Helical grating structure and preparation method thereof

Abstract

The invention relates to a helical grating structure and a preparation method thereof, and the preparation method comprises the steps: providing a transparent substrate; forming a plurality of mutually separated helical tooth structures on the surface of the transparent substrate through imprinting; forming a cut-off film on the surface of the helical tooth structure and the exposed surface of the transparent substrate, wherein the refractive index of the cut-off film is gradually increased from one end close to the helical tooth structure to the other end in the film thickness direction; forming a grating material layer on the surface of the cut-off film, wherein the refractive index of the grating material layer is greater than the material refractive index of the helical tooth structure; and the grating material layer is thinned until the top surface of the cut-off film is exposed, and a plurality of helical tooth gratings are formed. The helical-tooth grating structure with good morphology can be formed, and the diffraction efficiency of the helical-tooth grating is improved.

Description

Technical Field

[0001] This invention relates to the field of optical element technology, specifically to a helical toothed grating structure and its fabrication method. Background Technology

[0002] A serrated grating is a high-performance optical element with a periodic spatial structure. Essentially, it is a nanoscale periodic structure fabricated on a substrate surface, where the teeth are not perpendicular but at a specific tilt angle. This design is primarily intended to guide light in a specific direction, thereby significantly improving light energy utilization, i.e., diffraction efficiency. Serrated gratings for enhancing display diffraction waveguides are fabricated using typical micro-nano manufacturing methods, which are extremely challenging. The morphological issues arising from this fabrication method result in lower diffraction efficiency for serrated gratings. Summary of the Invention

[0003] The technical problem solved by this invention is to provide a slanted tooth grating structure and its preparation method. By pre-embedding a stop film, a grating material layer is directly deposited to form a slanted tooth grating structure with good morphology, thereby improving the diffraction efficiency of the slanted tooth grating.

[0004] To solve the above-mentioned technical problems, the present invention provides a method for fabricating a helical tooth grating, comprising: providing a transparent substrate; forming a plurality of mutually discrete helical tooth structures on the surface of the transparent substrate by imprinting, wherein adjacent helical tooth structures have grooves exposing the bottom surface of the transparent substrate, and the material of the helical tooth structures is imprinting adhesive; forming a stop film on the surface of the helical tooth structures and the exposed surface of the transparent substrate, wherein the refractive index of the stop film gradually increases from one end near the helical tooth structure to the other end in the film thickness direction; forming a grating material layer on the surface of the stop film, wherein the grating material layer fills the grooves, and the surface of the grating material layer is higher than the surface of the stop film, and the refractive index of the grating material layer is greater than the refractive index of the helical tooth structure; thinning the grating material layer until the top surface of the stop film is exposed, thereby forming a plurality of helical tooth gratings.

[0005] Optionally, the change in the refractive index of the stop film along the film thickness direction is expressed as: , where n Let be the refractive index variation function of the cutoff film, n be the refractive index of the cutoff film, n1 be the refractive index of the helical tooth structure, n2 be the refractive index of the grating material layer, z be the distance between the cutoff film and the helical tooth structure in the thickness direction, and h be the film thickness of the cutoff film.

[0006] Optionally, the thickness of the stop membrane is 2nm to 10nm.

[0007] Optionally, the thickness of the grating material layer is more than twice the thickness of the oblique tooth structure.

[0008] Optionally, the process for forming the grating material layer is chemical vapor deposition or electron beam evaporation.

[0009] Optionally, the method for forming the oblique tooth structure includes: forming an imprinting material layer on the surface of the transparent substrate; and performing nanoimprinting on the imprinting material layer using an imprinting mold to form the oblique tooth structure.

[0010] Optionally, the process for forming the stop film includes chemical vapor deposition.

[0011] Accordingly, the present invention also provides a helical tooth grating structure, comprising: a transparent substrate; a plurality of mutually discrete helical tooth structures, wherein adjacent helical tooth structures have grooves exposing the bottom surface of the transparent substrate, and the material of the helical tooth structures is an imprinting adhesive; a stop film located on the surface of the helical tooth structures and the exposed surface of the transparent substrate, wherein the refractive index of the stop film gradually increases from one end near the helical tooth structure to the other end in the film thickness direction; and a plurality of helical tooth gratings, wherein the helical tooth gratings fill the grooves and expose the top surface of the stop film, and the refractive index of the helical tooth gratings is greater than the refractive index of the helical tooth structures.

[0012] Optionally, the material of the stop film includes silicon oxide and titanium oxide, and the material of the helical grating includes at least one of titanium oxide and niobium oxide.

[0013] Optionally, the change in the refractive index of the stop film along the film thickness direction is expressed as: , where n Let be the refractive index variation function of the cutoff film, n be the refractive index of the cutoff film, n1 be the refractive index of the helical tooth structure, n2 be the refractive index of the grating material layer, z be the distance between the cutoff film and the helical tooth structure in the thickness direction, and h be the film thickness of the cutoff film.

[0014] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: The method for fabricating a serrated grating structure provided by this invention involves a transparent substrate. Several discrete serrated structures are formed on the surface of the transparent substrate through imprinting. Adjacent serrated structures have grooves that expose the bottom surface of the transparent substrate. The material of the serrated structures is imprinting adhesive. Therefore, the serrated structures serve as a template for fabricating the serrated grating in a single process. A stop-loss film is formed on the surface of the serrated structures and the exposed surface of the transparent substrate, thus stabilizing the serrated structures. Since the refractive index of the stop-loss film gradually increases from one end near the serrated structure to the other in the film thickness direction, a wide-bandwidth, reflection-free transition between the low-refractive-index imprinting adhesive and the high-refractive-index grating material is achieved, providing greater design freedom and better optical path modulation performance in diffractive waveguide optical applications. Because a grating material layer is formed on the surface of the stop-loss film, filling the grooves and with its surface higher than the surface of the stop-loss film, a grating material layer with serrations (located within the grooves) can be formed using the stop-loss film and the serrated structures. Because the grating material layer is isolated from the low-refractive-index material by the stop-film and the oblique tooth structure, the grating material layer is not affected by the oblique tooth structure material at the interface. Next, the grating material layer is thinned until the top surface of the stop-film is exposed, forming several oblique tooth gratings. Therefore, during the thinning process, the exposure of the stop-film stops at the expected target position, forming a self-aligned oblique tooth structure. Ultimately, an oblique tooth grating with good morphology and high refractive index is formed, further improving the diffraction efficiency of the oblique tooth grating.

[0015] Furthermore, since the thickness of the cutoff film is 2nm to 10nm, it can be used as a position signal to define the grating material layer without affecting the optical performance of the oblique tooth grating structure, thus forming an oblique tooth grating structure with good morphology, which is highly feasible. Attached Figure Description

[0016] Figures 1 to 6 This is a schematic diagram of each step in the fabrication method of the oblique tooth grating structure according to an embodiment of the present invention.

[0017] Explanation of reference numerals in the attached figures: 100. Transparent substrate; 200. Imprinted material layer; 210. Oblique tooth structure; 220. Groove; 300. Cut-off film; 400. Grating material layer; 410. Oblique tooth grating; h1, layer thickness of the helical tooth structure; h2, layer thickness of the grating material layer. Detailed Implementation

[0018] As described in the background section, the oblique tooth grating for enhanced display diffraction waveguides is fabricated using typical micro-nano manufacturing methods, which are extremely difficult. The morphological problems caused by the fabrication method result in low diffraction efficiency of the oblique tooth grating.

[0019] Specifically, to fabricate a serrated grating with high diffraction efficiency, one method involves using an etching process to directly remove a portion of the material from a deposited high-refractive-index film using a patterned (hard) mask. The resulting structure is the serrated grating. On one hand, this method places high demands on the tilting etching process. Firstly, it is often difficult to obtain consistent, high-quality filling through tilting deposition, and hard mask deposition is challenging. Secondly, multiple tilting depositions and etching processes require high consistency in the tilt angles across multiple processes, making it difficult to achieve good morphological quality and serrated depth. On the other hand, high-refractive-index materials themselves have stable structures, resulting in low etching efficiency. In particular, the hard mask is often fabricated as a straight-tooth structure, which differs significantly from the final serrated structure. The resulting structure struggles to achieve good morphological quality and serrated depth, leading to low diffraction efficiency for the serrated grating.

[0020] To solve the above-mentioned technical problems, the present invention provides a slanted tooth grating structure and its preparation method. By pre-embedding a stop film, a grating material layer is directly deposited to form a slanted tooth grating structure with good morphology, thereby improving the diffraction efficiency of the slanted tooth grating.

[0021] To make the above-mentioned objectives, features, and beneficial effects of the present invention more apparent and understandable, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification, claims, and drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a particular order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus. Additionally, directional terms such as above, below, up, down, upward, downward, left, right, etc., are used relative to exemplary embodiments as they are shown in the figures, with upward or upper directions pointing towards the top of the corresponding figure and downward or lower directions pointing towards the bottom of the corresponding figure.

[0023] Figures 1 to 6This is a schematic diagram of each step in the fabrication method of the oblique tooth grating structure according to an embodiment of the present invention.

[0024] Please refer to Figure 1 Provides a transparent substrate 100.

[0025] Specifically, transparent substrates can include glass, quartz, and silicon carbide.

[0026] Please refer to Figure 2 An embossed material layer 200 is formed on the surface of a transparent substrate 100.

[0027] In this embodiment, the material of the embossing material layer 200 is embossing adhesive.

[0028] Specifically, the imprinting adhesive may include at least one of fluorinated acrylic resin, fluorinated epoxy resin, and silicone organic resin.

[0029] Please refer to Figure 3 By imprinting, a number of mutually independent oblique tooth structures 210 are formed on the surface of the transparent substrate 100.

[0030] Among them, there is a groove 220 between adjacent oblique tooth structures 210 that exposes the bottom surface of the transparent substrate 100.

[0031] Specifically, the material of the helical tooth structure 210 is embossing adhesive.

[0032] In this embodiment, the refractive index of the printing adhesive is 1.5.

[0033] Specifically, the method for forming the oblique tooth structure 210 may include: forming an imprinting material layer 200 on the surface of a transparent substrate 100, and performing nanoimprinting on the imprinting material layer 200 using an imprinting mold to form the oblique tooth structure 210, wherein the imprinting mold is a pre-made imprinting mold with an oblique tooth structure.

[0034] Please refer to Figure 4 A stop film 300 is formed on the surface of the helical tooth structure 210 and the exposed surface of the transparent substrate 100.

[0035] Among them, the refractive index of the stop film 300 gradually increases from one end near the helical tooth structure 210 to the other end in the film thickness direction.

[0036] In this embodiment, the change in refractive index of the cutoff film 300 along the film thickness direction is expressed as follows: , where n Let be the refractive index variation function of the cutoff film 300, n be the refractive index of the cutoff film 300, n1 be the refractive index of the helical tooth structure 210, n2 be the refractive index of the grating material layer 400, z be the distance between the cutoff film 300 and the helical tooth structure 210 in the thickness direction, and h be the film thickness of the cutoff film 300.

[0037] Since the cutoff film 300 has a gradually changing refractive index in the film thickness direction, it can also achieve a wide-bandwidth, reflection-free transition between the low-refractive-index imprinting adhesive and the high-refractive-index grating material, reducing the optical influence of the cutoff film 300 on the finally fabricated oblique tooth grating 410. Furthermore, the setting with a gradually changing refractive index can provide higher design freedom and better optical path modulation performance in the optical application of diffractive waveguides.

[0038] In this embodiment, the material of the stop membrane 300 can be silicon oxide and titanium oxide.

[0039] In this embodiment, the method for forming the refractive index-gradient cutoff film 300 can be chemical vapor deposition.

[0040] Specifically, in the process of forming the refractive index-gradient cutoff film 300, the ratio of silicon oxide and titanium oxide can be modulated by adjusting the ratio between the reaction source materials, so that the refractive index of the cutoff film 300 at the contact helical tooth structure 210 is close to the refractive index of the helical tooth structure 210, the refractive index of the cutoff film 300 at the contact grating material layer 400 is close to the refractive index of the grating material layer 400, and the refractive index of the cutoff film 300 gradually increases from one end close to the helical tooth structure 210 to the other end in the film thickness direction.

[0041] In this embodiment, the thickness of the stop membrane 300 is 2nm to 10nm.

[0042] Since the thickness of the cutoff film 300 is 2nm to 10nm, it can be used as a position signal to define the grating material layer 400 without affecting the optical performance of the oblique tooth grating structure, thus forming an oblique tooth grating structure with good morphology and strong feasibility.

[0043] Please refer to Figure 5 A grating material layer 400 is formed on the surface of the stop film 300.

[0044] In this process, the grating material layer 400 fills the groove 220, and the surface of the grating material layer 400 is higher than the surface of the stop film 300. The refractive index of the grating material layer 400 is greater than the refractive index of the material of the helical tooth structure 210.

[0045] Specifically, the material of the grating material layer may include titanium oxide, niobium oxide, or a mixture of titanium oxide and niobium oxide.

[0046] In this embodiment, the thickness h2 of the grating material layer 400 is more than twice the thickness h1 of the helical tooth structure 210.

[0047] In other words, the thickness h2 of the grating material layer 400 is more than twice the thickness of the groove 220. The greater the thickness of the filling grating material layer 400, the smaller the surface undulation of the grating material layer 400 caused by the pre-imprinted material layer 200, which helps to form a well-shaped oblique tooth grating 410.

[0048] In this embodiment, the process for forming the grating material layer 400 can be chemical vapor deposition.

[0049] In another embodiment, the process for forming the grating material layer 400 can also be electron beam evaporation and tilted deposition after electron beam evaporation.

[0050] Please refer to Figure 6 The grating material layer 400 is thinned until the top surface of the stop film 300 is exposed, forming several oblique tooth gratings 410.

[0051] In this embodiment, the thinning process for the grating material layer 400 can be ion beam thinning.

[0052] Specifically, during the thinning process, the stop membrane 300 is used as the thinning termination membrane, and the endpoint signal is obtained through spectral signals.

[0053] In another embodiment, the process for thinning the grating material layer 400 can also be chemical mechanical polishing.

[0054] Specifically, during the thinning process, the stop membrane 300 is used as the thinning termination membrane, and the endpoint signal is obtained through spectral signals.

[0055] In this embodiment, a transparent substrate 100 is provided. A plurality of mutually independent oblique tooth structures 210 are formed on the surface of the transparent substrate 100 by imprinting. Adjacent oblique tooth structures 210 have grooves 220 that expose the bottom surface of the transparent substrate 100. The material of the oblique tooth structures 210 is imprinting adhesive. Therefore, the oblique tooth structures 210 serve as a template for fabricating the oblique tooth grating 410 and are formed in a single process. Based on this, a stop film 300 is formed on the surface of the oblique tooth structures 210 and the exposed surface of the transparent substrate 100. Therefore, the oblique tooth structures 210 are stabilized by the stop film 300. Since the refractive index of the stop film 300 gradually increases from one end near the oblique tooth structure 210 to the other in the film thickness direction, a wide-bandwidth, reflection-free transition between the low-refractive-index imprinting adhesive and the high-refractive-index grating material is achieved, providing greater design freedom and better optical path modulation performance in the optical application of diffractive waveguides. Since a grating material layer 400 is formed on the surface of the stop-off membrane 300, the grating material layer 400 fills the groove 220, and the surface of the grating material layer 400 is higher than the surface of the stop-off membrane 300, a grating material layer 400 with helical teeth (located within the groove 220) can be formed through the stop-off membrane 300 and the helical tooth structure 210. Because the refractive index of the grating material layer 400 is greater than the refractive index of the helical tooth structure 210, and the grating material layer 400 is isolated from the low-refractive-index helical tooth structure 210 by the stop-off membrane 300, the grating material layer 400 has a high refractive index and is unaffected by the material of the helical tooth structure 210 at the interface. Next, the grating material layer 400 is thinned until the top surface of the stop film 300 is exposed, forming a number of oblique tooth gratings 410. Therefore, during the thinning process, the exposure of the stop film 300 stops at the expected target position, forming a self-aligned oblique tooth structure 210. Finally, an oblique tooth grating 410 with good morphology and high refractive index is formed, which further improves the diffraction efficiency of the oblique tooth grating 410.

[0056] Accordingly, the present invention also provides a slanted tooth grating structure, comprising: a transparent substrate 100, a plurality of mutually independent slanted tooth structures 210, a stop film 300, and a plurality of slanted tooth gratings 410.

[0057] Several mutually independent oblique tooth structures 210, with grooves 220 between adjacent oblique tooth structures 210 exposing the bottom surface of the transparent substrate 100, and the material of the oblique tooth structure 210 is an embossing adhesive.

[0058] The stop film 300 is located on the surface of the oblique tooth structure 210 and the exposed surface of the transparent substrate 100. The refractive index of the stop film 300 gradually increases from one end closer to the oblique tooth structure 210 to the other end in the film thickness direction.

[0059] Several oblique tooth gratings 410 are provided, which fill the groove 220 and expose the top surface of the stop film 300. The refractive index of the oblique tooth gratings 410 is greater than that of the oblique tooth structure 210.

[0060] Specifically, the materials, forming process, working principle, specific implementation method and beneficial effects of the oblique tooth grating structure in the embodiments of the present invention can be found in the preparation method of the oblique tooth grating structure in the embodiments of the present invention, and will not be repeated here.

[0061] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for fabricating a helical toothed grating, characterized in that, include: Provide a transparent substrate; By imprinting, a plurality of mutually independent oblique tooth structures are formed on the surface of the transparent substrate, and there are grooves between adjacent oblique tooth structures that expose the bottom surface of the transparent substrate. The material of the oblique tooth structure is imprinting adhesive. A cutoff film is formed on the surface of the helical tooth structure and the exposed surface of the transparent substrate, and the refractive index of the cutoff film gradually increases from one end near the helical tooth structure to the other end in the film thickness direction; A grating material layer is formed on the surface of the stop film, the grating material layer fills the groove, and the surface of the grating material layer is higher than the surface of the stop film. The refractive index of the grating material layer is greater than the refractive index of the helical tooth structure. The grating material layer is thinned until the top surface of the stop film is exposed, forming a plurality of oblique tooth gratings.

2. The method for fabricating a helical toothed grating as described in claim 1, characterized in that, The change in the refractive index of the stop film along the film thickness direction is expressed as: , where n Let be the refractive index variation function of the cutoff film, n be the refractive index of the cutoff film, n1 be the refractive index of the helical tooth structure, n2 be the refractive index of the grating material layer, z be the distance between the cutoff film and the helical tooth structure in the thickness direction, and h be the film thickness of the cutoff film.

3. The method for fabricating a helical toothed grating as described in claim 2, characterized in that, The thickness of the stop membrane is 2nm to 10nm.

4. The method for fabricating a helical toothed grating as described in claim 2, characterized in that, The thickness of the grating material layer is more than twice the thickness of the oblique tooth structure.

5. The method for fabricating a helical toothed grating as described in claim 2, characterized in that, The process for forming the grating material layer is chemical vapor deposition or electron beam evaporation.

6. The method for fabricating a helical toothed grating as described in claim 2, characterized in that, The method for forming the helical tooth structure includes: An embossing material layer is formed on the surface of the transparent substrate; The oblique tooth structure is formed by nanoimprinting the embossing material layer using an embossing mold.

7. The method for fabricating a helical toothed grating as described in claim 2, characterized in that, The process for forming the stop film includes chemical vapor deposition.

8. A helical toothed grating structure, characterized in that, include: Transparent substrate; A plurality of mutually independent oblique tooth structures, with grooves between adjacent oblique tooth structures exposing the bottom surface of the transparent substrate, the material of the oblique tooth structure being an embossing adhesive; A stop film is located on the surface of the oblique tooth structure and the exposed surface of the transparent substrate, and the refractive index of the stop film gradually increases from one end near the oblique tooth structure to the other end in the film thickness direction. A plurality of oblique toothed gratings, the oblique toothed gratings filling the grooves and exposing the top surface of the cutoff film, wherein the refractive index of the oblique toothed gratings is greater than the refractive index of the oblique tooth structure.

9. The oblique tooth grating structure as described in claim 7, characterized in that, The material of the cutoff membrane includes silicon oxide and titanium oxide; the material of the helical grating includes at least one of titanium oxide and niobium oxide.

10. The oblique tooth grating structure as described in claim 7, characterized in that, The change in the refractive index of the stop film along the film thickness direction is expressed as: , where n Let be the refractive index variation function of the cutoff film, n be the refractive index of the cutoff film, n1 be the refractive index of the helical tooth structure, n2 be the refractive index of the grating material layer, z be the distance between the cutoff film and the helical tooth structure in the thickness direction, and h be the film thickness of the cutoff film.

Images