Interferential Multilayer Coating for Sunglasses
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Solution Overview
Problem
Conventional mirror coatings on sunglasses exhibit high backward reflection of visible light at high incident angles, which can be annoying for wearers, while maintaining high forward reflection at low incident angles is desirable, and existing solutions face challenges in controlling the thickness of metal layers for effective light transmission.
Innovation Solution
An optical article with an interferential multilayer coating comprising a stack of high refractive index and low refractive index materials, specifically designed to provide high reflective properties at low incident angles and antireflective properties at high incident angles, with a mean visible light reflection factor of less than or equal to 2.5% at angles between 35° and 55°, and higher than or equal to 2.5% at angles between 0° and 15°.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional mirror coatings are used to achieve high forward reflection at low incident angles, then the fashion aspect and forward reflection are improved, but backward reflection at high incident angles increases causing visual discomfort
Solution Approach 1:
The mirror coating is segmented into multiple thin layers with alternating high and low refractive indices. This segmentation allows different layers to handle different functions: some layers reflect light at low incident angles while other layers transmit light at high incident angles, thereby resolving the contradiction between forward reflection and backward reflection
Solution Approach 2:
The coating structure is designed with local quality variations where specific layers have optimized refractive indices and thicknesses to provide high reflection at low incident angles while maintaining high transmission at high incident angles. This local optimization allows the coating to exhibit different optical properties for different incident angles
2Loss of energy
If metal layers are made thinner to improve light transmission, then visual comfort is improved, but manufacturing precision and control become difficult
Solution Approach 1:
The invention changes the material parameters by using dielectric materials with high refractive indices (such as TiO2, Ta2O5, Nb2O5, SiN) instead of metal materials. This parameter change allows achieving the desired optical properties with thicker, more controllable layers that are easier to manufacture with conventional techniques
Solution Approach 2:
The coating uses composite structures with multiple dielectric layers of different refractive indices. This composite approach replaces the need for very thin metal layers with a multi-layer dielectric stack that provides equivalent or superior optical performance while being much easier to control during manufacturing
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 reduces backward reflection at high incident angles, improving visual comfort for wearers while maintaining the fashion aspect of mirror coatings, with specific embodiments achieving reflection factor ratios that enhance performance.
Implementation Method 1
an interferential multilayer coating comprising a stack of at least one layer of high refractive index material and at least one layer of low refractive index material
Implementation Method 2
comprising a stack of at least one layer of high refractive index material having a refractive index higher than 1.55 and at least one layer of low refractive index material having a refractive index of 1.55 or less
Data Source
AI summary
This optical article has a back face on the side of a wearer's eye, a front face opposite to the back face and, on at least one of the front and back faces, an interferential multilayer coating comprising a stack of at least one layer of high refractive index material having a refractive index higher than 1.55 and at least one layer of low refractive index material having a refractive index of 1.55 or less, the refractive indexes being expressed for a wavelength of 550 nm. The optical article is designed in such a manner that it has high reflective properties for low incident angles when viewing the article from its front or back face and antireflective properties for high incident angles when viewing the article from its front or back face.