Compound Light-Guide Optics With External Conjugate Image Injection
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Solution Overview
Problem
Existing near-eye displays require larger dimensions and complex manufacturing processes due to the need for beam splitters and coupling-in prisms that extend the length of the waveguide, especially for shallow-angle image injection, leading to increased projector aperture size and manufacturing complexity.
Innovation Solution
An optical system employing a light-guide optical element (LOE) with an external image conjugate generator and beam multiplier, using a stack of transparent plates with reflective and partially-reflecting surfaces to generate and inject a collimated image and its conjugate into the LOE, allowing for compact design and reduced manufacturing constraints.
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 injected into the waveguide, but the input aperture and projector size must be enlarged significantly
Solution Approach 1:
The patent introduces a beam multiplier component that creates multiple copies of the injected image in different angular directions. This transforms a single shallow-angle injection path into multiple propagation paths, allowing the system to achieve adequate illumination without requiring an oversized projector aperture
Solution Approach 2:
The beam multiplier is positioned to receive the injected image and pre-process it by generating conjugate images before these images enter the waveguide. This preliminary action of creating multiple image copies ensures that sufficient light is distributed across different angles, eliminating the need for an enlarged projector aperture
2Area of stationary object
If a beam splitter (mixer) is incorporated internally in the waveguide to generate conjugates, then the projector aperture can be reduced, but the waveguide length must be increased significantly
Solution Approach 1:
The patent extracts the beam multiplier function from the internal structure of the waveguide and positions it externally at the input aperture. This extraction eliminates the need for the waveguide to extend significantly to accommodate internal beam splitting components, while still achieving the desired image conjugation and angular distribution
Solution Approach 2:
The beam multiplier acts as an intermediary component between the projector and the waveguide. It performs the beam splitting and conjugation function in an external position, mediating the light path so that the waveguide itself does not need to be extended to accommodate this functionality
3Area of stationary object
If a beam splitter is incorporated internally in the waveguide, then the projector aperture can be reduced, but the manufacturing accuracy requirements increase due to parallelism constraints
Solution Approach 1:
By extracting the beam multiplier from the waveguide's internal structure and positioning it externally, the patent eliminates the stringent manufacturing requirements for internal parallelism. The external beam multiplier can be manufactured and aligned independently, without requiring the waveguide surfaces to maintain tight parallelism tolerances
Solution Approach 2:
The patent segments the optical system into distinct functional components: the projector, the external beam multiplier, and the waveguide. This segmentation allows each component to be manufactured and optimized independently, reducing the overall manufacturing complexity and precision requirements compared to an integrated internal beam splitter design
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
The system achieves optical aperture expansion without extending the waveguide length, enabling a compact near-eye display with simplified manufacturing and reduced projector aperture size, while maintaining efficient image propagation and coupling.
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
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.