Staggered polarization body holographic grating optical waveguide

Abstract

The invention discloses a staggered polarization holographic grating optical waveguide, which comprises an image source, an optical waveguide, an in-coupling optical element and a first out-coupling optical element, and is characterized in that light emitted by the image source enters the optical waveguide through the in-coupling optical element and is subjected to total internal reflection propagation in the optical waveguide; light is modulated by the out-coupling optical elements and then led out of the optical waveguide to enter human eyes, and the first out-coupling optical element comprises two kinds of polarization holographic grating units with gratings matched with the steering vector of the in-coupling optical element. All the grating units are locally distributed in a staggered mode, and two-dimensional pupil expansion can be achieved only through one alignment layer. The interlacing period of the grating units is related to the diffraction efficiency of the diffraction order, and the uniformity of exit pupil can be improved by regulating and controlling the spatial distribution of the interlacing period. According to the multi-grating staggered polarization body holographic grating, the steering function and the coupling-out function are achieved at the same time by only using one alignment layer in the out-coupling single area, and uniform out-coupling light intensity distribution can be achieved by optimally designing the staggered period.

Description

Technical Field

[0001] The present invention relates to the field of waveguide display technology, in particular to an alternating polarization holographic grating optical waveguide. Background Art

[0002] Optical waveguide display technology is responsible for replicating and expanding micro-image sources in augmented reality (AR) and head-up display (HUD) systems. With its remarkable lightweight and thin features and excellent ambient light transmittance, it has become a highly promising next-generation display technology solution. The optical waveguide consists of a substrate and a coupler, and the coupler is the core component that determines its optical performance. Among the many coupling technologies, the polariton holographic grating coupler has attracted attention due to its low preparation cost, high single-order diffraction efficiency, and large wavelength response range and angular response range. Currently, the two-dimensional pupil expansion of the polariton holographic grating mainly relies on L-type and cross-type structures. Among them, the L-type structure requires an additional steering grating, resulting in a reduced spatial share of the outcoupling area and higher losses. The cross-type is more compact, but requires multiple exposures and the process is more cumbersome. In addition, the current preparation method of the polariton holographic grating is mainly uniform exposure of the entire area. This method of uniform distribution of diffraction efficiency will lead to the problem that the outcoupling light intensity gradually decreases as the light propagates. Some studies have proposed using polarization compensation films to reduce light leakage to compensate for the far-end light intensity, but this does not fundamentally solve the problem of uneven light intensity distribution caused by periodically uniformly distributed diffraction efficiency. Summary of the Invention

[0003] The present invention aims to provide an interlaced polarizer holographic grating optical waveguide. In this system, two diffraction orders are formed by designing the coupled polarizer holographic gratings to be arranged in a periodic interlaced manner.

[0004] In order to achieve the above-mentioned purpose, the present invention proposes an alternating polarization holographic grating optical waveguide, the system of which includes: an image source (1), an optical waveguide (2), an in-coupling optical element (3) and a first out-coupling optical element (4), wherein light emitted by the image source (1) enters the optical waveguide (2) through the in-coupling optical element (3), undergoes total internal reflection and propagates inside the optical waveguide (2), and is modulated by the first out-coupling optical element (4) and then guided out of the optical waveguide (2) into the human eye (5). The first out-coupling optical element (4) includes two polarization holographic grating units whose gratings match the steering vector of the in-coupling optical element (3), and the two gratings are arranged in a locally periodic alternating arrangement to form two diffraction orders, so that the light after being deflected by the in-coupling optical element (3) undergoes the process of deflection and decoupling simultaneously in the region of the first out-coupling optical element (4), thereby realizing a two-dimensional polarization holographic grating optical waveguide based on a single alignment layer. The interleaving periods at different spatial positions may be consistent or inconsistent. When the interleaving periods at different spatial positions are inconsistent, the diffraction efficiency can be improved by adjusting the interleaving period so as to improve the diffraction direction away from the outcoupling optical element, thereby improving the exit pupil uniformity.

[0005] The image source (1) may be a two-dimensional image source or a three-dimensional image source.

[0006] The two-dimensional image source is one of LCOS, LED array and OLED.

[0007] The three-dimensional image source is one of a holographic image source and a light field image source.

[0008] The optical waveguide (2) may be a flat plate structure, a wedge-shaped structure or a curved structure.

[0009] The in-coupling optical element (3) is one of a geometric optical element and a diffractive optical element.

[0010] The shape of the interleaved unit of the first outcoupling optical element (4) is any polygon that satisfies the tessellation condition.

[0011] The sum of the steering vector of the in-coupling optical element (3) and the grating vectors of the two polarization holographic grating units included in the out-coupling optical element (4) satisfies:

[0012]

[0013] Where, is the steering vector of the in-coupling optical element (3), and They are respectively grating vectors of two polarization holographic grating units included in the outcoupling optical element (4).

[0014] The first outcoupling optical element (4) can be prepared by micro-nano pattern alignment.

[0015] The alignment layer of the first outcoupling optical element (4) can be prepared by dynamic exposure.

[0016] The alignment layer of the first outcoupling optical element (4) can be prepared by mask-based area exposure.

[0017] Compared with the prior art, the present invention achieves two beneficial effects: 1. The staggered polarizer holographic grating only requires one alignment layer to achieve two-dimensional pupil expansion in the outcoupling region. Compared with the L-type optical waveguide, it can effectively increase the spatial proportion of the optical waveguide outcoupling region and reduce the process difficulty compared with the cross-type optical waveguide; 2. The staggered polarizer holographic grating can expand the angular response range, which can further improve the optical performance of the polarizer holographic grating optical waveguide; 3. Since the efficiency of the uniform period polarizer holographic grating is consistent within the exit pupil range, the outcoupling light intensity will decrease with the increase in the number of outcouplings, thereby reducing the exit pupil uniformity. The diffraction efficiency of the staggered polarizer holographic grating is related to the staggered period. The staggered period of the polarizer holographic grating is reasonably set in the outcoupling region along the propagation direction of the light after incoupling, so that the outcoupling efficiency is converted from low efficiency to high efficiency. This can improve the disadvantage of the uniform period polarizer holographic grating with strong outcoupling at the near end and weak outcoupling at the far end, and improve the exit pupil uniformity. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic structural diagram of an alternating polarization holographic grating optical waveguide provided by the present invention;

[0019] Figure 2 A schematic structural diagram of an alternating polarization holographic grating optical waveguide provided by an embodiment of the present invention;

[0020] Figure 3 The grating vector relationship between the in-coupling optical element and the out-coupling optical element of the cross-polarizer holographic grating optical waveguide provided by the present invention;

[0021] Figure 4 This is a schematic structural diagram of an alternating polarization holographic grating optical waveguide provided in Example 2 of the present invention.

[0022] In the figure: 1. light source, 2. optical waveguide, 3. in-coupling optical element, 4. first out-coupling optical element based on an alternating polarizer holographic grating, 5. human eye, 6. second out-coupling optical element based on an alternating polarizer holographic grating with a varying period. DETAILED DESCRIPTION

[0023] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0024] Example 1

[0025] like Figure 1 As shown, the present invention proposes an alternating polarization holographic grating optical waveguide. The display system includes: an image source 1, an optical waveguide 2, an in-coupling optical element 3, and a first out-coupling optical element 4. Light emitted by the image source 1 enters the optical waveguide 2 through the in-coupling optical element 3, propagates inside the optical waveguide 2 by total internal reflection, and is modulated by the first out-coupling optical element 4 before being guided out of the optical waveguide 2 and entering the human eye 5. Specifically, the shape of the optical waveguide 2 can be a flat structure, a wedge structure, or a curved structure. In this embodiment, the optical waveguide 2 is a flat structure, and the material of the optical waveguide is BK7 glass.

[0026] Specifically, the image source 1 may be a two-dimensional image source or a three-dimensional image source. In this embodiment, the image source is a collimated Micro-LED image source.

[0027] Specifically, the in-coupling optical element 3 is one of a geometric optical element and a diffraction optical element. In this embodiment, the in-coupling optical element is a polarization holographic grating. In order to make the light propagate inside the optical waveguide, the diffraction angle of the polarization holographic grating should be greater than the critical angle of BK7 glass. Specifically, the first out-coupling optical element 4 is an interlaced polarization holographic grating. In this embodiment, Figure 2 As shown, the steering vector of the in-coupling optical element 3 and the grating vectors of the two polarization holographic grating units included in the first outcoupling optical element 4 and satisfy:

[0028]

[0029] Specifically, if Figure 3 As shown, the interleaving periods d1 and d2 of the interleaving polarization volume holographic grating are respectively twice the integer multiples of the periods of the alignment layer of the polarization volume holographic grating in the x direction and the y direction.

[0030] Specifically, the interleaving periods of the interleaved polarization holographic gratings in the outcoupling region are consistent.

[0031] Specifically, the alternating polarization holographic grating can be prepared by micro-nano pattern alignment.

[0032] Example 2

[0033] The difference from the above embodiment 1 is that, Figure 4 As shown, in this embodiment 2, the staggered period of the outcoupling grating region varies in the region, and the efficiency of outcoupling light is improved along the y direction.

[0034] Specifically, if Figure 4 As shown, the present invention proposes an alternating polarization holographic grating optical waveguide. The display system includes: an image source 1, an optical waveguide 2, an in-coupling optical element 3 and a second out-coupling optical element 6. The light emitted by the image source 1 enters the optical waveguide 2 through the in-coupling optical element 3, undergoes total internal reflection and propagates inside the optical waveguide 2, and is modulated by the second out-coupling optical element 6 and then guided out of the optical waveguide 2 to enter the human eye 5.

[0035] Specifically, the shape of the optical waveguide 2 can be a flat structure, a wedge structure, or a curved structure. In this embodiment, the optical waveguide 2 is a flat structure, and the material of the optical waveguide is BK7 glass.

[0036] Specifically, the image source 1 may be a two-dimensional image source or a three-dimensional image source. In this embodiment, the image source is a collimated Micro-LED image source.

[0037] Specifically, the in-coupling optical element 3 is a geometric optical element or a diffractive optical element. In this embodiment, the in-coupling optical element is a polarization holographic grating. To ensure that light propagates within the optical waveguide, the diffraction angle of the polarization holographic grating should be greater than the critical angle of BK7 glass.

[0038] Specifically, the second outcoupling optical element 6 is a staggered polarization holographic grating with a varying period. Figure 2 As shown, the steering vector of the in-coupling optical element 3 and the grating vectors of the two polarization holographic grating units included in the outcoupling optical element 4 and satisfy:

[0039]

[0040] Specifically, if Figure 3 As shown, the interleaving periods d1 and d2 of the interleaving polarization volume holographic grating are respectively twice the integer multiples of the periods of the alignment layer of the polarization volume holographic grating in the x direction and the y direction.

[0041] Specifically, the interleaving periods d1 and d2 of the interleaved polarization holographic grating in the outcoupling region gradually decrease along the y-axis light propagation direction from 20 times the period of the alignment layer of the polarization holographic grating in the x-direction and the y-direction respectively until 100% of the initial period. As the interleaving period decreases, the diffraction efficiency improves, and the grating efficiency distribution forms a gradient distribution from low efficiency to high efficiency along the y-axis light propagation direction. At the end near the in-coupling grating, the incident light intensity is strong but the coupling efficiency is low, and the out-coupled light intensity is weaker than that of a uniform period, allowing more light energy to propagate to the end away from the coupling grating. At the end away from the coupling grating, the incident light intensity is stronger than that of a uniform period, while the diffraction efficiency is higher, and the out-coupled light intensity is stronger than that of a uniform period. This alleviates the disadvantage of a uniform period optical waveguide, where the light output is strong near the coupling grating and weak away from the coupling grating, and improves light output uniformity.

[0042] Specifically, the alternating polarization holographic grating can be prepared by micro-nano pattern alignment.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one skilled in the art to which this invention pertains. The terms used in this specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0044] The above-mentioned embodiments only express several implementation methods of the present invention. The description thereof is relatively specific and detailed, but it cannot be understood as limiting the patent scope of the present invention. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. Such improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. An alternating polarization holographic grating optical waveguide, comprising an image source (1), an optical waveguide (2), an in-coupling optical element (3), and a first out-coupling optical element (4), wherein light emitted by the image source (1) enters the optical waveguide (2) through the in-coupling optical element (3), propagates by total internal reflection within the optical waveguide (2), and is modulated by the out-coupling optical element (4) before being guided out of the optical waveguide (2) and entering a human eye (5), characterized in that: The first out-coupling optical element (4) comprises two types of gratings and polarization holographic grating units that match the steering vector of the in-coupling optical element (3). The two gratings are arranged in a locally periodic staggered arrangement to form two diffraction orders, so that the light after being turned by the in-coupling optical element (3) undergoes the process of turning and out-coupling simultaneously within the region of the first out-coupling optical element (4), thereby realizing a two-dimensional polarization holographic grating optical waveguide based on a single alignment layer. The staggered periods at different spatial positions are consistent or inconsistent. When the staggered periods at different spatial positions are inconsistent, the diffraction efficiency is increased in a direction away from the in-coupling optical element by adjusting the staggered period, thereby improving the uniformity of the exit pupil.

2. The alternating polarization holographic grating optical waveguide according to claim 1, characterized in that: The image source (1) is a two-dimensional image source or a three-dimensional image source.

3. The alternating polarization holographic grating optical waveguide according to claim 2, characterized in that: The two-dimensional image source is one of LCOS, LED array and OLED.

4. The alternating polarization holographic grating optical waveguide according to claim 2, characterized in that: The three-dimensional image source is one of a holographic image source and a light field image source.

5. The alternating polarization holographic grating optical waveguide according to claim 1, characterized in that: The optical waveguide (2) is one of a flat plate structure, a wedge-shaped structure or a curved structure.

6. The alternating polarization holographic grating optical waveguide according to claim 1, characterized in that: The in-coupling optical element (3) is one of a geometric optical element and a diffractive optical element; The sum of the steering vector of the in-coupling optical element (3) and the grating vectors of the two polarization holographic grating units included in the first out-coupling optical element (4) satisfies: Where, is the steering vector of the in-coupling optical element (3), and They are respectively grating vectors of two polarization holographic grating units included in the first outcoupling optical element (4).

7. The alternating polarization holographic grating optical waveguide according to claim 1, characterized in that: The shape of the interleaved unit of the first outcoupling optical element (4) is any polygon that satisfies the tessellation condition.

8. The alternating polarization holographic grating optical waveguide according to claim 1, characterized in that: The first outcoupling optical element (4) is prepared by micro-nano pattern alignment.

9. The alternating polarization holographic grating optical waveguide according to claim 1, characterized in that: The alignment layer of the first outcoupling optical element (4) is prepared by dynamic exposure.

10. The alternating polarization holographic grating optical waveguide according to claim 1, characterized in that: The alignment layer of the first outcoupling optical element (4) is prepared by mask-based area exposure.

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