Superconducting Nanowire Single Photon Detector with Optical Cavity

Increasing the detection efficiency (DE) is a hot issue in the development of the superconducting nanowire single photon detector (SNSPD). In this work, a cavity-integrated structure coupled to the SNSPD is used to enhance the light absorption of nanowire. Ultra-thin Nb films are successfully prepared by magnetron sputtering, which are used to fabricate Nb/Al SNSPD with the curve of 100 nm and the square area of 4\times4 μm^2 by sputtering and the lift-off method. To characterize the optical and electrical performance of the cavity-integrated SNSPD, a reliable cryogenic research system is built up based on a He^3 system. To satisfy the need of light coupling, a packaging structure with collimator is conducted. Both DE and the dark count rates increase with I_\rm b. It is also found that the DE of SNSPD with cavities can be up to 0.17% at the temperature of 0.7 K under the infrared light of 1550 nm, which is obviously higher than that of the SNSPD directly fabricated upon silicon without any cavity structure.