Modeling and Characterization of the Effect of Misalignment between Microsphere-Sensor on the Sensitivity of Microsphere-Lens-Enhanced MWIR SLS Photodetectors

A microsphere lens integrated on top of an MWIR photodetector has exhibited an increase in detector overall sensitivity over a desired spectral bandwidth and, more importantly, a decrease in Noise-to-Signal-Ratio (NSR), as we have shown in our prior work. Using signal processing methods, we have also shown, for the first time, the existence of an adverse effect of microsphere misalignment on the detector's overall sensitivity. In this paper, we model and analyze the effect of various misalignment types between the microsphere-lens and the photodetector on the resulting detector sensitivity. As we show here, microsphere lens-sensor misalignment can result, to some varying degrees, in reduced spectral responses in microspheres-lens-enhanced MWIR photodetectors. We also model and analyze the effect of such misalignment on multiple SLS photodetector sizes, namely 35
$\mu\mathrm{m}$
and 40
$\mu \mathrm{m}$
, and microsphere material types, namely Sapphire and Polystyrene. In the case of Polystyrene material, the results show that the sensitivity of the microsphere-lens-enhanced detector is mainly and significantly reduced by the microsphere Polystyrene material alone around wavenumber 3000, due to the Polystyrene material spectral absorptions around that wavenumber.