CN114415285B - Grating waveguide display device capable of improving light energy coupling efficiency and near-to-eye display equipment - Google Patents
Grating waveguide display device capable of improving light energy coupling efficiency and near-to-eye display equipment Download PDFInfo
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- G—PHYSICS
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- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
- G02B6/0011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form
- G02B6/0013—Means for improving the coupling-in of light from the light source into the light guide
- G02B6/0015—Means for improving the coupling-in of light from the light source into the light guide provided on the surface of the light guide or in the bulk of it
- G02B6/0016—Grooves, prisms, gratings, scattering particles or rough surfaces
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- G—PHYSICS
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- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/01—Head-up displays
- G02B27/0101—Head-up displays characterised by optical features
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- G—PHYSICS
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- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
- G02B6/0011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form
- G02B6/0013—Means for improving the coupling-in of light from the light source into the light guide
- G02B6/0023—Means for improving the coupling-in of light from the light source into the light guide provided by one optical element, or plurality thereof, placed between the light guide and the light source, or around the light source
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Abstract
The invention discloses a grating waveguide display device and near-to-eye display equipment for improving light energy coupling efficiency, the display device comprises: the device comprises a waveguide substrate, a transmission type resonance waveguide grating and a 1/4 wave plate; the transmission type resonance waveguide grating is used as an incident grating and is arranged on the surface of the waveguide substrate; the 1/4 wave plate is embedded in the waveguide substrate, the upper and lower surfaces of the 1/4 wave plate are parallel to the upper and lower planes of the waveguide substrate, the optical axis direction of the 1/4 wave plate is parallel to the upper and lower surfaces of the wave plate and the upper and lower planes of the waveguide substrate, and the optical axis direction of the 1/4 wave plate forms an angle of 45 degrees with the electric field direction of incident polarized light. The 1/4 wave plate is positioned right below the transmission type resonance waveguide grating, and the projection range of the 1/4 wave plate in the vertical direction is positioned in the projection range of the transmission type resonance waveguide grating in the vertical direction. The grating waveguide display device can improve the light energy coupling efficiency and ensure the display quality.
Description
Technical Field
The invention relates to the field of grating waveguide display, in particular to a grating waveguide display device and near-to-eye display equipment.
Background
Augmented Reality (AR) and Virtual Reality (VR) are hot spot technology fields which are attracting attention in recent years, and with the development of 5G technology, the future market prospect of the technology is becoming clear, so that near-eye display technology is rapidly developed. The Augmented Reality (AR) is a technology of overlaying digital information (including characters, images, videos, etc.) onto the real physical world, and is characterized by having strong perspective and mobility, not affecting normal observation of the real environment, and bringing a practical feeling of moving scenes to users. The display system adopted by the AR glasses in the market at present is a combination of various micro display screens and optical elements such as a prism, a Bird back, a free-form surface, an optical waveguide and the like, and can couple a virtual image into human eyes. The grating waveguide display technology is considered as an essential optical scheme of the AR glasses to consumer level due to the light and thin property and high penetration property of external light, and has great development potential in terms of optical effect, appearance beautification and mass production prospect. The grating waveguide display technology utilizes diffraction grating to realize light incidence, turning and emergent, utilizes total reflection principle to realize light transmission, and transmits the image of the micro display to human eyes so as to see virtual images. The grating waveguide display device can be made as thin, light, thin and transparent as the common glasses lens due to the adoption of the total reflection principle which is the same as that of the optical fiber technology. The advantages of the grating waveguide are mainly reflected in that the area, the shape and the arrangement mode of the grating area can be flexibly adjusted according to the optical parameter requirements and the appearance design of the AR glasses.
However, the grating waveguide display technology is an emerging technology, and although the technology is rapidly developed at present, many challenges remain, such as improving the light energy utilization efficiency is one of the problems to be solved. The light energy coupling efficiency is improved, and the light energy coupling efficiency is not only dependent on the diffraction efficiency of the incident grating, but also is closely related to the area of the incident grating. Because if the width of the grating is too large, light coupled into the waveguide substrate is totally reflected and then is again incident into the incident grating, and is coupled out of the optical waveguide at the same angle as the incident light after being secondarily diffracted by the grating, so that a great part of light energy is lost. In order to avoid the loss of light energy caused by secondary diffraction of the grating, the width of the incident grating is generally limited, and the maximum grating width is as follows: w (W) max =2dtan θ, where D is the thickness of the waveguide substrate and θ is the angle between the light in the waveguide substrate and the normal to the waveguide substrate. It can be seen that the width of the incident grating is limited by the thickness of the waveguide substrate. Fig. 1 is a schematic diagram of the secondary diffraction of an incident grating in an optical waveguide. Because the width of the incident grating is wider, light coupled into the waveguide is totally reflected by the waveguide substrate and then is incident on the grating surface again to be diffracted for the second time so as to escape from the optical waveguide, thereby causing light energy loss and reducing the light efficiency of the near-to-eye display device; if the area of the incident grating is designed to be too small to avoid secondary diffraction (based on the optical parameters of AR glasses and the pursuit of AR products for aesthetic appearance and consumer comfort, the light and thin waveguide substrate is also sought at present), the matching with the projection system and thus near-to-eye display will be affectedImaging quality of the device.
Therefore, how to overcome the loss of light energy caused by the secondary diffraction of the incident grating and ensure the lightness, thinness and imaging quality of the AR display device is a problem to be solved in the current diffraction grating waveguide technology.
In view of this, the present invention has been made.
Disclosure of Invention
The invention aims to provide a grating waveguide display device and near-to-eye display equipment for improving light energy coupling efficiency, which can overcome light energy loss of incident grating secondary diffraction and improve light energy utilization efficiency on the premise of ensuring imaging quality and thinness of an AR display device, thereby solving the technical problems in the prior art.
The invention aims at realizing the following technical scheme:
the embodiment of the invention provides a grating waveguide display device for improving light energy coupling efficiency, which comprises the following components:
waveguide substrate、A transmission type resonant waveguide grating and a 1/4 wave plate; wherein,
the transmission type resonance waveguide grating is used as an incident grating and is arranged on the surface of the waveguide substrate;
the 1/4 wave plate is embedded in the waveguide substrate, and the optical axis direction of the 1/4 wave plate is parallel to the upper plane and the lower plane of the waveguide substrate and forms an angle of 45 degrees with the electric field direction of incident light.
The 1/4 wave plate is positioned right below the transmission type resonance waveguide grating, and the projection range of the 1/4 wave plate in the vertical direction is positioned in the projection range of the transmission type resonance waveguide grating in the vertical direction.
The embodiment of the invention also provides near-eye display equipment, which comprises a grating waveguide display device, wherein the grating waveguide display device adopts the grating waveguide display device for improving the light energy coupling efficiency.
Compared with the prior art, the grating waveguide display device for improving the light energy coupling efficiency has the beneficial effects that:
a transmission type resonance waveguide grating serving as an incident grating is arranged on the surface of a waveguide substrate, and a 1/4 wave plate with an optical axis direction forming an angle of 45 degrees with the electric field direction of incident light is embedded in the waveguide substrate right below the incident grating, so that the incident light is TE polarized. Because of the high selectivity of the transmission type resonance waveguide grating to the polarization state of the incident light, diffraction resonance is generated when the incident light is TE polarized, the TE polarized light coupled into the waveguide substrate deflects 90 degrees in the polarization direction after passing through the 1/4 wave plate twice, namely, the polarization state is converted into TM polarized light by the TE polarized light before the light is incident into the grating again after being totally reflected by the waveguide substrate, and the TM polarized light does not generate diffraction resonance when the TM polarized light is incident into the transmission type resonance waveguide grating, the + -1-level diffraction efficiency is extremely low, and most light reflects the echo guide plate, so that light energy loss caused by secondary diffraction is avoided, and the light energy coupling efficiency is improved. Meanwhile, the width of the incident grating is not too small, and the imaging quality can be ensured.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the description of the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of the secondary diffraction caused by the size of an incident grating in a grating waveguide display device provided by the prior art;
FIG. 2 is a schematic diagram of a light coupling end of a grating waveguide display device for improving light coupling efficiency according to an embodiment of the present invention;
fig. 3 is a schematic structural diagram of an incident grating of a grating waveguide display device according to an embodiment of the present invention;
FIG. 4 is a simulation of the incident grating diffraction efficiency RCWA of a grating waveguide display device for improving the coupling efficiency of light energy according to an embodiment of the present invention; the method comprises the steps of (a) performing RCWA simulation on the change of diffraction efficiency of light with 520, 520 nm and TE polarization on an incident grating along with the change of incident angle, (b) performing RCWA simulation on the change of diffraction efficiency of light with 520, 520 nm and TM polarization on the incident grating along with the change of incident angle;
FIG. 5 is a schematic cross-sectional view of a 1/4 wave plate of a grating waveguide display device according to an embodiment of the present invention;
FIG. 6 is a top view of a 1/4 wave plate of a grating waveguide display device according to an embodiment of the present invention; wherein, (a) is a schematic diagram of TE polarized incident light entering a 1/4 wave plate for the first time (the optical axis direction forms an angle of 45 degrees with an incident photoelectric vector); (b) A schematic diagram of the incident light passing through the 1/4 wave plate for the second time (the incident TE polarized light passes through the 1/4 wave plate for the second time, and the polarization direction is deflected by 90 degrees, so that the TE polarization is changed into TM polarization);
FIG. 7 is a schematic diagram of a grating waveguide display device according to an embodiment of the present invention, wherein light coupled into a waveguide substrate is incident again on the surface of an incident grating to undergo secondary diffraction; the method comprises the steps of (a) carrying out secondary diffraction on TE polarized light in a waveguide substrate which is incident on the surface of an incident grating again; (a) Schematic representation of the secondary diffraction of TM polarized light in the waveguide substrate that is again incident on the surface of the incident grating.
Detailed Description
The technical solutions in the embodiments of the present invention are clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention; it will be apparent that the described embodiments are only some embodiments of the invention, but not all embodiments, which do not constitute limitations of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to fall within the scope of the invention.
The terms that may be used herein will first be described as follows:
the term "and/or" is intended to mean that either or both may be implemented, e.g., X and/or Y are intended to include both the cases of "X" or "Y" and the cases of "X and Y".
The terms "comprises," "comprising," "includes," "including," "has," "having" or other similar referents are to be construed to cover a non-exclusive inclusion. For example: including a particular feature (e.g., a starting material, component, ingredient, carrier, formulation, material, dimension, part, means, mechanism, apparatus, step, procedure, method, reaction condition, processing condition, parameter, algorithm, signal, data, product or article of manufacture, etc.), should be construed as including not only a particular feature but also other features known in the art that are not explicitly recited.
The term "consisting of … …" is meant to exclude any technical feature element not explicitly listed. If such term is used in a claim, the term will cause the claim to be closed, such that it does not include technical features other than those specifically listed, except for conventional impurities associated therewith. If the term is intended to appear in only a clause of a claim, it is intended to limit only the elements explicitly recited in that clause, and the elements recited in other clauses are not excluded from the overall claim.
Unless specifically stated or limited otherwise, the terms "mounted," "connected," "secured," and the like should be construed broadly to include, for example: the connecting device can be fixedly connected, detachably connected or integrally connected; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the terms herein above will be understood by those of ordinary skill in the art as the case may be.
When concentrations, temperatures, pressures, dimensions, or other parameters are expressed as a range of values, the range is to be understood as specifically disclosing all ranges formed from any pair of upper and lower values within the range of values, regardless of whether ranges are explicitly recited; for example, if a numerical range of "2 to 8" is recited, that numerical range should be interpreted to include the ranges of "2 to 7", "2 to 6", "5 to 7", "3 to 4 and 6 to 7", "3 to 5 and 7", "2 and 5 to 7", and the like. Unless otherwise indicated, numerical ranges recited herein include both their endpoints and all integers and fractions within the numerical range.
The terms "center," "longitudinal," "transverse," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," etc. refer to an orientation or positional relationship based on that shown in the drawings, merely for ease of description and to simplify the description, and do not explicitly or implicitly indicate that the apparatus or element in question must have a particular orientation, be constructed and operated in a particular orientation, and therefore should not be construed as limiting the present disclosure.
The grating waveguide display device for improving the light energy coupling efficiency provided by the invention is described in detail below. What is not described in detail in the embodiments of the present invention belongs to the prior art known to those skilled in the art. The specific conditions are not noted in the examples of the present invention and are carried out according to the conditions conventional in the art or suggested by the manufacturer. The reagents or apparatus used in the examples of the present invention were conventional products commercially available without the manufacturer's knowledge.
As shown in fig. 2, an embodiment of the present invention provides a grating waveguide display device for improving light energy coupling efficiency, including:
waveguide substrate 100、A transmission type resonance waveguide grating 110 and a 1/4 wave plate 120; wherein,
the transmission type resonant waveguide grating 110 is arranged on the surface of the waveguide substrate 100 as an incident grating;
the 1/4 wave plate 120 is embedded in the waveguide substrate 100, and the upper and lower surfaces of the 1/4 wave plate 120 are parallel to the upper and lower planes of the waveguide substrate 100; the optical axis direction of the 1/4 wave plate 120 is parallel to the upper and lower surfaces of the 1/4 wave plate and the upper and lower planes of the waveguide substrate 100, and the optical axis direction of the 1/4 wave plate 120 forms an angle of 45 ° with the electric field direction of the incident polarized light.
The 1/4 wave plate 120 is located directly below the transmissive resonant waveguide grating 110, and the projection range of the 1/4 wave plate 120 in the vertical direction is within the projection range of the transmissive resonant waveguide grating 110 in the vertical direction, preferably, the projection ranges of the two are coincident or nearly coincident (i.e. the light coupled into the waveguide by the transmissive resonant waveguide grating 110 is guaranteed to necessarily pass through the 1/4 wave plate 120).
As shown in fig. 3, in the above-mentioned grating waveguide display device, the transmission type resonant waveguide grating 110 is composed of a waveguide substrate 20, a high refractive index layer 22, a low refractive index layer 24 and a grating layer 26 which are stacked in this order from bottom to top. The grating period, the height, the duty ratio and the thickness of the high refractive index layer and the low refractive index layer are values which enable the transmission type resonant waveguide grating to generate a resonant mode for light with a certain wavelength and an incident angle; the specific structural parameters of each layer are calculated and determined by RCWA (rigorous wave coupling algorithm), and the thicknesses of the high and low refractive index layers meet the phase matching，The energy of the resonance mode can be coupled into the high diffraction order and the highest diffraction efficiency can be achieved.
In the above-mentioned grating waveguide display device, the grating period of the grating layer 26 is a sub-wavelength lower than the wavelength of the incident light in vacuum, the height is 40 to 200nm, and the duty ratio is 30 to 70%; preferably, the grating period of the grating layer 26 is 300-600 nm;
the refractive index of the high refractive index layer 22 is 2.0-4.0, and the thickness is 30-300 nanometers;
the low refractive index layer 24 has a refractive index of 1.0 to 1.5 and a thickness of 30 to 200 nm.
As shown in fig. 5, the thickness of the 1/4 wave plate 120 satisfies the pi/2 phase difference between the o light and the e light generated after the incident light passes through the 1/4 wave plate 120;
namely (n) o - n e ) X d ≡cos θ= ±λ/4; wherein n is o ，n e Refractive index of o light and e light respectively; d is the thickness of the 1/4 wave plate; θ is the angle between the light and the normal of the 1/4 wave plate surface; lambda is the wavelength of light incident on the surface of the 1/4 wave plate.
The embodiment of the invention also provides near-eye display equipment, which comprises a grating waveguide display device, wherein the grating waveguide display device adopts the grating waveguide display device for improving the light energy coupling efficiency. Due to the adoption of the grating waveguide display device capable of improving the light energy coupling efficiency, the light energy coupling efficiency of the near-eye display device can be ensured, and the imaging quality of the near-eye display device can be ensured.
In summary, according to the grating waveguide display device for improving the optical energy coupling efficiency, the transmission type resonance waveguide grating is adopted as the incident grating, the 1/4 wave plate with the optical axis direction forming an angle of 45 degrees with the electric field direction of the incident light is embedded in the waveguide substrate, TE polarized light coupled into the waveguide substrate is deflected by 90 degrees to be converted into TM polarized light after passing through the 1/4 wave plate twice, diffraction resonance does not occur when the TM polarized light is incident into the transmission type resonance waveguide grating, the + -1-level diffraction efficiency is extremely low, and most of light is reflected back to the 1/4 wave plate, so that optical energy loss caused by secondary diffraction is avoided, and the optical energy coupling efficiency of the grating waveguide is improved. Meanwhile, the width of the incident grating is not limited, namely the area is not limited, and the imaging quality of the near-eye display device can be ensured.
In order to more clearly demonstrate the technical scheme and the technical effects provided by the invention, the grating waveguide display device for improving the optical energy coupling efficiency provided by the embodiment of the invention is described in detail below by using specific embodiments.
Examples
As shown in fig. 2, the present invention provides a grating waveguide display device for improving light energy coupling efficiency, which can overcome the problem of light energy loss caused by grating secondary diffraction in the existing grating waveguide structure, and the grating waveguide display device includes:
a waveguide substrate 100, a transmission type resonance waveguide grating 110 as an incident grating, and a 1/4 wave plate 120 embedded in the waveguide substrate 100; wherein,
the transmission type resonance waveguide grating 110 is disposed on the surface of the waveguide substrate 100, and the 1/4 wave plate 120 is embedded in the waveguide substrate 100 directly below the transmission type resonance waveguide grating 110.
As shown in fig. 3, the transmission type resonant waveguide grating 110 is composed of a waveguide substrate 20, a high refractive index layer 22, a low refractive index layer 24, and a grating layer 26 stacked in this order from bottom to top. The transmission type resonant waveguide grating can generate diffraction resonance on TE polarized incident light, the diffraction efficiency of +/-1 st order is 60 percent, the diffraction resonance on TM polarized incident light is not generated, the diffraction efficiency of +/-1 st order is lower than 10 percent,the diffraction efficiency of 1 st order is high, and the polarization state of incident light is highly selective. The grating period, the height, the duty ratio and the thickness of the high refractive index layer and the low refractive index layer are values which enable the resonant waveguide grating to generate a resonant mode for light with a certain wavelength and an incident angle, and specific structural parameters of each layer are calculated and determined by RCWA (rigorous wave coupling algorithm); the thickness of the high and low refractive index layers satisfies phase matching，The energy of the resonance mode can be coupled into the high diffraction order and the highest diffraction efficiency can be achieved.
As shown in fig. 4 (a) and (b), a 1/4 wave plate is embedded in the waveguide substrate 100, the incident light is TE polarized, and the optical axis direction of the 1/4 wave plate forms an angle of 45 ° with the electric field direction of the incident light, so that the TE polarized light coupled into the waveguide substrate 100 is polarized by 90 ° after passing through the 1/4 wave plate twice, that is, the polarization state of the light is converted from TE polarized light to TM polarized light before the light is incident on the grating again after being totally reflected by the waveguide substrate 100, see fig. 2. Because of the high selectivity of the transmission type resonant waveguide grating 110 to the polarization state of the incident light, the TM polarized light does not generate diffraction resonance when incident on the grating surface, the diffraction efficiency of the ±1st order is extremely low, and most of the light is reflected back to the waveguide substrate, thereby avoiding the light energy loss caused by secondary diffraction and improving the light energy coupling efficiency. Meanwhile, the width of the transmission type resonance waveguide grating 110 as an incident grating is not limited any more, and the imaging quality can be ensured.
As shown in FIG. 5, the optical axis direction of the 1/4 wave plate is parallel to the surface of the 1/4 wave plate, light of a certain wavelength is incident on the surface of the 1/4 wave plate 120, and the thickness of the 1/4 wave plate satisfies the phase difference of pi/2 generated between the ordinary light (o light) and the extraordinary light (e light) after the light passes through the 1/4 wave plate, namely (n light) o - n e ) d/cos θ= ±λ/4, where n o ，n e Refractive index of o light and e light respectively; d is the thickness of the 1/4 wave plate; lambda is the wavelength of light and theta is the angle between the light and the normal to the 1/4 wave plate surface.
As shown in fig. 2, the surface of the 1/4 wave plate embedded in the waveguide substrate 100 is parallel to the surface of the waveguide substrate, i.e., the optical axis direction is parallel to the upper and lower planes of the waveguide substrate 100; the electric field direction of the incident TE polarized light shown in fig. 2 is perpendicular to the paper surface (y-axis direction), and the optical axis direction of the 1/4 wave plate is at an angle of 45 ° to the y-axis, i.e., 45 ° to the electric field direction of the incident light, as shown in the top views of fig. 6 (a), (b).
The 1/4 wave plate arranged in the above manner can be determined according to the following deduction, which can ensure that incident TE polarized light is converted into TM polarized light, specifically:
let the electric vector E of TE polarized light be: e=acostwt (1);
after light enters the 1/4 wave plate, the electric field vector of the incident light is decomposed into o light vertical to the optical axis and e light parallel to the optical axis, and the optical axis direction of the 1/4 wave plate forms an angle of 45 degrees with the electric vector, namely:
E o =Asin45°coswt;
E e =Acos45°coswt; （2）；
e when light passes through the 1/4 wave plate o 、E e The phase difference between them increases by pi/2, namely:
E o （1） =Asin45°coswt;
E e （1） =Acos45°cos（wt+π/2）; （3）；
due to E o （1） 、E e （1） The amplitudes of (2) are identical, and are synthesized into circular polarization after passing through the 1/4 wave plate, namely, incident ray polarization is converted into circular polarization after passing through the 1/4 wave plate for the first time. As shown in FIG. 2, the circularly polarized light is totally reflected by the waveguide substrate 100 and then passes through the 1/4 wave plate again, E o 、E e The phase difference between them is again increased by pi/2, namely:
E o （2） =Asin45°coswt;
E e （2） =Acos45°cos（wt+π）=-Acos45°coswt=- E o （2） ; （4）；
that is, after the incident light is totally emitted by the waveguide substrate 100 and then passes through the waveguide substrate 100 for the second time, the circularly polarized light is converted into linearly polarized light, the polarization direction is changed by 90 degrees compared with the incident polarized light, and the TE polarized light is changed into TM polarized light. Due to the selectivity of the transmission type resonant waveguide grating 110 as an incident grating to the polarization state of the incident light, resonance diffraction does not occur when TM polarized light is incident to the incident grating, thereby avoiding light energy loss caused by secondary diffraction and improving light energy coupling efficiency.
TE polarized light incident from air undergoes diffraction resonance through the transmission type resonance waveguide grating 110, and as shown in fig. 4 (a), 1 st order diffraction is coupled into the optical waveguide, and the diffraction efficiency is higher than 60%. If the 1/4 wave plate 120 is not shown in fig. 2, the light is totally reflected by the optical waveguide and then enters the grating surface again to generate diffraction resonance again, and 60% of the light energy escapes from the optical waveguide due to secondary diffraction, as shown in fig. 7 (a). After the 1/4 wave plate is embedded in the waveguide substrate as shown in fig. 2, the light passes through the wave plate twice, the polarization state is converted from TE polarization to TM polarization, when the light is incident on the grating surface again, the TM polarized light does not generate diffraction resonance due to the high selectivity of the transmission type resonance waveguide grating to the polarization state of the incident light, and most of light energy is reflected back to the waveguide substrate (0R), as shown in fig. 7 (b), so that the light energy loss caused by secondary diffraction is avoided. Note that the angle of incidence of the light rays in fig. 7 is the angle in the waveguide substrate, and the light rays are re-incident on the grating surface at an angle greater than total reflection (> 32 °).
In summary, the grating waveguide display device of the embodiment of the invention can improve the light energy coupling efficiency and simultaneously ensure the light weight and the display quality of the display device.
The foregoing is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions easily contemplated by those skilled in the art within the scope of the present invention should be included in the scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims. The information disclosed in the background section herein is only for enhancement of understanding of the general background of the invention and is not to be taken as an admission or any form of suggestion that this information forms the prior art already known to those of ordinary skill in the art.
Claims (6)
1. A grating waveguide display device for improving light energy coupling efficiency, comprising:
waveguide substrate (100)、A transmission type resonance waveguide grating (110) and a 1/4 wave plate (120); wherein,
the transmission type resonance waveguide grating (110) is used as an incident grating and is arranged on the surface of the waveguide substrate (100);
the 1/4 wave plate (120) is embedded in the waveguide substrate (100), and the upper surface and the lower surface of the 1/4 wave plate (120) are respectively parallel to the upper plane and the lower plane of the waveguide substrate (100);
the optical axis direction of the 1/4 wave plate (120) is parallel to the upper and lower surfaces of the 1/4 wave plate and the upper and lower planes of the waveguide substrate (100) and forms an angle of 45 degrees with the electric field direction of the incident polarized light;
the 1/4 wave plate (120) is positioned right below the transmission type resonance waveguide grating (110), and the projection range of the 1/4 wave plate (120) in the vertical direction is positioned in the projection range of the transmission type resonance waveguide grating (110) in the vertical direction;
the thickness of the 1/4 wave plate (120) meets the phase difference of pi/2 generated between o light and e light after incident light passes through the 1/4 wave plate (120);
namely (n) o - n e ) X d ≡cos θ= ±λ/4; wherein n is o 、n e Refractive indexes of o light and e light respectively; d is the thickness of the 1/4 wave plate; θ is the angle between the light and the normal of the 1/4 wave plate surface; lambda is the wavelength of light incident on the surface of the 1/4 wave plate.
2. The grating waveguide display device for improving light energy coupling efficiency according to claim 1, wherein the waveguide substrate (100) is composed of a waveguide substrate (20), a high refractive index layer (22), a low refractive index layer (24) and a grating layer (26) which are stacked in this order from bottom to top;
wherein the grating period, height and duty cycle of the grating layer (26) and the thickness of the high refractive index layer (22) and the thickness of the low refractive index layer (24) are valued so as to enable the transmission type resonant waveguide grating to generate a resonant mode for light with a certain wavelength and an incident angle; the high refractive index layer (22) and the low refractive index layer (24) have thicknesses that satisfy phase matching.
3. The grating waveguide display device of claim 2, wherein the grating layer (26) has a grating period of sub-wavelength lower than the wavelength of incident light in vacuum, a height of 40-200 nm and a duty cycle of 30% -70%;
the refractive index of the high refractive index layer (22) is 2.0-4.0, and the thickness is 30-300 nanometers;
the low refractive index layer (24) has a refractive index of 1.0-1.5 and a thickness of 30-200 nm.
4. A grating waveguide display device according to claim 3, characterized in that the grating period of the grating layer (26) is 300-600 nm.
5. The grating waveguide display device of any one of claims 1 to 4, wherein the projection range of the 1/4 wave plate (120) in the vertical direction coincides with the projection range of the transmissive resonant waveguide grating (110) in the vertical direction.
6. A near-eye display device comprising a grating waveguide display device employing the grating waveguide display device of any one of claims 1 to 5 to improve light energy coupling efficiency.
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