Optical waveguide coupler based on flexible substrate and preparation method thereof

Abstract

The invention relates to an optical waveguide coupler based on a flexible substrate and a preparation method thereof, and belongs to the technical field of couplers. The method comprises the following steps: firstly, preparing a flexible substrate on a hard substrate through spin coating or imprinting, spin coating a lower cladding, preparing a lower rectangular waveguide core layer through an ultraviolet lithography technology, and spin coating a middle cladding; then preparing an upper rectangular waveguide core layer through an ultraviolet lithography technology on the basis, spin-coating an upper cladding, and stripping a hard board; and finally, preparing a lower reflection micro-mirror on the lower rectangular waveguide core layer through an excimer laser technology, plating a reflection film on the surface of the lower reflection micro-mirror, preparing an upper reflection micro-mirror on the upper rectangular waveguide core layer at a corresponding vertical position of the lower reflection micro-mirror through the excimer laser technology, and plating a reflection film on the surface of the upper reflection micro-mirror. The optical waveguide coupler prepared by the method realizes high-density interlayer interconnection, and is relatively high in application flexibility and high in interlayer coupling efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of couplers, and particularly relates to an optical waveguide coupler based on a flexible substrate and a preparation method thereof. Background Art

[0002] With the continuous growth of the demand for high-speed and high-density optical interconnections, traditional two-dimensional optical interconnection technologies are gradually evolving towards three-dimensional integrated optical interconnections with higher integration and more flexible configurations. In this process, the efficient coupling of optical signals between different waveguide layers has become a core technical challenge. Common three-dimensional coupling methods include technologies such as diffraction gratings, mode conversion, and reflective mirrors.

[0003] For flexible optical interconnection systems, the interlayer coupling scheme based on diffraction gratings is limited in terms of flexibility because the diffraction efficiency and coupling performance have high requirements for the stability of the optical wavelength and waveguide structure, and it is difficult to meet the high-efficiency coupling requirements in a dynamically bent environment. Although mode conversion technology can achieve mode conversion between different waveguide layers, it usually requires a long coupling length and does not have significant advantages in flexible photonic chips with limited space.

[0004] In contrast, the coupling scheme using reflective mirrors shows greater potential in flexible waveguides. In existing research, some scholars have used ultraviolet imprinting to fabricate reflective mirrors on flexible waveguides, achieving direct coupling between waveguides and vertical cavity surface emitting lasers (VCSELs) and photodetectors (PDs) (see the literature: Polymeric Waveguide Film withEmbedded Mirrors for Flexible Optical Interconnection). However, this scheme relies on metal imprinting molds and ultra-precision machining technologies for patterning, which may lead to a complex manufacturing process and high costs, especially in large-scale production. In contrast, reflective mirrors can not only achieve efficient coupling between different waveguide layers but also adapt to the geometric changes of flexible waveguides in dynamic bending and deformation.

[0005] Therefore, for the interlayer coupling of double-layer flexible polymer optical waveguides, it is urgent to explore a coupler and a preparation method that combine high efficiency and structural adaptability to meet the optical signal transmission requirements in a dynamic environment. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides an optical waveguide coupler based on a flexible substrate and a preparation method thereof. First, a flexible substrate is prepared on a rigid substrate by spin coating or imprinting. The lower cladding is spin coated, and the lower rectangular waveguide core layer is prepared by ultraviolet lithography technology. The intermediate cladding is spin coated. Then, on this basis, the upper rectangular waveguide core layer is prepared by ultraviolet lithography technology, the upper cladding is spin coated, and the hard board is peeled off. Finally, a lower reflecting mirror is prepared on the lower rectangular waveguide core layer by excimer laser technology, a reflecting film is deposited on the surface of the lower reflecting mirror, and an upper reflecting mirror is prepared on the upper rectangular waveguide core layer by excimer laser technology at a corresponding vertical position of the lower reflecting mirror, and a reflecting film is deposited on the surface of the upper reflecting mirror. The optical waveguide coupler prepared by this method realizes high-density interlayer interconnection, has relatively high application flexibility, and high interlayer coupling efficiency.

[0007] The first object of the present invention is to provide a preparation method of an optical waveguide coupler based on a flexible substrate, comprising the following steps:

[0008] S1. Prepare a flexible substrate on a rigid substrate;

[0009] S2. Prepare a lower cladding on the flexible substrate;

[0010] S3. Prepare a lower rectangular waveguide core layer on the lower cladding by ultraviolet lithography technology;

[0011] S4. Prepare an intermediate cladding on the lower rectangular waveguide core layer;

[0012] S5. Prepare an upper rectangular waveguide core layer on the intermediate cladding by ultraviolet lithography technology;

[0013] S6. Prepare an upper cladding on the upper rectangular waveguide core layer;

[0014] S7. Peel off the rigid substrate;

[0015] S8. Etch a 45° lower reflecting mirror on the lower rectangular waveguide core layer by excimer laser technology, and deposit a reflecting film on the surface of the lower reflecting mirror;

[0016] S9. Etch a 45° upper reflecting mirror on the upper rectangular waveguide core layer by excimer laser technology, and deposit a reflecting film on the surface of the upper reflecting mirror to obtain the optical waveguide coupler based on a flexible substrate; the position of the upper reflecting mirror is vertically aligned with the position of the lower reflecting mirror.

[0017] In an embodiment of the present invention, in S1, the rigid substrate is selected from a PCB board, an SOI substrate or a SiO2 substrate.

[0018] In an embodiment of the present invention, in S3 and S5, the lower rectangular waveguide core layer and the upper rectangular waveguide core layer have the same specifications and are vertically aligned.

[0019] In one embodiment of the present invention, in S7, the stripping method is selected from direct stripping, nitrogen blowing or alcohol immersion.

[0020] In one embodiment of the present invention, in S8 and S9, the process parameters of the excimer laser technology are as follows: the laser output wavelength is 193 nm, the pulse width is 5 ns, the pulse frequency is 7 Hz - 50 Hz, and the energy is 0.1 mJ - 10 mJ; the excimer laser technology realizes the required reflecting mirror by controlling the lithography path, mask pattern and etching times.

[0021] In one embodiment of the present invention, in S8 and S9, the number of reflecting mirrors is consistent with the number of rectangular waveguide core layers, and the end of the reflecting mirror is located on the horizontal plane where the surface of the rectangular waveguide core layer is located or penetrates the horizontal plane where the surface of the rectangular waveguide core layer is located.

[0022] In one embodiment of the present invention, in S8 and S9, the angular error between the lower reflecting mirror and the upper reflecting mirror is less than 2°, and they face the same or opposite directions, and the misalignment error between the lower reflecting mirror and the upper reflecting mirror in the waveguide transmission direction and the direction perpendicular to the waveguide transmission direction is less than 5 μm.

[0023] In one embodiment of the present invention, in S8 and S9, the reflective film is selected from a metal film or a dielectric high-reflection film, and the thickness is 50 nm - 100 nm.

[0024] In one embodiment of the present invention, the material of the flexible substrate is selected from polyimide and / or PMMA;

[0025] The materials of the lower cladding layer, the intermediate cladding layer and the upper cladding layer are the polymer negative photoresist EpoClad (MicroResist Technology GmbH);

[0026] The material of the lower rectangular waveguide core layer is the polymer negative photoresist EpoCore (Micro Resist Technology GmbH).

[0027] In one embodiment of the present invention, the thickness of the flexible substrate is 5 μm - 30 μm;

[0028] The thickness of the lower cladding layer is 15 μm - 83 μm;

[0029] The thickness of the lower rectangular waveguide core layer is 40 μm - 55 μm, the width is 40 μm - 55 μm, and the number is 3 - 12;

[0030] The thickness of the intermediate cladding layer is 10 μm - 100 μm, and the thickness of the intermediate cladding layer includes the thickness of the lower rectangular waveguide core layer;

[0031] The thickness of the upper cladding is 60 μm - 128 μm, and the thickness of the upper cladding includes the thickness of the upper rectangular waveguide core layer.

[0032] The second object of the present invention is to provide an optical waveguide coupler based on a flexible substrate prepared by the method described above.

[0033] In an embodiment of the present invention, when the directions of the lower reflecting mirror and the upper reflecting mirror are the same, light transmission between the same layers of the double-layer waveguide in the same direction can be achieved.

[0034] In an embodiment of the present invention, when the directions of the lower reflecting mirror and the upper reflecting mirror are opposite, light transmission between the opposite layers of the double-layer waveguide can be achieved.

[0035] The technical solution of the present invention has the following advantages compared with the prior art:

[0036] (1) In the preparation method of the present invention, reflecting mirrors are etched and coated with reflective films on the upper and lower rectangular waveguide core layers respectively, so that the optical coupling efficiency between the double-layer waveguides is significantly improved. The reflecting mirror can effectively guide the optical signal, optimize the coupling path between the waveguides, improve the transmission effect of the optical signal, and is particularly suitable for high-density and high-speed optical interconnection applications.

[0037] (2) The preparation method of the present invention enables the optical waveguide to have good flexibility and adaptability through the flexible substrate, and can adapt to complex optical interconnection environments. Especially in applications that require high-density integration, flexible waveguides have great advantages. By using excimer laser technology to precisely fabricate reflecting mirrors on the rectangular waveguide core layer, effective light reflection and coupling can be achieved. The reflecting mirror changes the propagation path of light, improves the optical coupling efficiency between the waveguides, and ensures better signal transmission. Coating with a reflective film can significantly improve the light reflectivity, reduce light loss, and thus enhance the coupling effect.

[0038] (3) The preparation method of the present invention can achieve extremely high graphic resolution through precise ultraviolet lithography technology, ensure the accurate size and position of the waveguide structure, and avoid the mold problems that occur in existing technologies such as ultraviolet imprinting. Through excimer laser technology, the etching depth and the angle of the reflecting mirror can be precisely controlled by a precise laser beam, so as to precisely manufacture the reflecting mirror. Compared with existing technologies such as V-cutting, excimer laser technology can precisely control the angle and surface morphology of the reflecting mirror without mechanical cutting, avoiding errors and surface roughness problems caused by cutting. Through ultraviolet lithography and excimer laser technology, deformation of the flexible substrate can be effectively avoided, ensuring the stability and consistency of processing.

[0039] (4) The preparation method of the present invention effectively fabricates a double-layer waveguide on a flexible substrate through ultraviolet lithography technology and performs necessary post-processing. This method allows for the subsequent fabrication of a reflection mirror and a reflection film after the double-layer waveguide is completed, and the preparation process has high flexibility and can adapt to different design requirements.

[0040] (5) While achieving high coupling efficiency, the preparation method of the present invention has good flexibility and adaptability. It can flexibly adjust the waveguide size, coupling angle, reflection film, etc. according to actual application requirements, so as to meet the requirements of different optical interconnection systems. It is particularly suitable for the requirements of large-scale industrial production of optical waveguide plates and can be mass-produced without affecting the waveguide performance. This is crucial for promoting the practical application of high-density optical waveguide plate interconnection technology.

[0041] (6) The optical waveguide coupler based on a flexible substrate of the present invention optimizes the optical transmission between waveguides through the combination of a double-layer waveguide design and a reflection mirror, greatly improving the coupling efficiency of optical signals and the signal transmission efficiency between waveguide layers. Since the manufacturing method and materials used for this rectangular waveguide have good physical stability, it can maintain good performance under long-term working conditions, especially in the scenarios of flexibility and high-density optical interconnection. This enables efficient coupling of optical signals between waveguides. Description of the Drawings

[0042] In order to make the content of the present invention easier to be clearly understood, the following further details the present invention according to specific embodiments of the present invention and in combination with the drawings, where:

[0043] Figure 1 It is the front view of the sample before peeling the PCB board in Embodiment 1 of the present invention;

[0044] Figure 2 It is the left view of the sample after peeling the PCB board in Embodiment 1 of the present invention;

[0045] Figure 3 It is the optical waveguide coupler based on a flexible substrate in Embodiment 1 of the present invention and its schematic diagram of co-directional transmission;

[0046] Figure 4 It is the optical waveguide coupler based on a flexible substrate in Embodiment 2 of the present invention and its schematic diagram of reverse transmission;

[0047] Figure 5 It is the graph of the simulation link loss of the optical waveguide coupler based on a flexible substrate in Embodiment 1 of the present invention varying with the angle of the inclined mirror;

[0048] Explanation of the accompanying symbols: 1-hard substrate, 2-flexible substrate, 3-lower cladding, 4-lower rectangular waveguide core layer, 5-middle cladding, 6-upper rectangular waveguide core layer, 7-upper cladding, 8-lower reflecting micromirror, 9-same upward reflecting micromirror, 10-reverse upper reflecting micromirror. DETAILED DESCRIPTION

[0049] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0050] In the present invention, unless otherwise specified, the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicating directions or positional relationships are only for the purpose of facilitating the description of the present invention and simplifying the description, and are not intended to indicate or imply that the devices or components referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as limiting the present invention; the terms "first", "second", and "third" are only used for descriptive purposes and should not be understood as indicating or implying relative importance; in addition, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, an indirect connection through an intermediate medium, or it can be internal communication between two components. For those of ordinary skill in the art, the specific meanings of the above terms in this patent can be understood according to specific circumstances.

[0051] In the present invention, unless otherwise specified, most of the masks used in the embodiments of the present invention do not leak light, and some of the rectangular waveguides leak light; the mask adopts a design of a rectangular waveguide array and an overlay mark, wherein the width and length of the rectangular waveguide can be designed according to actual needs, the spin coating thickness determines the thickness of the rectangular waveguide, and the width of the mask and the ultraviolet exposure time determine the width of the rectangular waveguide; the overlay mark is in the form of a cross or a grid, and is located at both ends of the rectangular waveguide; the rectangular waveguide and the overlay mark in the mask image are consistent with the size and position of the underlying waveguide.

[0052] In the present invention, unless otherwise specified, the polymer negative photoresist EpoClad used in the embodiments of the present invention is purchased from Micro Resist Technology GmbH, Germany, with the model number being EpoClad 10.

[0053] In the present invention, unless otherwise specified, the polymer negative photoresist EpoCore used in the embodiments of the present invention is purchased from Micro Resist Technology GmbH, Germany, with the model number being EpoCore 10.

[0054] Example 1

[0055] Refer to Figures 1 - 3 As shown, the optical waveguide coupler based on a flexible substrate and its preparation method of the present invention specifically include the following steps:

[0056] S1. Ultrasonically clean the rigid substrate 1 of the PCB board with acetone, alcohol, and deionized water respectively, then dry it with nitrogen, and bombard the surface with plasma to increase the adhesion between the rigid substrate 1 of the PCB board and the polyimide; Spin-coat polyimide on the rigid substrate 1 of the PCB board, and perform ultraviolet light irradiation and post-baking to form a flexible substrate 2 with a thickness of 20 μm;

[0057] S2. Spin-coat the polymer negative photoresist EpoClad on the flexible substrate 2, and perform ultraviolet light irradiation and post-baking to form a lower cladding 3 with a thickness of 30 μm;

[0058] S3. Spin-coat the polymer negative photoresist EpoCore on the lower cladding 3. After ultraviolet exposure and development in an air environment using a mask plate, obtain a lower rectangular waveguide core layer 4 with a specification of 50 μm × 50 μm × 3;

[0059] S4. Spin-coat the polymer negative photoresist EpoClad on the lower rectangular waveguide core layer 4, and perform ultraviolet light irradiation and post-baking to form an intermediate cladding 5 with a thickness of 100 μm;

[0060] S5. Refer to the preparation process of the lower rectangular waveguide core layer 4, and prepare an upper rectangular waveguide core layer 6 on the intermediate cladding 5 with the same specification as the lower rectangular waveguide core layer 4 and vertically aligned;

[0061] S6. Spin-coat the polymer negative photoresist EpoClad on the upper rectangular waveguide core layer 6, and perform ultraviolet light irradiation and post-baking to form an upper cladding 7 with a thickness of 100 μm;

[0062] S7. Peel the PCB board 1 by blowing it with nitrogen;

[0063] S8. Etch a 45° lower reflection mirror 8 on the lower rectangular waveguide core layer 4 through excimer laser technology (laser output wavelength is 193 nm, pulse width is 5 ns, pulse frequency is 20 Hz, energy is 0.1 mJ), and thermally evaporate a Au metal film with a thickness of 75 nm on the surface of the lower reflection mirror 8; The number of the lower reflection mirrors 8 is the same as the number of the lower rectangular waveguide core layer 4, and the depth of the lower reflection mirror 8 is 100 μm;

[0064] S9. Referring to the manufacturing process of the lower reflecting mirror 8, an upward reflecting mirror 9 at 45° is etched on the upper rectangular waveguide core layer 6, and a Au metal film with a thickness of 75 nm is thermally evaporated on the surface of the upper reflecting mirror 9, obtaining an optical waveguide coupler based on a flexible substrate, which can achieve the same-direction light transmission between double-layer waveguides; the position of the upward reflecting mirror 9 is vertically aligned with the position of the lower reflecting mirror 8, the angular error between the lower reflecting mirror 8 and the upward reflecting mirror 9 is less than 2°, and the misalignment error between the lower reflecting mirror 8 and the upward reflecting mirror 9 in the waveguide transmission direction and the direction perpendicular to the waveguide transmission direction is less than 5 μm.

[0065] Example 2

[0066] Referring to Figure 4 As shown, it is basically the same as Example 1, except that the upper reflecting mirror is a downward reflecting mirror 10, which can achieve the reverse-direction light transmission between double-layer waveguides.

[0067] Test Example 1

[0068] For the optical waveguide coupler based on a flexible substrate prepared in Example 1, the influence of the angle of the reflecting mirror (the synchronous change of the lower reflecting mirror and the upper reflecting mirror) on the insertion loss was explored, and the results are as Figure 5 shown. It can be seen from Figure 5 that when the angle of the reflecting mirror is 45°, the insertion loss is 1.36 dB, showing a relatively ideal coupling effect. However, as the angle of the reflecting mirror increases or decreases, the insertion loss increases to varying degrees. In particular, when the angle of the reflecting mirror changes within the range of 43.25° to 46.75°, the insertion loss will increase by about 0.5 dB. It shows that the slight change of the reflecting mirror angle has a significant impact on the performance of the optical waveguide interlayer coupler. Therefore, accurately controlling the reflecting mirror angle is crucial for optimizing the coupling efficiency and reducing the optical loss.

[0069] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A preparation method of an optical waveguide coupler based on a flexible substrate, characterized in that It includes the following steps: S1. Prepare a flexible substrate on a rigid substrate; S2. Prepare a lower cladding on the flexible substrate; S3. Prepare a lower rectangular waveguide core layer on the lower cladding through ultraviolet lithography technology; S4. Prepare an intermediate cladding on the lower rectangular waveguide core layer; S5. Prepare an upper rectangular waveguide core layer on the intermediate cladding through ultraviolet lithography technology; S6. Prepare an upper cladding on the upper rectangular waveguide core layer; S7. Peel off the rigid substrate; S8. Etch a 45° lower reflecting mirror on the lower rectangular waveguide core layer through excimer laser technology, and deposit a reflective film on the surface of the lower reflecting mirror; S9. Etch a 45° upper reflecting mirror on the upper rectangular waveguide core layer through excimer laser technology, and deposit a reflective film on the surface of the upper reflecting mirror to obtain the optical waveguide coupler based on the flexible substrate; the position of the upper reflecting mirror is vertically aligned with the position of the lower reflecting mirror.

2. The preparation method of the optical waveguide coupler based on a flexible substrate according to claim 1, wherein In S1, the rigid substrate is selected from a PCB board, an SOI substrate or an SiO2 substrate.

3. The preparation method of the optical waveguide coupler based on a flexible substrate according to claim 1, characterized in that In S3 and S5, the lower rectangular waveguide core layer and the upper rectangular waveguide core layer have the same specifications and are vertically aligned.

4. The preparation method of the optical waveguide coupler based on a flexible substrate according to claim 1, wherein, In S8 and S9, the number of reflecting mirrors is consistent with the number of rectangular waveguide core layers, and the ends of the reflecting mirrors are located on the horizontal plane where the surface of the rectangular waveguide core layer is located or penetrate the horizontal plane where the surface of the rectangular waveguide core layer is located.

5. The preparation method of the optical waveguide coupler based on a flexible substrate according to claim 1, wherein In S8 and S9, the process parameters of the excimer laser technology are: the laser output wavelength is 193 nm, the pulse width is 5 ns, the pulse frequency is 7 Hz - 50 Hz, and the energy is 0.1 mJ - 10 mJ.

6. The preparation method of the optical waveguide coupler based on a flexible substrate according to claim 1, characterized in that, In S8 and S9, the angular error between the lower reflecting mirror and the upper reflecting mirror is less than 2°, the orientations are the same or opposite, and the misalignment error between the lower reflecting mirror and the upper reflecting mirror in the waveguide transmission direction and the direction perpendicular to the waveguide transmission direction is less than 5 μm.

7. The preparation method of the optical waveguide coupler based on a flexible substrate according to claim 1, wherein, In S8 and S9, the reflective film is selected from a metal film or a dielectric high-reflection film, and the thickness is 50 nm - 100 nm.

8. The preparation method of the optical waveguide coupler based on a flexible substrate according to claim 1, wherein, The material of the flexible substrate is selected from polyimide and / or PMMA; The materials of the lower cladding, the intermediate cladding and the upper cladding are polymer negative photoresist EpoClad; The material of the lower rectangular waveguide core layer is polymer negative photoresist EpoCore.

9. The preparation method of the optical waveguide coupler based on a flexible substrate according to claim 1, wherein The thickness of the flexible substrate is 5 μm - 30 μm; The thickness of the lower cladding is 15 μm - 83 μm; The thickness of the lower rectangular waveguide core layer is 40 μm - 55 μm, the width is 40 μm - 55 μm, and the number is 3 - 12; The thickness of the intermediate cladding is 10 μm - 100 μm; The thickness of the upper cladding is 60 μm - 128 μm.

10. An optical waveguide coupler based on a flexible substrate prepared by the method according to any one of claims 1 - 9.

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