Superconducting nanowire single photon detector (SNSPD) has been widely used in quantum communication, quantum computing and other fields because of its excellent time jitter and response speed. However, due to the geometric structure of SNSPD nanowires, the performance indicators are counterbalanced, which limits its large-scale application. Combining high detection efficiency with high timing performance remains an outstanding challenge. In this work, we report a SNSPD with 12 μm small active area, which has high speed, high efficiency, low jitter and broadband absorption. Au/SiO<sub>2</sub> membrane cavity, which determined by finite element analysis simulation, is used to widen the optical response bandwidth. And it is easier to process and improve the alignment accuracy at the same time. The flat substrate is more conducive to the growth of superconducting thin films, so flattening process is introduced after the cavity. Device package is also optimized to match smaller detector. Self-aligned packaging makes optical alignment more convenient and time-saving. Special optical fibers with small mode-field diameters can reduce the negative effect of the detector on optical coupling. The detector achieved the maximum SDE of 82% at the central wavelength of 1310 nm at the temperature of 2.2 K, and the SDE of more than 65% in the wavelength range of 1200 nm-1600 nm, with DCR of 70 cps. The detector also exhibits a count rate of 40 MHz@3 dB and a time jitter of 38 ps, which is significantly improved compared with 23 μm active area detector. Furthermore, the minimum time jitter of 22 ps can be obtained by using low temperature amplifier readout. In this paper, high comprehensive performance detector is developed, which provides an important technical reference for practical and product SNSPD.
Superconducting nanowire single photon detector (SNSPD) has been widely used in many fields such as quantum computing, quantum key distribution and laser radar, due to its high detection efficiency, low dark count rate, high counting rate, and low timing jitter. In most cases, SNSPD works under the DC-bias mode that can detect single photons at any time they arrive. In cases like satellite laser ranging and singlephoton laser radar where the light pulses arrive regularly, the AC-bias mode enable SNSPD work with higher counting rates and lower background dark counts, which however require complicated readout due to the low signal-to-noise ratio of the photon response. In this paper, we report on an AC-biased SNSPD system with self-differential readout circuit. The system includes a 2-pixel SNSPD consisting of two parallel nanowires, which are biased with 100 MHz sinusoidal current. The output signals of these two nanowires are amplified and combined for the differential readout of the photon response. The resulting response pulse shows a ten times higher signal-to-noise ratio than the one extracted before self-differential readout. In addition, the dark counts are decreased by a factor of 4, and the count rates are increased by a factor of 1.5, comparing to the ones under the DC-bias mode. This work provides a specific method to read out the AC-biased SNSPD.
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