Slab Waveguide Collimator for Head-Mounted Displays
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Solution Overview
Problem
Existing visual display technologies, particularly for head-mounted displays, require compact and lightweight collimators to avoid user discomfort due to bulkiness and weight, while maintaining effective field of view and optical performance.
Innovation Solution
A waveguide-based collimator using a slab core structure with evanescently coupled cores and reflective or diffractive elements, allowing for efficient light confinement and conversion between optical modes, enabling a thin and lightweight design with a large pupil area and reduced optical aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If conventional collimators are used in head-mounted displays, then optical performance can be maintained, but the device becomes bulky and heavy causing user discomfort
Solution Approach 1:
The patent replaces conventional mechanical collimator structures with a waveguide-based optical system. The waveguide uses total internal reflection and evanescent wave coupling to achieve collimation, eliminating the need for bulky mechanical optical elements while maintaining optical performance through controlled light propagation modes.
Solution Approach 2:
The invention transitions from three-dimensional bulk optical elements to a two-dimensional waveguide plane. By confining light propagation to the waveguide core and using in-plane mode conversion, the system achieves collimation in a thin profile, dramatically reducing the weight and thickness of the collimator.
2Volume of moving object
If the collimator size is reduced for compactness, then weight and bulk are decreased, but field of view and optical performance may be compromised
Solution Approach 1:
The patent controls the field of view and collimation quality by adjusting waveguide parameters such as core thickness, refractive index contrast, and grating period. By optimizing these parameters, the system achieves a wide field of view within a compact volume, as the light propagation characteristics are tuned through material and geometric parameters rather than large optical elements.
Solution Approach 2:
The waveguide is divided into distinct functional regions: an input region for light coupling, a mode conversion region with periodic structures for transforming propagation modes, and an output region for collimated light extraction. This segmentation allows each region to be optimized independently, maintaining field of view performance while minimizing overall volume.
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 provides a compact, lightweight, and high-performance collimator that maintains a large field of view and reduces optical aberrations, suitable for near-eye displays and other applications, such as augmented and virtual reality.
Implementation Method 1
a slab core structure supporting first and second optical modes of propagation
Implementation Method 2
The slab core structure includes parallel evanescently coupled first and second slab cores
Implementation Method 3
a first reflector coupled to the slab core structure for reflecting the light beam to propagate back in the slab core structure
Data Source
AI summary
A compact collimator or projector includes a waveguide having a slab core structure supporting at least two lateral modes of propagation. A light beam coupled into a first mode propagates to an edge of the waveguide where it is reflected by a reflector to propagate back. Upon propagation back and forth, the light is converted into a second mode. An out-coupling region, such as an evanescent coupler, is provided to out-couple the light propagating in the second mode. The reflector may have focusing power to collimate the out-coupled light beam. The light beam may be converted from the first to the second mode without being reflected from a reflector.