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 internal reflecting surfaces that utilize total internal reflection and redirecting elements to couple light waves efficiently, allowing for a compact design with a significantly smaller input aperture and larger output aperture, and incorporating a redirecting prism to converge light waves into a smaller pupil.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional free-space optical module is used to provide a wide field-of-view, then the field-of-view is improved, but the device becomes larger, heavier and bulkier
Solution Approach 1:
The patent transitions from conventional free-space optical paths to a planar integrated waveguide structure, where light propagation is confined to two-dimensional guided modes within a thin substrate. This dimensional transformation enables wide field-of-view functionality to be achieved on a compact, lightweight planar platform rather than requiring bulky three-dimensional optical components
Solution Approach 2:
The patent integrates multiple optical functions (collimation, beam steering, field-of-view control) into a single planar waveguide device by incorporating diffractive optical elements and reflective surfaces directly onto the substrate. This merging of functions eliminates the need for separate optical components, reducing overall device weight and size while maintaining wide field-of-view performance
2Volume of moving object
If the input aperture is reduced for compactness, then the device size is reduced, but the light coupling efficiency deteriorates
Solution Approach 1:
The patent employs diffractive optical elements with specifically engineered periodic structures that manipulate light coupling parameters. These diffractive features enable efficient light coupling into the waveguide at reduced aperture sizes by controlling the diffraction angles and coupling modes, overcoming the typical trade-off between aperture size and coupling efficiency
Solution Approach 2:
The patent replaces conventional mechanical optical coupling methods (requiring large apertures and precise alignment) with diffractive optical coupling mechanisms. The diffractive structures create inherent angular selectivity and mode matching that enables efficient coupling with smaller apertures, substituting mechanical precision requirements with optical diffraction-based coupling
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 enables a high-quality image with a large eye-motion box and wide FOV, achieving brightness efficiency up to 90% and accommodating large eye movements, while maintaining a compact and lightweight form factor.
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.