High-Performance Ti Transition-Edge Sensor-based Photon-Number Resolving Detectors

Superconducting transition-edge sensor (TES)-based single-photon detectors with high detection efficiency, low dark count rate and photon-number resolving capability are suitable for many scientific applications. We have developed a high-performance Ti TES-based single-photon detector at a working wavelength of about 1550 nm. The TES with a critical temperature of around 200 mK has an active area of 10 μm × 10 μm, which is manually aligned to an ultra-high numerical aperture fiber with a mode field diameter of 4 μm, leading to a nearly perfect coupling efficiency. The Ti TES integrated into an optical cavity consisting of a dielectric mirror and an anti-reflection coating exhibits an absorption efficiency of 97% at 1550 nm. The fabricated TES shows an energy resolution of 0.21 eV using a 1540 nm pulsed source, and it can resolve up to 20 photons. The measured system detection efficiency is 95% ± 0.4%.