A signal processing and data analysis technique for accurate extraction and estimation of FTIR signal aberrations in microsphere-lens-enhanced MWIR photo detectors via system transfer functions mathematical modeling

Abstract

In this paper we focus on using signal processing techniques and mathematically-derived photo-detector models, with or without microsphere-lens-enhancement, to analyze, characterize and estimate the effect of integrated aberrations on microsphere-lens-enhanced single photo-detector sensitivity. One of the difficulties here relates to the noisy nature of detector FTIR experimental signals in the MWIR band. We show how modeling of the detector spectral response signal, combined with signal boundary-absorption partial replacement, is successfully effective in estimating integrated detector system aberrations. With the detector FTIR spectral data, considered, our findings show that (a) not all four microsphere materials, considered in this work, namely, Sapphire, SLG (Soda, Lime Glass), PS (Polystyrene) and BTG (Barium Titanate Glass) necessarily result in detector sensitivity increase at all MWIR wavelengths. The PS-microsphere-lens-enhanced detector sensitivity turns out to be less than that of the detector without enhancement in the 2700–3200 wavenumber band. This is due to the fact at this band the PS material exhibits additional significant spectral absorptions. (b) there seems to exist some global detector integrated aberrations introduced by factors such as the microsphere lens material and misalignment, silicone-or-rubber adhesive materiel, photo-detector system and others, that we globally extracted/estimated using the detector experimental FTIR spectral responses and their corresponding generated detector mathematical models. (c) comparison of single detector raw experimental spectral responses (with and without microsphere-lenses of different sizes and material types) to their respective resulting models, shows realistic synthesized detector FTIR data models. With the help of theses resulting detector FTIR response models, we are able to confirm our findings that, relatively independently of the increase in the sensitivity, the microsphere lens significantly decreases the sphere-enhanced-detector Noise to Signal Ratio (NSR), including in spectral bands of high absorption, noise, and aberration. That is, based on the data considered, (1) the resulting microsphere-enhanced photo-detector is generally less sensitive to noise in the MWIR than the mesa and (2) this, seemingly is so, independently of the detector sensitivity increase, for example, due to the microsphere size of a certain material type.