Preparation method of tapered waveguide and tapered waveguide

Abstract

The invention provides a tapered waveguide preparation method and a tapered waveguide, and belongs to the technical field of waveguides, and the tapered waveguide preparation method comprises the steps: S1, sequentially forming a lower coating layer and a first center layer on a substrate; s2, forming photoresist with an inclined side wall on the first central layer; s3, etching the first central layer by taking the photoresist with the inclined side wall as a mask to form a conical central layer; s4, adjusting the thickness of the conical central layer according to the application wavelength of the conical waveguide; and S5, forming an upper coating layer on the conical center layer to prepare the conical waveguide. The method has the beneficial effects that the photoresist with the inclined side wall is used as the mask to form the conical central layer with the inclined side wall, a gray scale photoetching plate or an expensive direct-writing gradient photoetching machine does not need to be additionally customized, the production cost is reduced, and the method can be popularized and applied in a large scale.

Description

Technical Field

[0001] The present invention relates to the field of waveguide technology, and in particular to a method for preparing a tapered waveguide and the tapered waveguide. Background Art

[0002] Waveguide is an indispensable component in integrated optoelectronic devices and can be widely used in optical power splitters, optical couplers, optical modulators, interferometer-based switches, semiconductor lasers and dense wavelength division multiplexing (DWDM) communication systems.

[0003] In the design and manufacturing process of waveguides, scattering loss is one of the important indicators for evaluating its transmission efficiency and quality. This loss is proportional to the square of the refractive index difference between the core layer and the cladding layer of the waveguide. Although the traditional silicon (Si) / silicon dioxide (SiO2) waveguide system has been maturely applied, it is limited by its large refractive index difference, resulting in relatively high scattering loss. When the wavelength of the light source is lower than 1100nm, it will encounter significant light absorption, which limits its application effect within a specific wavelength range. In contrast, the silicon nitride (SiN) / silicon dioxide (SiO2) waveguide system can theoretically significantly reduce scattering losses due to its smaller refractive index difference, thereby achieving efficient and low-loss light transmission in a wider wavelength range (such as 400-2000nm), making SiN / SiO2 waveguides widely used in fields including but not limited to extended reality displays (XR Displays), quantum computing, quantum sensing, data communications, gyroscopes, and telecommunications.

[0004] When traditional ridge waveguide and channel waveguide structures are optically coupled with lasers or single-mode optical fibers, there is a mode mismatch phenomenon, which leads to coupling loss, reduces the optical coupling efficiency, and increases the overall loss of the system.

[0005] To overcome the problem of modal mismatch, the mainstream solution in the prior art is to introduce a tapered structure into the waveguide. The tapered structure gradually changes the cross-sectional size and shape of the waveguide to achieve a smoother modal transition between the waveguide and the light source, thereby reducing the coupling loss caused by modal mismatch and improving the optical coupling efficiency.

[0006] However, despite the significant theoretical advantages of the tapered structure, its manufacturing process faces many challenges. The current mainstream manufacturing solution is to form a photoresist pattern with an inclined shape on the central layer through a grayscale mask, and transcribe the shape of the photoresist pattern to the central layer. This solution requires the combination of photoresist and grayscale mask to form a 3D tapered waveguide.

[0007] Another method for manufacturing a conical structure is to use 3D grayscale lithography to expose and develop the photoresist according to the shape and size of the conical structure to obtain a conical structure pattern of the photoresist layer, and then transfer the conical structure pattern of the photoresist layer to the top silicon layer. This method relies on 3D grayscale lithography.

[0008] In summary, the existing conical structure manufacturing process usually requires customized grayscale photomasks or expensive direct-write exposure equipment, which increases production costs and process complexity and is not conducive to large-scale promotion and application. Summary of the invention

[0009] In order to solve the above technical problems, the present invention provides a method for preparing a tapered waveguide and a tapered waveguide.

[0010] The technical problem solved by the present invention can be achieved by adopting the following technical solutions:

[0011] A method for preparing a tapered waveguide, comprising:

[0012] Step S1, forming a lower cladding layer and a first central layer in sequence on a substrate;

[0013] Step S2, forming a photoresist having inclined sidewalls on the first central layer;

[0014] Step S3, using the photoresist with the inclined sidewall as a mask, etching the first central layer to form a tapered central layer;

[0015] Step S4, adjusting the thickness of the tapered center layer according to the application wavelength of the tapered waveguide;

[0016] Step S5, forming an upper cladding layer on the tapered central layer to prepare the tapered waveguide.

[0017] Preferably, the substrate is any one of a silicon substrate, a glass substrate, a gallium arsenide substrate, an indium phosphide substrate, a gallium nitride substrate, and a sapphire substrate.

[0018] Preferably, step S2 comprises:

[0019] Step S21, coating photoresist on the first central layer;

[0020] Step S22 , exposing the photoresist and underexposing the photoresist to form the photoresist having inclined sidewalls on the first central layer.

[0021] Preferably, in step S22, the exposure time is adjusted according to the type of the photoresist to achieve underexposure.

[0022] Preferably, in step S22, adjusting the exposure time in the following manner includes:

[0023] If the photoresist is a positive photoresist, reducing the exposure time;

[0024] If the photoresist is a negative photoresist, increase the exposure time.

[0025] Preferably, in step S4, the thickness of the tapered central layer is increased according to the application wavelength of the tapered waveguide.

[0026] Preferably, in the step S5, after forming the upper cladding layer on the tapered central layer, the step further comprises:

[0027] The substrate, the lower cladding layer, the tapered central layer and the upper cladding layer are photolithographically and etched together in a first direction perpendicular to the substrate to prepare the tapered waveguide.

[0028] The present invention also provides a tapered waveguide, which is prepared by the tapered waveguide preparation method as described above, and the tapered waveguide comprises:

[0029] a lower cladding layer formed on the substrate;

[0030] A tapered central layer is formed on the lower cladding layer by etching using a photoresist having an inclined sidewall as a mask, wherein the thickness of the tapered central layer is related to the application wavelength of the tapered waveguide;

[0031] An upper cladding layer is formed on the tapered central layer.

[0032] Preferably, the tapered waveguide includes a first tapered waveguide portion, a second tapered waveguide portion and a third tapered waveguide portion in sequence in a first direction perpendicular to the substrate;

[0033] The thickness of the first tapered waveguide portion and the thickness of the third tapered waveguide portion remain unchanged, and the thickness of the second tapered waveguide portion decreases at a first preset taper trend until it becomes the same as the thickness of the third tapered waveguide portion;

[0034] The widths of the first tapered waveguide portion and the second tapered waveguide portion decrease in a second preset taper trend until they are the same as the width of the third tapered waveguide portion;

[0035] The width of the third tapered waveguide portion decreases at a third preset taper trend;

[0036] The second preset taper trend is different from the third preset taper trend.

[0037] Preferably, the second preset taper trend is greater than the third preset taper trend.

[0038] Preferably, the first tapered waveguide portion and the second tapered waveguide portion are multimode tapered waveguides, and the third tapered waveguide portion is a single-mode tapered waveguide.

[0039] The advantages or beneficial effects of the technical solution of the present invention are:

[0040] The tapered waveguide prepared by the present invention can reduce the light loss when coupled with a laser light source or an optical fiber, thereby improving the overall performance of the device; at the same time, in the process of preparing the tapered waveguide, a photoresist with inclined side walls is used as a mask to form a tapered central layer with inclined side walls, without the need for additional customized grayscale photolithography plates or expensive direct-write gradient photolithography machines, thereby reducing production costs and enabling large-scale promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of a process for preparing a tapered waveguide in a preferred embodiment of the present invention;

[0042] Figure 2a-2i FIG. 1 is a schematic diagram of the steps of the method for preparing a tapered waveguide in a preferred embodiment of the present invention; wherein: Figure 2a-2h is a cross-sectional schematic diagram, Figure 2i It is a top view;

[0043] Figure 3 In a preferred embodiment of the present invention, Figure 2d Top view of the medium reticle.

[0044] Description of reference numerals:

[0045] 100, substrate; 200, lower cladding layer; 300, first center layer; 301, tapered center layer; 302, second center layer; 400, photoresist; 500, upper cladding layer; 600, tapered waveguide; 601, first tapered waveguide portion; 602, second tapered waveguide portion; 603, third tapered waveguide portion; 700, photolithography plate. DETAILED DESCRIPTION

[0046] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0048] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0049] See also Figure 1 In a preferred embodiment of the present invention, based on the above problems existing in the prior art, a method for preparing a tapered waveguide is provided, wherein the tapered waveguide is a SiO2 / SiN / SiO2 structure, comprising:

[0050] Step S1, forming a lower cladding layer 200 and a first central layer 300 in sequence on a substrate 100;

[0051] First, if Figure 2a As shown, a substrate 100 is provided, and the substrate 100 can be made of different substrate materials, including but not limited to a silicon substrate, a glass substrate, a gallium arsenide (GaAs) substrate, an indium phosphide (InP) substrate, a gallium nitride (GaN) substrate, and a sapphire substrate. The substrate material can be selected according to specific application scenarios and design requirements to be suitable for different optoelectronic or microelectronic devices.

[0052] Subsequently, the provided substrate 100 is cleaned to remove organic pollutants such as grease, fingerprints, etc. on the surface of the substrate 100 .

[0053] After cleaning is completed, Figure 2b As shown, a lower cladding layer 200 is prepared on the upper surface of the substrate 100;

[0054] In this embodiment, the lower cladding layer 200 is made of SiO2. The SiO2 material is deposited on the upper surface of the substrate 100 by an evaporation process to form the lower cladding layer 200. The evaporation process heats the SiO2 source material to evaporate it, and then the evaporated gas molecules condense on the substrate surface to form a thin film.

[0055] like Figure 2c As shown, the first core layer 300 is formed on the lower cladding layer 200 .

[0056] In this embodiment, the first central layer 300 is made of SiN. SiN material can also be deposited on the upper surface of the lower cladding layer 200 by evaporation process to form the first central layer 300.

[0057] In this embodiment, the specific methods of evaporation include but are not limited to the following methods: plasma enhanced chemical vapor deposition (PECVD), low pressure chemical vapor deposition (LPCVD), atomic layer deposition (ALD), high temperature furnace tube deposition, electron beam evaporation (E-Gun), which can be flexibly selected according to actual production conditions.

[0058] Step S2, such as Figure 2d As shown, a photoresist 400 having an inclined sidewall is formed in the first central layer 300;

[0059] Specifically, the photoresist is uniformly coated on the surface of the first central layer 300 to form a photoresist layer of a certain thickness; the photoresist plate is closely contacted with the substrate coated with the photoresist 400 and placed under a photolithography machine for exposure to achieve patterning of the photoresist.

[0060] In this embodiment, Figure 3 As shown, the photomask 700 is a conventional contact photomask. The pattern on the photomask 700 is consistent with the pattern to be processed, and the surface of the photomask is clean and has no defects.

[0061] In the standard photolithography process, the specific thickness of each photoresist corresponds to an optimized photolithography energy, which is the product of the mercury lamp power and exposure time equipped by the photolithography machine, wherein the mercury lamp power is a fixed value. Conventional exposure operations generally use optimized photolithography energy for normal exposure, and the sidewalls of the photoresist are vertical under normal exposure. Different from conventional exposure operations, in this embodiment, by only changing the intensity of the exposure machine, the entire surface is deliberately underexposed, that is, the optimized photolithography time is adjusted to achieve a one-time operation so that the sidewalls of the photoresist 400 are sloped, and the slope position is determined by the photolithography plate.

[0062] When this embodiment is applied, the exposure energy can be further reduced. Since the power of the ultraviolet mercury lamp of a traditional contact lithography machine is usually fixed, in this embodiment, by adjusting the lithography time, the side wall of the photoresist can be made to be sloped after exposure. The slope formed by this deliberate underexposure is gentle, and the surface size changes less drastically, so that the multi-mode waveguide gradually changes into a single-mode waveguide, reducing the light loss when coupling with a laser light source or optical fiber, and improving the overall performance of the device. In addition, the use of traditional standard lithography processes does not require additional customized grayscale lithography plates, nor does it require the purchase of expensive direct-write gradient lithography machines, which reduces manufacturing costs, and because traditional standard lithography technology is mature, the yield rate of manufactured products is improved.

[0063] Furthermore, in addition to deliberate underexposure, the hard-bake temperature of the photoresist can be increased to further change the collimation of the photoresist sidewall to meet different processing requirements. The hard-bake temperature can be set by referring to the photoresist data sheet.

[0064] Step S3, such as Figure 2e and Figure 2f As shown, the first central layer 300 is etched using the photoresist 400 with inclined sidewalls as a mask to form a tapered central layer 301;

[0065] Specifically, the patterned photoresist layer 400 with inclined sidewalls is used as a mask, and a dry etching technique is adopted to perform etching on the first central layer 300. Due to the existence of the photoresist 400, the first central layer 300 below is protected.

[0066] Since one side edge of the photoresist 400 is sloped, that is, its thickness gradually decreases. As the etching proceeds, the thinner portion of the photoresist gradually loses its protective effect on the underlying material, thereby starting to etch the first central layer 300 below, transferring the inclined shape of the side wall of the photoresist 400 to the first central layer 300. After etching, the edge of the first central layer 300 presents a slope shape corresponding to the side wall of the photoresist 400, that is, a tapered central layer 301 is formed.

[0067] After the etching is completed, the remaining photoresist 400 is removed, and the tapered central layer 301 with the inclined sidewall is retained. The tapered structure of the first central layer 300 is etched by using the inclined sidewall of the photoresist 400 as a natural mask during the etching process.

[0068] Step S4, such as Figure 2g As shown, the thickness of the tapered center layer 301 is adjusted according to the application wavelength of the tapered waveguide 600;

[0069] Specifically, for a specific wavelength at which the tapered waveguide 600 is applied, the thickness of the tapered central layer 301 is dynamically adjusted to ensure that the waveguide achieves optimal optical performance at the wavelength.

[0070] Furthermore, the relationship between the thickness of the tapered central layer 301 (ie, the SiN waveguide) and the wavelength satisfies the following formula:

[0071]

[0072] Wherein, α represents the thickness of the conical center layer 301;

[0073] λ represents the specific wavelength to which the tapered waveguide 600 is applied;

[0074] n core represents the refractive index of the tapered central layer 301;

[0075] n cladding Represents the refractive index of the cladding layer.

[0076] The embodiment of the present invention realizes segmented production of SiN waveguide by re-evaporation of the central layer, solves the problem that the traditional standard photolithography process cannot accurately control the layer thickness, and can meet the transmission requirements of specific application wavelengths.

[0077] Step S5, such as Figure 2h As shown, an upper cladding layer 500 is formed on the tapered central layer 301 to prepare a tapered waveguide;

[0078] In this embodiment, the upper cladding layer 500 is made of SiO2. SiO2 material is deposited again on the upper surface of the conical center layer 301 by evaporation process to form the upper cladding layer 500. The surface of the upper cladding layer 500 also retains the conical structure of the conical center layer 301.

[0079] The tapered waveguide prepared by the present invention can reduce the light loss when coupled with a laser light source or an optical fiber, and improve the overall performance of the device; at the same time, in the process of preparing the tapered waveguide, a photoresist with inclined side walls is formed by using a photomask using underexposure technology, so that a tapered center layer is formed using it as a mask, without the need for additional customized grayscale photomasks or expensive direct-write gradient lithography machines, thereby reducing production costs and enabling large-scale promotion and application.

[0080] Specifically, the preparation process of the tapered waveguide of the present invention can be applied to different substrate materials. As a preferred embodiment, the substrate 100 is any one of a silicon substrate, a glass substrate, a gallium arsenide (GaAs) substrate, an indium phosphide (InP) substrate, a gallium nitride (GaN) substrate, and a sapphire substrate.

[0081] As a preferred embodiment, step S2 includes:

[0082] Step S21, coating a photoresist 400 on the first central layer 300;

[0083] In step S22 , the photoresist 400 is exposed and underexposed to form the photoresist 400 having an inclined sidewall on the first central layer 300 .

[0084] As a preferred implementation, in step S22, the exposure time is adjusted according to the type of photoresist to achieve underexposure.

[0085] Specifically, this embodiment adjusts the exposure time to achieve deliberate underexposure, and directly uses traditional standard photomasks and photoresists to shape the formation of the sidewall slope, and the formed slope is relatively gentle, thereby achieving a smooth transition from a multi-mode waveguide to a single-mode waveguide, reducing light loss when coupling with a laser light source or optical fiber, and thereby improving the overall performance and efficiency of the device.

[0086] As a preferred implementation, in step S22, adjusting the exposure time in the following manner includes:

[0087] If the photoresist type is positive photoresist, reduce the exposure time;

[0088] If the photoresist type is negative photoresist, increase the exposure time.

[0089] Specifically, after the positive photoresist is exposed, the photoresist in the exposed area becomes soluble in the developer, so that these areas are removed during the development process, leaving the pattern of the unexposed area. Therefore, in this embodiment, if a positive photoresist is used, the exposure time is reduced, that is, the optimized photolithography time is reduced, thereby forming a photoresist with inclined sidewalls.

[0090] In contrast to positive photoresist, negative photoresist becomes insoluble in developer after exposure, so the unexposed area is removed during the development process. Therefore, in this embodiment, if negative photoresist is used, the exposure time is increased, that is, the optimized photolithography time is increased, thereby forming a photoresist with inclined sidewalls.

[0091] Further, the photoresist 400 with the inclined sidewall is used as a mask to etch the first central layer 300 not covered by the photoresist 400. The photoresist 400 covers the first central layer 300 and protects the first central layer 300 below. As the etching proceeds, the inclined sidewall portion of the photoresist gradually loses its protective effect on the underlying material, thereby etching the first central layer 300 below the inclined sidewall, so that the edge of the tapered central layer 301 formed after etching also presents a slope shape corresponding to the sidewall of the photoresist 400.

[0092] As a preferred embodiment, in step S4, the thickness of the tapered central layer is increased according to the application wavelength of the tapered waveguide.

[0093] Specifically, according to the application wavelength of the tapered waveguide 600 , the second center layer 302 is formed on the tapered center layer 301 .

[0094] In this embodiment, the second center layer is made of SiN. SiN material is deposited again on the upper surface of the conical center layer 301 by an evaporation process to form the second center layer 302. The surface shape of the second center layer 302 is the same as the conical structure shape of the conical center layer 301, and the thickness of the conical center layer 301 is increased by the second center layer 302.

[0095] As the thickness of the cone center layer increases, its surface shape remains unchanged.

[0096] It should be noted that the thickness of the second central layer 302 can be set according to the performance parameters of the SiN waveguide at the target wavelength. As an example but not a limitation, the thickness of the second central layer 302 is 150 nm to 250 nm.

[0097] The SiN waveguide of the embodiment of the present invention is manufactured in sections, and can meet the transmission requirements of specific application wavelengths.

[0098] Furthermore, in step S1 , the thickness of the first central layer 300 is 8 μm to 10 μm.

[0099] Furthermore, in step S4, the thickness of the second central layer is 150 nm to 250 nm.

[0100] In this embodiment, the thickness of the lower cladding layer 200 may preferably be 2.5 μm.

[0101] In this embodiment, the thickness of the upper cladding layer 500 may preferably be 1.5 μm.

[0102] It should be noted that the thickness of the upper cladding layer, the first center layer, the second center layer, and the lower cladding layer of the tapered waveguide can be adjusted according to the mode size / wavelength of the integrated laser to achieve the best even-light efficiency at the Taper end and the single-mode output effect at the tail end.

[0103] Furthermore, the thickness of the tapered waveguide 600 varies in sections. Figure 2h As shown, the thickness of the tapered waveguide 600 changes in three stages. Starting from the Taper end, the thickness is kept constant at first, then decreases according to a certain trend (ie, the first preset taper trend below), and finally the thickness is kept constant.

[0104] As a preferred embodiment, in step S5, after forming the upper cladding layer 500 on the tapered central layer 301, the method further includes:

[0105] The substrate 100 , the lower cladding layer 200 , the tapered central layer 301 and the upper cladding layer 500 are photolithographically and etched together in a direction perpendicular to the substrate 100 to prepare a tapered waveguide.

[0106] Specifically, the substrate 100, the lower cladding layer 200, the tapered central layer 301 and the upper cladding layer 500 are photolithographically and etched together in a direction perpendicular to the substrate 100 using a photolithography process and a dry etching process to make the side wall of the SiO2 / SiN / SiO2 waveguide inclined.

[0107] For ease of understanding, in this article, the first direction perpendicular to the substrate 100 is the vertical direction from the upper cladding layer 500 to the substrate 100; the second direction parallel to the substrate 100 is the horizontal direction from the first tapered waveguide portion 601 to the third tapered waveguide portion 603, that is, the waveguide transmission direction, which is from the Taper end to the tail end.

[0108] The width described herein refers to a dimension or length perpendicular to the waveguide transmission direction, and the thickness refers to a dimension or thickness in a first direction perpendicular to the substrate 100 .

[0109] The taper end is the end close to the first tapered waveguide portion 601 , and may also be referred to as the incident end; the tail end is the end where the third tapered waveguide portion 603 is located.

[0110] Furthermore, the inclination of the side wall of the tapered waveguide 600 also changes in sections. Figure 2i As shown, the inclination of the sidewall of the tapered waveguide 600 changes in two stages. Starting from the taper end, it first decreases according to the second preset taper trend, and then decreases according to the third preset taper trend.

[0111] The second preset taper trend is greater than the third preset taper trend, that is, compared with the second preset taper trend, the third preset taper trend is gentler.

[0112] It should be noted that the first preset taper trend, the second preset taper trend and the third preset taper trend can be set as needed, and this embodiment does not limit their specific setting values.

[0113] The three-dimensional (3D) conical waveguide of SiO2 / SiN / SiO2 structure is prepared by the above preparation method, and the manufacturing process is simple and the cost is low. When the conical waveguide is optically coupled with a laser light source or an optical fiber, its mode matches, which reduces the even light loss, improves the optical coupling efficiency, and enhances the overall performance of the device.

[0114] At the same time, in the process of preparing the tapered waveguide, a photomask is used to form a photoresist with inclined side walls using underexposure technology, which is then used as a mask to form a tapered center layer. There is no need for additional customized grayscale photomasks or expensive direct-write gradient lithography machines, which reduces production costs and can be promoted and applied on a large scale.

[0115] like Figure 2h and Figure 2iAs shown, the present invention further provides a tapered waveguide 600, which is prepared by the above-mentioned method for preparing the tapered waveguide 600, and the tapered waveguide 600 includes:

[0116] A lower cladding layer 200 formed on the substrate 100;

[0117] The tapered central layer 301 is formed on the lower cladding layer 200 by etching using a photoresist 400 having an inclined sidewall as a mask, and the thickness of the tapered central layer 301 is related to the application wavelength of the tapered waveguide;

[0118] The upper cladding layer 500 is formed on the tapered core layer 301 .

[0119] Specifically, in a first direction perpendicular to the substrate 100 , the substrate 100 , the lower cladding layer 200 , the tapered central layer 301 and the upper cladding layer 500 of the waveguide structure are photolithographically and etched together by using photolithography and dry etching processes to form the tapered waveguide 600 .

[0120] In this embodiment, the lower cladding layer 200 is made of SiO 2 .

[0121] In this embodiment, the material of the conical central layer 301 is SiN, that is, the material of the first central layer 300 and the second central layer 302 are both SiN.

[0122] In this embodiment, the lower cladding layer 200 is made of SiO 2 .

[0123] As a preferred embodiment, the tapered waveguide 600 includes a first tapered waveguide portion 601, a second tapered waveguide portion 602 and a third tapered waveguide portion 603 in sequence in a first direction perpendicular to the substrate;

[0124] The thickness of the first tapered waveguide portion 601 and the thickness of the third tapered waveguide portion 603 remain unchanged, and the thickness of the second tapered waveguide portion 602 decreases at a first preset taper trend until it becomes the same as the thickness of the third tapered waveguide portion 603;

[0125] The widths of the first tapered waveguide portion 601 and the second tapered waveguide portion 602 decrease in a second preset taper trend until they are the same as the width of the third tapered waveguide portion 603;

[0126] The width of the third tapered waveguide portion 603 decreases at a third preset taper trend;

[0127] The second preset taper trend is different from the third preset taper trend.

[0128] Specifically, the tapered waveguide 600 is composed of three parts, namely, a first tapered waveguide part 601 , a second tapered waveguide part 602 , and a third tapered waveguide part 603 , which are arranged in sequence to form a continuous waveguide structure in the horizontal direction and the vertical direction.

[0129] The thickness (or height) of the first tapered waveguide portion 601 varies with the horizontal position, and its thickness remains unchanged, that is, it is a constant value in the vertical section. The width of the first tapered waveguide portion 601 in the horizontal section, starting from the Taper end, gradually decreases according to the second preset taper to the same width as the incident end section of the second tapered waveguide portion 602.

[0130] Different from the first tapered waveguide portion 601, the thickness (or height) of the second tapered waveguide portion 602 is not a constant value. Its thickness gradually decreases from the thickness of the first tapered waveguide portion 601 to the same thickness (or height) of the third tapered waveguide portion 603 in the vertical section according to the first preset taper. Its width continues to gradually decrease to the same width as the cross-section of the incident end of the third tapered waveguide portion 603 in the horizontal section according to the same variation trend as the width of the first tapered waveguide portion 601, i.e., the second preset taper.

[0131] The thickness of the third tapered waveguide portion 603 varies with the horizontal position, and its thickness also remains unchanged. The thickness of the third tapered waveguide portion 603 is different from the thickness of the first tapered waveguide portion 601 , and the thickness of the first tapered waveguide portion 601 is greater than the thickness of the third tapered waveguide portion 603 .

[0132] At the connecting end face of the second tapered waveguide portion 602 and the third tapered waveguide portion 603, the thickness has reached the single-mode thickness, and the width of the third tapered waveguide portion 603 is gradually reduced to the single-mode size according to the third preset taper in the horizontal cross section. Compared with the traditional single-mode waveguide with fixed width and fixed thickness, the change process from multi-mode waveguide to single-mode waveguide is further slowed down, thereby further reducing the loss.

[0133] As a preferred implementation, the second preset taper trend is greater than the third preset taper trend.

[0134] Specifically, the width variation trends of the first tapered waveguide portion 601 and the second tapered waveguide portion 602 are the same, and the width variation trends of the first tapered waveguide portion 601 and the second tapered waveguide portion 602 are greater than the width variation trend of the third tapered waveguide portion 603. The width variations of the first tapered waveguide portion 601 and the second tapered waveguide portion 602 are steeper, while the width variation of the third tapered waveguide portion 603 is gentler.

[0135] As a preferred embodiment, the first tapered waveguide portion 601 and the second tapered waveguide portion 602 are multi-mode tapered waveguides, and the third tapered waveguide portion 603 is a single-mode tapered waveguide.

[0136] Specifically, the first tapered waveguide portion 601 and the second tapered waveguide portion 602 support multi-mode light wave or microwave transmission, and the third tapered waveguide portion 603 supports single-mode light wave or microwave transmission.

[0137] When the tapered waveguide of the embodiment of the present invention is optically coupled with a laser light source or an optical fiber, its mode is matched, the even light loss is reduced, the optical coupling efficiency is improved, and the overall performance of the device is enhanced.

[0138] At the same time, the top conical structure of the waveguide is formed by etching using a photoresist 400 with an inclined sidewall as a mask, and the inclined sidewall of the photoresist 400 is formed using a standard photomask using underexposure technology. There is no need for additional customized grayscale photomasks or expensive direct-write gradient lithography machines, which reduces production costs and can be promoted and applied on a large scale.

[0139] The above are only preferred embodiments of the present invention, and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the contents of this specification and illustrations should be included in the protection scope of the present invention.

Claims

1. A method for preparing a tapered waveguide, characterized in that: include: Step S1, forming a lower cladding layer and a first central layer in sequence on a substrate; Step S2, forming a photoresist having inclined sidewalls on the first central layer; Step S3, using the photoresist with the inclined sidewall as a mask, etching the first central layer to form a tapered central layer; Step S4, adjusting the thickness of the tapered center layer according to the application wavelength of the tapered waveguide; Step S5, forming an upper cladding layer on the tapered central layer to prepare the tapered waveguide.

2. The preparation method according to claim 1, characterized in that: The substrate is any one of a silicon substrate, a glass substrate, a gallium arsenide substrate, an indium phosphide substrate, a gallium nitride substrate, and a sapphire substrate.

3. The preparation method according to claim 1, characterized in that: The step S2 comprises: Step S21, coating photoresist on the first central layer; Step S22 , exposing the photoresist and underexposing the photoresist to form the photoresist having inclined sidewalls on the first central layer.

4. The preparation method according to claim 3, characterized in that: In the step S22, the exposure time is adjusted according to the type of the photoresist to achieve underexposure.

5. The preparation method according to claim 4, characterized in that: In step S22, the exposure time is adjusted in the following manner: If the photoresist is a positive photoresist, reducing the exposure time; If the photoresist is a negative photoresist, increase the exposure time.

6. The preparation method according to claim 1, characterized in that: In the step S4, the thickness of the tapered central layer is increased according to the application wavelength of the tapered waveguide.

7. The preparation method according to claim 1, characterized in that: In the step S5, after forming the upper cladding layer on the tapered central layer, the step further includes: The substrate, the lower cladding layer, the tapered central layer and the upper cladding layer are photolithographically and etched together in a first direction perpendicular to the substrate to prepare the tapered waveguide.

8. A tapered waveguide, characterized in that The tapered waveguide is prepared by the method for preparing the tapered waveguide according to any one of claims 1 to 7, wherein the tapered waveguide comprises: a lower cladding layer formed on the substrate; A tapered central layer is formed on the lower cladding layer by etching using a photoresist having an inclined sidewall as a mask, wherein the thickness of the tapered central layer is related to the application wavelength of the tapered waveguide; An upper cladding layer is formed on the tapered central layer.

9. The tapered waveguide according to claim 8, characterized in that The tapered waveguide includes a first tapered waveguide portion, a second tapered waveguide portion and a third tapered waveguide portion in sequence in a first direction perpendicular to the substrate; The thickness of the first tapered waveguide portion and the thickness of the third tapered waveguide portion remain unchanged, and the thickness of the second tapered waveguide portion decreases at a first preset taper trend until it becomes the same as the thickness of the third tapered waveguide portion; The widths of the first tapered waveguide portion and the second tapered waveguide portion decrease in a second preset taper trend until they are the same as the width of the third tapered waveguide portion; The width of the third tapered waveguide portion decreases at a third preset taper trend; The second preset taper trend is different from the third preset taper trend.

10. The tapered waveguide according to claim 9, characterized in that The second preset taper trend is greater than the third preset taper trend.

11. The tapered waveguide according to claim 9, characterized in that The first tapered waveguide portion and the second tapered waveguide portion are multi-mode tapered waveguides, and the third tapered waveguide portion is a single-mode tapered waveguide.

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