Optical liquid level sensor based on cladding-mode resonance of specialty double-cladding fiber

A novel liquid-level sensor was proposed and studied by using a specialty double-cladding fiber (DCF). The sensor operates according to a light wavelength modulation method which results from the variation of the surrounding refractive index (RI). As the surrounding RI changes, the effective refractive index of cladding mode of DCF increases or decreases and the phase-matching condition changes, so does shift the resonance wavelength. In our experiments, the DCF sensor was exposed to different liquids with certified RI, and liquid levels were varied. Experimental results showed that the shift of the transmission spectra linearly depended on the fraction change of DCF immersed into the liquid. The liquid level sensitivities are 451.8 pm/mm and 1030.44 pm/mm for the different liquid with RI of 1.3514 and of 1.4286, respectively. The sensor has the advantages of large linear response range, as well as high sensitivity and simple structure et al.