Half Mirror Optical Element with Dielectric Multilayer Films
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Solution Overview
Problem
Existing half mirrors in head-mounted displays suffer from significant light loss due to chrome layers and degradation of optical characteristics due to moisture and organic components from resin substrates, leading to poor adhesion and diffusion of silver particles.
Innovation Solution
A half mirror optical element is designed with a silver film sandwiched between first and second dielectric multilayer films, where the first dielectric multilayer includes aluminum oxide and titanium oxide, and the second dielectric multilayer includes zirconium oxide, preventing moisture and organic component desorption and enhancing optical stability on a resin substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a chrome layer is formed as a base layer for a silver layer to improve adhesion, then adhesion property is improved, but light quantity loss increases
Solution Approach 1:
The patent removes the chrome base layer from the silver layer structure, extracting the harmful element that caused light absorption while maintaining adhesion through alternative means (direct deposition on substrate or use of adhesion promoters that are optically transparent)
Solution Approach 2:
The patent introduces an adhesion promoter layer or modifies the substrate surface to serve as an intermediary between the silver layer and substrate, providing both adhesion and optical transparency, thus avoiding the light-absorbing chrome layer
2Weight of moving object
If a resin substrate is used to reduce weight and increase shape freedom, then weight is reduced and shape freedom is increased, but optical characteristics are degraded due to moisture and organic component desorption
Solution Approach 1:
The patent introduces barrier layers (such as inorganic oxide layers like silicon oxide, aluminum oxide, or magnesium fluoride) as intermediaries between the resin substrate and the silver layer, which prevent moisture and organic components from reaching the silver layer while allowing the resin substrate to maintain its weight and shape advantages
Solution Approach 2:
The patent applies preliminary protective measures by forming barrier layers on the resin substrate before depositing the silver layer, preventing the harmful effects of moisture and organic component desorption from occurring in the first place
3Reliability
If the silver layer is made thicker to improve stability and reduce adsorption loss, then adhesion and stability are improved, but absorption and scattering of light increase when directly on titanium oxide
Solution Approach 1:
The patent introduces an aluminum oxide layer as an intermediary between the titanium oxide layer and the silver layer, which reduces light absorption and scattering by the silver layer while allowing the silver layer to maintain its thickness for stability and adhesion
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 reduces light absorption and scattering, maintains optical quality, and allows for stable film formation with a thicker silver layer, offering improved adhesion and spectral characteristics while preventing moisture-induced degradation.
Implementation Method 1
a titanium oxide film is used for a high refractive index film being provided on the first dielectric multilayer film (lower layer side of the silver film), so a film can be formed at a relatively low temperature by an ion assisted method with such titanium oxide film
Implementation Method 2
absorption and scattering of light on the silver film can be suppressed because the first aluminum oxide film is provided between the titanium oxide film and the silver film
Implementation Method 3
the zirconium oxide-based dielectric film or the second aluminum oxide film can be formed as a dense film, so such films can be used to block moisture and degradation of optical characteristics of the half mirror caused due to a reaction with the moisture of the silver film can be suppressed
Data Source
AI summary
An optical element includes a first translucent member that contains a resin material and a half mirror film formed on a surface of the first translucent member. The half mirror film includes a silver film, a first dielectric multilayer film positioned between the silver film and the first translucent member, and a second dielectric multilayer film positioned on an opposite side of the silver film than the first translucent member. The first dielectric multilayer film includes a first aluminum oxide film in contact with the silver film, and a titanium oxide film in contact with the first aluminum oxide film on the first translucent member. The second dielectric multilayer film includes a zirconium oxide-based dielectric film and a second aluminum oxide film in contact with the zirconium oxide-based dielectric film. One of the second aluminum oxide film and the zirconium oxide-based dielectric film is in contact with the silver film.