Superconducting nanowire single photon detector with efficiency over 90% at 2 μm wavelength

We here report a high system detection efficiency (SDE) superconducting single-photon detector (SSPD) at 2 μm wavelength. The device integrates a SiO₂/Ta₂O₅ distributed Bragg reflector (DBR) and a sandwich-structured double-layer NbN nanowire to enhance the optical absorption efficiency. A cold development technique is implemented to optimize the superconducting nanowires with sub-40-nm linewidths, thus enhancing the intrinsic detection efficiency (IDE). The fabricated SSPD shows an SDE exceeding 90% at 2 μm wavelength. Moreover, the detector allows an operational working temperature of 2.2 K provided by a compact GM cryo-cooler. This detector delivers excellent performance at the 2 μm wavelength, and its optimized structural design implies promising potential for extending detection toward longer infrared bands. It thus holds value for advancing high-sensitivity quantum technologies, mid-infrared optical communications, and dark matter detection research.