Abstract Body

Recently, superconducting nanowire single-photon detectors (SNSPDs) have been demonstrated to achieve saturate quantum efficiency at longer wavelengths up to 20 μm [1]. However, the detection efficiency of the reported devices was relatively low due to the small detection area and a lack of an efficient optical cavity. Here, we demonstrate a high-efficiency SNSPD integrated with a membrane optical cavity to increase the light absorption at 10 μm. The nanowire was made from 5 nm thick WSi_x film with a critical temperature of 2.68 K, showing a well saturated quantum efficiency at 10 μm. To increase the output signal amplitude, both avalanche detector structure and an impedance-matched readout were used. The nanowire was fabricated on a SOI wafer. After a backside etching process, only the top 2 μm thick silicon layer was remained. Combined with an addition silicon layer and a top gold mirror deposited on top of the nanowire, a membrane Fabry-Perot (FP) cavity was built. Simulation results indicated that this cavity can reach a maximum light absorption of 26.08 % at 10 μm. The detection efficiency was measured in a free-space coupling 300 mK cryostat, which was 20.69% at 10.18 μm. With this device and a tunable QCL pulsed laser, response spectrum from 8 μm to 12.5 μm and polarization dependence was measured. In addition, a 2×2 detector array using delay-line readout was also demonstrated.

References

[1] Gregor G., Alexander B.et al. Low-noise single-photon counting superconducting nanowire detectors at infrared wavelengths up to 29 µm, Optica 10, 1672-1678 (2023).

Figure 1. A diagram of the membrane cavity designed for 10 μm superconducting nanowire single-photon detector.

Keywords: Superconducting nanowire single-photon device (SNSPD), Mid-infrared, Fabry-Perot (FP) cavity, Free-space test system