Hyperspectral opportunities with next-generation QSIP arrays

Hyperspectral applications that employ gratings typically exploit only one grating order, since other orders that emerge from the grating at the same angle of dispersion would corrupt the spectrum measured with conventional FPAs. Previously, dualband infrared focal plane arrays (FPA), developed for multi-spectral imaging applications, have demonstrated advantages over conventional multi-FPA sensor configurations in compactness and band-to-band pixel registration. In addition, dualband and multiband FPA architectures of Quantum Structure Infrared Photodetector (QSIP) technology would enable applications beyond simple multi-spectral imaging. For example, In the case of dual- (or multi-) waveband FPAs, the different grating orders can be paired with the FPA wavebands, allowing high efficiency hyperspectral imaging over very broad wavelength regions. Exploiting the “third dimension” of FPA detecting layers for this type of hyperspectral application has been demonstrated previously. As time progresses, multi-waveband FPAs are expected to provide an increase in spectral information at the pixel level without the need for external (e.g. dispersive) optical elements. As the number of wavebands increases to the point of providing spectral overlap of adjacent spectral resolution elements, hyperspectral capability is then achieved by the FPA acting alone. This technology may someday become possible through advanced QSIP architectures having photons of different wavelength continuously absorbed at different depths, and their resulting photocurrents isolated with a vertical grid of contacts or an equivalent mechanism for transporting depth-dependent signal photocurrent to a read-out circuit unit cell.