Optical waveguide structure

Abstract

The utility model relates to an optical waveguide structure, which comprises a glass substrate, an optical waveguide layer and a filling layer, the optical waveguide layer is composed of a thinned wafer, the refractive index of the optical waveguide layer is higher than that of the glass substrate and that of the filling layer, and the optical waveguide layer is arranged on the glass substrate in a bonding manner. The optical waveguide layer is arranged on the glass substrate, the surface, away from the glass substrate, of the optical waveguide layer is provided with an etching grating structure, the filling layer is embedded in an etching gap of the etching grating structure, the outer side surface of the filling layer and the outer side surface of the etching grating structure are approximately located on the same plane, and / or the filling layer covers the outer side surface of the etching grating structure. According to the utility model, the glass substrate is used as the optical waveguide substrate, the bonded and thinned high refractive index wafer is used as the optical waveguide layer so as to form the predetermined etching grating structure, and the filling layer with the lower refractive index is used for filling the etching gap of the etching grating structure, so that the light emitting efficiency is improved, the coupling-out uniformity is ensured, and the rainbow pattern is reduced; the method has the advantages of stable process and easy mass production, and is suitable for large-batch process production.

Description

Technical Field

[0001] The utility model relates to the technical field of optical elements, in particular to an optical waveguide structure. Background Art

[0002] Optical waveguides are popular as a lightweight AR technology solution, especially the unique mass production and economy of diffraction optical waveguide technology, which has the possibility of becoming a mainstream technology. From the perspective of process preparation, the optical waveguide preparation process of surface relief grating can be divided into two categories, one is to prepare the grating by nanoimprinting, and the other is to prepare the grating by direct etching. The optical waveguide obtained by the imprinting method is limited by the manufacturing process of the imprinted adhesive material, and the refractive index is difficult to exceed 2.0, which makes it difficult to improve the diffraction efficiency of the grating; the imprinting process has restrictions on the aspect ratio of the grating, and usually the aspect ratio of the grating cannot exceed 3:1, which greatly limits the freedom of optical waveguide design. In addition, the imprinted adhesive material is an organic polymer material with unstable performance and is sensitive to physical environments such as light and temperature. Long-term outdoor wear will affect the service life of AR lenses.

[0003] The Chinese patent with publication number CN117572556A recently applied by the applicant discloses an AR optical waveguide structure that matches the refractive index of a lens and a processing method thereof. The optical waveguide structure includes a glass substrate and a grating layer arranged on the glass substrate. The glass substrate includes a high-refractive-index glass with a refractive index of more than 1.5, and the grating layer includes a combination of at least two of silicon oxide, titanium oxide, aluminum oxide, hafnium oxide, zirconium oxide, cerium oxide and silicon nitride; the processing method includes the following steps: S1 depositing a transparent dielectric film on the surface of the high-refractive-index glass; S2 obtaining an imprint template; S3 obtaining a substrate to be etched; S4 etching the surface of the substrate to be etched to remove the imprint glue in the grating structure area and the transparent dielectric film in the non-grating structure area to obtain the optical waveguide structure. The above method makes the selection of grating materials more flexible. Conventional semiconductor materials such as silicon oxide and metal oxide materials such as titanium oxide can all be used as grating materials. These materials have a high refractive index (≥2.0) in the visible light band and can achieve higher outcoupling efficiency. In addition, the physical properties of these materials are stable and not easily affected by the external environment, which is more beneficial to improving the stability of the optical waveguide.

[0004] At present, the most popular etching grating material is titanium oxide, which is deposited on the surface of a glass substrate by magnetron sputtering, thermal evaporation and other methods to serve as a substrate for making optical waveguides. The refractive index of titanium oxide is about 2.3 in the visible light band and has no absorption, making it an ideal grating material. However, this material has problems such as slow etching rate and difficulty in maintaining the cross-sectional morphology of the grating during the etching process. In addition, the metal sputtering products produced during the titanium oxide etching process will contaminate the etching cavity, making it difficult to ensure the yield and cleanliness. Therefore, although with the increasing perfection of etching equipment, mass production of etched optical waveguide products has become possible, titanium oxide gratings are currently not mass-produced due to limitations in the etching process. Utility Model Content

[0005] The problem to be solved by the utility model is to provide an optical waveguide structure in view of the above-mentioned deficiencies existing in the prior art. By combining the optical waveguide solutions of heterogeneous bonding, peeling and thinning and direct etching of wafers, the utility model solves the problems of low design freedom and short service life existing in the existing nanoimprint resin optical waveguide solutions, as well as the problem of inconvenience of coating and etching existing in the direct etching optical waveguide solution. While improving the light extraction efficiency, ensuring the coupling uniformity and reducing the rainbow pattern, the utility model is suitable for mass process production.

[0006] The above utility model object of the utility model is achieved through the following technical solutions:

[0007] An optical waveguide structure comprises a glass substrate, an optical waveguide layer composed of a thinned wafer, and a filling layer, wherein the refractive index of the optical waveguide layer is higher than the refractive indexes of the glass substrate and the filling layer, the optical waveguide layer is bonded to the glass substrate, and the surface of the optical waveguide layer facing away from the glass substrate has an etched grating structure, the filling layer is embedded in an etched gap of the etched grating structure, and the outer surfaces of the filling layer and the etched grating structure are approximately on the same plane, and / or the filling layer covers the outer surface of the etched grating structure.

[0008] By adopting the above technical scheme, high refractive index wafers such as silicon oxide, silicon nitride, etc., whose refractive index in the visible light band is above 2.60, have a fast etching rate, stable process, and various performances are much higher than titanium oxide. However, there is a defect that coating is very difficult. It is difficult to achieve high-quality film formation through conventional coating methods such as magnetron sputtering and evaporation. The overall method of directly obtaining the etched grating structure by the wafer avoids the coating problem. However, since there is currently no ideal silicon oxide and silicon nitride wafer cutting method, it is difficult to cut out the ideal AR lens shape, which is very unfavorable for the later production of AR lens products. The utility model proposes to bond an optical waveguide layer composed of thinned wafers on a glass substrate that is easy to shape cut, that is, a high A high-quality wafer film is formed, and then an etched grating structure is formed on the surface of the wafer film. This structural design not only overcomes the problem that the wafer is difficult to coat, but also avoids the problem that the wafer is difficult to cut. In addition, the etched gap of the etched grating structure can be filled with material by coating or the like. The refractive index of the material should be lower than the refractive index of the wafer, and a filling layer is formed, which can further improve the various performances of the optical waveguide structure and is suitable for mass process production. By adopting the above structure, a glass substrate is used as the optical waveguide substrate, and a high-refractive-index wafer that has been bonded and thinned is used as the optical waveguide layer to form a predetermined etched grating structure, and a lower refractive-index filling layer is used to fill the etched gap of the etched grating structure. While improving the light extraction efficiency, ensuring the coupling uniformity, and reducing the rainbow pattern, it has the advantages of stable process and easy mass production, and is suitable for mass process production.

[0009] The utility model is further configured as follows: the refractive index of the glass substrate is 1.50-1.90.

[0010] The adoption of the above technical solution is beneficial to improving the light extraction efficiency.

[0011] The utility model is further configured as follows: the thickness of the glass substrate is 0.30-0.80 mm.

[0012] The adoption of the above technical solution is helpful to improve the light extraction efficiency.

[0013] The utility model is further configured that: the refractive index of the thinned wafer of the optical waveguide layer is above 2.60.

[0014] The adoption of the above technical solution is beneficial to improving light extraction efficiency and ensuring coupling uniformity.

[0015] The utility model is further configured that: the thinned wafer of the optical waveguide layer is a silicon carbide wafer or a gallium nitride wafer.

[0016] By adopting the above technical solution, preferably using silicon carbide wafers, it is beneficial to improve light extraction efficiency and ensure coupling uniformity.

[0017] The utility model is further configured as follows: the thickness of the optical waveguide layer is 0.5-3.0 μm.

[0018] The adoption of the above technical solution is beneficial to improving light extraction efficiency and ensuring coupling uniformity.

[0019] The utility model is further configured as follows: the optical waveguide layer is arranged on the glass substrate by direct bonding, warm pressure bonding, and / or optical bonding.

[0020] By adopting the above technical solution, it is preferred to use high-temperature bonding to complete the connection between the optical waveguide layer and the glass substrate, and then the optical waveguide layer is thinned to the thickness required for etching the grating structure, and an etched grating structure is prepared on the surface of the optical waveguide layer, including coupling-in, turning and coupling-out areas, so that the light from the projection optical machine continues to expand the pupil after passing through the etched grating structure and finally forms an image in front of the human eye, forming a virtual image.

[0021] The utility model is further configured as follows: the etched grating structure is a sub-wavelength grating structure composed of multiple straight tooth gratings, slanted tooth gratings, and / or blazed gratings and arranged in a one-dimensional or two-dimensional array, and the grating period of the etched grating structure is 200~400nm, the duty cycle is 40~60%, the etching height is 100~250nm, the inclination angle of the slanted tooth grating is 20~45°, and the blaze angle of the blazed grating is 20~45°.

[0022] By adopting the above technical solution, it is beneficial to improve the light extraction efficiency and ensure the coupling uniformity.

[0023] The utility model is further configured that: the refractive index of the filling layer is below 2.00.

[0024] The adoption of the above technical solution is helpful to reduce rainbow lines.

[0025] The utility model is further configured as follows: the filling layer is composed of silicon oxide or silicon nitride.

[0026] By adopting the above technical solution, in order to further eliminate rainbow patterns, silicon oxide or silicon nitride material can be filled on the surface of the prepared etched grating structure. The filling of silicon oxide or silicon nitride material can exist only in the etched gap or can be higher than the surface of the etched grating structure. By filling with silicon oxide or silicon nitride material, the diffraction of external ambient light can be suppressed.

[0027] In summary, the beneficial technical effects of the utility model are as follows: by using a glass substrate as an optical waveguide substrate, a high-refractive-index wafer that has been bonded and thinned is used as an optical waveguide layer to form a predetermined etched grating structure, and a lower-refractive-index filling layer is used to fill the etched gap of the etched grating structure, while improving the light extraction efficiency, ensuring the coupling uniformity, and reducing rainbow patterns, it has the advantages of stable process and easy mass production, and is suitable for large-scale process production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the partial structure of the optical waveguide structure of Example 1 of the utility model.

[0029] Figure 2 It is a schematic diagram of the partial structure of the optical waveguide structure of Example 4 of the utility model.

[0030] Figure 3 This is a graph showing how the diffraction efficiency of the optical waveguide structure of Example 1 of the utility model changes with the field of view angle.

[0031] Figure 4 This is a graph showing how the diffraction efficiency of the optical waveguide structure of Example 2 of the utility model changes with the field of view angle.

[0032] Figure 5 This is a graph showing how the diffraction efficiency of the optical waveguide structure of Example 3 of the utility model changes with the field of view angle.

[0033] Figure 6 It is a graph showing the variation of the -1 order diffraction efficiency of the optical waveguide structure of Example 5 of the utility model and Comparative Example 1 with the oblique incident angle.

[0034] In the figure, 1. glass substrate; 2. optical waveguide layer; 21. etched grating structure; 3. filling layer. DETAILED DESCRIPTION

[0035] In order to make the technical means, creative features, objectives and functions achieved by the present invention clearer and easier to understand, the present invention is further described below in conjunction with the accompanying drawings and specific implementation methods.

[0036] Example 1: Reference Figure 1 , is an optical waveguide structure disclosed in the utility model, comprising a glass substrate 1 composed of a high refractive index glass with a refractive index of 1.70, an optical waveguide layer 2 composed of a thinned silicon carbide wafer with a refractive index of 2.70, and a filling layer 3 composed of a silicon oxide material with a refractive index of 1.50, which are stacked in sequence. The thickness of the glass substrate 1 is 0.50 mm, and the thickness of the optical waveguide layer 2 is 0.5 μm.

[0037] The optical waveguide layer 2 is arranged on the glass substrate 1 by bonding, and the surface of the optical waveguide layer 2 facing away from the glass substrate 1 has an etched grating structure 21. Preferably, the connection between the optical waveguide layer 2 and the glass substrate 1 is completed by high-temperature bonding, and then the optical waveguide layer 2 is thinned to the thickness required for etching the grating structure 21, and the etched grating structure 21 is prepared on the surface of the optical waveguide layer 2, including coupling-in, turning and coupling-out regions, so that the light from the projection optical machine continuously expands the pupil after passing through the etched grating structure 21 and finally forms an image in front of the human eye to form a virtual image.

[0038] The etched grating structure 21 is a sub-wavelength grating structure composed of a plurality of straight tooth gratings and arranged in a one-dimensional array, and the grating period of the etched grating structure 21 is 360nm, the duty cycle is 50%, and the etching height is 120nm.

[0039] The filling layer 3 is embedded in the etched gap of the etched grating structure 21, and the filling layer 3 and the outer surface of the etched grating structure 21 are approximately on the same plane. In order to further eliminate the rainbow pattern, the surface of the prepared etched grating structure 21 can be filled with silicon oxide or silicon nitride material. The filling of silicon oxide or silicon nitride material can only exist in the etched gap, or it can be higher than the surface of the etched grating structure 21. The diffraction of external ambient light can be suppressed by filling with silicon oxide or silicon nitride material.

[0040] The implementation principle of this embodiment is:

[0041] S1 substrate preparation, using RCA cleaning method to clean high refractive index glass and silicon carbide wafer respectively, using O2 plasma to pre-treat the two bonded surfaces to improve the hydrophilicity of the surface, and obtain glass substrate 1 and optical waveguide;

[0042] S2 high temperature bonding, the glass substrate 1 and the optical waveguide sheet are bonded in a manner that the bonding surfaces face each other, and are directly bonded from the center to the edge, and high temperature annealing is performed to further improve the bonding strength, thereby obtaining a composite substrate;

[0043] S3 thinning and stripping, using laser irradiation stripping technology or polishing technology to thin the optical waveguide sheet of the composite substrate to a predetermined thickness with good flatness;

[0044] S4 grating fabrication, using electron beam exposure (EBL), photolithography, or nanoimprinting technology to achieve grating patterning on the surface of the optical waveguide sheet of the composite substrate, and then using reactive ion etching (RIE), plasma etching (ICP), reactive ion beam etching (RIBE) and the like to transfer the patterned grating structure to the optical waveguide sheet to obtain an optical waveguide layer 2 with an etched grating structure 21;

[0045] S5 coating, filling the surface of the optical waveguide layer 2 with silicon oxide by coating, to obtain a filling layer 3.

[0046] Embodiment 2: is an optical waveguide structure disclosed in the present utility model, which is different from Embodiment 1 in that the etched grating structure 21 is a sub-wavelength grating structure composed of multiple slanted gratings and arranged in a one-dimensional array, and the grating period of the etched grating structure 21 is 360nm, the duty cycle is 50%, the etching height is 200nm, and the inclination angle of the slanted grating is 30°.

[0047] Example 3: is an optical waveguide structure disclosed in the present utility model. It is different from Example 1 in that the etched grating structure 21 is a sub-wavelength grating structure composed of multiple blazed gratings and arranged in a one-dimensional array, and the grating period of the etched grating structure 21 is 360nm, the etched height is 140nm, and the blazed angle of the blazed grating is 20°.

[0048] Example 4: Reference Figure 2 , is an optical waveguide structure disclosed in the present utility model, which is different from Example 1 in that the filling layer 3 covers the outer surface of the etched grating structure 21.

[0049] Example 5: is an optical waveguide structure disclosed in the present utility model. It is different from Example 1 in that the etched grating structure 21 is a sub-wavelength grating structure composed of multiple straight-tooth gratings and arranged in a one-dimensional array, and the grating period of the etched grating structure 21 is 400nm, the duty cycle is 50%, and the etching height is 100nm.

[0050] Comparative Example 1 is an optical waveguide structure disclosed in the present utility model, which is different from Example 5 in that the filling layer 3 is not included.

[0051] Experimental Example 1: The optical waveguide structures of Examples 1 to 3 were tested to verify the difference in diffraction efficiency between titanium oxide grating and silicon carbide grating in the optical waveguide, wherein the glass substrate 1 selected was the same, and the grating structures involved included common grating structures in optical waveguides such as straight grating, tilted grating, and blazed grating. The results are shown in FIG. Figures 3-5 In the figure, the blue line represents the silicon carbide grating, and the red line represents the titanium oxide grating.

[0052] from Figures 3-5 It can be seen that within a certain FOV range, regardless of straight grating, tilted grating or blazed grating, the diffraction efficiency of silicon carbide grating with a higher refractive index is higher than that of titanium oxide grating, which results in higher light output brightness in the final optical waveguide product.

[0053] Experimental Example 2: The optical waveguide structures of Example 5 and Comparative Example 1 were tested to verify that the silicon carbide grating filled with silicon oxide material can suppress rainbow lines. Figure 6The -1st order diffraction efficiency changes with the oblique incident angle after the out-coupling grating area is filled with silicon oxide material. The red line in the figure represents the optical waveguide structure of Example 5, and the blue line represents the optical waveguide structure of Comparative Example 1.

[0054] from Figure 6 It can be seen that the rainbow pattern comes from the external ambient light incident on the surface of the out-coupling grating at an oblique angle. After the first diffraction of the grating, the diffracted light is received by the human eye, affecting the user's senses. Usually, the suppression of rainbow patterns can be achieved by reducing the -1 order diffraction efficiency, that is, the diffraction efficiency of external light passing through the out-coupling grating is extremely low. Due to the high refractive index of the silicon carbide grating, the -1 order diffraction efficiency can be effectively suppressed by appropriately filling the etched gap with silicon oxide material.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the utility model rather than to limit it. Although the utility model has been described in detail with reference to the preferred embodiments, ordinary technicians in the field should understand that the technical solution of the utility model can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the utility model, which should be included in the scope of the claims of the utility model.

Claims

1. An optical waveguide structure, characterized in that: The invention comprises a glass substrate (1), an optical waveguide layer (2) composed of a thinned wafer, and a filling layer (3); the refractive index of the optical waveguide layer (2) is higher than the refractive index of the glass substrate (1) and the filling layer (3); the optical waveguide layer (2) is bonded to the glass substrate (1), and a surface of the optical waveguide layer (2) facing away from the glass substrate (1) has an etched grating structure (21); the filling layer (3) is embedded in an etched gap of the etched grating structure (21), and the outer surfaces of the filling layer (3) and the etched grating structure (21) are approximately on the same plane, and / or the filling layer (3) covers the outer surface of the etched grating structure (21).

2. An optical waveguide structure according to claim 1, characterized in that: The refractive index of the glass substrate (1) is 1.50-1.

90.

3. An optical waveguide structure according to claim 2, characterized in that: The thickness of the glass substrate (1) is 0.30-0.80 mm.

4. The optical waveguide structure according to claim 1, characterized in that: The thinned wafer refractive index of the optical waveguide layer (2) is above 2.

60.

5. An optical waveguide structure according to claim 4, characterized in that: The thinned wafer of the optical waveguide layer (2) is a silicon carbide wafer or a gallium nitride wafer.

6. An optical waveguide structure according to claim 5, characterized in that: The thickness of the optical waveguide layer (2) is 0.5-3.0 μm.

7. The optical waveguide structure according to claim 1, characterized in that: The optical waveguide layer (2) is arranged on the glass substrate (1) by direct bonding, warm pressure bonding, and / or optical bonding.

8. The optical waveguide structure according to claim 1, characterized in that: The etched grating structure (21) is a sub-wavelength grating structure composed of a plurality of straight tooth gratings, slanted tooth gratings, and / or blazed gratings and arranged in a one-dimensional or two-dimensional array, and the grating period of the etched grating structure (21) is 200-400nm, the duty cycle is 40-60%, the etching height is 100-250nm, the tilt angle of the slanted tooth grating is 20-45°, and the blazed angle of the blazed grating is 20-45°.

9. The optical waveguide structure according to claim 1, characterized in that: The refractive index of the filling layer (3) is below 2.

00.

10. An optical waveguide structure according to claim 9, characterized in that: The filling layer (3) is composed of silicon oxide or silicon nitride.

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