Simultaneous Measurement of Humidity and Temperature with Cytop-reduced Graphene Oxide-overlaid Two-mode Optical Fiber Sensor

Highlights [Display omitted] A polymer-overlaid two-mode microfiber knot resonator (TMM-KR) was designed to measure relative humidity (RH) and temperature simultaneously in a living condition. The device is composed of two main optical features: two-mode microfiber (TMM, slow-varying term) and two-mode knot resonator (TMKR, fast-varying term). After fabricating a TMM by non-adiabatically tapering a conventional single mode fiber (SMF), we designed C-rGO-overlaid TMM as a polymer-overlaid optical sensor to evaluate the response and recovery times. The effective group refractive index between fundamental and cladding modes, HE11 and HE12, respectively, of the TMM-KR reduced to nearly zero by optimizing the waist diameter of the optical microfiber, and the sensitivities of the proposed sensor remarkably enhanced to 0.603 nm/%, and -0.79 nm/oC, for RH and temperature, respectively. Our calculated and experimental results demonstrated that the proposed micro-structure of the C-rGO-overlaid TMM-KR will provide optical properties that can be applied for practical use of environment sensing.