Patent Publication Number: US-2020292820-A1

Title: Near-eye display device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of China application serial no. 201910186957.2, filed on Mar. 13, 2019. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The disclosure relates to a display device, and more particularly, to a near-eye display device. 
     Description of Related Art 
     In the field of near-eye display for augmented reality (AR), there are two main mechanisms for introducing image information into the human eye, including a freeform prism and a waveguide plate. The main issues with the freeform prism are the large thickness and weight and the introduction of significant image distortion. In contrast, the framework using the waveguide plate is obviously thinner and lighter and has a larger eye box. However, although the framework of the waveguide plate does not introduce image distortion, it introduces several image display defects, such as ghosting, a mirror image, reduced uniformity, chromatic aberration, etc. There are currently three main frameworks of waveguide plates, including the holographic type, the surface relief grating type, and the geometrical beam splitter type. Due to the limitation of chromatic aberration and the influence on the ambient light, the former two are faced with more challenges than the geometrical beam splitter-type waveguide plate. 
     The information disclosed in this Background section is only for enhancement of understanding of the background of the described technology and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Further, the information disclosed in the Background section does not mean that one or more problems to be resolved by one or more embodiments of the invention was acknowledged by a person of ordinary skill in the art. 
     SUMMARY OF THE INVENTION 
     The invention provides a near-eye display device that can eliminate the defect of a mirror image. 
     Other purposes and advantages of the invention may be further understood from the technical features recited herein. To achieve one, part, or all of the above purposes or other purposes, an embodiment of the invention provides a near-eye display device. The near-eye display device includes a light engine, a first light waveguide, and a second light waveguide. The light engine provides an image. The first light waveguide reproduces the image of a view angle region in a first direction. The first light waveguide includes a plurality of first beam splitters arranged along the first direction. The second light waveguide is disposed at an incident light area on one side of the first light waveguide. The second light waveguide reproduces the image of a view angle region in a second direction. The second light waveguide includes a plurality of second beam splitters arranged along the second direction. The second light waveguide has a first surface and a second surface opposite to the first surface. The first surface faces the first light waveguide. An included angle is present between each of the second beam splitters and the second surface. The included angle is between 0 and 90 degrees and is not equal to 45 degrees. 
     Based on the above, the near-eye display device of the embodiment of the invention has a two-dimensional geometry-type waveguide plate framework, which may eliminate a mirror image. 
     Other objectives, features and advantages of the invention will be further understood from the further technological features disclosed by the embodiments of the present invention wherein there are shown and described preferred embodiments of this invention, simply by way of illustration of modes best suited to carry out the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a schematic view of a near-eye display device according to an embodiment of the invention. 
         FIG. 2  is a top view of the near-eye display device according to the embodiment of  FIG. 1 . 
         FIG. 3  is a side view of the near-eye display device according to the embodiment of  FIG. 1 . 
         FIG. 4  is a side view of a light engine and a second light waveguide according to the embodiment of  FIG. 1 . 
         FIG. 5  is a side view of the second light waveguide according to the embodiment of  FIG. 1 . 
         FIG. 6  is a schematic view of an input image according to an embodiment of the invention. 
         FIG. 7  is a schematic view of an output image according to an embodiment of the invention. 
         FIG. 8  is a schematic view of an output image according to a related example of the invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” etc., is used with reference to the orientation of the Figure(s) being described. The components of the present invention can be positioned in a number of different orientations. As such, the directional terminology is used for purposes of illustration and is in no way limiting. On the other hand, the drawings are only schematic and the sizes of components may be exaggerated for clarity. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms “connected,” “coupled,” and “mounted” and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings. Similarly, the terms “facing,” “faces” and variations thereof herein are used broadly and encompass direct and indirect facing, and “adjacent to” and variations thereof herein are used broadly and encompass directly and indirectly “adjacent to”. Therefore, the description of “A” component facing “B” component herein may contain the situations that “A” component directly faces “B” component or one or more additional components are between “A” component and “B” component. Also, the description of “A” component “adjacent to” “B” component herein may contain the situations that “A” component is directly “adjacent to” “B” component or one or more additional components are between “A” component and “B” component. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive. 
       FIG. 1  is a schematic view of a near-eye display device according to an embodiment of the invention.  FIG. 2  is a top view of the near-eye display device according to the embodiment of  FIG. 1 .  FIG. 3  is a side view of the near-eye display device according to the embodiment of  FIG. 1 .  FIG. 4  is a side view of a light engine and a second light waveguide according to the embodiment of  FIG. 1 .  FIG. 5  is a side view of the second light waveguide according to the embodiment of  FIG. 1 . Referring to  FIG. 1  to  FIG. 5 , a near-eye display device  100  of the embodiment includes a light engine  130 , a first light waveguide  110 , and a second light waveguide  120 .  FIG. 1  shows a two-dimensional waveguide plate framework configured to eliminate a mirror image. In the embodiment, the near-eye display device  100  projects an image  600 , in which the mirror image is eliminated, to a projection target  200 , such as an eye pupil of a user. 
     In the embodiment, the light engine  130  provides an image  400 . The first light waveguide  110  reproduces the image of a view angle region in a first direction Y. The first light waveguide  110  includes a plurality of first beam splitters BS 1  arranged along the first direction Y. The plurality of first beam splitters BS 1  are spaced apart from each other between two opposite surfaces of the first light waveguide  110 . The second light waveguide  120  is disposed at an incident light area  111  on one side of the first light waveguide  110 . The second light waveguide  120  reproduces the image of a view angle region in a second direction X. The second light waveguide  120  includes a plurality of second beam splitters BS 2  arranged along the second direction X. The second light waveguide  120  has a first surface S 1  and a second surface S 2 . The second surface S 2  is opposite to the first surface S 1  in a third direction Z. The first direction Y, the second direction X and the third direction Z are perpendicular to each other. The first surface S 1  faces the first light waveguide  110  and corresponds to the incident light area  111  of the first light waveguide  110 . The plurality of second beam splitters BS 2  are parallel and spaced apart from each other between the first surface S 1  and the second surface S 2  of the second light waveguide  120 . An included angle 0 is present between the second beam splitters BS 2  and the second surface S 2 . The included angle θ is between 0 and 90 degrees and is not equal to 45 degrees. As shown in  FIG. 3 , for example, the included angle θ is an included angle between 15 and 44 degrees or between 46 and 60 degrees. In  FIG. 4 , the included angle 0 is, for example, 30 degrees, and the angle of the emission light is the same as the angle of the incident light regardless of where it is located. 
     A width d of the incident light area  111  of the first light waveguide  110  in the first direction Y and a total width D of the second light waveguide  120  in the first direction Y satisfy: 0.5D&lt;d&lt;2D. In the embodiment, the width d of the incident light area  111  of the first light waveguide  110  in the first direction Y may be equal to the total width D of the second light waveguide  120  in the first direction Y (as shown in  FIG. 2 ), and the width d of the incident light area  111  of the first light waveguide  110  in the first direction Y may also be close to the total width D of the second light waveguide  120  in the first direction Y. In  FIG. 4  and  FIG. 5 , after the image  400  provided from the light engine  130  enters the second light waveguide  120 , the first direction Y dimension (horizontal dimension) of the image  400  does not undergo total reflection by the surfaces on the left and right sides when transmitted in the second light waveguide  120 . Therefore, the mirror image generated due to total reflection in the first direction Y dimension can be eliminated. 
     In the embodiment, as an incident light port  500  through which the image  400  provided by the light engine  130  is transmitted to the second light waveguide  120  is enlarged, the incident light area of the first light waveguide  110  may correspondingly cover a beam splitter framework including more than one beam splitter in an area corresponding to a total light output area of the second light waveguide  120  for outputting light. For example, in  FIG. 1  and  FIG. 2 , the incident light area  111  of the first light waveguide  110  correspondingly covers the area which at least two first beam splitters are arranged in. Here, the incident light area  111  covers the area that four first beam splitters are arranged in as an example, but the invention is not limited to this number. In the embodiment, the incident light area  111  covers four first beam splitters which are parallel and spaced apart from each other, and the inclination direction of the first beam splitters covered by the incident light area  111  is opposite to the inclination direction of the other first beam splitters BS 1 . In other words, the inclination direction of the first beam splitters covered by the incident light area  111  is configured to guide the image from the second light waveguide  120  to the other first beam splitters BS 1 , and the inclination direction of the other first beam splitters BS 1  is configured to guide the received image to the projection target  200 . The first beam splitters  112 ,  114 ,  116  are arranged along the first direction Y. The first beam splitter  112  covered by the incident light area  111  is, for example, a beam splitter having a reflectance of 100%. The first beam splitter  114  is, for example, a beam splitter having a reflectance of 50% and a transmittance of 50%. The first beam splitter  116  is, for example, a beam splitter having a reflectance of 33% and a transmittance of 67%. In other embodiments, the first beam splitter  112  having a reflectance of 100% may be replaced with a reflection mirror or any optical component that can totally reflect the light from the second light waveguide  120  to the first beam splitter  114 , and the invention is not limited thereto. In addition, since the plurality of beam splitters are arranged at the incident light area  111  of the first light waveguide  110 , the size increase of the first light waveguide due to the enlarged incident light port  500  can also be reduced. 
       FIG. 6  is a schematic view of an input image according to an embodiment of the invention.  FIG. 7  is a schematic view of an output image according to an embodiment of the invention.  FIG. 8  is a schematic view of an output image according to a related example of the invention. Referring to  FIG. 6  to  FIG. 8 , an input image  400  shown in  FIG. 6  is, for example, the image  400  input from the light engine  130  to the second light waveguide  120  as shown in  FIG. 4 . An output image  600  shown in  FIG. 7  is, for example, the image  600  output from the first light waveguide  110  to the projection target  200  (e.g., an eye pupil) as shown in  FIG. 2 . 
     In the related example of  FIG. 8 , if the included angle θ between the second beam splitters of the second light waveguide and the surface of the second light waveguide is equal to 45 degrees, the image in the view angle of the second direction X dimension (vertical dimension) provided by the light engine  130  is symmetrically distributed when transmitted in the second light waveguide  120 . Therefore, an output image  800  of the second light waveguide includes a mirror image of the vertical dimension caused by total reflection during transmission. In the embodiment of  FIG. 6  and  FIG. 7 , if the included angle θ between the second beam splitters of the second light waveguide and the surface of the second light waveguide is equal to 30 degrees, the image in the view angle of the vertical dimension provided by the light engine is asymmetrically distributed when transmitted in the second light waveguide  120  (as shown in  FIG. 5 ), until the image is transmitted to the plurality of second beam splitters BS 2 . When the image is transmitted to the plurality of second beam splitters BS 2 , the image is converted to be symmetrically distributed (as shown in  FIG. 4 ) and reflected to the first light waveguide  110 . Therefore, the mirror image in the second direction X can be eliminated. Accordingly, in the framework of the embodiments of the invention, a virtual image result without a mirror image can be obtained, as shown in  FIG. 7 . 
     In summary of the above, the embodiments of the invention have at least one of the following advantages or effects. In the embodiments of the invention, the near-eye display device has a two-dimensional waveguide plate framework including two light waveguides. At least two beam splitters are provided in the incident light area of the first light waveguide to receive an image from the second light waveguide. The included angle between the second beam splitters of the second light waveguide and the surface of the second light waveguide is not equal to 45 degrees. In addition, the width of the second light waveguide is increased so that the image does not undergo total reflection by the surfaces on the two sides when transmitted in the second light waveguide. Therefore, in the framework of the embodiments of the invention, the mirror image can be eliminated. 
     The foregoing description of the preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form or to exemplary embodiments disclosed. Accordingly, the foregoing description should be regarded as illustrative rather than restrictive. Obviously, many modifications and variations will be apparent to practitioners skilled in this art. The embodiments are chosen and described in order to best explain the principles of the invention and its best mode practical application, thereby to enable persons skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use or implementation contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents in which all terms are meant in their broadest reasonable sense unless otherwise indicated. Therefore, the term “the invention”, “the present invention” or the like does not necessarily limit the claim scope to a specific embodiment, and the reference to particularly preferred exemplary embodiments of the invention does not imply a limitation on the invention, and no such limitation is to be inferred. The invention is limited only by the spirit and scope of the appended claims. The abstract of the disclosure is provided to comply with the rules requiring an abstract, which will allow a searcher to quickly ascertain the subject matter of the technical disclosure of any patent issued from this disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Any advantages and benefits described may not apply to all embodiments of the invention. It should be appreciated that variations may be made in the embodiments described by persons skilled in the art without departing from the scope of the present invention as defined by the following claims. Moreover, no element and component in the present disclosure is intended to be dedicated to the public regardless of whether the element or component is explicitly recited in the following claims.