Gradient Optical Elements via Ionic Liquid Diffusion

Solution Overview

Problem

Current photopolymer systems for producing optical elements with gradient structures face limitations in sensitivity, resolution, and refractive index modulation, leading to restricted thickness and mechanical flexibility, and are prone to high shrinkage and energy-intensive illumination processes.

Innovation Solution

A process involving the mixing of polymerizable monomers with ionic liquids to generate a refractive index gradient through directed diffusion initiated by a potential difference, achieved via local polymerization or polycondensation, allowing for sharper and more precise refractive index modulation with reduced shrinkage and improved durability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If free-radical polymerization is used to produce photopolymers, then the refractive index gradient can be formed, but severe shrinkage occurs and the material thickness is restricted to up to 150 μm

Engineering Contradiction:

Improverefractive index gradientVSAvoidmaterial thickness

Core Design Contradiction:

Manufacturing precisionVSLength of moving object

Solution Approach 1:

The patent changes the polymerization mechanism from free-radical to cationic polymerization, which fundamentally alters the reaction parameters and results in minimal shrinkage while maintaining the ability to form refractive index gradients through monomer diffusion during the polymerization process

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention uses a composite system consisting of monomers dispersed in a polymer matrix, where the matrix provides structural support and the monomers provide the refractive index modulation capability. This composite approach allows for greater design flexibility and reduced shrinkage compared to pure photopolymer systems

Inventive Principle:

Principle #40Composite materials

2Manufacturing precision

If free-radical polymerization is used, then the gradient structure can be formed, but high shrinkage occurs in the illuminated regions

Engineering Contradiction:

Improvegradient structureVSAvoidshrinkage

Core Design Contradiction:

Manufacturing precisionVSLoss of substance

Solution Approach 1:

The patent changes the polymerization mechanism from free-radical to cationic polymerization, which fundamentally alters the reaction parameters and results in minimal shrinkage while maintaining the ability to form refractive index gradients through monomer diffusion during the polymerization process

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention uses a two-step process where first a matrix structure is created, then monomers are introduced and polymerized to create the gradient structure. This copying approach allows the gradient to form without the shrinkage issues of direct polymerization

Inventive Principle:

Principle #26Copying

3Loss of substance

If epoxides are used as monomers to reduce shrinkage, then shrinkage is reduced, but higher energy is required for writing the optical information

Engineering Contradiction:

ImproveshrinkageVSAvoidillumination energy

Core Design Contradiction:

Loss of substanceVSUse of energy by moving object

Solution Approach 1:

The patent changes the polymerization mechanism from free-radical to cationic polymerization, which fundamentally alters the reaction parameters and results in minimal shrinkage while maintaining the ability to form refractive index gradients through monomer diffusion during the polymerization process

Inventive Principle:

Principle #35Parameter changes

4Loss of substance

If cationically polymerizable monomers are used, then shrinkage is reduced, but the material has to be illuminated twice with different wavelengths

Engineering Contradiction:

ImproveshrinkageVSAvoidillumination process

Core Design Contradiction:

Loss of substanceVSDevice complexity

Solution Approach 1:

The patent changes the polymerization mechanism from free-radical to cationic polymerization, which fundamentally alters the reaction parameters and results in minimal shrinkage while maintaining the ability to form refractive index gradients through monomer diffusion during the polymerization process

Inventive Principle:

Principle #35Parameter changes

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 approach enables the production of optical elements with significantly improved refractive index gradients, increased flexibility, and reduced shrinkage, enabling the creation of both thin and thick optical elements with enhanced stability and optical properties.

Implementation Method 1

the diffusion of monomers having an increased or reduced refractive index compared to a surrounding liquid matrix can be used for producing a refractive index gradient

Methodology Applied

Scientific EffectDiffusion: Diffusion

Implementation Method 2

This effect, which is known in the case of polymers as the Colburn-Haines effect, can lead after subsequent polymerization to a product having a refractive index gradient

Methodology Applied

Scientific EffectPhotopolymerization: Photopolymerisation

Data Source

PatentUS8389592B2Optical elements with gradient structure

Publication Date: 2013.03.05 LEIBNIZ INSTITUT FUR NEUE MATERIALIEN GMBH

AI summary

Optical elements, in particular for holographic applications, have a gradient structure formed by a refractive index gradient and include one or more organic polymers and at least one ionic liquid.