Room-Temperature SWIR Night Vision Using Strained InGaAs and Spectral Filtering
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Solution Overview
Problem
Conventional SWIR imagers face challenges with high dark current levels, limited sensitivity, and the need for cooling, making them unsuitable for night vision applications in the 1-2.5 μm spectral range, especially when resources such as size, weight, cost, and power are constrained.
Innovation Solution
A novel SWIR imager system operating near room temperature with a cut-off wavelength up to 2.5 μm, utilizing a photodetector with a strained InGaAs epitaxial structure and a spectral filter to selectively filter out light shorter than 1.8 μm, allowing for dual-mode reflective and thermal imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If cooled detectors are used to improve sensitivity in the 1-2.5 μm spectral range, then detection sensitivity is improved, but system size, weight, cost and power consumption increase
Solution Approach 1:
The patent changes the operating temperature parameter from cryogenic to room temperature, and adjusts the spectral response parameters by using strained InGaAs/InP superlattice structures with specific bandgap engineering to achieve extended cut-off wavelengths up to 2.5 μm while operating without cooling
Solution Approach 2:
The patent employs composite material structures including strained InGaAs/InP superlattice layers combined with specific contact layers and buffer layers to create a detector that achieves high sensitivity at room temperature, replacing the need for simple cooled detector designs
2Measurement precision
If cooled detectors are used to improve sensitivity in the 1-2.5 μm spectral range, then detection sensitivity is improved, but system complexity and cost increase
Solution Approach 1:
The patent changes the operating temperature parameter from cryogenic to room temperature, eliminating the need for complex cooling systems while maintaining high detection sensitivity through optimized semiconductor heterostructure design
3Device complexity
If un-cooled detectors are used to reduce system size and cost, then system simplicity is improved, but detection sensitivity and signal-to-noise ratio deteriorate
Solution Approach 1:
The patent employs composite material structures including strained InGaAs/InP superlattice layers combined with specific contact layers and buffer layers to create a detector that achieves high sensitivity at room temperature
Solution Approach 2:
The patent applies local quality optimization by creating specific regions within the detector structure with different properties - strained superlattice absorption layers for high quantum efficiency, graded buffer layers for dislocation control, and optimized contact layers for charge collection, achieving high sensitivity in specific spectral regions while operating at room temperature
4Measurement precision
If the cut-off wavelength is extended beyond 1.7 μm to improve thermal radiation detection, then thermal imaging capability is improved, but dark current increases causing noise and reducing signal-to-noise ratio
Solution Approach 1:
The patent changes the bandgap parameter through strained superlattice design, achieving extended cut-off wavelengths up to 2.5 μm while controlling dark current through the quantum confined Stark effect and optimized well depths in the superlattice structure
Solution Approach 2:
The patent employs composite material structures including strained InGaAs/InP superlattice layers combined with specific contact layers and buffer layers to create a detector that achieves high quantum efficiency at extended wavelengths while maintaining low dark current through the superlattice configuration
5Measurement precision
If the cut-off wavelength is extended beyond 1.7 μm to improve thermal radiation detection, then thermal imaging capability is improved, but system noise increases due to dark current
Solution Approach 1:
The patent changes the bandgap parameter through strained superlattice design, achieving extended cut-off wavelengths up to 2.5 μm while controlling noise through the quantum confined Stark effect and optimized well depths in the superlattice structure that suppress carrier generation
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
Enables low-noise, high-sensitivity night vision capable of detecting thermal radiation without cooling, with improved dynamic range and reduced noise equivalent temperature difference, allowing for effective imaging in various conditions.
Implementation Method 1
a photodetector having a cut-off wavelength of 2.5 microns under the room temperature conditions
Implementation Method 2
a spectral filter located in an optical path of light propagating toward the photodetector. The spectral filter is configured and operable to selectively filter out light of wavelength shorter than a predetermined value
Implementation Method 3
an optical system for collecting light and focusing collected light onto a photodetector
Data Source
AI summary
A night vision system and method for imaging an object at or near room temperature and in the wavelength region up to 2.5 microns is described. The includes a photodetector having a cut-off wavelength of 2.5 microns under the room temperature, an optical system configured for collecting light and focusing the collected light onto the photodetector, and a spectral filter located in an optical path of light propagating toward the photodetector. The spectral filter is configured and operable to selectively filter out light of wavelength shorter than a predetermined value, thereby gradually shifting operation of the night vision system from mostly reflection mode to a combined reflection and thermal mode, to allow the night vision system to detect light reflected from and emitted by the object being imaged.