Maximizing photon absorption into thin active structures can be the limiting factor for
photodetector efficiency. In this work, a fiber-coupled tunable cavity is demonstrated,
designed to achieve close to unity absorption of photons into a thin film superconducting
nanowire single photon detector (SNSPD). A technique for defining a stable cavity between
the end of a telecommunications optical fiber and a reflective substrate is described and
realized. Cavity resonances are demonstrated both through the tuning of input wavelength …