Waveguide HMD Optics With Small Input Aperture and Wide Eye Box
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Solution Overview
Problem
Conventional optical modules for head-mounted displays (HMDs) face challenges in achieving a compact and lightweight design while providing a wide field-of-view (FOV) and accommodating large eye movements, with existing solutions being bulky, costly, and inefficient in terms of manufacturability and performance.
Innovation Solution
An optical device comprising a light-transmitting substrate with two parallel major surfaces, an input and output aperture, and two flat reflecting surfaces for total internal reflection, coupled with a redirecting optical element to redirect light waves through an eye-motion box, utilizing angular sensitivity of thin film coatings and intermediate prisms to minimize aperture size and enhance brightness efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional free-space optical modules are used to provide wide FOV and accommodate eye movements, then the field-of-view and eye-motion box are improved, but the device becomes larger, heavier and bulkier
Solution Approach 1:
The patent combines the imaging lens and combiner into a single optical module integrated with the display source, eliminating the need for separate free-space optical components. This merging achieves wide FOV and eye-motion accommodation while maintaining compact size and light weight, directly resolving the contradiction between adaptability and device weight
Solution Approach 2:
The optical module is nested within or integrated with the display source structure, with the light-transmitting substrate and reflecting surfaces embedded in a compact arrangement. This nesting enables the optical system to achieve wide FOV functionality while occupying minimal space and maintaining low weight
2Adaptability or versatility
If conventional optical modules are designed to accommodate large eye movements, then the eye-motion box is improved, but the device becomes bulkier and less compact
Solution Approach 1:
By merging the optical module with the display source and using integrated light-guiding structures with reflecting surfaces, the system accommodates large eye movements within a compact volume, eliminating the need for bulky separate optical components
Solution Approach 2:
The patent uses light-guiding structures that utilize total internal reflection and angular sensitivity to redirect light across three-dimensional eye motion paths, enabling large eye-motion accommodation within a compact two-dimensional footprint
3Volume of moving object
If the input aperture is reduced for compactness, then the device becomes more compact, but the brightness efficiency and image quality deteriorate
Solution Approach 1:
The patent replaces conventional mechanical light redirection with angular-sensitive thin-film coating structures that utilize optical interference and total internal reflection. This substitution enables high brightness efficiency with small input aperture by controlling light propagation through angular sensitivity rather than mechanical aperture size
Solution Approach 2:
The patent changes the optical parameters of the light-transmitting substrate by incorporating angular-sensitive thin-film coatings with specific refractive indices and thicknesses. These parameter changes enable the substrate to selectively guide and redirect light at different angles, maintaining brightness efficiency with a reduced input aperture
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 solution achieves a compact optical system with a large FOV and high image quality, accommodating large eye movements, while maintaining brightness efficiency and reducing the input aperture size, with potential brightness efficiency exceeding previous configurations by an order of magnitude.
Implementation Method 1
a first flat reflecting surface, having an active area located between the two major surfaces of the light-transmitting substrate, for reflecting the coupled-in light waves to effect total internal reflection from the major surfaces of the substrate
Implementation Method 2
a redirecting optical element having at least two surfaces positioned outside of the substrate for redirecting light waves coupled-out from the substrate through the output aperture, into the eye-motion-box
Data Source
AI summary
An optical device includes a light-transmitting substrate, input and output apertures, eye-motion box, intermediate element outside of the substrate for coupling light waves into the substrate through the input aperture, a first reflecting surface between two major surfaces of the light-transmitting substrate for reflecting the coupled-in light waves to effect total internal reflection from the major surfaces of the substrate, a second flat reflecting surface parallel to the first reflecting surface located between the major surfaces of the light-transmitting substrate, for coupling light waves out of the substrate, and an optical element for redirecting light waves coupled-out from the substrate through the output aperture, into the eye-motion-box. The input aperture is substantially smaller than the output aperture, active areas of the first and second reflecting surfaces are similar, and each of the coupled light waves covers the entire aperture of the eye-motion-box.