A photonic-crystals enabled spectrometer for remote sensing of greenhouse gases

Abstract

As global climate change poses one of the most important challenges this century, there is an increasing demand to monitor trace gases with high spatial and temporal resolution. To accomplish this these instruments need to be compact to have constellations of satellites or be able to be equipped on High Altitude Platform Systems. Recently, we introduced a novel highly compact spectrometer instrument concept for trace gas retrieval, making use of photonic crystal filters instead of traditional diffraction based optics. Here the photonic crystal filter transmission profiles are specifically tailored to retrieve the desired trace gases. A particular challenge for this new type of instrument is the design optimization. In addition to traditional performance trade-offs, such as SNR (F-number) and system complexity, the photonic crystal transmission functions also depend on the F-number of the system. Since it is extremely computationally demanding to compute the transmission of many filters for different F-numbers (brute-force optimization approach), a more tailored method is needed. In this work we present a method how to perform a trade-off regarding F-number and trace gas retrieval performance by pre-selecting filters and analyze the performance for these filters as function of F-number. These results show, for the first time, that the sensitivity of the photonic crystal filters to the F-number of the system can substantially degrade the performance compared to only SNR based optimization. It appears that the pre-selected filters, for which the analysis is performed, are particular sensitive the the F-number of the system. This indicates the need for a method to identify robust photonic crystal transmission profiles.