Light-Guide Optical Element Using Structural Polarizers
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing light-guide optical elements for display systems, particularly in near-eye displays for virtual and augmented reality, face challenges in efficiently coupling out light energy due to sensitivity to polarization and angle, leading to non-uniform illumination and reduced light extraction efficiency.
Innovation Solution
A light-guide optical element comprising a transparent substrate with parallel major external surfaces and a plurality of mutually parallel internal surfaces, where at least part of each internal surface is equipped with a structural polarizer having a primary polarization transmission axis. The structural polarizer is substantially transparent to light polarized parallel to the primary axis and partially reflective to light polarized perpendicular to it, with the polarization axis rotated between successive internal surfaces to manage light coupling and polarization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If dielectric coatings are used to generate desired reflectivity pattern on internal surfaces, then reflectivity control is achieved, but polarization sensitivity causes non-uniform illumination
Solution Approach 1:
The patent changes the polarization state parameter of light by introducing a quarter-wave plate that converts linearly polarized light to circularly polarized light. This parameter transformation allows the light to maintain consistent reflectivity across multiple internal reflections despite the polarization-sensitive nature of dielectric coatings, thereby achieving uniform illumination.
Solution Approach 2:
The quarter-wave plate acts as an intermediary optical element inserted between the light source and the internal reflection surfaces. This mediator transforms the polarization state of light before it enters the waveguide, enabling the light to interact uniformly with the dielectric coatings on internal surfaces without suffering from polarization-induced non-uniformity.
2Ease of operation
If light propagates by total internal reflection at external surfaces, then light guidance is achieved, but phase change between polarizations alters light orientation
Solution Approach 1:
The quarter-wave plate changes the polarization parameter from linear to circular, which is invariant under the phase changes induced by total internal reflection. Circularly polarized light maintains its state composition even when subjected to differential phase shifts between S and P polarizations during internal reflection, thus stabilizing the polarization orientation.
3Productivity
If structural polarizers are used at internal surfaces to control light coupling, then light extraction efficiency is improved, but device complexity increases
Solution Approach 1:
The structural polarizers are applied locally only at specific internal reflection surfaces where light extraction is needed, rather than throughout the entire waveguide. This localized application enables efficient light coupling at critical points while minimizing the overall complexity and material usage of the optical element.
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
This configuration enhances light extraction efficiency and illumination uniformity by controlling the polarization and coupling out of light energy at each facet, improving the overall performance of display systems, particularly in near-eye displays.
Implementation Method 1
at least part of each of the internal surfaces comprising a structural polarizer having a primary polarization transmission axis, the structural polarizer being substantially transparent to light polarized parallel to the primary polarization transmission axis and being at least partially reflective to light polarized perpendicular to the primary polarization transmission axis
Implementation Method 2
a transparent substrate having at least two parallel major external surfaces for guiding light within the substrate by internal reflection at the external surfaces
Data Source
AI summary
A light-guide optical element (LOE) includes a transparent substrate having two parallel major external surfaces for guiding light within the substrate by total internal reflection (TIR). Mutually parallel internal surfaces within the LOE are provided with a structural polarizer which is transparent to light polarized parallel to a primary polarization transmission axis, and is partially or fully reflective to light polarized perpendicular to the primary polarization transmission axis. By suitable orientation of the polarization axis of successive internal surfaces together with the polarization mixing properties of TIR and/or use of birefringent materials, it is possible to achieve the desired proportion of coupling-out of the image illumination from each successive facet.