide 131 with a gradually increasing width along the light propagation direction, a second straight waveguide 132 and a second cone waveguide 133 with a gradually decreasing width along the light propagation direction, the double-layer cone waveguide 131 includes a second cone and a first cone stacked on the second cone, and the cone tails of the first cone and the second cone are flush;

[0059] S130 : depositing an upper cladding layer 113 on the lower cladding layer 112 , wherein the upper cladding layer 113 covers the first waveguide 120 and the second waveguide 130 .

[0060] Among them, before etching, the parameters of each structure must be determined first. Since the insertion loss of the end face coupler mainly comes from the mismatch between the end face mode field and the laser mode spot area, it is necessary to first determine the parameters of the end face mode field, the cone tip width of the light-entering end face of the second waveguide 130, the center distance between the two second waveguides 130, and then determine the body width of the second waveguide 130 and the cone tip width of the first waveguide 120. Use the Launch MOST Scanner module of the RSOFT simulation software to determine the above parameters in turn. Etch the silicon material layer according to the determined parameters.

[0061] Optional, such as Figure 4 , Figure 5 As shown, etching the silicon material layer to form the first waveguide 120 and the second waveguide 130 on the lower cladding layer 112 includes:

[0062] S121: performing a first etching on the silicon material layer through a first photomask to form a preformed structure of the first waveguide 120 and the second waveguide 130 on the lower cladding layer 112, wherein the preformed structure is a second straight waveguide, a second cone waveguide and a preform of a double-layer cone, and the preform of the double-layer cone is a cone whose bottom area is the same as the bottom area of ​​the second cone and whose height is the sum of the heights of the first cone and the second cone;

[0063] S122 : performing a second etching on the preformed structure through a second photomask to form a second waveguide 130 .

[0064] Before performing the first etching, the first etching range, that is, the preformed structure of the first waveguide 120 and the second waveguide 130, is determined according to the simulation results of the RSOFT simulation software. The preformed structure includes a preform of a second straight waveguide 132, a second tapered waveguide 133 and a double-layer tapered waveguide 131. Then, a first mask that can etch the first etching range is made according to the first etching range. The first mask is placed on the silicon material layer. The laser light source performs the first etching on the silicon material layer through the first mask. The first etching depth is 220nm, that is, the height of the silicon material layer.

[0065] Similarly, before the second etching, a second photomask for the second etching should be prepared according to the width range and the starting and ending positions of the first cone. It should be noted here that because the first cone is stacked on the second cone, a preform of the double-layer cone waveguide 131 has been etched in the preformed structure, that is, a cone with a height of 220nm. The preform has the same outer contour as the second cone, and the height is the height of the first cone plus the second cone. At this time, it is only necessary to etch the depth of the first cone downward on the preform of the double-layer cone waveguide 131 to form the double-layer cone waveguide 131. Therefore, the etching range of the second photomask should fall within the etching range of the first photomask, and the light-transmitting area of ​​the second photomask should not be larger than the area of ​​the second cone. Then, the second photomask is set on the preformed structure of the second waveguide 130, and the laser is used for etching. The laser light source etches the preformed structure of the second waveguide 130 through the second photomask to form the double-layer cone waveguide 131, and the second waveguide 130 is also formed.

[0066] In one possible implementation of the embodiment of the present invention, Figure 3 , Figure 5 As shown, after depositing the upper cladding layer 113 on the lower cladding layer 112, the method further includes:

[0067] S140: polishing and grinding the light emitting end faces and light incident end faces of the upper cladding 113 and the lower cladding 112 respectively; and polishing and grinding the top surface of the upper cladding.

[0068] When the laser is incident on the end face coupler, if the incident light end faces of the upper cladding 113 and the lower cladding 112 of the end face coupler are rough, those skilled in the art should know that the rough incident light end faces will cause scattering of the laser at the incident light end faces, resulting in scattering losses. The smoother the incident light end faces, the smaller the scattering losses. Polishing and grinding the incident light end faces of the upper cladding 113 and the lower cladding 112 to obtain a smooth incident light end face and improve the flatness of the end face can effectively reduce the scattering losses. Similarly, polishing and grinding the light output end faces of the upper cladding 113 and the lower cladding 112 can also further reduce the scattering losses.

[0069] Because the end face coupler is made by depositing materials layer by layer, the top of the upper cladding layer 113 is rough. In order to obtain a smooth upper surface and reduce the laser scattering from the end face coupler from the upper cladding layer 113, the top surface of the upper cladding layer 113 is also polished.

[0070] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An end coupler, It is characterized in that The invention comprises a silicon substrate and a lower cladding and an upper cladding stacked on the silicon substrate, a first waveguide and a second waveguide for co-directional light transmission are arranged between the lower cladding and the upper cladding, the second waveguide is symmetrically arranged on two opposite sides of the first waveguide, the first waveguide comprises a first tapered waveguide and a first straight waveguide connected along a light propagation direction, the tapered tail of the first tapered waveguide is connected to the first straight waveguide, the second waveguide comprises a double-layer tapered waveguide with a gradually increasing width along the light propagation direction, a second straight waveguide and a second tapered waveguide with a gradually decreasing width along the light propagation direction, the tapered tip of the first tapered waveguide is flush with the tapered tail of the second tapered waveguide, the double-layer tapered waveguide comprises a second cone and a first cone stacked on the second cone, the first cone is flush with the tapered tail of the second cone, and incident light is incident from the double-layer tapered waveguide; The distance between the cone tip of the first cone and the cone tip of the second cone is between 5 and 50 μm, and the cone tail widths of the first cone and the second cone are the same; The ratio of the height of the first cone to the height of the second cone is between 1:1 and 1:2.

2.

2. The end coupler according to claim 1, It is characterized in that The width of the cone tip of the second cone is between 180 and 350 nm.

3. The end coupler according to claim 1, It is characterized in that The distance between the cone tip of the first cone waveguide and the light incident end face is between 50 and 120 μm, and the ratio of the width of the cone tip of the first cone waveguide to the width of the first straight waveguide is between 1:2 and 1:

3.

4. The end coupler according to claim 3, It is characterized in that The width of the second straight waveguide is between 200 nm and 350 nm.

5. The end coupler according to claim 1, It is characterized in that The distance between two of the second waveguides is between 0.9 μm and 1.2 μm.

6. A method for preparing an end coupler according to any one of claims 1 to 5, It is characterized in that include: Providing an SOI wafer, the SOI wafer comprising a silicon substrate, a lower cladding layer and a silicon material layer sequentially arranged on the silicon substrate, the lower cladding layer being silicon dioxide; Etching the silicon material layer to form a first waveguide and a second waveguide on the lower cladding, wherein the second waveguide includes two and is symmetrically arranged on opposite sides of the first waveguide, the first waveguide includes a first tapered waveguide and a first straight waveguide connected along a light propagation direction, the tapered tail of the first tapered waveguide is connected to the first straight waveguide, the second waveguide includes a double-layer tapered waveguide with a gradually increasing width along the light propagation direction, a second straight waveguide, and a second tapered waveguide with a gradually decreasing width along the light propagation direction, the double-layer tapered waveguide includes a second cone and a first cone stacked on the second cone, and the first cone is flush with the cone tail of the second cone; An upper cladding layer is deposited on the lower cladding layer, and the upper cladding layer covers the first waveguide and the second waveguide.

7. The method for preparing the end coupler according to claim 6, It is characterized in that After depositing the upper cladding layer on the lower cladding layer, the method further comprises: The light emitting end face and the light incident end face of the upper cladding and the lower cladding are polished and ground respectively; and the top surface of the upper cladding is polished and ground.

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