The SNSPD device 100a is operated with a photon (illustrated by light beam 10) approaching from the top of the device 100a, e.g., with normal incidence relative to the substrate 124. The working principle of the SNSPD device is that the to-be-detected photon comes from top and shines on the SNPSD. Absorption of the photon, either on initial impingement or upon reflection from the DBR, creates a hot spot on the NbN nanowire 20) which raises the temperature of the NbN above critical temperature so that a portion of the wire is no longer in the superconductive state. A region around the hot spot can experience current crowding, resulting in a higher current density than the critical current density, which can disrupt the superconductive state for the entire wire. The change in the NbN wire from the superconducting state to the normal resistive state can be electrically detected by flowing a current through the device and monitoring voltage differences between the electrodes.

Another form of superconducting nanowire single photon detector (SNSPD) device includes a waveguide to input photons into the detector along an axis generally parallel to the surface of the substrate. FIGS. 9A and 9B illustrate a device 100b configured as a superconducting nanowire single photon detector (SNSPD) and having a waveguide 138. The device 100b can use any configuration of the seed layer 103 discussed above.