Diffractive Optical Element Resin Refractive Index Control
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Solution Overview
Problem
Phase-difference type diffractive optical elements face issues with shape deviation of diffraction gratings due to interaction between resin materials, leading to unwanted diffracted light and reduced diffraction efficiency, especially when the body and optical adjustment layer are composed of resin materials.
Innovation Solution
A diffractive optical element comprising a body made of a first resin with a diffraction grating and an optical adjustment layer made of a second resin, where the refractive index of the first resin is smaller than that of the second resin, and the refractive index dispersion is greater, with a solubility parameter difference between 0.8 and 2.5 cal/cm^3^1/2, and optionally containing inorganic particles, to minimize interaction and maintain optical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the body and optical adjustment layer are composed of resin materials with similar solubility parameters, then the manufacturing process is simplified, but the diffraction grating shape deviates and unwanted diffracted light occurs
Solution Approach 1:
The patent applies parameter changes by controlling the solubility parameter difference between the first resin (body) and second resin (optical adjustment layer) to be within 0.8-2.5 (cal/cm³)¹/². This specific parameter range prevents excessive interaction between materials while maintaining manufacturability, resolving the contradiction between ease of manufacture and grating shape accuracy
Solution Approach 2:
The patent uses composite material principles by combining two different resin materials with controlled solubility parameter differences. The body uses a first resin and the optical adjustment layer uses a second resin with specifically controlled solubility parameter difference, creating a composite structure that maintains both manufacturability and precision
2Reliability
If the refractive index difference between body and optical adjustment layer is increased, then diffraction efficiency improves, but wavelength dependence increases causing uneven color and flares
Solution Approach 1:
The patent applies parameter changes by precisely controlling the refractive index difference between the two resin materials. The refractive index of the first resin is set to be smaller than the second resin, but the difference is controlled to prevent excessive wavelength dependence, thus maintaining high diffraction efficiency while minimizing harmful wavelength effects
Solution Approach 2:
The patent applies local quality by having different refractive indices at different locations (body vs. optical adjustment layer) to optimize diffraction efficiency locally, while the solubility parameter control ensures this local optimization doesn't cause global wavelength dependence problems
3Reliability
If glass is used as the body material, then refractive index control is improved, but micromachining becomes more difficult and mold durability decreases
Solution Approach 1:
The patent applies this principle by using resin materials instead of glass for the body, accepting that resin molds have lower durability than glass molds. This trade-off is acceptable because resin allows easier micromachining and the mold can be replaced more economically than glass molds
Solution Approach 2:
The patent applies parameter changes by selecting resin materials with specific refractive index ranges (first resin: 1.4-1.7, second resin: 1.5-1.8) to achieve adequate refractive index control without the manufacturing difficulties of glass
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 suppresses deformation of the diffraction grating and occurrence of unwanted diffracted light, ensuring good optical characteristics and high diffraction efficiency by controlling the refractive index and solubility interactions between the resin materials.
Implementation Method 1
a diffraction grating for diffracting light is provided on a body
Implementation Method 2
a phase-difference type diffractive optical element in which, in order to reduce the wavelength dependence of diffraction efficiency, a diffraction grating is provided on the surface of a body that is composed of an optical material, the diffraction grating being covered by an optical adjustment layer
Implementation Method 3
refractive indices of the two types of optical materials at the wavelength λ are n1(λ) and n2(λ)
Data Source
AI summary
A diffractive optical element according to the present invention includes: a body 1 being composed of a first optical material containing a first resin, and having a diffraction grating 2 on a surface thereof; and an optical adjustment layer 3 being composed of a second optical material containing a second resin, and provided on the body 1 so as to cover the diffraction grating 2. The first optical material has a refractive index which is smaller than a refractive index of the second optical material; the refractive index of the first optical material has a wavelength dispersion which is greater than a wavelength dispersion of the refractive index of the second optical material; and a difference in solubility parameter between the first resin and the second resin is no less than 0.8 [cal/cm3]1/2 and no more than 2.5 [cal/cm3]1/2.