Two-dimensional pupil-expanding waveguide optical module

Abstract

A two-dimensional pupil-expanding waveguide optical module relates to the field of optical waveguides and comprises an image source, a waveguide element, a coupling-in element, a turning element and a coupling-out element. The turning element comprises a top grating and a bottom grating; the top grating is arranged on the upper surface of the waveguide element, and the bottom grating, the coupling-in element and the coupling-out element are arranged on the lower surface of the waveguide element; light emitted by the image source is subjected to total reflection in the waveguide element after being diffracted by the coupling-in element; after at least two times of total reflection in the waveguide, the light is diffracted by the top grating and is vertically emitted to the bottom grating, so that expansion in the first direction is realized; the light emitted from the top layer grating is emitted to the other direction after vertically emitting to the bottom layer grating, so that the turning of the light is realized; and the light emitted by the bottom grating is reflected totally at least once in the waveguide element, is diffracted by the coupling-out element and then is emitted to human eyes, so that expansion in a second direction is realized. According to the invention, two-dimensional pupil expansion of image light is realized, the volumes of a coupling element and a projection light machine are reduced, and the manufacturing difficulty of a waveguide element is simplified.

Description

Technical Field

[0001] The present invention relates to the field of optical waveguides, and in particular to a two-dimensional pupil expansion waveguide optical module. Background Art

[0002] At present, diffraction optical waveguide technology has the advantages of large exit pupil, large field of view, light weight, compactness, and high transmittance. Therefore, it is one of the devices with the most large-scale application prospects in augmented reality head-mounted display devices.

[0003] The augmented reality head-mounted display system is mainly composed of a micro display, a collimating lens group, a diffractive optical waveguide, and a system circuit, wherein the diffractive waveguide is composed of a coupling element, a waveguide substrate, and an outcoupling grating. The most significant advantage of the diffractive waveguide used in the field of display equipment is that it can realize the pupil expansion function, effectively solving the trade-off relationship between the volume size, exit pupil size, and field of view of traditional optical display devices, thereby achieving a display effect of a small volume and a large exit pupil.

[0004] Several common pupil expansion schemes for diffraction waveguides include "L" type and "Y" type waveguide structures, each of which has its own advantages and disadvantages in terms of preparation difficulty and imaging quality. Both waveguide structures contain at least three different gratings, which can be simply summarized as in-coupling gratings, relay gratings, and out-coupling gratings. In order to eliminate the dispersion caused by each grating, the sum of the K vectors of these three gratings must be zero, which requires strict control of the exposure angle during the grating preparation process, which will greatly increase the difficulty of preparation. For waveguide displays, two-dimensional pupil expansion waveguides can greatly increase the exit pupil size, thereby improving the display performance of the waveguide. Therefore, the problem of how to reduce the difficulty of preparing two-dimensional pupil expansion waveguides without increasing the system volume and achieving high-quality imaging effects needs to be solved urgently. Summary of the invention

[0005] The purpose of the present invention is to solve the above-mentioned problems in the prior art and provide a two-dimensional pupil expansion waveguide optical module, which realizes the two-dimensional pupil expansion of image light through a coupling element, a waveguide element, a turning element integrated by upper and lower layers of gratings, and a coupling element, thereby reducing the volume of the coupling element and the projection optical machine and simplifying the manufacturing difficulty of the waveguide element.

[0006] In order to achieve the above object, the present invention adopts the following technical scheme:

[0007] A two-dimensional pupil expansion waveguide optical module comprises an image source, a waveguide element, an incoupling element, a turning element and an outcoupling element; the turning element comprises a top grating and a bottom grating; the top grating is arranged on the upper surface of the waveguide element, and the bottom grating is arranged on the lower surface of the waveguide element and is located below the top grating; the incoupling element and the outcoupling element are arranged on the lower surface of the waveguide element, and the incoupling element and the bottom grating are arranged on the same side, and the outcoupling element is arranged parallel to the bottom grating and is located on the other side of the waveguide element; wherein, light emitted from the image source is diffracted by the incoupling element and then totally reflected in the waveguide element; after at least two total reflections in the waveguide, the light is diffracted by the top grating of the turning element and then vertically emitted to the bottom grating, thereby realizing expansion in a first direction; the light emitted from the top grating is vertically emitted to the bottom grating and then emitted in another direction, thereby realizing the turning of the light; the light emitted by the bottom grating is totally reflected in the waveguide element at least once and then diffracted by the outcoupling element and then emitted to the human eye, thereby realizing expansion in a second direction.

[0008] The angle between the outgoing light of the coupling element and the lower surface of the waveguide element is greater than the critical reflection angle of the waveguide element substrate; the angle between the outgoing light of the bottom grating of the turning element and the upper surface of the waveguide element is greater than the critical reflection angle of the waveguide element substrate.

[0009] The top layer grating and the bottom layer grating are diffraction gratings or volume holographic gratings.

[0010] The sizes of the top grating and the bottom grating are comparable.

[0011] The coupling-in element and the coupling-out element are diffraction gratings or volume holographic gratings.

[0012] The area of ​​the coupling-in element is smaller than the area of ​​the coupling-out grating.

[0013] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0014] The two-dimensional pupil expansion waveguide optical module provided by the present invention realizes the two-dimensional pupil expansion of the image light through the coupling element, the waveguide element, the turning element integrated by the upper and lower layers of gratings, and the coupling element, and can obtain a larger exit pupil. On the one hand, the volume of the entire waveguide and the projection optical machine is reduced; on the other hand, the difficulty of the two-dimensional pupil expansion waveguide manufacturing process is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the structure of the present invention; wherein the coupling element 2, the coupling element 4, and the bottom grating 32 are located on the lower surface of the waveguide element 1, and the top grating 31 is located on the upper surface of the waveguide element 1;

[0016] Figure 2 This is a schematic diagram of one-dimensional expansion of the light beam of the present invention;

[0017] Figure 3 It is a schematic diagram of two-dimensional expansion of the light beam of the present invention;

[0018] Figure 4 Schematic diagram of light beam vector expansion of the present invention.

[0019] Figure numerals: waveguide element 1, coupling element 2, turning element 3, coupling element 4, light cluster one 5, light cluster two 6, top grating 31, bottom grating 32. DETAILED DESCRIPTION

[0020] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0021] Example 1

[0022] like Figure 1 The two-dimensional pupil expansion waveguide optical module of this embodiment includes: an image source, a waveguide element 1, a coupling element 2, a turning element 3 and a coupling element 4; the turning element 3 includes a top grating 31 and a bottom grating 32;

[0023] The waveguide element 1 comprises an upper surface close to the human eye and a lower surface far from the human eye; the top grating 31 is arranged on the upper surface of the waveguide element 1, the bottom grating 32 is arranged on the lower surface of the waveguide element 1, and the bottom grating 32 is arranged directly below the top grating 31, and the top grating 31 and the bottom grating 32 are equal in size; the coupling element 2 is arranged on the lower surface of the waveguide element 1 and on the same side as the bottom grating 32, and the coupling element 4 parallel to the bottom grating 32 is arranged on the other side of the lower surface of the waveguide element 1;

[0024] Among them, the light emitted by the image source is diffracted by the coupling element 2 and then totally reflected in the waveguide element 1; after at least two total reflections in the waveguide element 1, it is diffracted by the top grating 31 of the turning element 3 and then vertically emitted to the bottom grating 32, thereby realizing expansion in the first direction; after diffracting by the bottom grating 32, it is emitted in another direction, thereby realizing the turning of the light; the light emitted by the bottom grating 32 is totally reflected at least once in the waveguide element 1, then diffracted by the coupling element 4 and then emitted to the human eye, thereby realizing expansion in the second direction.

[0025] like Figures 2 to 4As shown, the light emitted by the image source hits the coupling element 2, and then propagates in the waveguide element 1 along the +Y direction at a propagation angle that satisfies the total reflection condition. After at least two total reflections, it reaches the top grating 31 of the turning element 3. After reaching the top grating 31, part of the light is diffracted, and the other part of the light continues to propagate under the total reflection condition and is diffracted after reaching the top grating 31. During this propagation process, the light beam continuously diffracts and replicates to form a light cluster 5, realizing a one-dimensional exit pupil expansion in the +Y direction. The light cluster 5 formed by the diffraction of the top grating 31 of the turning element 3 is vertically emitted to the bottom grating 32, and then propagates in the waveguide in the +X direction under the total reflection condition. After at least one total reflection, it reaches the coupling element 4. After reaching the coupling element 4, part of the light is diffracted out of the waveguide, and the other part of the light is still propagated under the total reflection condition. In this process, the light beam continuously replicates and expands in the +X direction, and finally forms a light cluster 26 that can be incident on the human eye or other optical systems, realizing a two-dimensional pupil expansion of the image light.

[0026] In this embodiment, the waveguide element 1 of the two-dimensional pupil expansion waveguide optical module is an optical glass or resin with a refractive index of 1.3 to 2.2 and is in the shape of a rectangular body. The coupling-in element 2 and the coupling-out element 4 can be a diffraction grating or a volume holographic grating, etc. Each top grating 31 of the turning element 3 has a predetermined diffraction efficiency, and the diffraction efficiency of multiple gratings gradually decreases from the end of the incident coupling-in element 2 to the other end of the waveguide element 1, thereby achieving uniform expansion of the image light along the +Y direction. Each coupling-out grating of the coupling-out element 4 also has a predetermined diffraction efficiency, and the diffraction efficiency of multiple gratings gradually decreases from the end of the turning element 3 to the other end of the waveguide element 1, thereby achieving uniform expansion of the image light along the +X direction, and then achieving uniform expansion of the light in the two-dimensional direction.

[0027] During preparation, the coupling-in element 2 corresponds to the coupling-out element 4, and the top grating 31 of the turning element 3 corresponds to the bottom grating 32, and they have similar processing parameters and can use similar processing techniques, thereby reducing the cost and manufacturing difficulty of the waveguide element.

[0028] In summary, the two-dimensional pupil expansion waveguide optical module provided by the present invention realizes the two-dimensional pupil expansion of the image light through the coupling element, the waveguide element, the turning element integrated by the upper and lower layers of gratings, and the coupling element, thereby reducing the volume of the coupling element and the projection optical machine, and simplifying the manufacturing difficulty of the waveguide element.

Claims

1. A two-dimensional pupil expansion waveguide optical module, characterized in that: The invention comprises an image source, a waveguide element, an incoupling element, a turning element and an outcoupling element; the turning element comprises a top grating and a bottom grating; the top grating is arranged on the upper surface of the waveguide element, the bottom grating is arranged on the lower surface of the waveguide element and is located below the top grating; the incoupling element and the outcoupling element are arranged on the lower surface of the waveguide element, and the incoupling element and the bottom grating are arranged on the same side, and the outcoupling element is arranged parallel to the bottom grating and is located on the other side of the waveguide element; wherein, light emitted from the image source is totally reflected in the waveguide element after being diffracted by the incoupling element; after at least two total reflections in the waveguide, the light is diffracted by the top grating of the turning element and then vertically emitted to the bottom grating, thereby realizing expansion in a first direction; the light emitted from the top grating is vertically emitted to the bottom grating and then emitted to another direction, thereby realizing the turning of the light; the light emitted from the bottom grating is totally reflected in the waveguide element at least once and then diffracted by the outcoupling element and then emitted to the human eye, thereby realizing expansion in a second direction.

2. The two-dimensional pupil expansion waveguide optical module according to claim 1, characterized in that: The angle between the outgoing light of the coupling element and the lower surface of the waveguide element is greater than the critical reflection angle of the waveguide element substrate; the angle between the outgoing light of the bottom grating of the turning element and the upper surface of the waveguide element is greater than the critical reflection angle of the waveguide element substrate.

3. The two-dimensional pupil expansion waveguide optical module according to claim 1, characterized in that: The top layer grating and the bottom layer grating are diffraction gratings or volume holographic gratings.

4. The two-dimensional pupil expansion waveguide optical module according to claim 1, characterized in that: The sizes of the top grating and the bottom grating are comparable.

5. The two-dimensional pupil expansion waveguide optical module according to claim 1, characterized in that: The coupling-in element and the coupling-out element are diffraction gratings or volume holographic gratings.

6. The two-dimensional pupil expansion waveguide optical module according to claim 1, characterized in that: The area of ​​the coupling-in element is smaller than the area of ​​the coupling-out grating.

Images