SNSPD With Ultimate Low System Dark Count Rate Using Various Cold Filters

Suppressing the dark count rate (DCR) is one of the main issues in the development of the superconducting nanowire single-photon detector . Here, we study the effect of suppressing DCR using the various optical bandpass filters cooled at 3 K. The DCR, which is dominated by the background blackbody radiation at room temperature through an optical fiber, can be strongly suppressed by introducing the cold filter. Using the bulk commercial filter with the bandwidth of 10 nm and the high transmission above 85%, the DCR is improved about 29 dB with 2.4 dB of decrease in the system detection efficiency (η). The noise equivalent power reaches $1.5\,\times \,10^{-18}$ and the figure of merit reaches $1.8\,\times \,10^{9}$ . These values are compared to the results using other type of filters.