Substrate-Guided Optical Device for Wide Field-of-View Displays
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Solution Overview
Problem
Conventional compact optical modules for head-mounted and head-up displays are bulky, heavy, and limited in field-of-view, making them impractical for compact and mobile applications, and suffer from chromatic dispersion issues with high-quality holographic displays.
Innovation Solution
A light-transmitting substrate with selectively reflecting surfaces that utilize total internal reflection and anisotropic or angularly sensitive coatings to achieve a wide field-of-view and compact design, allowing for a larger eye-motion-box and accommodating large eye movements, while minimizing chromatic dispersion and enabling use with wide spectral sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional free-space optical modules are used to achieve required field-of-view, then imaging quality is maintained, but device size and weight increase significantly
Solution Approach 1:
The patent combines the combiner and imaging lens functions into a single integrated optical element. The light-transmissive substrate serves simultaneously as the combiner for reflecting display light into the user's eye and as the imaging lens for focusing external scene light, eliminating the need for separate components and reducing overall device weight and size.
Solution Approach 2:
The optical element performs multiple functions: it acts as a beam splitter/combiner for the display image, as an imaging lens for the external scene, and as a protective window. This multi-functionality allows a single component to replace what would traditionally require multiple separate optical elements, thereby reducing weight.
2Device complexity
If conventional optical modules are designed for moderate performance, then device complexity is reduced, but field-of-view and image quality deteriorate
Solution Approach 1:
The patent utilizes the refractive index parameter of the light-transmissive substrate to achieve both combining and imaging functions. By carefully selecting and controlling the refractive index and thickness of the substrate, the optical element can simultaneously provide the required beam splitting ratio and imaging performance across a wide field-of-view, maintaining high quality without increased complexity.
3Illumination intensity
If display source is offset from combiner to illuminate entire surface, then illumination coverage is improved, but device size and installation space increase
Solution Approach 1:
The display source is integrated directly with the combiner surface rather than being offset. The light-transmissive substrate serves as both the combiner and the mounting platform for the display source, allowing the source to be positioned in the same plane as the combiner surface. This integration eliminates the need for additional installation space while ensuring complete illumination coverage of the combiner surface.
4Volume of moving object
If compact optical design is implemented, then device size is reduced, but eye-motion-box and viewing angle range are limited
Solution Approach 1:
The patent utilizes the third dimension (substrate thickness) to solve the contradiction between compactness and eye-motion accommodation. By optimizing the thickness of the light-transmissive substrate, the design allows sufficient light path length for wide viewing angles and large eye-motion-box while maintaining a compact overall form factor. The substrate thickness provides the necessary optical path without increasing the lateral dimensions of the device.
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, high-quality optical system with a wide field-of-view and large eye-motion-box, reducing the size and weight of displays, enhancing image quality, and allowing for practical implementation in head-mounted and head-up displays, as well as mobile devices like cellular phones.
Implementation Method 1
optical means for coupling light waves into said substrate by total internal reflection
Implementation Method 2
a plurality of partially reflecting surfaces carried by said substrate
Data Source
AI summary
There is provided an optical device, including a light-transmitting substrate having two major surfaces and edges, an optical element (16) for coupling light waves into the substrate by total internal reflexion, and a plurality of partially reflecting surfaces (22a, 22b, 22c) carried by the substrate. The partially reflecting surfaces are parallel to each other and are not parallel to any of the edges of the substrate. At least one of the partially reflecting surfaces (22a, 22b, 22c) does not intersect with at least one of the two major surfaces, and the optical element (16) intersects with at least one of the two major surfaces.