Nonideal optical cavity structure of superconducting nanowire single   photon detector
  Optical cavity structure has been proven to be a crucial factor for obtaining high detection efficiency in superconducting nanowire single photon detector (SNSPD). Practically, complicated fabrication processes may result in a non-ideal optical cavity structure. The cross-sectional transmission electron microscope (TEM) image of SNSPD fabricated in this study shows unexpected arc-shaped optical cavities which could have originated due to the over-etching of SiO2 layer while defining NbN nanowire. The effects of the arc-shaped optical cavity structure, such as the wavelength dependence of the optical absorption efficiency for different polarization, were analyzed by performing optical simulations using finite-difference time-domain method. The central wavelength of the device is found to exhibit a blue shift owing to the arced cavity structure. This effect is equivalent to the flat cavity with a reduced height. The results may give interesting reference for SNSPD design and fabrication. 
Hao Li, Weijun Zhang, Lixing You, Lu Zhang, Xiaoyan Yang, Xiaoyu Liu,   Sijing Chen, Chaolin Lv, Wei Peng, Zhen Wang, and Xi...
cond-mat.supr-con physics.optics