Superconducting Nanowire Single-Photon Detectors

Our objective is to design and build a compact system that provides turnkey readiness for commercial and defense use of SNSPDs. Conventional SNSPDs face several limits that lead to tradeoffs between detection efficiency, bandwidth, dark count rate, jitter and operating temperature, and therefore prevent simultaneous realization of DARPA desired parameters in one device. We propose that amorphous NbTiN has significant advantages in providing the combined performances. A design tradeoff exists between detection efficiency and detector bandwidth: only very short nanowires can reach GHz bandwidth, however high detection efficiency requires large footprint to increase absorption. We provide two solutions. The first detector is based upon travelling wave design which already demonstrated internal efficiency above 90%, bandwidth beyond 1GHz and DCR below 0.1Hz, all in one detector. To achieve similar ?system? performances, ActiveOpto will develop glass chip for low-loss detector pigtailing. The second design utilizes a low-fill-factor nanowire sandwiched in a membrane cavity strongly coupled to a near field fiber. Both designs enable simultaneous high bandwidth and system efficiency. Separate measures are taken for modal filtering of blackbody radiation and reduction of DCR. To enable SWaP, we present a low frequency cryocooler that allows closed cycle operation at 2K.