Polarization interference element and filter
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing band-pass filters experience a shift in wavelength at which maximum transmittance occurs when light is incident from an oblique direction, leading to undesirable spectral changes.
Innovation Solution
A polarization interference element with multiple retardation layer sets, each comprising a first and second retardation layer with specific Nz factors (0.3 to 0.7) and intersecting in-plane slow axes, and controlled in-plane retardations, is arranged between two polarizers to minimize wavelength shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional band-pass filter is used, then light transmission in a specific wavelength range is achieved, but wavelength shift occurs when light is incident from an oblique direction
Solution Approach 1:
The filter is divided into multiple retardation layers (first and second retardation layers) with different Nz factors and in-plane retardations. Each layer segment contributes differently to the overall optical path difference, and their combined effect compensates for wavelength shifts caused by oblique incidence, thereby improving wavelength stability across different incident angles.
Solution Approach 2:
The patent employs parameter changes by setting specific Nz factor ranges (0.1 < |Nz1| < 0.5 and 0.5 < |Nz2| < 0.9) and in-plane retardation values for each retardation layer. By carefully controlling these parameters, the optical path difference becomes less sensitive to incident angle variations, maintaining wavelength stability while allowing broader angular acceptance.
2Manufacturing precision
If the Nz factor and in-plane retardation are optimized for normal incidence, then maximum transmittance is achieved at the design wavelength, but performance degrades for oblique incidence
Solution Approach 1:
The patent introduces asymmetry by using retardation layers with different Nz factors (one with |Nz| < 0.5 and the other with |Nz| > 0.9) rather than identical layers. This asymmetric configuration creates a compensatory effect where the different refractive index characteristics of each layer counterbalance the wavelength shift caused by oblique incidence, extending angular tolerance while maintaining spectral precision.
Solution Approach 2:
The patent adds another dimension to the design by considering not only the in-plane retardation but also the Nz factor (which relates to the thickness-direction refractive index). This multi-dimensional parameter control allows optimization for both normal and oblique incidence by adjusting the combination of in-plane and thickness-direction optical properties.
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 effectively suppresses wavelength shifts when light is incident from an oblique direction, maintaining consistent maximum transmittance and spectral characteristics.
Implementation Method 1
each set consisting of a first retardation layer and a second retardation layer, in which an Nz factor of the first retardation layer and an Nz factor of the second retardation layer are each independently 0.3 to 0.7, an in-plane slow axis of the first retardation layer and an in-plane slow axis of the second retardation layer intersect with each other
Implementation Method 2
polarization interference element including two or more retardation layer sets in a thickness direction
Data Source
AI summary
A polarization interference element that minimizes wavelength shift at maximum transmittance when light is incident at an oblique angle, particularly when used between two polarizers. The polarization interference element includes two or more retardation layer sets arranged in the thickness direction. Each set consists of a first retardation layer and a second retardation layer. The Nz factor for both the first and second retardation layers is independently between 0.3 and 0.7. The in-plane slow axes of the first and second retardation layers intersect, and the in-plane retardation of the first and second retardation layers are equal. The invention further encompasses a filter incorporating this polarization interference element.