Graphene-coated three-twisted-taper and four-twisted-taper for highly sensitive temperature and strain sensing

Fiber-optic sensor has emerged fast development and greatly applied in various fields. In this paper, by manually fire-drawing method of single mode fibers, we propose and fabricate two kinds of ultra-compact graphene-coated three-twisted-taper and four-twisted-taper for the highly sensitive temperature and strain sensing. Due to the asymmetric and twisted structure induced more propagating modes in the tapered fiber, and excellent optical propeties of surface plasmon polariton (spp) effect and fast thermal response of graphene, a number of high-order modes are confined and stably transmit in the twisted taper to enhance the multi-mode interference, followed by the optical sensitivity improvement. For the case of three-twisted-taper with coated graphene, high sensitivities of -66.2 pm/ºC for temperature sensing and -173.4 pm/µε for tensile strain sensing are measured in sequence. For the case of graphene-coated four-twisted-taper, high sensitivities of -61.7 pm/ºC for temperature sensing and -103.2 pm/µε for tensile strain sensing are measured. Comparatively, twisted tapers without coated graphene are also proposed for the temperature and strain sensing with relatively small sensitivities, further verifying the advantage of coated graphene on the fiber-optic sensing. This results will open a brand-new door in the temperature and strain sensing fields with easy fabrication process, ultra-compact structure and high sensitivities.