Bandpass Filter Stack for Zero Angle-Induced Wavelength Shift
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Solution Overview
Problem
Optical filters experience performance degradation due to angle of incidence (AOI) changes, leading to shifts in band edges and inaccurate measurements, especially at high angles, causing noise and measurement errors in optical systems.
Innovation Solution
An optical filter assembly with a thickness greater than a threshold value and a layer structure of alternating high and low refractive index materials, designed to minimize center wavelength shift to less than a second threshold value for angles up to 30 degrees, ensuring minimal angle shift and stable passband performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional optical filter is used, then the filter can be manufactured with standard thickness, but the center wavelength shifts significantly (blue shift) when the angle of incidence deviates from the configured angle
Solution Approach 1:
The patent changes the thickness parameter of the optical filter from standard thickness to a specific range (greater than first threshold and less than second threshold). This parameter change fundamentally alters the filter's angular response characteristics, transforming it from one that exhibits significant blue shift at high angles to one that maintains stable center wavelength across a wide angle range (0 to at least 30 degrees).
Solution Approach 2:
The patent employs a composite layer structure consisting of alternating layers of first and second materials with different refractive indices. This composite structure, combined with the specific thickness requirement, creates an optical filter that compensates for angular deviations and maintains wavelength stability, directly addressing the harmful effect of angle sensitivity.
2Measurement precision
If the optical filter thickness is increased to reduce angle shift, then center wavelength stability improves, but the filter becomes more complex and harder to manufacture
Solution Approach 1:
The patent defines a specific thickness range for the optical filter (greater than first threshold value and less than second threshold value). This precise parameter specification optimizes the balance between achieving adequate angle shift compensation and avoiding excessive thickness that would increase manufacturing complexity. The solution is not simply to make the filter thicker, but to optimize the thickness within defined boundaries.
3Measurement precision
If the optical filter is designed for narrow bandwidth, then spectral selectivity improves, but the filter becomes more sensitive to angle of incidence changes
Solution Approach 1:
The patent applies a specific thickness range to the optical filter that simultaneously achieves narrow bandwidth operation and reduced angular sensitivity. This parameter optimization allows the filter to maintain spectral selectivity while being less sensitive to angle of incidence variations, resolving the typical trade-off between these two performance characteristics.
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 improved measurement accuracy, reduced noise, and enhanced signal-to-noise ratio by minimizing angle-induced shifts, enabling energy-efficient and high-performance optical systems.
Implementation Method 1
a filter stack of alternating layers of a first material with a first refractive index and a second material with a second refractive index
Data Source
AI summary
In some implementations, an optical filter assembly includes an optical filter disposed on a first side of a substrate, wherein the optical filter has a thickness greater than a first threshold value, and wherein the optical filter is configured to experience a center wavelength shift of less than a second threshold value for a particular operating center wavelength and for a range of angles of incidence from 0 degrees to at least a third threshold value.