Optical waveguide structure design method based on transmittance matching

Abstract

The invention relates to an optical waveguide structure design method based on transmittance matching, and the method comprises the following steps: S1, setting the refractive indexes of a waveguide substrate and a grating structure, selectively filling the grating structure with a low-refractive-index material according to a preset optical performance index, and determining the structural parameters of the grating structure, obtaining transmittance curves of a structural region and a non-structural region on the waveguide substrate in a visible light range; and S2, selectively arranging a composite film and / or a microstructure in the non-structural region according to the transmittance curve obtained in the S1, so that the transmittance difference of the structural region and the non-structural region in the visible light range does not exceed 5.5%, and obtaining the diffraction optical waveguide. The high-refractive-index waveguide substrate has the advantages that the transmittance of the high-refractive-index waveguide substrate is improved, the transmittance difference between the structural area and the non-structural area is reduced, and the optical performance and the attractiveness are guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of diffractive optical waveguides, and in particular to a design method of an optical waveguide structure based on transmittance matching. Background Art

[0002] Augmented reality technology (AR) realizes the seamless integration of the real world and virtual images through the combination of a micro display screen and optical elements, providing users with an immersive visual experience. In this integration process, the light guiding device plays a key role, and the optical waveguide technology is the core technical solution to achieve this integration. This technology uses the principle of total internal reflection to ensure the effective conduction of light, enabling users to naturally integrate into the virtual world while maintaining the perception of the real world. Among many optical waveguide technologies, diffractive optical waveguides have gradually become the dominant technical path in the AR field due to their high production yield. However, due to the diffractive structures adopted at different positions in the diffractive optical waveguide, the transmittance of these structural regions to ambient light decreases compared to the non-structural regions. This difference enables users to perceive uneven brightness regions inside the lens when using AR devices, which affects the clear observation of the external environment and reduces the wearing comfort.

[0003] A Chinese patent with the publication number CN118330806A discloses a diffractive optical waveguide, including: a waveguide substrate, the surface of the waveguide substrate includes a grating structure region and a non-grating structure region, and the grating structure region includes a grating structure formed by imprinting a glue material; wherein, the difference between the average value of the light transmittance of the grating structure region in the visible light band and the average value of the light transmittance of the non-grating structure region in the visible light band is less than or equal to 5% to hide the grating structure. The above diffractive optical waveguide improves the transmittance of the structural region by reducing the duty cycle, period, and depth of the grating structure (n = 1.8). Although this method can approximately match the transmittance of the structural region and the non-structural region, it reduces the design freedom of the diffractive optical waveguide and affects its optical performance to a certain extent.

[0004] A Chinese patent with the publication number CN119846766A discloses a diffractive optical waveguide for augmented reality display, which includes a waveguide substrate and a first grating and a second grating disposed on the waveguide substrate. The first grating is configured to couple input light carrying image information into the waveguide substrate and cause it to propagate through total internal reflection. The second grating includes a diffractive relief structure configured to at least expand the pupil of the light propagating into it. Wherein, the diffractive optical waveguide further includes an optical film layer that at least covers the second grating and includes a filling structure that fills the voids in the diffractive relief structure of the second grating and forms an overflow layer that protrudes above the diffractive relief structure. Since under the same conditions, the transmittance of a low refractive index material is higher than that of a high refractive index material, the above diffractive optical waveguide fills the structural area with an optical film layer of a lower refractive index to hide the grating structure, but this method is only applicable to waveguide substrates with a refractive index below 1.8. For cases with a higher refractive index (n>2.0), this method will affect the waveguide transmission performance. Summary of the Invention

[0005] The problem to be solved by the present invention is to provide a method for designing an optical waveguide structure based on transmittance matching in view of the above deficiencies in the prior art, which has the advantages of improving the transmittance of a high refractive index waveguide substrate, reducing the transmittance difference between the structural area and the non-structural area, and ensuring optical performance and aesthetics.

[0006] The above object of the present invention is achieved by the following technical solutions: A method for designing an optical waveguide structure based on transmittance matching includes the following steps: S1 Set the refractive indices of the waveguide substrate and the grating structure. According to the preset optical performance indicators, selectively fill a low refractive index material on the grating structure, and then determine the structural parameters of the grating structure, and obtain the transmittance curves of the structural area and the non-structural area on the waveguide substrate in the visible light range. S2 According to the transmittance curves obtained in S1, selectively set a composite film and / or microstructures in the non-structural area so that the transmittance difference between the structural area and the non-structural area in the visible light range does not exceed 5.5%, and obtain a diffractive optical waveguide.

[0007] Further, in S1, the refractive index of the waveguide substrate exceeds 1.5. And / or, the material of the waveguide substrate is one of optical glass, optical resin, lithium niobate, and silicon carbide.

[0008] Further, in S1, the refractive index of the grating structure exceeds 1.5. And / or, the material of the grating structure is one or several composite materials of optical glass, optical resin, lithium niobate, silicon carbide, titanium dioxide, and silicon nitride.

[0009] Furthermore, in the step S1, the refractive index of the low refractive index material does not exceed 1.5; and / or, the low refractive index material is a composition of one or more of a hardening solution, silicon dioxide, and magnesium fluoride; and / or, the height difference between the low refractive index material and the grating structure is 0 to 5 μm.

[0010] Even further, in the step S1, the grating period of the grating structure is 250 to 400 nm; and / or, the width of the grating teeth of the grating structure is 100 to 280 nm; and / or, the height of the grating teeth of the grating structure is 30 to 250 nm.

[0011] Further, in the step S2, the composite film is composed of a plurality of alternately arranged low refractive index thin films and a plurality of high refractive index thin films.

[0012] Even further, in the step S2, the material of the low refractive index thin film is a composition of one or more of magnesium fluoride, silicon dioxide, silicon nitride, aluminum oxide, and hafnium oxide; and / or, the thickness of the low refractive index thin film is 50 to 200 nm.

[0013] Even further, in the step S2, the material of the high refractive index thin film is a composition of one or more of titanium oxide, silicon, and tantalum oxide.

[0014] and / or, the thickness of the high refractive index thin film is 30 to 100 nm.

[0015] Further, in the step S2, the microstructure is nano-columns arranged in a two-dimensional array, the cross-section of the nano-columns is circular or polygonal, and the period of the nano-columns does not exceed the grating period of the grating structure.

[0016] Even further, in the step S2, the period of the nano-columns is 100 to 200 nm; and / or, the height of the nano-columns is 40 to 210 nm; and / or, the width of the nano-columns in the first array direction is 20 to 100 nm, and the width in the second array direction is 20 to 100 nm; and / or, the material of the nano-columns is a composite material of one or more of optical glass, optical resin, lithium niobate, silicon carbide, titanium dioxide, and silicon nitride.

[0017] In some diffractive optical waveguide designs, in order to achieve better optical effects, it is usually necessary to partition the grating structure, that is, there are differences in the structural parameters of the grating structure in adjacent regions, which results in differences in the transmittance itself between different grating partitions. In response to this situation, the average transmittance between different grating partitions can be calculated, and the design of the transmittance matching layer in the non-structural region can be carried out based on this average value.

[0018] In summary, the beneficial technical effects of the present invention are as follows: By setting the refractive indices of the waveguide substrate and the grating structure and selectively filling low-refractive-index materials on the grating structure, the transmittance of the high-refractive-index waveguide substrate can be effectively improved; at the same time, by selectively setting composite films and / or microstructures in the non-structural region, the transmittance difference between the structural region and the non-structural region is further reduced. This not only does not damage the optical properties of the diffractive optical waveguide itself but also ensures the optical performance and aesthetics of the diffractive optical waveguide. This method is not only applicable to waveguide substrates and grating structures of various materials, but also through fine-tuning of structural parameters and material selection, precise matching of transmittance is achieved, providing a new solution for the design of diffractive optical waveguides in augmented reality technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic structural diagram of the diffractive optical waveguide according to Embodiment 1 of the present invention.

[0020] Figure 2 is a transmittance curve diagram of the grating structures with different refractive indices in the visible light range according to Embodiment 1 of the present invention.

[0021] Figure 3 is a transmittance curve diagram of the grating structure with n = 2.6 before and after filling according to Embodiment 1 of the present invention.

[0022] Figure 4 is a schematic structural diagram of the diffractive optical waveguide according to Embodiment 2 of the present invention.

[0023] Figure 5 is a transmittance curve diagram of the structural region and the non-structural region on the waveguide substrate in the visible light range according to Embodiment 2 of the present invention.

[0024] Figure 6 is a schematic structural diagram of the diffractive optical waveguide according to Embodiment 3 of the present invention.

[0025] Figure 7 is a schematic diagram of the connection relationship between the waveguide substrate and the microstructures according to Embodiment 3 of the present invention.

[0026] Figure 8 is a transmittance curve diagram of the structural region and the non-structural region on the waveguide substrate in the visible light range according to Embodiment 3 of the present invention.

[0027] Figure 9It is a schematic structural diagram of the diffractive optical waveguide according to Embodiment 4 of the present invention.

[0028] Figure 10 It is a transmittance curve graph of the structural region and the non-structural region on the waveguide substrate in the visible light range according to Embodiment 4 of the present invention.

[0029] Figure 11 It is a transmittance curve graph of the structural region and the non-structural region on the waveguide substrate in the visible light range according to Embodiment 5 of the present invention.

[0030] Figure 12 It is a schematic structural diagram of the diffractive optical waveguide according to Embodiment 6 of the present invention.

[0031] Figure 13 It is a schematic diagram of the connection relationship between the waveguide substrate and the microstructure according to Embodiment 6 of the present invention.

[0032] Figure 14 It is a transmittance curve graph of the structural region and the non-structural region on the waveguide substrate in the visible light range according to Embodiment 6 of the present invention. Specific Embodiments

[0033] In order to make the technical means, creative features, achieved purposes and functions of the present invention clearer and easier to understand, the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0034] Embodiment 1: Refer to Figure 1 , a method for designing an optical waveguide structure based on transmittance matching disclosed in the present invention, includes the following steps. S1 Set the refractive indices of the waveguide substrate and the grating structure, and selectively fill the low-refractive-index material on the grating structure according to the preset optical performance indexes, thereby determining the structural parameters of the grating structure, and obtaining the transmittance curves of the structural region and the non-structural region on the waveguide substrate in the visible light range. S2 According to the transmittance curves obtained in S1, selectively set the composite film and / or microstructure in the non-structural region to make the transmittance difference between the structural region and the non-structural region in the visible light range not exceed 5.5%, so as to obtain a diffractive optical waveguide.

[0035] Specifically, in S1, after selecting a suitable waveguide substrate and grating structure, design the diffractive light wave according to the preset optical performance indexes; refer to Figure 2, the transmittance of the waveguide substrate and grating structure with low refractive index is relatively high, while that of the waveguide substrate and grating structure with high refractive index is relatively low. To improve the transmittance of the structure region, especially for the case where the refractive index is relatively high (n>2.0), a low refractive index material can be filled in the grating gaps of the grating structure. The low refractive index material can be flush with the top of the grating structure or overflow and cover the top surface of the grating structure. Generally, the refractive index of the low refractive index material needs to be much smaller than the smaller one of the refractive indices of the waveguide substrate and the grating structure. And according to different filling materials, the filling methods can be spin coating, injection, deposition, etc.; at the same time, for the grating structure filled with the low refractive index material, the two need to be designed as a complete grating structure to obtain the structural parameters that meet the optical performance indicators. When the waveguide substrate and the grating structure are made of the same material, it can be patterned and prepared based on the waveguide substrate through electron beam exposure, photolithography, etc., and combined with the etching process to realize the transfer of the pattern to the waveguide substrate to form the grating structure. On the contrary, a film is pre-coated on the waveguide substrate and then the grating structure is formed; finally, the transmittance of the diffractive optical waveguide that meets the optical performance is calculated or tested. Using common calculation methods such as RCWA and FDTD, the transmittance curve in the visible light range is calculated, or the transmittance curve is obtained by testing with a spectrometer, and the result is as Figure 3 shown.

[0036] In S2, according to the transmittance curve obtained in S1, when the transmittance difference between the structure region and the non-structure region exceeds 5.5%, the transmittance matching design can be carried out in the non-structure region on the same side as the grating structure. The methods are not limited to the composite film design, the micro-structure design, or the combination design of the composite film and the micro-structure; for the composite film design, usually only one layer of low refractive index thin film and one layer of high refractive index thin film are needed to complete the transmittance modulation of the non-structure region, so as to achieve the purpose of matching the transmittance of the structure region, and it can be adjusted according to the actual optical performance indicators; for the micro-structure design, it is necessary to first ensure that the introduction of the micro-structure does not affect the transmission characteristics of the diffractive optical waveguide itself, that is, the period of the micro-structure is much smaller than the grating period of the grating structure. It can be patterned and prepared based on the waveguide substrate through electron beam exposure, photolithography, etc., and combined with the etching process to realize the transfer of the pattern to the waveguide substrate to form the micro-structure, or a film can be pre-coated on the waveguide substrate and then the micro-structure is formed; for the combination design of the composite film and the micro-structure, this can further improve the design freedom to achieve a better matching effect.

[0037] Example 2: Refer to Figure 4 , which is a method for designing an optical waveguide structure based on transmittance matching disclosed by the present invention. The difference from Example 1 is that it includes the following steps, S1 Select an optical resin with a refractive index of 1.8 as the waveguide substrate, and select an optical resin with a refractive index of 1.8 as the grating structure. According to the preset optical performance indicators, fill silica (low refractive index material) with a refractive index of 1.46 on the grating structure, and control the height difference d between the low refractive index material and the grating structure to be 100 nm. Furthermore, determine that the grating period P of the grating structure is 385 nm, the grating tooth width w is 266 nm, the grating tooth height h is 57 nm, and obtain the transmittance curves of the structural area and the non-structural area on the waveguide substrate within the visible light range; S2 According to the transmittance curves obtained in S1, no composite film and microstructures are provided in the non-structural area, so that the transmittance difference between the structural area and the non-structural area within the visible light range < 1.6%. Refer to Figure 5 , to obtain a diffractive optical waveguide with a transmittance > 90%.

[0038] Example 3: Refer to Figure 6 and Figure 7 , a method for designing an optical waveguide structure based on transmittance matching disclosed in the present invention. The difference from Example 1 is that it includes the following steps, S1 Select an optical glass with a refractive index of 2.0 as the waveguide substrate, and select an optical glass with a refractive index of 2.0 as the grating structure. According to the preset optical performance indicators, no low refractive index material is filled on the grating structure. Furthermore, determine that the grating period P of the grating structure is 340 nm, the grating tooth width w is 105 nm, the grating tooth height h is 35 nm, and obtain the transmittance curves of the structural area and the non-structural area on the waveguide substrate within the visible light range; S2 According to the transmittance curves obtained in S1, microstructures are provided in the non-structural area. The microstructures are nano-columns arranged in a two-dimensional array. The cross-section of the nano-columns is diamond-shaped, and the period P x =P y is 180 nm, the height H is 201 nm, the width L x in the first array direction is 75 nm, and the width L y in the second array direction is 85 nm, and the material is optical glass, so that the transmittance difference between the structural area and the non-structural area within the visible light range < 3.2%. Refer to Figure 8 , to obtain a diffractive optical waveguide with a transmittance > 85%.

[0039] Example 4: Refer to Figure 9 , a method for designing an optical waveguide structure based on transmittance matching disclosed in the present invention. The difference from Example 1 is that it includes the following steps, S1 Select optical glass with a refractive index of 2.0 as the waveguide substrate, select titanium dioxide with a refractive index of 2.4 as the grating structure, fill a hardening liquid with a refractive index of 1.45 (low refractive index material) on the grating structure according to the preset optical performance indicators, and control the height difference d between the low refractive index material and the grating structure to be 1 μm. Furthermore, determine that the grating period P of the grating structure is 362 nm, the grating tooth width w is 217 nm, and the grating tooth height h is 60 nm, and obtain the transmittance curves of the structured area and the unstructured area on the waveguide substrate in the visible light range; S2 According to the transmittance curves obtained in S1, set a composite film in the unstructured area. The composite film consists of a 135-nm-thick silicon dioxide film (low refractive index film) on the upper layer and a 40-nm-thick tantalum oxide film (high refractive index film) on the lower layer, so that the transmittance difference between the structured area and the unstructured area in the visible light range is <4.5%, referring to Figure 10 , to obtain a diffractive optical waveguide with a transmittance >70%.

[0040] Example 5: A method for designing an optical waveguide structure based on transmittance matching disclosed in the present invention. The difference from Example 1 is that it includes the following steps, S1 Select silicon carbide with a refractive index of 2.6 as the waveguide substrate, select silicon carbide with a refractive index of 2.6 as the grating structure, fill a hardening liquid with a refractive index of 1.45 (low refractive index material) on the grating structure according to the preset optical performance indicators, and control the height difference d between the low refractive index material and the grating structure to be 1 μm. Furthermore, determine that the grating period P of the grating structure is 288 nm, the grating tooth width w is 173 nm, and the grating tooth height h is 50 nm, and obtain the transmittance curves of the structured area and the unstructured area on the waveguide substrate in the visible light range; S2 According to the transmittance curves obtained in S1, set a microstructure in the unstructured area. The composite film consists of a 107-nm-thick hafnium oxide film (low refractive index film) on the upper layer and a 35-nm-thick titanium dioxide film (high refractive index film) on the lower layer, so that the transmittance difference between the structured area and the unstructured area in the visible light range is <5.5%, referring to Figure 11 , to obtain a diffractive optical waveguide with a transmittance >70%.

[0041] Example 6: Referring to Figure 12 and Figure 13 , a method for designing an optical waveguide structure based on transmittance matching disclosed in the present invention. The difference from Example 1 is that it includes the following steps, S1 Select silicon carbide with a refractive index of 2.6 as the waveguide substrate, and select silicon carbide with a refractive index of 2.6 as the grating structure. According to the preset optical performance indicators, fill silicon dioxide (low refractive index material) with a refractive index of 1.46 on the grating structure, and control the height difference d between the low refractive index material and the grating structure to be 100 nm. Furthermore, determine that the grating period P of the grating structure is 295 nm, the grating tooth width w is 201 nm, and the grating tooth height h is 35 nm, and obtain the transmittance curves of the structural area and the non-structural area on the waveguide substrate in the visible light range; S2 According to the transmittance curves obtained in S1, set a composite film in the non-structural area. The microstructure is nano-columns arranged in a two-dimensional array. The cross-section of the nano-columns is rectangular, and the period P of the nano-columns x =P y is 150 nm, the height H is 209 nm, the width L in the first array direction x is 45 nm, and the width L in the second array direction y is 30 nm, and the material is silicon carbide, so that the transmittance difference between the structural area and the non-structural area in the visible light range is <2.3%. Refer to Figure 14 , to obtain a diffractive optical waveguide with a transmittance >80%.

[0042] Finally, 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 them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for designing an optical waveguide structure based on transmittance matching, characterized in that: The following steps are included: S1 sets the refractive index of the waveguide substrate and the grating structure, and selectively fills the grating structure with a low refractive index material according to a preset optical performance index, thereby determining the structural parameters of the grating structure, and obtaining the transmittance curves of the structured area and the unstructured area on the waveguide substrate in the visible light range; S2 selectively arranges a composite film and / or a microstructure in the non-structured area according to the transmittance curve obtained in S1, so that the transmittance difference between the structured area and the non-structured area in the visible light range does not exceed 5.5%, thereby obtaining a diffraction optical waveguide.

2. The optical waveguide structure design method based on transmittance matching according to claim 1, characterized in that: In said S1, the refractive index of the waveguide substrate exceeds 1.5; And / or, the material of the waveguide substrate is one of optical glass, optical resin, lithium niobate and silicon carbide.

3. The optical waveguide structure design method based on transmittance matching according to claim 1, characterized in that: In said S1, the refractive index of the grating structure exceeds 1.5; And / or, the material of the grating structure is one or a composite material of several of optical glass, optical resin, lithium niobate, silicon carbide, titanium dioxide and silicon nitride.

4. The optical waveguide structure design method based on transmittance matching according to claim 3, characterized in that: In said S1, the refractive index of the low refractive index material does not exceed 1.5; And / or, the low refractive index material is a combination of one or more of hardening liquid, silicon dioxide and magnesium fluoride; And / or, the height difference between the low refractive index material and the grating structure is 0-5 μm.

5. The optical waveguide structure design method based on transmittance matching according to claim 4, characterized in that: In S1, the grating period of the grating structure is 250-400 nm; And / or, the grating teeth width of the grating structure is 100-280 nm; And / or, the grating teeth height of the grating structure is 30-250 nm.

6. The optical waveguide structure design method based on transmittance matching according to claim 1, characterized in that: In the above S2, the composite film is composed of several layers of low-refractive-index thin films and several layers of high-refractive-index thin films arranged alternately.

7. The optical waveguide structure design method based on transmittance matching according to claim 6, characterized in that: In S2, the material of the low refractive index film is one or a combination of magnesium fluoride, silicon dioxide, silicon nitride, aluminum oxide and hafnium oxide; And / or, the thickness of the low refractive index film is 50~200nm.

8. The optical waveguide structure design method based on transmittance matching according to claim 6, characterized in that: In S2, the material of the high refractive index film is one or a combination of titanium oxide, silicon and tantalum oxide; And / or, the thickness of the high refractive index film is 30-100 nm.

9. The optical waveguide structure design method based on transmittance matching according to claim 1, characterized in that: In S2, the microstructure is nanocolumns arranged in a two-dimensional array, the cross-section of the nanocolumns is circular or polygonal, and the period of the nanocolumns does not exceed the grating period of the gate structure.

10. The optical waveguide structure design method based on transmittance matching according to claim 9, characterized in that: In said S2, the period of the nanorods is 100-200 nm; and / or, the height of the nanopillars is 40 to 210 nm; and / or, the width of the nanorods in the first array direction is 20-100 nm, and the width in the second array direction is 20-100 nm; And / or, the material of the nanocolumn is one or a composite material of several of optical glass, optical resin, lithium niobate, silicon carbide, titanium dioxide and silicon nitride.

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