Hybrid Signal Processing for Automatic Detection and Removal of Material Absorption and Noise From Microsphere-Lens-Enhanced Midwave Infrared Type II Strained Layer Superlattice Photodetectors

Infrared imaging systems are an essential part of many fields of study, typically used for military and airborne surveillance, manufacturing, security, night vision, threat detection, medical imaging, and inspection, to name a few. One of the best-performing systems in the midwave infrared is the type-II strained layer superlattice (SLS) photodetectors. They require external subzero cooling at very low temperatures. While technically capable of operating at higher temperatures, this reduces their sensitivity while increasing their noise-to-signal ratio (NSR). Additionally, previous research showed that detector sensitivity could be improved by integrating a microsphere lens into the photodetector. Still, the microsphere-lens-enhanced photodetector Fourier transform infrared response (FTIR) shows that this microsphere lens also introduces material absorption. New signal processing, analysis, and computational methods are needed to automatically detect and remove material absorption, aberrations, and to improve their performance. This article proposes hybrid methods using experimental data and computational models to smooth, detect, characterize, and reduce material absorption and noise from FTIR data collected from microsphere-lens-enhanced MWIR SLS detectors. Using the percent area lost performance metric of photodetectors with and without microsphere lens enhancement. We propose a novel combination method for improving the overall FTIR signal performance based on piecewise polynomial fit and a Hilbert-transform-based algorithm. Our results show that for different types/sizes of microsphere-lens material and detector sizes, these algorithms can quantify the increase in sensitivity of MWIR SLS detectors while automatically finding and quantifying microsphere-lens material-based absorption and reducing their adverse effects on the SLS detector across the MWIR spectral band.