Hybrid Interference Filter With Absorption Layer for Back-Reflection
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Solution Overview
Problem
Existing interference filters suffer from undesirable back-reflection, which reduces signal-to-noise ratio and spectral accuracy, particularly in optical sensors like image sensors, due to the coupling of transmission and reflection spectra.
Innovation Solution
A hybrid interference filter design incorporating an absorption layer made of optically absorbing materials, such as indium tin oxide (ITO), decouples transmission and reflection spectra by introducing absorption, reducing back-reflection intensity by a factor of five compared to all-dielectric filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an all-dielectric interference filter is used, then transmission and reflection spectra are achieved, but back-reflection increases and signal-to-noise ratio deteriorates
Solution Approach 1:
The patent employs a hybrid filter structure combining dielectric layers with an absorption layer made of optically absorbing material (such as ITO - indium tin oxide). This composite structure allows the filter to achieve both transmission and absorption functions, effectively reducing back-reflection while maintaining signal transmission. The absorption layer is positioned between the dielectric stack and the substrate, creating a multi-functional composite system that addresses the back-reflection problem without sacrificing optical performance.
2Measurement precision
If an interference filter with alternating high and low index layers is used, then wavelength-selective transmission is achieved, but spectral coupling causes back-reflection
Solution Approach 1:
The absorption layer acts as an intermediary element between the dielectric interference stack and the substrate. This intermediate layer absorbs the light that would otherwise be reflected back from the substrate, preventing the harmful back-reflection while allowing the interference filter to maintain its wavelength-selective transmission properties. The absorption layer mediates the interaction between the incident light and the substrate, eliminating the problematic feedback loop.
3Adaptability or versatility
If a short-pass or long-pass filter is used, then wavelength filtering is achieved, but cut-off wavelength region suffers from increased back-reflection
Solution Approach 1:
The absorption layer is strategically positioned and designed to provide localized absorption specifically in the cut-off wavelength region where back-reflection is most problematic. The layer's optical properties are optimized to target the specific wavelength range where the interference filter transitions from transmission to reflection, providing localized suppression of back-reflection without affecting the overall wavelength filtering capability of the filter.
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 hybrid filter design significantly reduces back-reflection, improves signal-to-noise ratio, and minimizes spectral shifts, enhancing performance in optical sensors under various incidence angles.
Implementation Method 1
The at least one absorption layer is comprised of an optically absorbing material which is arranged on the substrate
Implementation Method 2
The filter stack comprises alternating layers of optical coatings with different refractive indices arranged on the substrate
Data Source
AI summary
An interference filter comprises a substrate, a filter stack and at least one absorption layer. The filter stack comprises alternating layers of optical coatings with different refractive indices arranged on the substrate. The at least one absorption layer is comprised of an optically absorbing material which is arranged on the substrate.