Diffractive Optical Element Film Refractive Index Control
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Solution Overview
Problem
Diffractive optical elements with films on grating surfaces face increased light reflectance, leading to issues like flare and ghost effects, which affect diffraction efficiency and image quality.
Innovation Solution
A diffractive optical element design that includes a first and second diffraction grating with films between them, where the refractive indices and thicknesses of the films are carefully controlled to satisfy specific conditional expressions, reducing reflectance and phase aberration, thereby improving diffraction efficiency and minimizing flare and ghost effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If films are formed on grating surfaces to obtain diffractive optical element at low cost, then manufacturing cost is reduced, but light reflectance of each grating surface increases
Solution Approach 1:
The patent applies local quality by differentiating the treatment of films on different surfaces. The conditional expressions control the refractive index and thickness of films specifically on grating wall surfaces versus grating surfaces, allowing optimized local properties to reduce reflectance on grating surfaces while maintaining waveguide functionality on grating wall surfaces
Solution Approach 2:
The patent uses parameter changes by precisely controlling the refractive index and thickness parameters of the films. The conditional expressions (nha−n1)×dha≤0.05 and (nsa−n1)×dsa≤0.05 establish specific parameter ranges that minimize reflectance while preserving the waveguide effect, transforming the film properties to resolve the contradiction
2Reliability
If films are formed on grating surfaces, then waveguide effect is achieved improving diffraction efficiency, but phase aberration increases
Solution Approach 1:
The patent applies local quality by restricting the waveguide film formation primarily to grating wall surfaces through controlled refractive index and thickness parameters. This localized approach maintains the necessary waveguide effect for diffraction efficiency while minimizing film presence on grating surfaces that would cause phase aberration
Solution Approach 2:
The patent uses the film parameters as intermediaries to balance two competing requirements. By adjusting refractive index and thickness within specific ranges, the films act as a mediator that provides waveguide functionality while controlling their impact on phase aberration
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 controlled refractive indices and thicknesses of the films between the diffraction gratings reduce reflectance and enhance diffraction efficiency, leading to improved image quality by minimizing flare and ghost effects across a wide wavelength range.
Implementation Method 1
diffractive optical element including a first diffraction grating, a second diffraction grating
Implementation Method 2
nha is an average refractive index of parts of the film that are formed between a grating wall surface of the first diffraction grating and a grating wall surface of the second diffraction grating
Implementation Method 3
the diffractive optical element including the films on the grating surfaces carries a risk of an increase in the light reflectance of each grating surface
Data Source
AI summary
A diffractive optical element 10 includes a first diffraction grating 4, a second diffraction grating 5, films 6 formed between the first diffraction grating 4 and the second diffraction grating 5. The DOE 10 satisfies a conditional expression of n2<n1<nha, where nha is an average refractive index of films 6b formed between grating wall surfaces 4b and grating wall surfaces 5b at a wavelength of 550 nm, n1 is a refractive index of the first diffraction grating 4 at a wavelength of 550 nm, and n2 is a refractive index of the second diffraction grating 5 at a wavelength of 550 nm. The films 6b and films 6a that are formed between grating surfaces 4a and grating surfaces 5a satisfy a predetermined relationship.