Plasmonic Photon Sorters and Their Potential for Use in Compact Multispectral Imagers at Visible and Infrared Wavelengths
NORWEGIAN DEFENCE RESEARCH ESTABLISHMENT KJELLER
Pagination or Media Count:
Spectral imaging extracts rich information from the incoming light and has many military applications. Polarimetric imaging is also an active field of study with many potential applications. Many sensor technologies exist for spectral and polarimetric imaging, but these generally involve scanning or subsampling, since the dataset is three-dimensional while photodetector arrays are at most two-dimensional. Recently, it has been shown how surface plasmons may be used to sort photons arriving at a detector array by placing plasmonic antenna structures on top of the array. Each antenna structure concentrates light of a particular wavelength andor polarization onto one detector element. Importantly, the antennas of a group of neighbouring detector elements are overlapped to form a superpixel capable of separating different components of the incoming light. Thus photons of different wavelengths arriving at the same location on the antenna structure may be routed to different detector elements. This has potential for use in snapshot multispectral and polarimetric imaging. The photon sorting capability has been demonstrated experimentally in the visible spectral range. No fundamental difficulties are expected in translating these results into the thermal infrared spectral range. Indeed, the antenna structures for thermal infrared wavelengths will be easier to fabricate due to the relatively long wavelength. The photon sorter concept has some specific issues and limitations, most importantly the polarization-dependent coupling efficiency which leads to reflection loss of a large fraction of the incoming light. However this may not be problematic in the 8 to 12 m spectral range, where the number of photons per frame time is usually larger than the charge collection capacity of a photovoltaic detector.