Diffractive Optical Element Absorption Coefficient Design
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Solution Overview
Problem
Existing diffractive optical elements with stacked optical members face challenges in reducing wavelength dependency of diffraction efficiency, limiting the selection of optical materials due to requirements for formability, impact resistance, and transparency, while maintaining high diffraction efficiency.
Innovation Solution
A diffractive optical element is designed with first and second optical members stacked and a diffraction grating formed at their interface, where the absorption coefficient and grating height satisfy specific expressions to achieve high diffraction efficiency across a wide wavelength range, allowing for the use of materials with higher absorption coefficients and expanding the range of optical material selection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a relatively low-refractive high-dispersive optical material and a relatively high-refractive low-dispersive optical material are stacked to reduce wavelength dependency, then wavelength dependency of diffraction efficiency is reduced, but the range of optical material selection is narrowed due to formability, impact resistance, and transparency requirements
Solution Approach 1:
The patent changes the key parameter from refractive index combination to absorption coefficient combination. By specifying that the first optical member has a higher absorption coefficient than the second optical member, the patent enables material selection based on absorption properties rather than refractive index properties, thus expanding the range of usable materials while maintaining wavelength independence of diffraction efficiency
Solution Approach 2:
The patent uses a composite structure of two different optical materials with different absorption coefficients. This composite approach allows combining materials that would not work in traditional designs, such as polycarbonate with higher absorption coefficient paired with materials having lower absorption coefficients, thereby expanding material selection flexibility
2Adaptability or versatility
If optical materials with higher absorption coefficients are used to expand material selection, then the range of optical material selection is expanded, but diffraction efficiency may decrease
Solution Approach 1:
The patent applies local quality by assigning different absorption coefficient characteristics to different parts of the stacked structure. The first optical member with higher absorption coefficient is positioned in a specific location, while the second optical member with lower absorption coefficient occupies another position. This spatial differentiation of absorption properties allows the system to tolerate higher absorption in one region while maintaining overall high diffraction efficiency through the complementary low-absorption region
Solution Approach 2:
The patent converts the potentially harmful effect of light absorption into a beneficial design parameter. By deliberately selecting materials where the first optical member has higher absorption coefficient than the second, the patent transforms what would normally be a loss mechanism into a controllable design variable that enables expanded material selection while maintaining diffraction efficiency through the specific relationship defined in the absorption coefficient ratio
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 maintains high diffraction efficiency and reduces wavelength dependency, enabling the use of non-transparent materials like polycarbonate and expanding the selection of optical materials, thereby improving optical performance and flexibility in material choice.
Implementation Method 1
a diffraction grating is formed at an interface between the first and second optical members
Data Source
AI summary
In a diffractive optical element, first and second optical members are stacked, and a diffraction grating is formed at an interface between the first and second optical members. In the diffractive optical element, an absorption coefficient α (mm−1) of the first optical member and a grating height h (μm) of the diffraction grating satisfy expressions (1) and (2):α≧0.04 (1)h≦263.18×α−0.9454 (2).