Development of a Fast Response Titanium-Gold Bilayer Optical TES With an Optical Fiber Self-Alignment Structure

We developed a Ti/Au bilayer optical superconducting transition edge sensor (TES) laying on an optical fiber self-aligned structure. The bilayer approach enables us to control the superconducting transition temperature T
_C
, which results in 8-μm-square-sized TES with T
_C
as high as 314.0 mK. Moreover, the TES device is micro-machined so that it can be easily assembled with an optical fiber via a self-aligned method. Our TES device achieved a system photon detection efficiency (PDE) of 83.6% at 940 nm with an energy resolution of 0.21 eV. Electrical and effective time constants (rise time and decay time) were as short as 74 and 75 ns, respectively. We also theoretically analyzed the imperfect system PDE. According to this analysis, the imperfection originated mainly from misalignment between the TES and the optical fiber, and the system PDE will be increased up to >95% by use of an optical fiber with a smaller mode field diameter.