An Optical Solution Concentration Sensor Based on Periodical Pressure-Induced Long-Period Fiber Gratings

A fiber-optic solution concentration sensor employing a periodical pressure-induced long-period grating is proposed. The sensor is based on a composite optical waveguide which is made of a standard single-mode fiber, a Teflon-cannula and the medium under test. Experiment has been carried out to measure the concentration of the sodium chloride (NaCl) solution. The results show that the central resonance wavelength shift has an approximately linear relationship with the concentration of the NaCl solution, where a sensitivity of 0.128 nm/wt.% for the LP14 mode coupling in a concentration range from 0% to 25% is measured.