Biconical fiber sensor using wavelength modulation

A wavelength-modulation-based fiber optic sensor is used to measure salt concentration and temperature. The sensor consists of a biconical fiber filter. Theoretically, the wavelength shift response of the sensor is linearly related to changes in the refractive index of the external medium surrounding the sensor ina specific region. The device sensitivity is enhanced by reducing the radius of the taper waist. The theoretical predictions are confirmed by experimental results. A wavelength-modulation-based all-fiber sensor demonstrated salt concentration and temperature measurements with errors of 0.05% (mass fraction) and 0.2 °C, respectively. The differential modulation of the pass or notch bands in a biconical fiber filter may be used for simul taneous sensing of salt concentration and temperature.