Blazed Diffractive Optical Element Interlayer Ghosting
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Solution Overview
Problem
Existing blazed diffractive optical elements suffer from ghosting issues due to direct lamination of blazed members, which leads to unwanted refraction and total reflection effects, affecting optical performance.
Innovation Solution
Incorporating an interlayer with a refractive index between the blazed members, where the refractive index of the first blazed member is higher than the interlayer, and the interlayer's refractive index is higher than the second blazed member, along with a specific grating height and thickness configuration to suppress ghosting by controlling the critical angle and refractive indices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a first blazed member and a second blazed member are directly laminated, then the device complexity is reduced, but ghosting occurs due to unwanted refraction and total reflection effects
Solution Approach 1:
An interlayer with refractive index N is introduced between the first blazed member (refractive index Na) and the second blazed member (refractive index Nb), where Na > N > Nb. This intermediary layer prevents direct contact between the blazed members, eliminating total reflection at their interface and reducing unwanted refraction effects that cause ghosting.
Solution Approach 2:
The refractive index of the interlayer is specifically designed to be intermediate between the refractive indices of the two blazed members. By controlling this parameter (Na > N > Nb), the optical path of light is optimized to prevent total internal reflection while maintaining diffraction functionality.
2Reliability
If the interlayer thickness is increased to suppress ghosting, then the optical performance is improved, but the device length increases
Solution Approach 1:
The interlayer thickness t is designed to satisfy h > t·tanθc, where h is the grating height and θc is the critical angle. This partial thickness is sufficient to prevent total reflection and suppress ghosting, without unnecessarily increasing the device length. The condition provides the minimum required thickness for optimal performance.
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 interlayer configuration effectively reduces ghosting by increasing the distance light travels before refraction and minimizing total reflection, enhancing the optical performance of the blazed diffractive optical element.
Implementation Method 1
the plurality of diffraction gratings includes: a first combination part including two diffraction gratings made of materials M1A and M1B different from each other in which grating side surfaces of grating parts contact with each other or are disposed close to each other in a grating pitch direction
Implementation Method 2
the values of refractive indices N1Aw and N1Bw of the materials M1A and M1B forming the first combination part at a wavelength (w) (nm), Abbe numbers v1A and v1B of the materials M1A and M1B
Data Source
AI summary
A blazed diffractive optical element includes: a blazed diffraction grating pair that includes a first blazed member and a second blazed member and functions as a diffraction grating with the first blazed member and the second blazed member; and an interlayer that is positioned between the first blazed member and the second blazed member, in which in a case where a refractive index of the first blazed member is represented by Na, a refractive index of the interlayer is represented by N, and a refractive index of the second blazed member is represented by Nb, a magnitude relationship of Na>N>Nb is satisfied.