A method for fabricating an integrated optical waveguide with a concave mirror

Abstract

This invention discloses a method for fabricating an integrated optical waveguide with a concave mirror, comprising the following steps: spin-coating a cladding adhesive onto a substrate using a photomask and subjecting it to ultraviolet exposure; obtaining a rectangular groove with one end being semi-cylindrical after development; filling the rectangular groove with cladding adhesive and performing high-speed spin-coating to obtain a concave groove on the semi-cylindrical shape; depositing a high-reflectivity film on the concave groove to obtain a concave mirror; spin-coating a core layer adhesive, and obtaining an optical waveguide core layer with a concave mirror after exposure and development; spin-coating the cladding adhesive again, and obtaining an upper cladding layer for the optical waveguide after exposure; finally obtaining an optical waveguide with a concave mirror.

Description

Technical Field

[0001] This invention belongs to the field of microfabrication technology, specifically relating to a method for fabricating an integrated optical waveguide with a concave mirror. Background Technology

[0002] With the increasing demand for communication capacity and speed, optical backplane interconnect technology based on printed circuit boards (PCBs) has attracted widespread attention from researchers at home and abroad due to its advantages such as large bandwidth, low power consumption, low cost, resistance to electromagnetic interference and high integration.

[0003] Vertical coupling technology is one of the key technologies. Currently, the main methods for achieving vertical coupling include: tilted mirror method (application publication number: CN 105397300A), waveguide grating coupling method (application publication number: CN102540349A), and spherical concave mirror method (application publication number: CN 110216383A). The first two methods can initially solve the vertical coupling requirement between optical fibers and waveguides, but the resulting numerical aperture matching problem in optical devices leads to relatively low vertical coupling efficiency. The spherical concave mirror method can reduce the coupling loss between optical fibers and waveguides caused by numerical aperture mismatch. The main fabrication methods include chemical etching method (application publication number: CN 1272182A), water molecule-resistant fabrication method (application publication number: CN 103395739A), laser cold processing method (application publication number: CN 110216383A), and ultraviolet grayscale lithography method (application publication number: CN 110673261A). The latter two methods offer relatively higher precision compared to the former two, but the concave mirrors used for vertical coupling require secondary processing on the fabricated waveguide, which demands relatively high technical skill. Because multiple processing steps are necessary, it can easily introduce more losses or cause misalignment between the waveguide and the concave mirror, thereby increasing vertical coupling loss. Summary of the Invention

[0004] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0005] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0006] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for fabricating an integrated optical waveguide with a concave mirror.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: spin-coating a lower cladding layer onto a cleaned substrate; using a positive photomask, performing ultraviolet exposure and development to obtain a rectangular groove with one end being semi-cylindrical; filling a relatively thin layer of cladding adhesive, and using high-speed rotation to obtain a concave groove; depositing a reflective film on the concave groove; spin-coating a core layer with a thickness lower than the first layer of cladding adhesive, and performing exposure and development; finally preparing an upper cladding layer.

[0008] Based on the inventive concept described above, the present invention adopts the following technical solution:

[0009] 1) Spin-coat the cleaned substrate with polymer coating adhesive;

[0010] 2) Use a photomask for ultraviolet exposure;

[0011] 3) Develop the sample to obtain a rectangular groove with one end being semi-cylindrical;

[0012] 4) Fill the rectangular groove with a coating adhesive and spin coat it at high speed to obtain a concave groove;

[0013] 5) Apply a reflective coating to the concave groove area;

[0014] 6) Spin-coat the core layer and expose and develop it;

[0015] 7) Prepare the upper cladding layer.

[0016] In a preferred embodiment of the preparation method of the present invention, in step 1), the substrate is a PCB board, a SiO2 substrate, or an SOI substrate. The cleaning process includes ultrasonic cleaning with acetone, alcohol, and deionized water, followed by drying with nitrogen gas and surface treatment with plasma to increase the adhesion between the substrate and the coating adhesive. The thickness of the spin-coated polymer coating adhesive is much greater than the thickness of the core layer prepared later. In a preferred embodiment of the preparation method of the present invention, in step 2), the mask adopts an integrated design of a rectangular waveguide and a semi-circular concave mirror with a diameter greater than the width of the waveguide. The surface shape of the concave mirror can be semi-circular, quadratic aspherical, or freeform.

[0017] In a preferred embodiment of the preparation method described in this invention, in step 2), the photomask consists of a positive and a negative mask. The positive mask is used in conjunction with a negative cladding adhesive. The rectangular and concave portions of the positive mask do not allow light to pass through, while most of the remaining portion does. After exposure, the negative cladding adhesive undergoes a cross-linking reaction, and the unexposed portions are washed away, forming a groove structure. The negative mask is used in conjunction with a positive cladding adhesive. The rectangular and concave portions of the negative mask allow light to pass through, while most of the remaining portion does not. The exposed areas of the positive cladding adhesive undergo a decomposition reaction, and the exposed areas are washed away, forming a groove structure.

[0018] In a preferred embodiment of the preparation method described in this invention, in step 4), the thickness of the cladding adhesive is much smaller than the thickness of the first cladding layer and the waveguide core layer. An ultrathin cladding adhesive is prepared by high-speed spin coating to form waveguide grooves and concave mirror grooves with a certain thickness. If the polymer cladding adhesive is a negative adhesive, the entire sample is exposed; if the cladding adhesive is a positive adhesive, it is not exposed.

[0019] In a preferred embodiment of the preparation method described in this invention, in step 5), the film in the coating is a metal film or a dielectric high-reflection film.

[0020] In a preferred embodiment of the preparation method described in this invention, in step 6), if the core layer adhesive is a negative adhesive, the exposure area is the waveguide groove area, the core layer adhesive of the concave mirror portion is not exposed and is removed by development; if the core layer adhesive is a positive adhesive, the exposure area is the area other than the waveguide groove area, and the exposed portion is removed by development.

[0021] Beneficial effects of this invention:

[0022] This invention proposes an integrated fabrication technique for optical waveguides with concave mirrors. The main advantages are that the waveguide and concave mirror are fabricated as a single unit, eliminating the need for secondary processing, reducing the risk of misalignment, avoiding unnecessary losses, simplifying the fabrication process, achieving high processing precision, low cost, low surface roughness, and high vertical coupling efficiency. This method is suitable for the requirements of large-scale industrial production of optical backplanes and advances the application of optical backplane interconnect technology. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0024] Figure 1 This is a schematic flowchart of the one-time photolithography fabrication method for the integrated waveguide concave mirror described in this invention.

[0025] Figure 2 This is a schematic diagram of the fabrication of the lower cladding layer on a substrate.

[0026] Figure 3 This is a schematic diagram of a positive photomask.

[0027] Figure 4 This is a schematic diagram of a negative photomask.

[0028] Figure 5 This is a schematic diagram of the three-dimensional structure of the waveguide concave mirror after ultraviolet exposure of the lower cladding.

[0029] Figure 6 This is a schematic left view of the waveguide concave mirror after ultraviolet exposure of the lower cladding.

[0030] Figure 7 This is a top view of the waveguide after the second lower cladding layer has been filled.

[0031] Figure 8 This is a schematic diagram of the waveguide left after filling the second lower cladding layer.

[0032] Figure 9 This is a schematic diagram of the waveguide front view after filling the second lower cladding layer.

[0033] Figure 10 This is a schematic diagram of a reflective coating.

[0034] Figure 11 This is a schematic diagram of the left side after the core layer has been prepared.

[0035] Figure 12 This is a schematic diagram of the front view after the core layer is prepared.

[0036] Figure 13 This is a schematic diagram of the left view after the upper cladding layer has been prepared.

[0037] Figure 14 This is a schematic diagram of the front view after the upper cladding layer has been prepared. Detailed Implementation

[0038] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0039] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0040] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0041] Example 1

[0042] This embodiment provides a method for fabricating a waveguide and a spherical concave mirror using a single photolithography step when both the cladding and core layers are negative resists. See also Figure 1 As shown, the process includes the following steps S1 to S7:

[0043] Step S1: The substrate 1 is pre-treated by ultrasonic cleaning with acetone, alcohol and deionized water respectively. A lower cladding layer 2 with a thickness of 60 μm is prepared on the substrate. The lower cladding layer adhesive is a negative photoresist, which can be prepared by spin coating or blade coating.

[0044] Step S2: Prepare a positive mask, ensuring that the waveguide and concave mirror sections are light-proof. The spherical concave mirror section is a semicircle with a diameter larger than the width of the waveguide. Based on the thickness of the lower cladding, select the exposure dose for ultraviolet exposure in an air environment.

[0045] Step S3: Develop the sample to obtain a semi-cylindrical rectangular groove.

[0046] Step S4: Fill the sample with a 10μm thick cladding adhesive and expose the entire sample to obtain a concave groove.

[0047] Step S5: Spray gold onto the concave groove to a thickness of 50 nm.

[0048] Step S6: Spin-coat negative waveguide core layer adhesive, expose the waveguide, and leave the remaining parts unexposed and developed away. The core layer adhesive thickness is approximately 50 μm.

[0049] Step S7: Prepare the upper coating layer by exposing the entire sample to the same negative adhesive as the lower coating layer.

[0050] Example 2

[0051] This embodiment provides a method for fabricating waveguides and aspherical / freeform concave mirrors using a single photolithography process when both the cladding adhesive and the core adhesive are positive adhesives.

[0052] In this example, the photoresist used for the cladding layer in step S1 is positive photoresist.

[0053] Due to the properties of the adhesive, a negative mask is selected in step S2, unlike the mask in Example 1. The negative mask is mostly light-free, except for the rectangular waveguide and concave areas. The mask pattern is drawn using a grayscale image. The rectangular waveguide area is completely light-leaking, and the concave mirror area is fitted into a polynomial form according to the different curvatures of the required freeform surface. This polynomial is then converted into the exposure dose corresponding to the radius at each location, allowing for the creation of aspherical, freeform, and other concave mirrors.

[0054] In step S3, the rectangular waveguide and the concave groove portion undergo a splitting reaction after exposure and are removed after development, while the other parts are retained, forming a rectangular groove with one end being semi-cylindrical.

[0055] Step S4: The cladding adhesive should be a positive waveguide adhesive. After high-speed spin coating, no exposure is required to obtain a concave groove.

[0056] Step S6: Select positive photoresist for the core layer, and expose and develop all parts except the waveguide area.

[0057] In step S7, the upper cladding can be selected as air, further reducing process steps and lowering losses.

[0058] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for fabricating an integrated optical waveguide with a concave mirror, characterized in that: This fabrication method uses an integrated positive photomask to fabricate an optical waveguide with a concave mirror at one end. The specific steps are as follows: S1 has a first layer of photosensitive, low-refractive-index polymer undercoating adhesive spin-coated onto the substrate; In S1, the thickness of the first lower cladding adhesive layer is much greater than the thickness of the core layer. S2 uses a photomask to perform ultraviolet exposure on the lower cladding layer; The mask pattern in the S2 is a rectangular waveguide and a concave mirror structure with a diameter greater than the width of the rectangle. The concave mirror surface can be semi-circular, quadratic aspherical, or freeform. S3 develops the sample after UV exposure to obtain a rectangular groove with one end being semi-cylindrical. S4 fills the rectangular groove with adhesive and rotates at high speed to obtain a concave groove in the semi-cylindrical area. S5 applies a reflective coating to the concave groove; S6 spin-coating of a low-thickness core layer adhesive, followed by exposure and development; S7 is used to prepare the upper cladding.

2. The method for fabricating an integrated optical waveguide with a concave mirror according to claim 1, characterized in that... The mask is a positive mask, used in conjunction with a negative coating adhesive to obtain a groove structure.

3. The method for fabricating an integrated optical waveguide with a concave mirror according to claim 1, characterized in that... The thickness of the cladding adhesive filling in S4 is much smaller than the thickness of the first cladding adhesive. A high-speed spin coating method is used to obtain waveguide grooves and concave mirror grooves, and the entire sample is exposed.

4. The method for fabricating an integrated optical waveguide with a concave mirror according to claim 1, characterized in that... In step S5, a reflective film is deposited on the concave groove. The reflective film is not limited to a metal film or a higher-order dielectric film.

5. The method for fabricating an integrated optical waveguide with a concave mirror according to claim 1, characterized in that... In S6, the core layer adhesive is a negative adhesive, the exposure area is the waveguide groove area, the core layer adhesive of the concave mirror part is not exposed and is removed by development.

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