Advanced superconducting optical detectors

We have investigated advanced superconducting optical and infrared detectors for their integration with superconductive active circuits. The detectors are based on ultra-thin NbN striplines. NbN is the material of choice for single photon optical and infrared detectors, as already demonstrated in the literature. The detectors so far proposed are based on conceptually simple, although difficult to realize, sub-micrometric meander type structures. Most applications of such detectors require some treatment of the signal generated, either as pulse shaping or signal amplification, to fully exploit the detection capabilities, such as sub-ns response time and proportional response. We have developed a room temperature process that, while preserving reasonable superconducting properties of NbN, allows a simple integration of the detectors in Nb-based circuits. Moreover we have developed a passivation technique, by using a protective AlN layer on top of the NbN one. The developed technology allows complex detector configurations, such as integrated RSFQ circuits or SQUID readout, to be relatively easily realized. The response of our NbN strip to photon irradiation will be presented.