Lightguide Display Recirculation for Brighter Uniform Image Output
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Solution Overview
Problem
Existing lightguide-based displays suffer from significant light loss at the extremities, leading to reduced efficiency and brightness due to the use of low-reflectivity coupling-out arrangements to minimize disturbance, resulting in a non-uniform image output.
Innovation Solution
The implementation of a stacked lightguide configuration with reflective coupling configurations and planar mirrors to recirculate light within the lightguide system, either through a second lightguide or by polarization management, ensuring that light is reintroduced and propagated in a reversed direction to enhance brightness and uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If low-reflectivity coupling-out arrangements are used to minimize disturbance to the scene viewed by the observer, then the observer's view of the real world is preserved, but significant light loss occurs at the extremities of the lightguide resulting in reduced efficiency and image brightness
Solution Approach 1:
The patent implements light recirculation to maintain continuous useful action. Light that would otherwise be lost at the extremities is reflected back into the lightguide by mirrors and recirculated through the coupling-out arrangement multiple times, allowing the useful light to continue interacting with the observer repeatedly rather than being discarded after a single pass.
Solution Approach 2:
The patent applies discarding and recovering by capturing light that would be discarded at the lightguide extremities. Mirrors positioned at the ends reflect this light back into the lightguide, where it is recovered and recirculated through the coupling-out arrangement, transforming what would be waste light into useful illumination.
2Object-affected harmful factors
If low-reflectivity coupling-out arrangements are used, then the scene viewed by the observer is minimally disturbed, but image brightness and uniformity are reduced
Solution Approach 1:
The recirculation system ensures continuous useful action by maintaining light in the optical path for multiple passes. The mirrors reflect light back into the lightguide, allowing the coupling-out arrangement to repeatedly extract light toward the observer, thereby maintaining high image brightness without increasing the reflectivity of the coupling-out surfaces.
3Productivity
If light is recirculated through the lightguide system, then overall efficiency and brightness are increased, but the system complexity increases with additional mirrors and stacked lightguide configuration
Solution Approach 1:
The patent resolves the complexity issue by transitioning to another dimension - using a stacked configuration of multiple lightguides rather than complicating a single lightguide. This vertical stacking approach allows light recirculation to occur in a different spatial dimension, managing complexity through dimensional expansion rather than increasing the complexity of individual components.
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 recirculation of light within the lightguide system increases overall efficiency and brightness, allowing for enhanced image delivery with improved uniformity and reduced loss, particularly in augmented reality displays and other applications.
Implementation Method 1
a first lightguide comprising a block of transparent material having two mutually-parallel major surfaces for supporting propagation of image light by internal reflection at the major surfaces
Implementation Method 2
the lightguide containing at least one set of internal mutually-parallel partially-reflecting surfaces obliquely angled to the major surfaces so as to progressively couple-out part of the image light propagating in a first direction
Implementation Method 3
a first reflective coupling configuration comprising at least one planar mirror, the first reflective coupling configuration deployed to reflect the image light transmitted by the set of partially-reflecting surfaces and propagating in the first lightguide in the first direction so as to propagate within the second lightguide in a second direction having a reversed in-plane component from the first direction
Data Source
AI summary
A display includes a lightguide arrangement in which at least part of the image light is not coupled-out from the lightguide during a first pass of a coupling-out arrangement, and is recirculated so as to pass repeatedly the coupling-out arrangement. In one set of embodiments, recirculation of light is performed via a separate lightguide. In another set of embodiments, light is recirculated within a single lightguide, employing polarization management to avoid unwanted interactions between the light and the coupling-out arrangement.