Microwave Resonators for Weak Light Detection at Telecom Wavelength

Abstract

Abstract-We report the experimental measurements of weak light signal at 1550 nm wavelength with a high-quality factor microwave coplanar waveguide (CPW) resonators. The quality factor of this niobium λ/4 CPW resonator is measured as Q = 7.4 × 10 5 at ultra-low temperature (20 mK). With this device, we developed a technique to implement the proper fiber-resonator coupling, and realized the desirable weak light detection at telecommunication wavelength with 35 pW resolution by probing the shift of resonance frequency (f 0 ). We found that the resonator shift increases with the increasing light power (from 11.7 pW to 9.77 nW), similar to the effects of increasing the system temperature (from 20 mK to 800 mK). The observed blue shifts of f 0 (with the increasing of either the temperature and the applied light powers) are thoroughly deviated from the usual Mattis-Bardeen theory prediction, and could be explained by the effects relating to the two-level system existed on surface of the CPW device.