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Suppressing Spectral Crosstalk for Improved Infrared Imaging Performance

Suppressing Spectral Crosstalk for Improved Infrared Imaging Performance

Researchers from Northwestern University developed a new approach that addresses spectral cross-talk problem in dual-band infrared photodetectors

A team of researchers from Northwestern University significantly reduced a type of image distortion caused by the presence of spectral cross-talk between dual-band long-wavelength photodetectors. The findings published in the journal IEEE Journal of Quantum Electronics on November 22, 2018, facilitates development of new generation of high spectral-contrast infrared imaging devices that can be used in various sectors such as medicine, defense and security, planetary sciences, and art preservation.

According to Manijeh Razeghi, Walter P. Murphy Professor of Electrical and Computer Engineering in the McCormick School of Engineering, dual-band photodetectors offer several benefits in infrared imaging such as higher quality images and more available data for image processing algorithms. However, the performance of the system can be limited by spectral cross-talk interference between the two channels. The interference may lead to poor spectral contrast, thereby reducing output of infrared camera technology. Dual-band imaging can be used to observe objects in multiple wavelength channels through a single infrared camera. Moreover, the use of dual-band detection in night-vision cameras can aid to better distinguish between moving targets and objects in the background.

Spectral cross-talk is a type of distortion that emerges when a portion of the light from one wavelength channel is absorbed by the second channel. Moreover, the distortion increases as the detection wavelengths get longer. To address the issue, the team developed a novel version of a distributed Bragg reflector (DBR), which is a highly-refractive, layered material that is placed between channels separating the two wavelengths. DBR is widely used as optical filters to reflect target wavelengths. However, the team is the first to adapt the structure to divide two channels in an antimonide type-II superlattice photodetector, which is a vital element of night-vision cameras. The team compared the quantum efficiency levels of two long-wavelength infrared photodetectors with and without the air-gapped DBR. The results revealed a notable spectral suppression and the quantum efficiency levels were as low as 10%, when air-gapped DBR was used. The team used theoretical calculations and numerical simulation to confirm the results.