Solution concentration sensor based on a Long-Period fiber grating

摘要

We report a new fiber-optical solution concentration sensor based on an etched long-period fiber grating with one opening head coated with a silver film, which is written symmetrically by three beams of focused high-frequency CO_2 laser pulses in a standard single-mode fiber (Corning SMF-28). This sensor is tested with two kinds of solution, i.e. sugar and CaCl_2, and the experimental results show that this etched fiber-optical sensor with one opening head is flexible to operate and has very high resolution. The resolution of this sensor increases with approximate linearity, as the concentration of solution increases, and the resolutions for sugar solution at low and high concentrations are 1.65 (g/l) and 1.36 (g/l), respectively. Its average resolution has been improved above 28% after the cladding radius of this sensor is reduced to 61 μm by etching with HF acid. The method of etching with HF acid can also be used to tune the resonant wavelengths of a long-period fiber grating.