Infrared Detector Window Integrating Diffraction Grating
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Solution Overview
Problem
Current infrared detectors face challenges in achieving low defectivity and cost-effective manufacturing of optical filters with strict spectral transmission specifications, particularly due to the high cost and variability of multilayer interference filters, and the limited optimization potential of micro-structured gratings.
Innovation Solution
The combination of an interference multilayer filter on one face of the window with a diffractive grating on the other face, using standard manufacturing techniques like photolithography and dry etching, to control the spectral properties and reduce defects, allowing for high-pass filtering and improved reproducibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multilayer interference filters are used to control spectral transmission, then spectral filtering performance is improved, but manufacturing cost and defectivity increase
Solution Approach 1:
The filter is divided into two distinct parts: a planar multilayer interference filter for spectral filtering and a micro-structured diffraction grating for spatial separation. This segmentation allows each component to be optimized independently - the interference filter for spectral control and the grating for spatial filtering, reducing overall manufacturing complexity and cost while maintaining performance
Solution Approach 2:
A diffraction grating is introduced as an intermediary element between the interference filter and the detector. This grating mediates the optical path by spatially separating wavelengths, allowing the interference filter to operate at relaxed spectral specifications while achieving the same effective filtering result through the combination of spectral and spatial filtering
2Reliability
If filter thickness is reduced to decrease defects, then defect density is improved, but spectral transmission control deteriorates
Solution Approach 1:
The solution transitions from relying solely on thickness control in the vertical dimension to utilizing spatial dimensionality through the diffraction grating. The grating's periodic structure in the lateral dimension provides spectral filtering capability, allowing the interference filter layers to be thinner with fewer defects while maintaining spectral control through the combined spectral-spatial filtering mechanism
3Volume of moving object
If miniaturization of detector is pursued, then detector dimensions are improved, but filter defect specifications become more stringent
Solution Approach 1:
By segmenting the filtering function into spectral filtering (interference filter) and spatial filtering (diffraction grating), the system achieves effective filtering with reduced sensitivity to filter defects. This allows detector miniaturization without proportionally increasing filter defect stringency, as the grating provides robust spatial filtering that compensates for filter imperfections
Solution Approach 2:
The invention changes the filtering parameters from relying exclusively on spectral parameters (filter thickness, layer indices) to incorporating spatial parameters (grating period, orientation). This parameter transformation allows relaxed spectral filter specifications while maintaining effective filtering performance in miniaturized detectors
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 approach significantly reduces the density and size of structural defects, enhances manufacturing yield, and lowers costs while maintaining precise control over spectral transmission, achieving better defectivity and performance than traditional methods.
Implementation Method 1
The internal face is textured so as to present a periodic grating of patterns, forming a diffraction grating designed to attenuate the overall optical transmission of the window over a second range of wavelengths, in the range from 5 μm to 8 μm
Implementation Method 2
The outer face is provided with an interference multilayer filter designed to attenuate the overall optical transmission of the window over a first range of wavelengths, in the range from 2 μm to 5 μm
Data Source
Figure 1~3
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Figure 6~7
AI summary
The detector (10) has a package containing sensitive retina (14) and comprising a window (22), which includes a substrate (28) partially transparent in a wavelength range between 2-14 micrometers. An optical filter i.e. multilayer interference filter (32), is formed on an internal surface (34) of the window, and attenuates the incident radiation in an interval of wavelength range between 2-8 micrometers. A periodic diffraction grating (36) is formed on an external surface of the window and attenuates the incident radiation in another interval of the wavelength range between 2-8 micrometers. The sensitive retina is a two-dimensional assembly of bolometric membranes. The window is made of a mineral substrate such as silicon or germanium.