Superconducting nanowire single-photon detectors (SNSPDs) with both high system detection efficiency (SDE) and low dark count rate (DCR) play significant roles in quantum information processes and various applications. The background dark counts of SNSPDs originate from the room temperature blackbody radiation coupled to the device via a fiber. Therefore, a bandpass filter (BPF) operated at low temperature with minimal insert loss is necessary to suppress the background DCR. Herein, a low-loss BPF integrated on a single-mode fiber end-face was designed, fabricated and verified for the low temperature implement. The fiber end-face BPF was featured with a typical passband width about 40 nm in the 1550 nm telecom band and a peak transmittance of over 0.98. SNSPD with high SDE fabricated on a distributed Bragg reflector was coupled to the BPF. The device with such a BPF showed an SDE of 80% at a DCR of 0.5 Hz, measured at 2.1 K. Compared the same device without a BPF, the DCR was reduced by over 13 dB with an SDE decrease of <3%.

Superconducting nanowire single-photon detector on dielectric optical films for visible and near infrared wavelengths Lixing You, Hao Li, Weijun Zhang et al. Characterisation of amorphous molybdenum silicide (MoSi) superconducting thin films and nanowires Archan Banerjee, Luke J Baker, Alastair Doye et al.

We demonstrate a large active area superconducting single-nanowire photon detector with a diameter of Φ100 μm. The detector was fabricated on a Si substrate with distributed Bragg reflector acting as an optical cavity and coupled with a 105 μm multi-mode optical fiber. Owing to the extensive kinetic inductor caused by the large sensitive area of the detector, the response waveform exhibited a large overshoot, causing the device to latch with the increasing bias current. By adding a resistor in series with the device, the overshoot was suppressed, and the maximal bias current increased from 25 to 31 μA. A well-saturated detection efficiency with a maximal value of 65% was achieved at the wavelength of 532 nm. Moreover, the maximal counting rate improved from 1 to 10 MHz.