Light-Guide Optical Element With External Beam Multiplier
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Solution Overview
Problem
Existing near-eye displays require larger waveguides and projectors due to the need for structures like beam splitters or coupling-in prisms, which increase the dimensions and manufacturing complexity, especially for shallow-angle image injection.
Innovation Solution
An optical system using a light-guide optical element (LOE) with an external image conjugate generator and beam multiplier, which includes a stack of transparent plates with reflective and partially-reflecting surfaces, allowing for compact aperture expansion and efficient image filling without extending the waveguide length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a coupling-in prism is used to direct rays into the waveguide at shallow angles, then the image can be coupled into the waveguide, but the input aperture and projector size must be increased
Solution Approach 1:
The patent introduces a beam multiplier component that creates multiple virtual images of the input aperture in different spatial dimensions. This allows the physical projector aperture to remain small while effectively filling the waveguide with light rays from multiple apparent source positions, resolving the contradiction between coupling efficiency and aperture size
Solution Approach 2:
The beam multiplier acts as an intermediary optical element between the small projector aperture and the waveguide. It generates conjugate images that redirect light into the waveguide at the required shallow angles without requiring the projector itself to have a large aperture
2Area of stationary object
If a beam splitter (mixer) is incorporated internally in the waveguide to generate conjugates, then a smaller input aperture can be used, but the waveguide length and manufacturing complexity increase
Solution Approach 1:
The patent extracts the beam splitting and conjugate generation function from the internal structure of the waveguide and places it in a separate external beam multiplier component. This eliminates the need for internal mixers that would extend the waveguide length, while still achieving the desired conjugate image generation for aperture reduction
3Area of stationary object
If a beam splitter (mixer) is incorporated internally in the waveguide, then a smaller input aperture can be used, but the manufacturing precision requirements increase due to parallelism constraints
Solution Approach 1:
By removing the beam splitter from the waveguide substrate and placing it in a separate external component, the patent eliminates the stringent parallelism requirements between the beam splitter and waveguide surfaces. The external beam multiplier can be independently aligned and manufactured without requiring sub-micron parallelism with the waveguide, significantly reducing manufacturing precision constraints
Solution Approach 2:
The patent segments the optical system into distinct functional components: the waveguide for light propagation and the external beam multiplier for conjugate generation. This segmentation allows each component to be optimized and manufactured independently, reducing the cumulative precision requirements that would arise from integrating multiple functions into a single monolithic waveguide structure
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Achieves compact and efficient image propagation and coupling-out, reducing the size and manufacturing complexity of near-eye displays by using an external image conjugate generator and beam multiplier, enabling smaller projectors and waveguides.
Implementation Method 1
a light-guide optical element (LOE) formed from transparent material and having first and second mutually-parallel major external surfaces for supporting propagation of an image by internal reflection at the first and second major external surfaces
Implementation Method 2
the waveguide is preferably planar. For best performance, both the image and its conjugate should completely fill the waveguide, so that illumination corresponding to each pixel of the image and each pixel of the conjugate image is present at every point within the thickness of the waveguide
Data Source
AI summary
An optical system (100) for directing an image towards a user for viewing includes a light-guide optical element (LOE) (10) having parallel major external surfaces (11a, 11b) for supporting propagation of an image by internal reflection, a coupling-out arrangement for coupling out the image towards an eye of the user, and a coupling-in aperture. An image projector (114) includes an image generator (32) for generating an image, collimating optics (31) for collimating the image, and an image conjugate generator (20, 33, 34). The image projector is coupled to the coupling-in aperture so as to introduce both the collimated image and its conjugate image into the LOE prior to the images impinging on either of major external surfaces. The image conjugate generator may be a second image generator (33), or may employ one or more reflecting surface (22, 23, 24, 34) non-contiguous with the major external surfaces of the LOE.