Polarization Interference Filter Structure for Stable Oblique Incidence
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Solution Overview
Problem
Existing band-pass filters lack a novel configuration that effectively transmits light in a specific wavelength range while shielding other wavelengths, particularly when light is incident from oblique directions, leading to wavelength shifts.
Innovation Solution
A polarization interference element comprising birefringent layers with in-plane and thickness-direction periodic structures, where birefringent layers have equal in-plane retardations and intersecting slow axes, and are sandwiched between polarizers in a crossed nicols state, with specific retardation settings to function as a λ/2 plate for a specific wavelength range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional band-pass filters are used, then light transmission in specific wavelength range is achieved, but wavelength shifts occur when light is incident from oblique directions
Solution Approach 1:
The filter is divided into multiple birefringent layers with different optical properties (different retardations and slow axis orientations). Each layer segment contributes to wavelength-selective transmission, and their combined effect creates a robust band-pass characteristic that remains stable for oblique incident light. The segmentation into layers with specific retardation ratios (e.g., 1:2, 1:3) ensures that wavelength shifts are compensated.
Solution Approach 2:
Different regions of the filter (different layers) have locally optimized optical properties. The first birefringent layer has specific retardation and slow axis orientation, while the second layer has different properties (retardation ratio and orthogonal or angled slow axis). This local quality differentiation allows each layer to contribute uniquely to wavelength selection, maintaining stability against oblique incidence.
2Reliability
If dielectric multi-layer films are used for band-pass filtering, then wavelength selectivity is achieved, but the structure becomes complex
Solution Approach 1:
The patent replaces complex dielectric multi-layer film structures with a simpler system based on birefringent layers. Instead of using multiple dielectric layers with precisely controlled thicknesses and refractive indices, the invention uses birefringent materials with controlled retardations and slow axis orientations. This substitution simplifies the manufacturing process while maintaining wavelength-selective transmission.
Solution Approach 2:
The filter uses composite structures of birefringent layers with different optical properties. The first and second birefringent layers are combined in a specific configuration (with retardation ratios and specific slow axis orientations), creating a composite material system that achieves wavelength selectivity through the synergistic effect of the individual layers' birefringence properties.
3Reliability
If polarizer and birefringent crystal combinations are used, then band-pass filtering is achieved, but the number of components increases
Solution Approach 1:
The patent merges the functions of multiple birefringent layers into a unified filter structure. The first and second birefringent layers work together as an integrated system, where their combined optical effects (retardation and slow axis orientation) directly produce band-pass filtering. This merging eliminates the need for separate polarizer and birefringent crystal components, reducing the total number of components while maintaining filtering 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 solution provides a band-pass filter that effectively transmits light in a specific wavelength range and shields other wavelengths, minimizing wavelength shifts even when light is incident from oblique directions, and allows for adjustable bandwidth by varying the number of birefringent layers.
Implementation Method 1
the birefringent layer includes an in-plane periodic structure layer having a periodic structure in which two types of unit layers having different refractive indices are alternately laminated adjacent to each other in an in-plane direction
Implementation Method 2
polarization interference element including two or more birefringent layer sets in a thickness direction
Implementation Method 3
two types of unit layers having different refractive indices are alternately laminated adjacent to each other
Data Source
AI summary
Provided is a novel polarization interference element that can be used for a band-pass filter and the like. The polarization interference element has two or more birefringent layer sets in a thickness direction, each set consisting of two birefringent layers, in which the birefringent layer includes an in-plane periodic structure layer having a periodic structure in which two types of unit layers having different refractive indices are alternately laminated adjacent to each other in an in-plane direction, slow axes of the birefringent layers constituting the birefringent layer set intersect with each other, and in-plane retardations of the two birefringent layers constituting the birefringent layer set are equal to each other.