Optical Filter Stack Layout for Low Cross-Talk Spectral Sensing
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Solution Overview
Problem
Existing hyperspectral optical sensing devices face issues with cross-talk and reduced accuracy due to overlap between filter channels and a small signal-to-noise ratio.
Innovation Solution
The optical sensing device employs a photodetector array with a filter stack comprising lower dielectric mirrors and a spacer stack, forming Fabry-Perot interferometers with different center wavelengths for each filter channel, which reduces cross-talk and enhances spectral sensitivity by creating distinct transmission spectra for each photodetector.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional filter stacks are used in hyperspectral optical sensing devices, then the device can cover a spectral range of several hundreds of nanometers, but cross-talk and overlap between filter channels occur, reducing measurement precision
Solution Approach 1:
The filter stack is segmented into multiple independent Fabry-Perot interferometer units, each with distinct mirror thicknesses and spectral characteristics. This segmentation allows each filter channel to operate independently with minimal overlap, resolving the cross-talk issue while maintaining broad spectral coverage through the combination of multiple channels.
Solution Approach 2:
Different regions of the filter stack are assigned different local qualities through varying mirror thicknesses and material compositions. Each local region (filter channel) is optimized for specific wavelength ranges, creating distinct transmission spectra that minimize overlap. This local differentiation enables precise spectral separation while collectively covering a broad range.
2Adaptability or versatility
If filter channels are designed with overlapping spectral ranges to increase coverage, then the spectral range is extended, but cross-talk between channels increases and signal-to-noise ratio decreases
Solution Approach 1:
The spectral characteristics of each filter channel are controlled by changing key parameters such as mirror thickness, spacer layer dimensions, and material refractive indices. By precisely adjusting these parameters, each channel's transmission spectrum is optimized to achieve minimal overlap with adjacent channels while maintaining continuous spectral coverage, thereby preserving signal-to-noise ratio.
3Measurement precision
If the thickness of lower mirrors is varied to create distinct transmission spectra, then filter channel separation is improved, but manufacturing precision requirements increase
Solution Approach 1:
The lower mirrors are fabricated with predetermined, optimized thickness values during the manufacturing process. These preliminary thickness specifications are carefully calculated to achieve the desired spectral separation. By establishing these parameters in advance through design optimization, the manufacturing process can follow well-defined specifications, reducing the actual precision burden during production while achieving high filter channel separation.
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
This configuration improves the accuracy of signal deconvolution and spectral analysis by minimizing overlap between filter channels, allowing for more precise detection of electromagnetic radiation across a wide range of wavelengths.
Implementation Method 1
forming Fabry-Perot interferometers with different center wavelengths for each filter channel
Implementation Method 2
The filter stack comprises at least two first lower dielectric mirrors and at least two second lower dielectric mirrors
Implementation Method 3
forming Fabry-Perot interferometers with different center wavelengths for each filter channel, which reduces cross-talk and enhances spectral sensitivity
Implementation Method 4
The first photodetector and the second photodetector are capable of detecting electromagnetic radiation hitting the photodetector array and reaching the photodetectors
Data Source
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AI summary
An optical sensing device (10) comprises a photodetector array (11) comprising at least one first photodetector (12) and at least one second photodetector (13), the photodetector array (11) being arranged on a semiconductor substrate (14). The optical sensing device (10) further comprises a filter stack (15) arranged on the substrate (14) and covering the photodetector array (11). The filter stack (15) comprises at least two first lower dielectric mirrors (16) and at least two second lower dielectric mirrors (17), where a first and a second lower mirror (16, 17) are arranged above the first photodetector (12) and a first and a second lower mirror (16, 17) are arranged above the second photodetector (13), and where the first lower mirrors (16) have a different thickness in vertical direction (z) which is perpendicular to the main plane of extension of the substrate (14) than the second lower mirrors (17). The filter stack (15) further comprises a spacer stack (18) arranged on the first and second lower mirrors (16, 17), and an upper dielectric mirror (19) arranged on the spacer stack (18) and covering the photodetector array (11). Furthermore, a method for manufacturing an optical sensing device (10) is provided.