Diffractive optical waveguide and near-eye display device

Abstract

A diffractive optical waveguide and a near-eye display device. The diffractive optical waveguide comprises a waveguide substrate (1). The waveguide substrate (1) comprises a functional region (2) and a non-functional region (3). The functional region (2) comprises a coupling-in grating region (21) and a coupling-out grating region (22). At least part of the non-functional region (3) is provided with an anti-reflection structure (31). Light incident to the coupling-in grating region (21) enters the waveguide substrate (1) from the coupling-in grating region (21), and is totally internally reflected in the waveguide substrate (1) and is transmitted to the coupling-out grating region (22) to be emitted. The reflection of light incident to the non-functional region (3) is reduced by the anti-reflection structure (31), so as to improve the transmittance of the diffraction optical waveguide.

Description

Diffractive optical waveguide and near-eye display device

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on November 20, 2023, with application number 202311553513.0, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] Embodiments of the present application relate to the field of display technology, for example, to a diffraction optical waveguide and a near-eye display device. Background Art

[0003] With the rapid development of virtual reality (VR) and augmented reality (AR) technologies, people have put forward higher requirements for achieving a more realistic immersive experience. As one of the key technologies for AR display, optical waveguide technology can guide light in front of the user's eyes to present virtual information. At present, AR technology has been widely used in many fields such as education, entertainment, and medical care, and has made remarkable progress. However, there are still some technical challenges and limitations in AR display devices in related technologies. One of them is the selection and optimization of optical waveguide materials. High refractive index materials are a core element for achieving efficient AR diffraction optical waveguides. Traditional optical waveguide materials, such as glass and polymers, usually have a low refractive index, which limits the compactness of the optical waveguide structure and the imaging quality. To avoid this situation, some new high refractive index materials have been studied and developed in recent years. These materials usually have a higher refractive index and can more effectively guide and transmit light beams to achieve AR image displays with higher resolution, brightness and contrast.

[0004] While high-refractive-index materials possess excellent optical properties, they also commonly suffer from low transmittance. When light passes through the interface between air and the material, reflection occurs. The greater the difference between the refractive indices of air and the material, the more energy is reflected, resulting in a decrease in the material's transmittance.

[0005] Summary of the Invention

[0006] In view of this, embodiments of the present application provide a diffraction light waveguide and a near-eye display device to avoid the low transmittance of the diffraction light waveguide formed of a high refractive index material in the related art.

[0007] According to one aspect of the present application, a diffractive optical waveguide is provided, comprising a waveguide substrate, wherein the waveguide substrate comprises a functional area and a non-functional area;

[0008] The functional area includes an in-coupling grating area and an out-coupling grating area, and at least a portion of the non-functional area is provided with an anti-reflection structure;

[0009] The light incident on the coupling-in grating region enters the waveguide substrate from the coupling-in grating region, is transmitted through total internal reflection in the waveguide substrate, and is emitted from the coupling-out grating region;

[0010] The light incident on the non-functional area passes through the anti-reflection structure to reduce reflection, thereby improving the transmittance of the diffraction light waveguide.

[0011] The antireflection structure may be provided on at least part of the non-functional area on one side of the waveguide substrate, or on both sides of the waveguide substrate. Furthermore, the functional areas provided on the waveguide substrate may be provided on the same side or on different sides.

[0012] According to another aspect of the present application, a near-eye display device is provided, comprising the diffraction optical waveguide described in any one of the first aspects. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG1 is a schematic top view of the structure of a diffraction optical waveguide provided in an embodiment of the present application;

[0014] FIG2 is a schematic diagram of the structure along the section line AA′ in FIG1 ;

[0015] FIG3 is a schematic diagram of the structure along the section line BB′ in FIG1 ;

[0016] Figures 4 and 5 are schematic diagrams of another structure along the section line BB' in Figure 1;

[0017] FIG6 is a schematic diagram of the optical paths of light transmitted through two diffraction optical waveguides provided in an embodiment of the present application;

[0018] FIG7 is a schematic diagram of a partial top view of a non-functional area of ​​a diffractive optical waveguide provided in an embodiment of the present application;

[0019] FIG8 is a graph showing a change in transmittance versus duty cycle of a diffraction optical waveguide according to an embodiment of the present application;

[0020] FIG9 is a graph showing a transmittance-depth variation curve of a diffraction optical waveguide provided in an embodiment of the present application;

[0021] FIG10 is another schematic diagram of the structure along the section line BB′ in FIG1 ;

[0022] FIG. 11 is another schematic structural diagram along the section line AA′ in FIG. 1 . DETAILED DESCRIPTION

[0023] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in a sequence other than those illustrated or described herein. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0024] FIG1 is a schematic top view of the structure of a diffraction optical waveguide provided in an embodiment of the present application, FIG2 is a schematic diagram of the structure along the section line AA′ in FIG1 , and FIG3 is a schematic diagram of the structure along the section line BB′ in FIG1 . Referring to FIG1-FIG3 , the diffraction optical waveguide provided in an embodiment of the present application includes a waveguide substrate 1, which includes a functional region 2 and a non-functional region 3. The functional region 2 includes an in-coupling grating region 21 and an out-coupling grating region 22, and the non-functional region 3 is provided with an anti-reflection structure 31. Referring to FIG2 , light S1 incident on the in-coupling grating region 21 enters the waveguide substrate 1 from the in-coupling grating region 21, is totally internally reflected in the waveguide substrate 1, and is transmitted to the out-coupling grating region 22 for exit. Referring to FIG3 , light S2 incident on the non-functional region 3 is reduced in reflection by the anti-reflection structure 31, thereby improving the transmittance of the diffraction optical waveguide.

[0025] For example, the diffraction optical waveguide provided in the embodiment of the present application includes a waveguide substrate 1, on which a functional area 2 and a non-functional area 3 are provided, the functional area 2 includes a coupling-in grating area 21 and a coupling-out grating area 22, the coupling-in grating area 21 is provided with a coupling-in grating 221, and the coupling-out grating area 22 is provided with a coupling-out grating 222, wherein the shapes of the coupling-in grating 221 and the coupling-out grating 223 shown in FIG2 are only schematic, and can be designed according to actual conditions during specific implementation, and the embodiment of the present application does not limit this. In this embodiment, the light S1 incident on the coupling-in grating area 21 (emitted by the optical machine) is diffracted by the coupling-in grating 211 of the coupling-in grating area 21 into the waveguide substrate 1, and the diffracted light beam satisfies the total internal reflection condition in the waveguide substrate 1, is totally internally reflected between the upper and lower surfaces of the waveguide substrate 1, and is transmitted to the coupling-out grating area 22 for exit. In other embodiments, the functional region may further include a turning grating region, in which a turning grating is provided. Light incident on the in-coupling grating region, after being modulated by the in-coupling grating, is transmitted toward the turning grating region through total internal reflection. After being turned and expanded by the turning grating within the turning grating region, it is transmitted to the out-coupling grating region for exit. In a specific implementation, the turning grating region may include at least two sub-turning regions, for example, disposed on either side of the in-coupling grating region. The in-coupling grating, turning grating, and out-coupling grating may be one-dimensional or two-dimensional gratings. The specific grating shape may be designed as a straight tooth grating, a skew tooth grating, a blazed grating, etc., and may be designed based on actual circumstances. In another embodiment, the in-coupling grating region and the out-coupling grating region may be divided into zones with multiple gratings of different periods, different duty cycles, and different depths to improve the performance of the diffraction waveguide. For example, the out-coupling grating may have a grating depth that increases as it moves away from the in-coupling grating to improve diffraction efficiency, reduce the impact of reduced light intensity, and enhance image uniformity. In another embodiment, a functional grating may be designed around the outcoupling grating so that light that cannot be emitted from the outcoupling grating to the human eye can be returned to the outcoupling grating area for utilization, thereby improving light utilization.

[0026] When light S2 (ambient light) incident on the non-functional area 3 passes through the anti-reflection structure 31, the anti-reflection structure 31 can reduce the reflection of the light on the surface of the waveguide substrate 1. Moreover, unlike the coupling grating, the anti-reflection structure 31 will not cause the light incident on the waveguide substrate 1 to produce other diffraction orders that can be totally internally reflected within the waveguide substrate 1. It only produces transmission diffraction orders and reflection diffraction orders. Since no other orders of diffraction are produced, the light energy of the transmission diffraction order is increased, thereby improving the transmittance of the diffraction waveguide. It should be noted that the anti-reflection structure 31 shown in Figure 3 is arranged on the lower surface of the waveguide substrate 1 for schematic purposes only. In other embodiments, it can be arranged on the upper surface of the waveguide substrate 1, or on both the upper and lower surfaces of the waveguide substrate 1. The specific implementation can be designed according to actual conditions.

[0027] The diffractive optical waveguide provided in the embodiments of the present application utilizes an anti-reflection structure provided on a non-functional region. This causes light incident on the non-functional region to undergo transmission diffraction after passing through the anti-reflection structure, thereby improving the transmittance of the diffractive optical waveguide. For example, when the anti-reflection structure is not provided on the non-functional region, most of the light incident on the non-functional region is reflected back, resulting in low transmittance. However, when the anti-reflection structure is provided on the non-functional region, the light diffracts after passing through the anti-reflection structure, modulating the light and increasing the light energy of the transmitted diffraction order while reducing the light energy of the reflected diffraction order, thereby achieving the anti-reflection effect.

[0028] For example, with continued reference to FIG. 3 , the antireflection structure 31 includes a periodically arranged grating.

[0029] For example, to achieve an anti-reflection effect, light needs to be diffracted after passing through the grating, and the light needs to be modulated so that the light energy of the transmitted diffraction order is increased and the light energy of the reflected diffraction order is reduced. It should be noted that the grating shape of the present application is a straight grating as an example, which is not a limitation of the present application. In other embodiments, the grating shape can be a blazed grating, a tilted grating, etc., and the present application does not limit this.

[0030] In order to improve the light transmittance, referring to FIG3 , the grating in this embodiment includes a one-dimensional grating, and the period of the one-dimensional grating satisfies: Where D represents the period of the one-dimensional grating, λ min Represents the minimum wavelength of the light incident on the one-dimensional grating, N2 represents the refractive index of the waveguide substrate, N1 represents the refractive index of air, and α represents the incident angle of the light incident on the one-dimensional grating. Among them, the light incident on the one-dimensional grating is the light whose transmittance needs to be improved in the embodiment of the present application. This condition is to make the light within the light band that needs to be enhanced produce only transmission diffraction orders and reflection diffraction orders after passing through the anti-reflection structure within the above-mentioned periodic range, and no other diffraction orders will be produced. Therefore, compared with the periodic structure that produces other diffraction orders in addition to transmission diffraction orders and reflection diffraction orders, it can increase the light energy in the direction of the transmission diffraction order (distribute the energy of other diffraction orders to the transmission diffraction order), thereby achieving an increase in light transmittance. In addition, when the above conditions are met, the larger the period, the higher the transmittance.

[0031] In an embodiment of the present application, a one-dimensional grating is fabricated in the non-functional region 3 of the waveguide substrate 1. Specifically, the one-dimensional grating can be fabricated by adding an additional layer of material to the waveguide substrate 1 or directly on the substrate, causing light to undergo transmission diffraction at the interface, reducing reflection efficiency and increasing transmittance. For example, Figures 4 and 5 are schematic diagrams of another structure along section line BB′ in Figure 1. Referring to Figure 4, the diffraction optical waveguide further includes a dielectric layer 4 disposed on at least one side of the waveguide substrate (Figure 4 uses one side as an example, which is not a limitation of the embodiment of the present application), with the grating located in the dielectric layer 4. Referring to Figure 5, the grating is directly disposed on the surface of at least one side of the waveguide substrate 1 (Figure 5 uses one side as an example, which is not a limitation of the embodiment of the present application).

[0032] For example, Figure 6 shows the optical paths of light transmitted through two diffractive waveguides according to embodiments of the present invention. The upper figure shows a diffractive waveguide without an anti-reflection structure in the prior art. Taking a substrate with a refractive index of 2.0 as an example, the transmittance of 532nm light from air into the substrate is T1 = 88.889%, the transmittance of 532nm light from the substrate into air is T2 = 88.889%, and the total transmittance is T = T1 * T2 = 79.0125%. The lower figure shows a diffractive waveguide with an anti-reflection structure according to embodiments of the present invention. A one-dimensional grating with a period of 150nm, a duty cycle of 50%, and a depth of 100nm is fabricated at two refractive index boundaries. The transmittance of 532nm light from air into the substrate is T1′ = 99.242%, the transmittance of 532nm light from the substrate into air is T2′ = 99.242%, and the total transmittance is T′ = T1′ * T2′ = 98.4897%.

[0033] In another embodiment of the present application, the grating may further include a two-dimensional grating, and the period of the two-dimensional grating satisfies:

[0034] Among them D i represents the maximum period in the two-dimensional grating, i = 1 or 2, λ min represents the minimum wavelength of the light incident on the two-dimensional grating, N2 represents the refractive index of the waveguide substrate, N1 represents the refractive index of air, and α represents the incident angle of the light incident on the two-dimensional grating.

[0035] FIG7 is a schematic diagram of a partial top view of a non-functional area of ​​a diffraction waveguide provided by an embodiment of the present application. Referring to FIG7 , the two-dimensional grating is arranged in an array, D2 is the period of the grating along the first direction X, and D1 is the period of the grating along the second direction Y. The first direction X and the second direction Y intersect. In the above, D i Is the maximum period in the two-dimensional grating, that is, if the period D2 in the first direction X is greater than the period D1 in the second direction Y, then determine Di The value of is D2. If the period D2 in the first direction X is less than the period D1 in the second direction Y, then determine D i The value of is D1. This condition ensures that light within the wavelength range requiring enhanced transmittance, after passing through the two-dimensional grating, only produces transmission diffraction orders and reflection diffraction orders, and no other diffraction orders. Thus, compared to periodic structures that generate other diffraction orders in addition to transmission and reflection diffraction orders, this structure increases the light energy in the direction of the transmission diffraction orders (distributing the energy of other diffraction orders to the transmission diffraction orders), thereby increasing light transmittance. When the above conditions are met, the larger the period, the higher the transmittance.

[0036] For example, using a material with a refractive index of 2.3 as an example, the transmittance of 450nm light entering the material from air is T1 = 84.481%, and the transmittance of 450nm light entering the material from the material into air is T2 = 84.481%, with a total transmittance of T = T1 * T2 = 71.3704%. When a two-dimensional grating with a period of 100nm * 100nm, a duty cycle of 50%, and a depth of 100nm is fabricated at the interface between two refractive index boundaries, the transmittance of 450nm light entering the material from air is T1′ = 94.772%, and the transmittance of 450nm light entering the material from the material into air is T2′ = 94.772%, with a total transmittance of T′ = T1′ * T2′ = 89.8173%.

[0037] In order to improve the light transmittance, in addition to designing the period of the grating, the duty cycle and depth of the grating can also be designed. For example, the duty cycle of the grating is greater than or equal to 10% and less than or equal to 90%.

[0038] For example, referring to FIG3 , the duty cycle of the grating refers to the ratio between the medium width D0 and the grating period D in the grating. The size of the grating duty cycle directly affects the distribution of light intensity and the transmission performance. Therefore, in one embodiment of the present application, the duty cycle of the grating is greater than or equal to 10% and less than or equal to 90%.

[0039] For example, the duty cycle range is greater than or equal to 35% and less than or equal to 65%.

[0040] Figure 8 shows a graph of transmittance versus duty cycle for a diffraction waveguide according to an embodiment of the present application. Referring to Figure 8 , transmittance is analyzed for vertically incident 450nm light, with a material refractive index of 2.0, a grating period of 200nm, and a height of 50nm. The grating duty cycle is scanned. As shown in Figure 8 , transmittance can be increased by simply forming a periodic grating modulation. Therefore, the duty cycle range is greater than or equal to 10% and less than or equal to 90%. For example, the duty cycle range is greater than or equal to 35% and less than or equal to 65%.

[0041] Figure 9 is a graph showing the transmittance-depth variation of the diffraction waveguide provided in an embodiment of the present application. Figure 9 analyzes the transmittance of vertically incident 340nm, 530nm, and 650nm light. The material refractive index is 2.0, the grating period is 100nm, the duty cycle is 50%, and the grating height is scanned. The depth modulation of the light is periodic, and the depth of the grating is greater than or equal to Less than or equal to λ represents the wavelength of the light incident on the grating. Within this range, efficient anti-reflection is achieved for all wavelengths requiring enhanced transmittance. As shown in Figure 9, different grating depths can be designed for different wavelengths to maximize the anti-reflection effect. For light of the same wavelength, a variety of grating heights (curve peaks) can be designed. For light within a specific wavelength range, the grating height with the best effect can be adaptively selected for processing.

[0042] In another embodiment of the present application, the anti-reflection structure may further include a non-periodic structure located on the surface of the waveguide substrate, wherein the distance L between the two farthest points in the projection pattern of the non-periodic structure on the plane where the waveguide substrate is located is less than the minimum wavelength λ of the light incident on the anti-reflection structure. min , that is: L<λ min The maximum gap l between the non-periodic structures is smaller than the minimum wavelength λ of the light incident on the antireflection structure. min , that is: l<λ min The light incident on the anti-reflection structure is the light whose transmittance needs to be improved.

[0043] For example, in addition to processing one-dimensional or two-dimensional gratings on the waveguide substrate as disclosed in the above-mentioned application embodiments, non-periodic structures can also be processed on the waveguide substrate. The non-periodic micro-nanostructure destroys the flatness of the edge of the medium and reduces the efficiency of its mirror reflection. Because the structure is not periodic, the light will not be diffracted.

[0044] FIG10 is another schematic diagram of a structure along section line BB′ in FIG1 . Referring to FIG10 , for example, an antireflection film 5 is provided in the non-functional region, located between the waveguide substrate 1 and the antireflection structure 31. An antireflection film is an optical element whose primary function is to reduce reflection losses on the element surface to improve optical efficiency. The refractive index of such a film is typically between that of glass and air. The antireflection film is composed of one or more transparent dielectric thin films, including but not limited to magnesium fluoride, titanium oxide, lead sulfide, lead selenide, ceramic infrared antireflection films, and vinyl silsesquioxane hybrid films.

[0045] For example, a grating may be further processed on the antireflection film 5 coated in the non-functional area, including a one-dimensional grating or a two-dimensional grating, and the period of the grating needs to meet the requirements of the above embodiment.

[0046] FIG11 is another schematic structural diagram along the section line AA′ in FIG1 . Referring to FIG11 , for example, the antireflection structure 31 is an antireflection film.

[0047] For example, in this embodiment, the functional region comprises a stacked waveguide substrate 1 and a dielectric layer 4 (e.g., a transparent adhesive layer). The in-coupling grating 221 and the out-coupling grating 222 are disposed on the dielectric layer 4. The non-functional region comprises a stacked waveguide substrate 1 and an anti-reflection film 5. By providing the anti-reflection film 5 in the non-functional region, light interference occurs where the anti-reflection film is provided, thereby reducing reflection and improving transmittance. Compared to the related art method of providing an anti-reflection film on the dielectric, this reduces losses due to multiple interfacial refractions, thus facilitating improved light transmittance.

[0048] Based on the same technical concept, embodiments of the present application also provide a near-eye display device. The near-eye display device may be augmented reality glasses that include any of the diffractive optical waveguides provided in the embodiments of the present application. Therefore, the augmented reality glasses provided in the embodiments of the present application possess the corresponding beneficial effects of the diffractive optical waveguides provided in the embodiments of the present application, which will not be further elaborated here.

Claims

1. A diffractive optical waveguide, comprising: a waveguide substrate, on which a functional region and a non-functional region are included; the functional region includes an input grating region and an output grating region, and at least a part of the non-functional region is provided with an anti-reflection structure; light incident on the input grating region enters the waveguide substrate from the input grating region, and is totally internally reflected in the waveguide substrate and transmitted to the output grating region for output; light incident on the non-functional region is reduced in reflection through the anti-reflection structure to improve the transmittance of the diffractive optical waveguide.

2. The diffractive optical waveguide according to claim 1, wherein, the anti-reflection structure includes a grating arranged periodically.

3. The diffractive optical waveguide according to claim 2, wherein, The grating includes a one-dimensional grating, and the period of the one-dimensional grating satisfies: Wherein, D represents the period of the one-dimensional grating, λ min represents the minimum wavelength of the light incident on the one-dimensional grating, N 2 represents the refractive index of the waveguide substrate, N 1 represents the refractive index of air, and α represents the incident angle of the light incident on the one-dimensional grating.

4. The diffractive optical waveguide according to claim 2, wherein, The grating includes a two-dimensional grating, and the period of the two-dimensional grating satisfies: where D i represents the maximum period in the two-dimensional grating, i = 1 or 2, λ min represents the minimum wavelength of the light incident on the two-dimensional grating, N 2 represents the refractive index of the waveguide substrate, N 1 represents the refractive index of air, and α represents the incident angle of the light incident on the two-dimensional grating.

5. The diffractive optical waveguide according to claim 2, wherein, the duty cycle of the grating is greater than or equal to 10% and less than or equal to 90%.

6. The diffractive optical waveguide according to claim 5, wherein, the duty cycle of the grating is greater than or equal to 35% and less than or equal to 65%.

7. The diffractive optical waveguide according to claim 2, wherein, The depth of the grating is greater than or equal to less than or equal to where λ represents the wavelength of the light incident on the grating.

8. The diffractive optical waveguide according to claim 1, wherein, The antireflection structure includes an aperiodic structure located on the surface of the waveguide substrate, and the distance L between the two points with the farthest distance in the projection pattern of the aperiodic structure in the plane where the waveguide substrate is located is less than the minimum wavelength λ of the light incident on the antireflection structure min , that is: L < λ min ; The maximum gap l between the aperiodic structures is less than the minimum wavelength λ incident on the antireflection structure min , i.e.: l < λ min .

9. The diffractive optical waveguide according to claim 1, wherein, an anti-reflection film is provided in the non-functional region, and the anti-reflection film is located between the waveguide substrate and the anti-reflection structure.

10. The diffractive optical waveguide according to claim 1, wherein, the anti-reflection structure is an anti-reflection film.

11. The diffractive optical waveguide according to claim 1, wherein, the anti-reflection structure is directly provided on the surface of at least one side of the waveguide substrate, or a dielectric layer is provided on at least one side of the waveguide substrate, and the anti-reflection structure is provided on the dielectric layer.

12. A near-eye display device, comprising the diffractive optical waveguide according to any one of claims 1 to 11.

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