Lcos-optical-engine-based compact single-layer full-color ar optical waveguide

Abstract

An LCoS-based compact single-layer full-color AR optical waveguide, comprising an LCoS optical engine (1), a parallel plate (2), a coupling-in graded-period polarization volume lens (3) and a two-dimensional coupling-out polarization volume grating (4), wherein the LCoS optical engine (1) is connected to the parallel plate (2) by means of optical bonding; the coupling-in graded-period polarization volume lens (3) achieves the effects of light collimation and light defection and coupling, and undergoes graded-period processing to extend the wavelength bandwidth thereof to a visible light range; and the two-dimensional coupling-out polarization volume grating (4) is used for expanding light in two directions, thereby achieving a pupil expansion effect. The full-color AR optical waveguide solves the problem of an LCoS optical engine being excessively large due to the reliance on a projection lens, thereby enabling the implementation of a compact single-layer full-color AR optical waveguide.

Description

Small-size single-layer full-color AR optical waveguide based on LCoS optical engine TECHNICAL FIELD

[0001] The present application relates to the field of augmented reality, and in particular to a small-area single-layer full-color AR optical waveguide based on an LCoS optical engine. BACKGROUND

[0002] Augmented Reality (AR) is a display technology that seamlessly combines virtual information with the real world. It enables the experience of visual, auditory, gustatory, and tactile information that is difficult to experience in the real world, by using computer image rendering, human-computer interaction, and three-dimensional space modeling. Currently, the main AR display technologies include the half-reflective half-transmissive cubic prism scheme used by Google Glass, the free-form surface prism scheme used by the BT-200 series of Epson, and the embedded half-reflective half-transmissive film scheme used by the Israeli company Lumus. These schemes basically achieve the basic functions and requirements of the augmented reality display system, but they also have obvious defects such as small display field of view, small exit pupil, large volume, and heavy weight, which affect the display experience and wearing comfort of consumers.

[0003] With the continuous development of AR technology, micro-displays have become the best solution for high-performance displays required by portable devices. Currently, the main micro-displays include digital display processing technology, micro light-emitting diodes, organic light-emitting diodes, and silicon-based liquid crystal displays (LCoS). Among them, LCoS outperforms other technologies in terms of color accuracy and resolution, making it suitable for AR devices that require high image quality, but it is relatively large in size.

[0004] For AR optical waveguide imaging system, the performance of the coupling element directly affects the system efficiency and imaging quality of the optical waveguide near-eye display system. Holographic volume grating (VHG) is coupled based on volume grating Bragg diffraction, which can realize high-efficiency single-stage diffraction. In addition, the response bandwidth of VHG is relatively narrow, which makes it have higher transparency to external light field, meeting the needs of AR application, but the relatively narrow response bandwidth also brings problems such as smaller field of view and color performance. The new type of polarization volume grating (PVG) has the same diffraction characteristics as VHG, which can produce high-efficiency single-stage Bragg diffraction under volume effect, thereby ensuring the optical coupling efficiency and image transmission quality of the waveguide system. In addition, PVG has the advantage of a response bandwidth much larger than that of traditional VHG, and also exhibits the Pacharatnam-Berry (PB) phase polarization response characteristics that VHG does not have, so that it can achieve lens effect by modulating the phase. SUMMARY

[0005] The application aims to solve the problem that the LCoS optical engine depends on the projection lens with too large volume, and proposes a small-volume single-layer full-color AR optical waveguide based on LCoS, which can realize a single-layer full-color AR optical waveguide with small volume.

[0006] Technical scheme: A small-volume single-layer full-color AR optical waveguide based on LCoS, comprising an LCoS light engine, a parallel plate, a coupling-in gradually changing period polarization volume holographic lens, and a two-dimensional coupling-out polarization volume holographic grating; the parallel plate serves as a total internal reflection light transmission function; the light emitted by the LCoS light engine is incident into the coupling-in gradually changing period polarization volume holographic lens through the parallel plate, the coupling-in gradually changing period polarization volume holographic lens has the effects of light collimation and light deflection coupling, and the wavelength bandwidth of the light is expanded to the visible light range through the period changing processing; the light emitted by the coupling-in gradually changing period polarization volume holographic lens is incident into the two-dimensional coupling-out polarization volume holographic grating through the parallel plate, and the two-dimensional coupling-out polarization volume holographic grating is used to expand the light to two directions, thereby achieving the effect of pupil expansion.

[0007] Preferably, the parallel plate is located between the LCoS light engine and the coupling-in gradually changing period polarization volume holographic lens and the two-dimensional coupling-out polarization volume holographic grating.

[0008] Preferably, the LCoS light engine and the parallel plate are connected in an optical cementing manner.

[0009] Preferably, the gradually changing period polarization volume holographic lens is a diffractive optical element with continuously changing lateral and longitudinal periods, the lateral period changes as a function of position, ensuring the spherical phase modulation of the incident wave into a plane wave, and the longitudinal period is modulated by the mask during the curing process to widen the Bragg diffraction wavelength bandwidth of the polarization volume holographic lens.

[0010] Preferably, the rotation angle of the liquid crystal molecules of the gradually changing period polarization volume holographic lens under the linear gradient pitch distribution in the y direction is calculated by the following formula:

[0011] wherein Λ x is the period length along the lateral direction, d is the thickness of the polarization volume holographic grating material, Λ y0 and Λ y1 are the lengths corresponding to the longitudinal rotation periods of the liquid crystal near the orientation layer and the other surface of the polarization volume holographic grating, respectively; the longitudinal period changes linearly from Λ y0 to Λ y1 in space.

[0012] Preferably, the diffraction wavelength bandwidth of the polarization volume holographic grating under the gradient pitch distribution and the uniform pitch distribution structure of the gradually changing period polarization volume holographic lens is 400-700 nm, and the larger the gradient pitch change range Λ y0 -Λ y1 is, the wider the wavelength bandwidth will be.

[0013] Preferably, the two-dimensional out-coupling polarization volume holographic grating is two layers of liquid crystals with opposite rotation directions, wherein the left-handed cholesteric phase liquid crystal diffracts left-handed circularly polarized light in one direction, and the right-handed cholesteric phase liquid crystal diffracts right-handed circularly polarized light in the other direction, achieving the effect of two-dimensional pupil expansion realized by a single grating.

[0014] Beneficial effects: The small-size single-layer full-color AR optical waveguide of the present application realizes the effects of light collimation and light deflection coupling through the coupling-in gradually changing period polarization volume holographic lens, and the wavelength bandwidth is expanded to the visible light range through the variable period processing; the light is expanded in two directions through the two-dimensional out-coupling polarization volume holographic grating, achieving the effect of pupil expansion. The present application solves the problem of the large size of the projection lens relied on by the LCoS light engine, and realizes the small-size single-layer full-color AR optical waveguide. BRIEF DESCRIPTION OF DRAWINGS

[0015] Fig. 1 is a structure schematic diagram of a small-size single-layer full-color AR optical waveguide based on an LCoS light engine provided in an embodiment of the present application;

[0016] Fig. 2 is a micro-nano structure schematic diagram of a gradually changing period polarization volume holographic lens of a small-size single-layer full-color AR optical waveguide based on an LCoS light engine provided in an embodiment of the present application;

[0017] Figure 3 is a wavelength bandwidth diagram of a small volume single-layer full-color AR optical waveguide gradient period polarization volume holographic lens based on LCoS optical engine provided in an embodiment of the present application;

[0018] Figure 4 is a two-dimensional coupling-out grating position diagram of a small volume single-layer full-color AR optical waveguide based on LCoS optical engine provided in an embodiment of the present application. DETAILED DESCRIPTION

[0019] The specific embodiments of the present application will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments. It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0020] As shown in Figure 1, it is a small volume single-layer full-color AR optical waveguide structure diagram provided in an embodiment of the present application, which includes LCoS optical engine 1, parallel plate 2, coupling-in gradient period polarization volume holographic lens 3, two-dimensional coupling-out polarization volume holographic grating 4. Among them, the LCoS optical engine 1 is connected with the parallel plate 2 in an optical cementing manner; the coupling-in gradient period polarization volume holographic lens 3 plays the effect of light collimation and light deflection coupling, and the wavelength bandwidth is expanded to the visible light range through the variable period processing; the two-dimensional coupling-out polarization volume holographic grating 4 is used to expand the light to two directions, which plays the effect of pupil expansion.

[0021] The parallel plate 2 is located between the LCoS optical engine 1 and the coupling-in gradient period polarization volume holographic lens 3 and the two-dimensional coupling-out polarization volume holographic grating 4.

[0022] The LCoS optical engine 1 is attached to the parallel plate 2. The parallel plate plays the role of total internal reflection light transmission. The parallel plate and the in-out coupling grating together constitute an optical waveguide.

[0023] As shown in Figure 2, it is a small volume single-layer full-color AR optical waveguide gradient period polarization volume holographic lens micro-nano structure diagram provided in an embodiment of the present application. 200nm-400nm, 100nm-200nm are the transverse periods at different positions; 1μm-20μm is the thickness range of the polarization volume holographic lens. The gradient period polarization volume holographic lens 3 is a diffractive optical element with continuous change of transverse and longitudinal periods, the transverse period change is a function of position, which ensures that the spherical phase of the incident wave is modulated to a plane wave, and the longitudinal period is modulated by the mask in the curing process, so as to widen the Bragg diffraction wavelength bandwidth of the polarization volume holographic lens.

[0024] As shown in Figure 3, the wavelength bandwidth of the small-size single-layer full-color AR optical waveguide gradient period polarization volume holographic lens provided by the embodiment of the present application is shown in the schematic diagram. The gradient pitch distribution of the gradient period polarization volume holographic lens 3 is the same as the diffraction wavelength bandwidth of the polarization volume holographic grating under the uniform pitch distribution structure, which is 400-700 nm, and the greater the gradient pitch variation range (Λy0-Λy1) is, the wider the wavelength bandwidth will be. The liquid crystal molecule rotation angle of the gradient period polarization volume holographic lens 3 under the linear gradient pitch distribution in the y direction can be calculated by the following formula:

[0025] Where Λx is the period length along the transverse (x direction), d is the thickness of the polarization volume holographic grating material, Λy0 and Λy1 are the lengths corresponding to the longitudinal rotation periods of the liquid crystal near the orientation layer and the other surface of the polarization volume holographic grating, respectively. At this time, the longitudinal period is no longer a constant value, but varies linearly from Λy0 to Λy1 in space.

[0026] As shown in Figure 4, the two-dimensional coupling-out grating position of the small-size single-layer full-color AR optical waveguide provided by the embodiment of the present application is shown in the schematic diagram. The left side of the schematic diagram is the LCoS light engine 5 and the coupling-in gradient period polarization volume holographic lens 6, and the right side of the schematic diagram is the two-dimensional coupling-out polarization volume holographic grating 7 and the parallel plate 8. The two-dimensional coupling-out polarization volume holographic grating 7 is a two-layer liquid crystal with opposite rotation directions, wherein the left-handed cholesteric phase liquid crystal diffracts the left-handed circularly polarized light in one direction, and the right-handed cholesteric phase liquid crystal diffracts the right-handed circularly polarized light in the other direction, achieving the effect of two-dimensional pupil expansion by a single grating.

Claims

1. A small-volume single-layer full-color AR optical waveguide based on LCoS, characterized in that, It includes an LCoS optical engine, a parallel plate, an inserted graded-periodic polarizer holographic lens, and a two-dimensional extracted polarizer holographic grating. The parallel plate serves to transmit total internal reflection light. The light emitted by the LCoS optical engine passes through the parallel plate and enters the inserted graded-periodic polarizer holographic lens, which collimates and deflects the light, and through periodic processing, extends the wavelength bandwidth of the light to the visible light range. The light emitted by the inserted graded-periodic polarizer holographic lens passes through the parallel plate and enters the two-dimensional extracted polarizer holographic grating, which expands the light in two directions, thus achieving a pupil-expanding effect.

2. The small-volume single-layer full-color AR optical waveguide according to claim 1, characterized in that, The parallel plate is located between the LCoS optical engine and the coupled-in graded periodic polarizer holographic lens and the two-dimensional coupled-out polarizer holographic grating.

3. The small-volume single-layer full-color AR optical waveguide according to claim 1, characterized in that, The LCoS optical engine is connected to the parallel plate by optical bonding.

4. The small-volume single-layer full-color AR optical waveguide according to claim 1, characterized in that, The gradient periodic polarizer holographic lens is a diffractive optical element with continuously changing transverse and longitudinal periods. Its transverse periodicity is a function of position, ensuring that the spherical phase of the incident wave is modulated into a plane wave. Its longitudinal period is modulated by the diffraction of the mask during the curing process to broaden the Bragg diffraction wavelength bandwidth of the polarizer holographic lens.

5. The small-volume single-layer full-color AR optical waveguide according to claim 1, characterized in that, The rotation angle of the liquid crystal molecules under the linear gradient pitch distribution in the y-direction of the gradient periodic polarizer holographic lens is calculated by the following formula: Among them Λ x It is the period length along the transverse direction, d is the thickness of the polarizing holographic grating material, and Λ is the period length along the transverse direction. y0 and Λ y1 These are the lengths corresponding to the longitudinal rotation period of the liquid crystal near the other surface of the alignment layer and the polarizer holographic grating; the longitudinal period is spatially from Λ y0 Linear change to Λ y1 .

6. The small-volume single-layer full-color AR optical waveguide according to claim 5, characterized in that, The gradient pitch distribution of the gradient periodic polarizer holographic lens and the diffraction wavelength bandwidth of the polarizer holographic grating under the uniform pitch distribution structure are 400–700 nm, and the gradient pitch variation range is Λ. y0 ~Λ y1 The larger the wavelength, the wider the bandwidth.

7. The small-volume single-layer full-color AR optical waveguide according to claim 1, characterized in that, The two-dimensional coupled polarizer holographic grating consists of two layers of liquid crystals with opposite rotation directions. The left-handed cholesteric liquid crystal responds to left-handed circularly polarized light and diffracts it in one direction, while the right-handed cholesteric liquid crystal responds to right-handed circularly polarized light and diffracts it in another direction, thus achieving the effect of two-dimensional pupil expansion with a single grating.

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