Antireflective Optical Element With Porous Layer

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Solution Overview

Problem

Conventional antireflective coatings for optical elements, whether interference-based or gradient refractive index, face limitations in environmental resistance and spectral range, with interference coatings being limited by refractive indices of materials and gradient coatings being fragile and sensitive to external conditions.

Innovation Solution

An optical element with an intermediate coating of alternating dense thin layers and a porous layer extending over the substrate, where the porous layer has a lower refractive index than the dense layers, achieved through oblique angle deposition, providing improved antireflective properties and resistance to environmental conditions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If an interference-based multilayer antireflective coating is used, then resistance to environmental conditions is improved, but the spectral range and antireflective performance are limited by refractive indices of materials

Engineering Contradiction:

Improveresistance to environmental conditionsVSAvoidspectral range

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent applies porous materials by depositing a porous layer on top of the dense multilayer antireflective coating. This porous layer has a refractive index lower than 1.45, which is lower than the refractive indices of the dense layers (1.67 and 2.11). The porous structure enables the coating to achieve broader spectral range antireflective performance while the underlying dense layers maintain environmental resistance.

Inventive Principle:

Principle #31Porous materials

Solution Approach 2:

The patent uses composite materials by combining dense inorganic layers (TiO2 with refractive index 2.11 and SiO2 with refractive index 1.67) with a porous outer layer. This composite structure integrates the environmental durability of dense materials with the optical performance benefits of porous materials having lower refractive index, resolving the contradiction between reliability and adaptability.

Inventive Principle:

Principle #40Composite materials

2Reliability

If a gradient refractive index antireflective coating is used, then antireflective performance is improved, but mechanical strength and resistance to environmental conditions deteriorate

Engineering Contradiction:

Improveantireflective performanceVSAvoidmechanical strength

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The patent applies the nested doll principle by placing a porous layer (which provides excellent antireflective performance) on top of dense multilayer coating (which provides mechanical strength). The dense layers act as a robust substrate that protects the porous outer layer, while the porous layer delivers superior optical performance. This nested structure resolves the contradiction between antireflective performance and mechanical strength.

Inventive Principle:

Principle #7Nested doll (Nesting)

3Reliability

If porous layers are used to achieve gradient refractive index, then antireflective performance is improved, but sensitivity to external conditions increases

Engineering Contradiction:

Improveantireflective performanceVSAvoidsensitivity to external conditions

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent carefully controls the porosity of the outer layer to be between 5% and 70%, optimizing the balance between antireflective performance and environmental resistance. The porous structure provides low refractive index for excellent antireflective properties while the controlled porosity level and underlying dense layers prevent excessive sensitivity to humidity and temperature changes.

Inventive Principle:

Principle #31Porous materials

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 offers enhanced antireflective performance over a wide spectral range while maintaining mechanical strength and resistance to environmental factors, suitable for use in optronic devices and aircraft applications.

Implementation Method 1

the porous layer having a third refractive index, the third refractive index being lower than the first and second refractive indices

Methodology Applied

Scientific EffectRefraction: Refraction

Implementation Method 2

The successive layers 14a, 14b have thicknesses, measured along optical axis A, and refractive indices determined so as to minimize the reflected light intensity by means of a destructive interference phenomenon

Methodology Applied

Scientific EffectInterference: Interference

Implementation Method 3

Such porous layers 24a are for example obtained by methods using glancing angle deposition (abbreviated as GLAD) or oblique angle deposition (abbreviated as OAD)

Methodology Applied

Scientific EffectPhysical Vapour Deposition: Physical Vapour Deposition

Data Source

PatentUS20240427057A1Antireflective optical element

Publication Date: 2024.12.26 SAFRAN ELECTRONICS & DEFENSE (FR)

AI summary

An optical element includesa transparent substrate andan intermediate coating extending over at least one main surface of the substrate. The intermediate coating has a plurality of dense thin layers which alternate in having a first index refractive index and a second refractive index, the first refractive index being greater than the second refractive index.The optical element further includesat least one porous layer extending over the intermediate coating, opposite the substrate. The porous layer has a third refractive index that is lower than the first and second refractive indices.