  Despite very efficient superconducting nanowire single-photon detectors
(SNSPDs) reported recently, combining their other performance advantages such
as high speed and ultra-low timing jitter in a single device still remains
challenging. In this work, we present a perfect absorber model and
corresponding detector design based on a micron-long NbN nanowire integrated
with a 2D-photonic crystal cavity of ultra-small mode volume, which promises
simultaneous achievement of near-unity absorption, gigahertz counting rates and
broadband optical response with a 3 dB bandwidth of 71 nm. Compared to previous
stand-alone meandered and waveguide-integrated SNSPDs, this perfect absorber
design addresses the trade space in size, efficiency, speed and bandwidth for
realizing large on-chip single-photon detector arrays.
