Substrate-guide optics field curvature mitigation
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Solution Overview
Problem
Conventional optical modules for head-mounted displays become bulky and impractical as the desired field-of-view increases, suffering from manufacturability issues and sensitive eye-motion-box viewing angles, which limit pupil motion and image quality due to field curvature aberrations.
Innovation Solution
The optical system employs a substrate-guide optical element with a field lens arrangement or a curved electronic display source to mitigate field curvature, expanding the optical aperture and compensating for divergence or convergence of light rays, thereby enhancing image quality and reducing bulkiness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a conventional free-space optical module is used, then the system can achieve a moderate field-of-view, but the system becomes larger, heavier and bulkier
Solution Approach 1:
The patent embeds multiple optical functions (collimating, field curvature correction, beam expansion, combining) within a single integrated substrate-guide optical element. The substrate acts as a waveguide that contains and directs light through multiple internal reflecting surfaces, nesting what would traditionally be separate optical components into one compact unit, thereby achieving moderate FOV without increasing overall module size
Solution Approach 2:
The patent transitions from conventional free-space optics to substrate-guided optics, utilizing the substrate thickness dimension as an additional optical path. Light is coupled into the substrate and guided through internal reflections between the front and back surfaces, effectively using the z-dimension (substrate thickness) to achieve optical path length and functionality without increasing the x-y plane footprint
2Device complexity
If a flat electronic display source is used with collimating optics, then the system structure is simple, but field curvature aberration degrades image quality
Solution Approach 1:
The patent introduces a field lens as an intermediary optical element positioned between the flat electronic display source and the collimating optics. This field lens acts as a mediator that pre-corrects the field curvature aberration before light enters the collimating system, enabling the use of a simple flat display source while maintaining high image quality without complex curved display structures
3Volume of stationary object
If compact optical solutions are implemented, then the system size is reduced, but the eye-motion-box becomes very small and the system becomes sensitive to eye movements
Solution Approach 1:
The patent implements a beam expansion function within the substrate-guide optical element that dynamically adapts the optical aperture size. The expansion optics magnify the effective aperture at the eye plane relative to the input aperture, creating a larger eye-motion-box that tolerates pupil movements while maintaining compact physical dimensions. This dynamic aperture multiplication allows the system to be both compact and tolerant of eye movements
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 effectively mitigates field curvature aberrations, expanding the optical aperture and improving image quality while maintaining compactness, allowing for a larger field-of-view and more comfortable reading experiences in head-mounted displays.
Implementation Method 1
a coupling-in optical arrangement for coupling light waves emanating from the electronic display source into the light-transmitting substrate to effect total internal reflection of the coupled-in light waves between the major external surfaces of the light-transmitting substrate
Data Source
AI summary
A light-transmitting substrate has at least a first and a second major external surface. An electronic display source emanates light waves. A coupling-in optical arrangement couples light waves from the electronic display source into the light-transmitting substrate to effect total internal reflection of the coupled-in light waves between the major external surfaces of the light-transmitting substrate. An optical element is deployed in an optical path for light waves to traverse from the electronic display source into the light-transmitting substrate. The optical element defines a field curvature that causes light rays of the traversing light waves to diverge or converge. A lens is deployed in the optical path and reduces the field curvature. The electronic display source has a curvature that is matched to the reduced field curvature to counteract the divergence or convergence of the light rays caused by the reduced field curvature.