Dual-parameter optical fiber sensor based on concatenated down-taper and multimode fiber

A novel dual-parameter optical fiber sensor based on a single-mode fiber (SMF) down-taper and multimode fiber (MMF) is proposed and demonstrated. The sensor structure is formed by cascading a down-taper and MMF through a segment of SMF. The transmission spectrum exhibits response of the interference between core and different cladding modes. Two interference dips can be observed within a certain range of detection. Due to the different wavelength shifts of the selected two dips, simultaneous measurement of temperature and liquid level can be achieved. Experiment results indicate a good linear relation between the wavelength shift and external parameters (temperature and liquid level). The measured temperature sensitivities are 0.02 nm/°C and 0.031 nm/°C, and liquid level sensitivities are 0.022 nm/mm and 0.07 nm/mm, respectively. In addition, the fiber sensor has the advantages of compact size, simple fabrication and cost-effective.