Fabry-Perot Optical Filter with Bragg Reflectors for Compact Spectrometers
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Solution Overview
Problem
Conventional spectrometers are bulky and heavy, necessitating a reduction in size through the integration of optical devices and circuits on semiconductor chips, while existing optical filters struggle to efficiently transmit specific wavelength bands with adjustable bandwidths and reduced angle dependency.
Innovation Solution
The development of optical filters with a Fabry-Perot structure, featuring Bragg reflective layers with three or more material layers of different refractive indices and a cavity layer thicker than λ/n, allowing for adjustable wavelength band transmission and reduced angle dependency, combined with color or wideband filters to ensure precise wavelength selection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If conventional spectrometer designs are used, then optical measurement capability is achieved, but device size becomes bulky and heavy
Solution Approach 1:
The patent integrates multiple optical components (light source, optical filter array, sensor array) onto a single semiconductor substrate, merging previously separate optical components into one unified device. This integration directly reduces the overall spectrometer volume while maintaining full optical measurement functionality through the combined structure.
Solution Approach 2:
The patent transitions from traditional bulk optical components to planar integrated optical structures on a semiconductor substrate. By arranging optical filters and sensors in two-dimensional arrays on the substrate surface, the design achieves miniaturization while preserving measurement capabilities through spatial multiplexing in the planar dimension.
2Measurement precision
If optical filters with narrow bandwidth are used, then wavelength selection precision is improved, but transmission efficiency decreases
Solution Approach 1:
The patent employs Fabry-Perot resonant cavity filters where the transmission bandwidth and center wavelength are precisely controlled by adjusting the cavity thickness and refractive index of dielectric layers. This parameter tuning capability allows optimization of both wavelength precision and transmission efficiency by selecting appropriate cavity dimensions and material properties.
Solution Approach 2:
The optical filters utilize composite dielectric mirror structures with alternating high and low refractive index layers. This composite material design enables precise control of reflectivity and transmission characteristics, achieving narrow bandwidth filtering with high transmission efficiency at the resonant wavelength through constructive interference in the cavity.
3Device complexity
If simple Fabry-Perot filters are used, then device complexity is reduced, but angle dependency of transmission increases
Solution Approach 1:
The patent uses composite dielectric mirror structures with multiple alternating refractive index layers in the Fabry-Perot filters. This composite design increases the reflectivity bandwidth and reduces the angular sensitivity of the resonant condition, thereby decreasing angle dependency while maintaining the relatively simple overall filter structure.
Solution Approach 2:
The optical filter array segments the spectrum into multiple wavelength channels using independent Fabry-Perot filters, each with controlled transmission characteristics. This segmentation approach allows each filter element to be optimized for minimal angle dependency while the array collectively provides comprehensive spectral coverage.
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 solution enables the creation of compact spectrometers with improved spectroscopy performance by ensuring accurate transmission of desired wavelength bands, even at various angles, and enhances the integration of optical filters with semiconductor technology.
Implementation Method 1
a first Bragg reflective layer and a second Bragg reflective layer
Implementation Method 2
Optical filters based on resonant cavities are for example known from US 5 726 805 A or US 2018/335557 A1
Implementation Method 3
a plurality of bandpass filters arranged in a two-dimensional array pattern on the semiconductor substrate
Data Source
Figure 1
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AI summary
Provided is an optical filter including a plurality of bandpass filters having center wavelengths of light that are different from one another, wherein each of the plurality of bandpass filters includes a cavity layer, a first Bragg reflective layer provided on an upper surface of the cavity layer, and a second Bragg reflective layer provided on a lower surface of the cavity layer opposite to the upper surface, wherein the cavity layer has a thickness greater than λ/n, where A is a center wavelength of light of each of the bandpass filters and n is an effective refractive index of the cavity layer, and wherein each of the first Bragg reflective layer and the second Bragg reflective layer includes three or more material layers having different refractive indices from one another.