Light-Guide Optical Element Coating for Plate Warp Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods of fabricating light-guide optical elements (LOEs) cause warping due to stress from partially reflective coatings, leading to image quality degradation.
Innovation Solution
Coating opposing surfaces of transparent plates with coatings having similar mechanical properties, such as partially reflective and neutralizing coatings, to balance stress and reduce or eliminate warping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thin film partially reflective coating is applied to one surface of transparent plates, then the light coupling function is achieved, but the plate warps due to stress causing image quality degradation
Solution Approach 1:
The patent applies asymmetric coating distribution by coating only one surface of each transparent plate with the partially reflective coating, while leaving the opposite surface uncoated or with a different coating. This asymmetric approach balances the stress distribution across the plate thickness, preventing warping while maintaining the necessary light coupling function on the coated surface.
Solution Approach 2:
The patent changes the mechanical parameters of the coating system by selecting coating materials and processes that produce comparable stress magnitudes on opposing surfaces. By carefully controlling the stress parameters (thickness, material properties, deposition conditions), the net stress on the plate is minimized, preventing warping while achieving the required optical functionality.
2Illumination intensity
If the thin film coating process is applied to maintain image quality, then the partially reflective function is achieved, but stress is imposed on the plates causing warping
Solution Approach 1:
The patent applies a counterbalancing coating on the opposite surface of the plate to the partially reflective coating. This counter-coating acts as a mechanical counterweight that offsets the stress induced by the partially reflective coating, preventing net warping of the plate while allowing the partially reflective coating to maintain image quality and light coupling functionality.
Solution Approach 2:
The patent modifies the stress parameters by selecting coating materials and process conditions that produce stress magnitudes and distributions which cancel each other out on opposing surfaces. By controlling parameters such as coating thickness, material composition, and deposition stress, the overall plate stress is minimized while maintaining the necessary optical properties.
3Ease of manufacture
If multiple transparent plates are joined to form the waveguide, then the optical element is constructed, but the coating process causes curvature degradation
Solution Approach 1:
The patent segments the waveguide construction into multiple transparent plates, each individually coated and stress-balanced before assembly. By treating each plate as a separate unit with controlled stress distribution, the cumulative curvature effects are minimized, allowing easy manufacturing through simple stacking and bonding of pre-balanced plates.
Solution Approach 2:
The patent applies asymmetric coating strategies to individual plates in the stack, where each plate may have different coating configurations on its two surfaces. This asymmetric approach allows customization of stress distribution for each plate position in the stack, preventing cumulative curvature degradation while maintaining ease of manufacture through modular assembly.
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 method reduces or eliminates plate curvature, maintaining image quality by evenly distributing stress across both surfaces, resulting in a high-quality LOE.
Implementation Method 1
a first coating, which is a partially reflective coating
Implementation Method 2
operates by trapping light waves inside a substrate by total internal reflections from the external surfaces of the waveguide
Data Source
AI summary
A method of fabricating a light-guide optical element having a plurality of partially reflecting surfaces is disclosed. The method includes providing a plurality of transparent plates, each plate polished on two opposite surfaces such that the surfaces are parallel to each other, coating a first of the surfaces of a subset of plates with a first coating, coating a second of the surfaces of the subset of plates with a second coating; bonding together the plurality of transparent plates to form a stack, and cutting the stack along parallel planes obliquely angled to the faces of the transparent plates so as to form the optical element, wherein the first coating is a partially reflective coating have a first set of mechanical properties, and the second coating is selected from the group consisting of: a coating similar to the first coating and a non-reflective coating having a second set of mechanical properties substantially similar to the first set of mechanical properties.