Optical waveguide coupler based on hard substrate and preparation method thereof

Abstract

The invention relates to an optical waveguide coupler based on a hard substrate and a preparation method thereof, and belongs to the technical field of couplers. The method comprises the following steps: preparing a lower rectangular waveguide core layer on a hard substrate through an ultraviolet lithography technology; preparing a lower reflecting micro-mirror through an excimer laser technology, and plating a reflecting film on the surface of the lower reflecting micro-mirror; then preparing an upper rectangular waveguide core layer through an ultraviolet lithography technology on the basis; preparing an upper reflecting micro-mirror at a corresponding vertical position of the lower reflecting micro-mirror through an excimer laser technology, and plating a reflecting film on the surface of the upper reflecting 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 rigid 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 levels. The transfer and coupling of optical signals between different waveguide layers have become key technical challenges.

[0003] Currently, common three-dimensional coupling methods include technologies such as using diffraction gratings, mode conversion, and reflection mirrors. Among them, the interlayer coupling scheme based on a diffraction grating diffracts light to an adjacent waveguide layer by changing the propagation direction of light. However, this method has certain limitations: on the one hand, diffraction has high requirements for the optical wavelength, and on the other hand, the diffraction efficiency is also limited, making it difficult to achieve efficient interlayer coupling. The interlayer coupling scheme of mode conversion completes the mode conversion between different waveguide layers through the medium of unbound modes. However, this method usually requires a long waveguide coupling length to achieve the conversion between bound modes and unbound modes, and thus does not have obvious advantages in highly integrated photonic chips.

[0004] In contrast, the coupling scheme based on a reflection mirror can effectively achieve efficient coupling between large-size polymer waveguide layers. However, although the V-cut technology adopted in existing research can achieve high-precision angle control when preparing an inclined mirror, it has many limitations, such as high process difficulty, limited material applicability, high equipment cost, surface roughness problems, and insufficient scalability. These disadvantages seriously limit its application in large-scale production and complex optical devices (see the literature: Surface Input / Output Optical Splitter Film for Multilayer Optical Circuits).

[0005] Therefore, in view of the demand for interlayer coupling of double-layer polymer optical waveguides, it is urgent to develop a new preparation method to achieve the manufacture of couplers with high efficiency, low cost, and scalability. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a waveguide coupler based on a hard substrate and a preparation method thereof. A lower rectangular waveguide core layer is prepared on the hard substrate by ultraviolet lithography technology; a lower reflecting mirror is prepared by excimer laser technology, and a reflective film is deposited on the surface of the lower reflecting mirror; then an upper rectangular waveguide core layer is prepared by ultraviolet lithography technology on this basis; an upper reflecting mirror is prepared by excimer laser technology at a corresponding vertical position of the lower reflecting mirror, and a reflective film is deposited on the surface of the upper reflecting mirror; the 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 a waveguide coupler based on a hard substrate, comprising the following steps:

[0008] S1. Prepare a lower cladding layer on the hard substrate;

[0009] S2. Prepare a lower rectangular waveguide core layer on the lower cladding layer by ultraviolet lithography technology;

[0010] S3. Prepare a first intermediate cladding layer on the lower rectangular waveguide core layer;

[0011] S4. Etch a 45° lower reflecting mirror on the lower rectangular waveguide core layer by excimer laser technology, and deposit a reflective film on the surface of the lower reflecting mirror;

[0012] S5. Prepare a second intermediate cladding layer on the first intermediate cladding layer and the lower reflecting mirror together;

[0013] S6. Prepare an upper rectangular waveguide core layer on the second intermediate cladding layer by ultraviolet lithography technology;

[0014] S7. Prepare an upper cladding layer on the upper rectangular waveguide core layer;

[0015] S8. Etch a 45° upper reflecting mirror on the upper rectangular waveguide core layer by excimer laser technology, and deposit a reflective film on the surface of the upper reflecting mirror to obtain the waveguide coupler based on the hard substrate; the position of the upper reflecting mirror is vertically aligned with the position of the lower reflecting mirror.

[0016] In an embodiment of the present invention, in S1, the hard substrate is selected from a PCB board, an SOI substrate or an SiO2 substrate. Using a PCB board, an SOI substrate, an SiO2 substrate, etc. as the waveguide substrate ensures the physical stability and durability of the waveguide during long-term use; the hard substrate has strong mechanical strength and thermal stability, and is very suitable for optical interconnection systems requiring high reliability and long-term operation.

[0017] In an embodiment of the present invention, in S2 and S6, the lower rectangular waveguide core layer and the upper rectangular waveguide core layer have the same specifications and are vertically aligned.

[0018] In one embodiment of the present invention, in S4 and S8, 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. By controlling the lithography path, mask pattern, and etching times, the required reflective mirror is realized.

[0019] In one embodiment of the present invention, in S4 and S8, the number of reflective mirrors is consistent with the number of rectangular waveguide core layers, and the end of the reflective mirror is located on the horizontal plane where the surface of the rectangular waveguide core layer is located or passes through the horizontal plane where the surface of the rectangular waveguide core layer is located.

[0020] In one embodiment of the present invention, in S4 and S8, the angular error between the lower reflective mirror and the upper reflective mirror is less than 2°, and they face the same or opposite directions. Moreover, the misalignment error between the lower reflective mirror and the upper reflective mirror in the waveguide transmission direction and the direction perpendicular to the waveguide transmission direction is less than 5 μm.

[0021] In one embodiment of the present invention, in S4 and S8, the reflective film is selected from a metal film or a dielectric high-reflection film, and the thickness is 50 nm - 100 nm.

[0022] In one embodiment of the present invention, the materials of the lower cladding, the first intermediate cladding, the second intermediate cladding, and the upper cladding are polymer negative photoresist EpoClad (Micro Resist Technology GmbH);

[0023] The material of the lower rectangular waveguide core layer is polymer negative photoresist EpoCore (Micro Resist Technology GmbH).

[0024] In one embodiment of the present invention, the thickness of the lower cladding is 30 μm - 60 μm;

[0025] 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;

[0026] The thickness of the first intermediate cladding is 60 μm - 128 μm, and the thickness of the first intermediate cladding includes the thickness of the lower rectangular waveguide core layer;

[0027] The thickness of the second intermediate cladding is 10 μm - 30 μm;

[0028] 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.

[0029] The second object of the present invention is to provide an optical waveguide coupler based on a hard substrate prepared by the method described above.

[0030] In an embodiment of the present invention, when the directions of the lower reflecting mirror and the upper reflecting mirror are the same, light can be transmitted between the same layers of the double-layer waveguide in the same direction.

[0031] In an embodiment of the present invention, when the directions of the lower reflecting mirror and the upper reflecting mirror are opposite, light can be transmitted between the opposite layers of the double-layer waveguide.

[0032] The technical solution of the present invention has the following advantages compared with the prior art:

[0033] (1) In the preparation method of the present invention, reflecting mirrors are etched on the upper and lower rectangular waveguide core layers respectively and a reflective film is deposited, 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, and improve the transmission effect of the optical signal, which is particularly suitable for high-density and high-speed optical interconnection applications.

[0034] (2) Through the precise ultraviolet lithography process in the preparation method of the present invention, extremely high graphic resolution can be achieved, ensuring the accurate size and position of the waveguide structure. Ultraviolet lithography can ensure the accuracy of the waveguide structure at the micron level, avoiding the geometric distortion problems that occur in existing technologies such as ultraviolet imprinting. Through the excimer laser technology, the etching depth and the angle of the reflecting mirror can be precisely controlled by an accurate laser beam, so as to precisely manufacture a reflecting mirror with a higher reflectivity and better surface smoothness. Compared with existing technologies such as V-cutting, the excimer laser technology can precisely control the angle and surface morphology of the reflecting mirror without mechanical cutting, avoiding the thermal effect and surface roughness problems caused by cutting.

[0035] (3) The surface roughness of the rectangular waveguide and the reflecting mirror manufactured by the preparation method of the present invention through ultraviolet lithography and excimer laser technology is significantly lower than that of existing technologies such as ultraviolet imprinting and V-cutting. The surface roughness is usually controlled below 60 nm, greatly improving the reflectivity and coupling efficiency. Moreover, ultraviolet lithography and excimer laser technology provide higher consistency and repeatability, ensuring the stability of the rectangular waveguide and reflecting mirror structures in large-scale production. In addition, since the excimer laser technology can precisely control the microstructure of the reflecting mirror, the optical quality of the reflecting surface is guaranteed and the reflectivity is relatively high. Compared with the reflecting surface of the V-cutting technology, the reflecting surface prepared by the excimer laser has a higher light reflection efficiency, reducing the light loss caused by incomplete reflection.

[0036] (4) The preparation method of the present invention is particularly suitable for large-scale industrial production and can meet the production requirements of hard substrate waveguides. Utilizing the high stability and durability of the hard substrate, this method can carry out large-scale production while ensuring performance, which is of great significance for promoting the wide application of high-density optical waveguide board interconnection technology.

[0037] (5) The preparation method described in the present invention is easy to operate, and can flexibly adjust the size of the waveguide, the coupling angle, the design of the reflective film, etc., so as to meet the specific requirements of different optical interconnection systems. Whether it is the waveguide size, the coupling efficiency or the reflectivity, it can be optimized according to the actual application requirements to ensure the best optical transmission effect.

[0038] (6) The optical waveguide coupler based on a hard substrate described in the present invention adopts a double-layer waveguide design, combines a reflective mirror and an optimized waveguide size, enabling efficient coupling of optical signals between waveguides. The use of the reflective mirror effectively reduces optical loss and improves the signal transmission efficiency between waveguide layers. It is particularly suitable for scenarios requiring high-efficiency energy transmission and high-density integration, such as optical interconnection systems. Description of the Drawings

[0039] 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 in conjunction with the drawings, where:

[0040] Figure 1 Schematic diagram of the optical waveguide coupler based on a hard substrate and its co-directional transmission in Embodiment 1 of the present invention;

[0041] Figure 2 Left view of the optical waveguide coupler based on a hard substrate in Embodiment 1 of the present invention;

[0042] Figure 3 Physical diagram of the optical waveguide coupler based on a hard substrate in Embodiment 1 of the present invention;

[0043] Figure 4 End view of the optical waveguide coupler based on a hard substrate in Embodiment 1 of the present invention;

[0044] Figure 5 Schematic diagram of the optical waveguide coupler based on a hard substrate and its reverse transmission in Embodiment 2 of the present invention;

[0045] Figure 6 Test results of the overall link loss of the optical waveguide coupler based on a hard substrate in Embodiment 1 of the present invention;

[0046] Figure 7 Surface roughness of the reflective mirror of the optical waveguide coupler based on a hard substrate in Embodiment 1 of the present invention;

[0047] Description of the reference numerals: 1 - hard substrate, 2 - lower cladding, 3 - lower rectangular waveguide core layer, 4 - first intermediate cladding, 5 - lower reflective mirror, 6 - second intermediate cladding, 7 - upper rectangular waveguide core layer, 8 - upper cladding, 9 - co-directional upper reflective mirror, 10 - reverse-directional upper reflective mirror. Detailed Description of the Invention

[0048] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it. However, the exemplified embodiments are not intended to limit the present invention.

[0049] In the present invention, unless otherwise specified, the orientation or positional relationship indicated by terms such as "inside", "above", "below", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation of the present invention; the terms "first", "second", "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance; in addition, unless otherwise clearly specified and defined, the terms "installed", "connected", "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 directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two elements. 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.

[0050] In the present invention, unless otherwise specified, most of the photomasks used in the embodiments of the present invention are light-tight, and the rectangular waveguides are light-leaking; the photomask adopts the design of a rectangular waveguide array and alignment marks, 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, the width of the photomask and the ultraviolet exposure time determine the width of the rectangular waveguide; the alignment marks are in the form of a cross or a grid, and the positions are at both ends of the rectangular waveguide; the rectangular waveguides and alignment marks in the photomask are consistent with the size and position of the lower-layer waveguides.

[0051] 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, and the model is EpoClad 10.

[0052] 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, and the model is EpoCore 10.

[0053] Example 1

[0054] Referring to Figure 1 - Figure 2 As shown, the optical waveguide coupler based on a hard substrate and its preparation method of the present invention specifically include the following steps:

[0055] S1. Ultrasonically clean the hard 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 hard substrate 1 of the PCB board and the negative polymer photoresist; spin-coat the negative polymer photoresist EpoClad on the hard substrate 1 of the PCB board, and perform ultraviolet light exposure and post-baking to form a lower cladding 2 with a thickness of 30 μm.

[0056] S2. Spin-coat the negative polymer photoresist EpoCore on the lower cladding 2. After ultraviolet exposure and development in an air environment using a mask plate, a lower rectangular waveguide core layer 3 with a specification of 50 μm × 50 μm × 3 is obtained.

[0057] S3. Spin-coat the negative polymer photoresist EpoClad on the lower rectangular waveguide core layer 3, and perform ultraviolet light exposure and post-baking to form a first intermediate cladding 4 with a thickness of 60 μm.

[0058] S4. Etch a 45° lower reflecting mirror 5 on the lower rectangular waveguide core layer 3 by 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 reflecting mirror 5; the number of the lower reflecting mirrors 5 is the same as that of the lower rectangular waveguide core layer 3, and the depth of the lower reflecting mirror 5 is 60 μm.

[0059] S5. Spin-coat the negative polymer photoresist EpoClad on both the first intermediate cladding 4 and the lower reflecting mirror 5, and perform ultraviolet light exposure and post-baking to form a second intermediate cladding 6 with a thickness of 20 μm.

[0060] S6. Referring to the preparation process of the lower rectangular waveguide core layer 3, prepare an upper rectangular waveguide core layer 7 with the same specification as the lower rectangular waveguide core layer 6 and vertically aligned on the second intermediate cladding 6.

[0061] S7. Spin-coat the negative polymer photoresist EpoClad on the upper rectangular waveguide core layer 7, and perform ultraviolet light exposure and post-baking to form an upper cladding 8 with a thickness of 60 μm.

[0062] S8. Referring to the preparation process of the lower reflecting mirror 5, etch a 45° upward reflecting mirror 9 on the upper rectangular waveguide core layer 7, and thermally evaporate a Au metal film with a thickness of 75 nm on the surface of the upper reflecting mirror 9 to obtain an optical waveguide coupler based on a hard substrate, which can realize the transmission of light between double-layer waveguides in the same direction; the position of the upward reflecting mirror 9 is vertically aligned with the position of the lower reflecting mirror 5, the angular error between the lower reflecting mirror 5 and the upward reflecting mirror 9 is less than 2°, and the misalignment error between the lower reflecting mirror 5 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.

[0063] Example 2

[0064] Refer to Figure 5 As shown, it is basically the same as Example 1, except that the upper reflection mirror is the reverse upper reflection mirror 10, which can realize the reverse inter-layer light transmission of the double-layer waveguide.

[0065] Test Example 1

[0066] Perform an overall link loss test on the optical waveguide coupler based on the hard substrate prepared in Example 1: First, use an 850 nm light source, align the 50 μm diameter jumper and the 50 μm diameter jumper, and measure the input power of the waveguide; then adjust the waveguide to align with the 50 μm diameter input jumper at the input end and the waveguide output end to align with the 50 μm diameter output jumper at the output end; finally, measure the output power with a power meter. The flexible waveguide link loss is calculated according to the formula I = -10lg(P out / P in ), where P out and P in refer to the waveguide output power and input power respectively. The test results are as shown in Figure 6 . It can be seen from Figure 6 that the average loss of the optical waveguide coupler based on the hard substrate is about 9 dB. The main sources of loss include the coupling efficiency between waveguides and the optical loss of the waveguide structure itself.

[0067] In addition, the surface roughness of the 45° reflection mirror of the optical waveguide coupler based on the hard substrate in Example 1 was measured with a profilometer, and the results are as shown in Figure 7 . It can be seen from Figure 7 that the surface roughness of the reflection mirror is 55.63 nm, indicating that by optimizing the waveguide structure and adjusting the manufacturing process, the link loss can be significantly reduced and the performance of the overall system can be improved.

[0068] Obviously, the above embodiments are only 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 hard substrate, characterized in that, It includes the following steps: S1. Prepare a lower cladding on a rigid substrate; S2. Prepare a lower rectangular waveguide core layer on the lower cladding through ultraviolet lithography technology; S3. Prepare a first intermediate cladding on the lower rectangular waveguide core layer; S4. 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; S5. Prepare a second intermediate cladding on the first intermediate cladding and the lower reflecting mirror together; S6. Prepare an upper rectangular waveguide core layer on the second intermediate cladding through ultraviolet lithography technology; S7. Prepare an upper cladding on the upper rectangular waveguide core layer; S8. 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 rigid 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 hard 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 hard substrate according to claim 1, wherein, In S2 and S6, the lower rectangular waveguide core layer and the upper rectangular waveguide core layer have the same specifications and are vertically aligned.

4. The manufacturing method of the optical waveguide coupler based on a hard substrate according to claim 1, characterized in that In S4 and S8, 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.

5. The preparation method of the optical waveguide coupler based on a hard substrate according to claim 1, characterized in that, In S4 and S8, the number of reflecting mirrors is the same as 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 passes through the horizontal plane where the surface of the rectangular waveguide core layer is located.

6. The manufacturing method of the optical waveguide coupler based on a hard substrate according to claim 1, characterized in that, In S4 and S8, 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 manufacturing method of the optical waveguide coupler based on a hard substrate according to claim 1, characterized in that, In S4 and S8, 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 hard substrate according to claim 1, characterized in that, The materials of the lower cladding, the first intermediate cladding, the second 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 hard substrate according to claim 1, characterized in that, The thickness of the lower cladding is 30 μm - 60 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 first intermediate cladding is 60 μm - 128 μm; The thickness of the second intermediate cladding is 10 μm - 30 μm; The thickness of the upper cladding is 60 μm - 128 μm.

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

Images