A single layer colour holographic lightguide display device

Abstract

The application provides a single-layer color holographic optical waveguide display device, and the application is provided with an in-coupling grating and an out-coupling grating which can respond to image light of different fields of view, and the grating periods of the in-coupling grating and the out-coupling grating are the same, so that the fields of view corresponding to the image light of different fields of view are connected with each other, thereby realizing single-layer waveguide color display. Compared with other optical waveguide color schemes, the application has the advantages of light and thin, simple process, low cost and being conducive to mass production.

Description

Technical Field

[0001] The embodiments of this application belong to the field of AR display technology, and in particular relate to a single-layer color holographic waveguide display device. Background Technology

[0002] Diffractive waveguide display technology is an important development direction in the field of augmented reality (AR). Diffractive waveguide displays mainly include two types: surface relief gratings and holographic gratings. Due to the dispersion effect of the diffraction grating, the diffraction angles corresponding to different wavelengths of incident light at the same diffraction order are different. That is, the angles at which image light of different colors is transmitted by total internal reflection in the waveguide are different. This results in a small field of view that can be achieved when displaying full color in a single-layer waveguide. Furthermore, under the action of the same diffraction grating, there are significant differences in diffraction efficiency corresponding to different wavelengths, resulting in poor color uniformity of the image.

[0003] Therefore, in order to alleviate or solve the above-mentioned technical problems and realize full-color display of optical waveguides, one of the existing technologies is to solve the above problems by stacking multiple optical waveguides. This solution requires each layer of optical waveguide to be designed with a diffraction grating for a different color channel. However, this solution has problems such as complex manufacturing process, high cost, low diffraction efficiency and large volume of multi-layer waveguides. Another solution is to use a single-layer waveguide multiplexing grating or a combination of multiple gratings. However, this solution has complex design, low diffraction efficiency and ghosting effect caused by dispersion. Summary of the Invention

[0004] To address or mitigate the problems in the prior art, embodiments of the present invention provide a single-layer color holographic optical waveguide display device, comprising an image output device, a coupling grating, a coupling output grating, and an optical waveguide;

[0005] The image output device comprises a microdisplay and a collimating lens assembly. The microdisplay outputs image light of three wavelengths—red, green, and blue—which is emitted into an optical waveguide via the collimating lens assembly. The three wavelengths of image light correspond to different fields of view.

[0006] Both the insertion grating and the output grating are tilted holographic gratings, and both are composed of a polymer matrix and liquid crystal. The refractive index of the polymer matrix is ​​1.45 ~ 1.65; the thickness of the insertion grating and the output grating is 2 μm ~ 10 μm.

[0007] The input grating and the output grating have the same grating period;

[0008] The coupled grating responds to the image light of the three wavelengths of red, green and blue, and then propagates through the optical waveguide in a total internal reflection manner to the coupled grating. Finally, the coupled grating emits a single-layer color display image with the three wavelengths of red, green and blue arranged and connected in sequence according to their Bragg angles.

[0009] As a preferred embodiment of this application, the device further includes a folding grating;

[0010] The folded grating is disposed in the optical waveguide. The grating period of the folded grating is less than the grating periods of the input grating and the output grating, and the optical vectors of the input grating, the output grating and the folded grating form a closed triangle.

[0011] As a preferred embodiment of this application, the tilted holographic volume gratings are all transmission gratings and / or reflection gratings.

[0012] In a preferred embodiment of this application, the tilt angle of the transmissive grating is 45°~71.5°, and the tilt angle of the reflective grating is 18.5°~45°.

[0013] In a preferred embodiment of this application, the grating period of the coupled-in grating and the coupled-out grating is 175nm ~ 10μm.

[0014] In a preferred embodiment of this application, the refractive indices of the input grating and the output grating are 0.01 to 0.1.

[0015] In a preferred embodiment of this application, the optical waveguide has a thickness of 1 mm to 2.5 mm and a refractive index of 1.5 to 2.0.

[0016] Compared with existing technologies, this application provides a single-layer color holographic waveguide display device. This application achieves interconnected fields of view for image light from different viewing angles by using input and output gratings that respond to image light from different viewing angles, and by setting the grating periods of the input and output gratings to be the same. This enables single-layer waveguide color display. Compared with other waveguide color solutions, this application has advantages such as thinner and lighter design, simpler manufacturing process, lower cost, and suitability for mass production. Attached Figure Description

[0017] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. Some specific embodiments of this application will be described in detail below with reference to the accompanying drawings in an exemplary and non-limiting manner. The same reference numerals in the drawings designate the same or similar parts or components. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings:

[0018] Figure 1 This is a schematic diagram of the structure of a single-layer color holographic waveguide display device provided in an embodiment of this application;

[0019] Figure 2 This is a schematic diagram of another single-layer color holographic waveguide display device provided in the embodiments of this application;

[0020] Figure 3 This is a schematic diagram of different field-of-view distributions of the microdisplay provided in the embodiments of this application;

[0021] Figure 4 This is a schematic diagram of the structure of a single-layer color holographic waveguide display device provided in an embodiment of this application;

[0022] Figure 5 This is a schematic diagram of the image source display content provided in an embodiment of this application;

[0023] Figure 6 Examples (a) and (b) are embodiments of the Bragg diffraction distribution of a transmissive volume grating at different wavelengths provided in this application. Detailed Implementation

[0024] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some, not all, of the embodiments of the present application. All other embodiments obtained by those skilled in the art based on the embodiments of the present application without creative effort should fall within the scope of protection of the present application.

[0025] like Figure 1 As shown, this application provides a single-layer color holographic optical waveguide 03 display device, including: an image output device 01, a coupling grating 02, a coupling output grating 04, and an optical waveguide 03;

[0026] Image light with different fields of view is output by the image output device 01. After being diffracted by the coupling grating 02, the image light with different fields of view is sequentially injected into the optical waveguide 03 and propagated to the coupling grating 04 by total internal reflection. After being diffracted again by the coupling grating 04, the light exits the optical waveguide 03 and enters the human eye for imaging and display.

[0027] In this embodiment, specifically, the coupling grating 02 couples the image light output from the image output device 01 into the optical waveguide 03, where it is transmitted via total internal reflection. When the image light reaches the output end of the optical waveguide 03, it is again coupled out of the optical waveguide 03 by diffraction of the output grating 04. Through the design and fabrication of the holographic grating, the Bragg angles corresponding to different wavelengths are sequentially separated under the diffraction of the coupling grating 02 and the output grating 04, thereby enabling the display of images corresponding to their respective colors under different viewing fields. In other words, a single optical waveguide 03 can be used for color display using only the coupling grating and the output grating.

[0028] Wherein, the coupled-in grating 02 and the coupled-out grating 04 are both holographic gratings formed by polymer-dispersed liquid crystal holographic exposure, and the grating periods of the coupled-in grating 02 and the coupled-out grating 04 are the same.

[0029] This embodiment can achieve one-dimensional pupil dilation.

[0030] like Figure 2 As shown, the device further includes a folded grating 05; the folded grating 05 is disposed in the optical waveguide 03, the grating period of the folded grating 05 is less than the grating periods of the input grating 02 and the output grating 04, and the optical vectors of the input grating 02, the output grating 04 and the folded grating 05 form a closed triangle.

[0031] In this embodiment, both the input grating 02 and the output grating 04 are tilted volume gratings. The input grating 02 is responsible for coupling image light from different fields of view into the input waveguide 01. The folding grating 05 expands and transmits the light in the waveguide 01 along the grating direction. The output grating 04 expands the light in another direction while coupling the light out of the waveguide 01 and into the human eye for imaging. This embodiment can achieve two-dimensional pupil expansion.

[0032] Image lights from different fields of view, when passed through a specific grating (optimized grating period, tilt angle, and material refractive index modulation), can be seamlessly integrated into a complete image, representing three colors, and have a higher diffraction efficiency than surface relief gratings.

[0033] Specifically, such as Figure 3 and Figure 4As shown in this embodiment, the image output device 01 is a projection system, which consists of a microdisplay 01-1 and a collimating lens assembly 01-2. The image light output by the microdisplay 01-1 is composed of three parts: red (R), green (G), and blue (B), each corresponding to a different field of view, denoted as view F1, view F2, and view F3, respectively. The optical waveguide 03 serves as the light propagation carrier, with an incident light area and an exit light area on its surface. The incident light area corresponds to the coupling grating 02, and the exit light area corresponds to the coupling out grating 04. When incident light from different fields of view passes through the coupling grating 02, it enters the optical waveguide 03 sequentially under the diffraction effect of the coupling grating 02, propagates to the coupling out grating 04 by total internal reflection, and then exits the optical waveguide 03 after further diffraction to form an image in the human eye.

[0034] Due to the unique Bragg diffraction properties of holographic gratings, Bragg diffraction is selective not only in direction but also in wavelength. Lattice diffraction can be classified according to lattice type and the monochromaticity of the light source. Based on lattice classification, there are two types: single-crystal Bragg diffraction and polycrystalline Bragg diffraction.

[0035] Bragg diffraction, the energy of Bragg diffraction is mainly concentrated in the low diffraction orders (such as 0th order, +1 or -1 order), so it has high diffraction efficiency and has the technical advantage of displaying high brightness compared with surface relief grating waveguide 03; at the same time, the Bragg angle of the holographic grating is different for the reconstructed incident light of different wavelengths.

[0036] In the above formula, P is the period of the volume grating, and n is the refractive index of the medium surrounding the volume grating. , , These correspond to the wavelengths of incident red (R), green (G), and blue (B) light, respectively. , , Each corresponds to a Bragg angle for different incident light, so the transmission of incident light of different wavelengths under different fields of view is unaffected, meaning there is almost no dispersion effect.

[0037] In this embodiment of the application, the micro-display image source can be a micro-light-emitting diode (Micro-LED), a micro-organic light-emitting diode (Micro-OLED), an off-axis optical projection system (LCOS), or other micro-display projectors; wherein, the image content displayed by the image source is composed of three parts: red (R), green (G), and blue (B), each corresponding to a different field of view.

[0038] The holographic volume grating is composed of a polymer matrix and liquid crystal, and is prepared by holographic exposure; and the coupled-in and coupled-out volume gratings have the same period, and can be either transmissive or reflective volume gratings, or a combination of transmissive and reflective gratings;

[0039] like Figure 5 and Figure 6 As shown, the holographic grating can respond to the wavelengths of red (R), green (G), and blue (B) in its respective field of view, and ensures that the Bragg angles corresponding to each wavelength are arranged and connected sequentially without field-of-view overlap; (for example, for a horizontal 30° field of view, , , They are located within the field of view intervals of (-15°, -5°), (-5°, 5°), and (5°, 15°), respectively.

[0040] In one embodiment of this application, the holographic volume grating is a tilted volume grating, wherein the tilt angle of the reflective grating is 18.5°~45°, and the tilt angle of the transmissive grating is 45°~71.5°.

[0041] In one embodiment of this application, the grating period of the holographic volume grating is 175nm ~ 10μm;

[0042] In one embodiment of this application, the thickness of the holographic grating is 2 μm to 10 μm;

[0043] In one embodiment of this application, the average refractive index of the polymer material is 1.45 to 1.65;

[0044] In one embodiment of this application, the refractive index of the holographic volume grating is 0.01~0.1;

[0045] The optical waveguide 03 has a thickness of 1mm to 2.5mm and a refractive index of 1.5 to 2.0. Ordinary glass with a refractive index of 1.52 is preferred, as its manufacturing cost is relatively lower than that of high-refractive glass, and its transmittance is higher than 92% and its haze is less than 5%.

[0046] This application utilizes holographic exposure to fabricate tilted volume gratings on a specific polymer material, each responding to different wavelengths of red (R), green (G), and blue (B) light under different fields of view. Furthermore, the fields of view corresponding to the red (R), green (G), and blue (B) image lights are interconnected, thereby enabling single-layer waveguide color display. Compared to other waveguide color solutions, this application offers advantages such as thinness, simple manufacturing process, low cost, high brightness, and virtually no chromatic dispersion, and is also suitable for mass production.

[0047] This application provides a single-layer color waveguide display device. First, this application differs from other color waveguide solutions (current color waveguide displays typically use multiple waveguides or multiple gratings, both of which lead to volume or cost issues; while another solution, multi-wavelength multiplexing, has higher requirements for manufacturing processes, and multiplexing results in low diffraction efficiency and stray light problems). This application achieves color display by fabricating a single-layer grating on a single-layer waveguide. This is mainly achieved by adjusting the grating layout and structural parameters, using self-developed polymer materials, and then through software simulation to obtain the connection of the field of view angles under the diffraction of the same grating at different wavelengths, without reducing the diffraction efficiency, thus realizing a single-layer color waveguide display.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A single-layer color holographic waveguide display device, characterized in that, Includes an image output device, a coupling grating, an output grating, and an optical waveguide; The image output device comprises a microdisplay and a collimating lens assembly. The microdisplay outputs image light of three wavelengths—red, green, and blue—which is emitted into an optical waveguide via the collimating lens assembly. The three wavelengths of image light correspond to different fields of view. Both the insertion grating and the output grating are tilted holographic gratings, and both are composed of a polymer matrix and liquid crystal. The refractive index of the polymer matrix is ​​1.45 ~ 1.65; the thickness of the insertion grating and the output grating is 2 μm ~ 10 μm. The input grating and the output grating have the same grating period; The coupled grating responds to the image light of the three wavelengths of red, green and blue, and then propagates through the optical waveguide to the coupled grating in a total internal reflection manner. Finally, the coupled grating emits a single-layer color display image with the Bragg angles corresponding to the three wavelengths of red, green and blue arranged in sequence. The tilted holographic volume gratings are all transmission gratings and / or reflection volume gratings; The tilt angle of the transmissive grating is 45°~71.5°, and the tilt angle of the reflective grating is 18.5°~45°; The grating periods of the coupled-in grating and coupled-out grating are 175 nm ~ 10 μm; The refractive indices of the input and output gratings are 0.01 to 0.

1. The optical waveguide has a thickness of 1mm to 2.5mm and a refractive index of 1.5 to 2.

0. The device also includes a folding grating. The folded grating is disposed in the optical waveguide. The grating period of the folded grating is less than the grating periods of the input grating and the output grating, and the optical vectors of the input grating, the output grating and the folded grating form a closed triangle.

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