Modeling optical microfiber loops for seawater sensing.

Based on resonant and waveguiding properties of optical microfiber loops, we theoretically investigated silica microfiber loop resonators (MLRs) for refractive index (RI) and salinity sensing of seawater. Dependences of sensitivity and detection limit on probing wavelength, fiber diameter, and ring diameter are calculated with typical parameters of seawater. Our results show that the sensitivity of MLRs increases with the increasing wavelength and the decreasing diameter of the microfiber. Bending loss and absorption loss are both important factors to determine the detection limit. By optimizing the parameters of the sensing system, RI sensitivity and salinity detection limit can reach 10(-6) RI units (RIU) and 10(-2) ‰ (10 ppm), respectively. The model presented here may be helpful for developing microscale fiber sensors for seawater detection with high sensitivity, low detection limit, and miniaturized sizes.