Theoretical and experimental study on the optimum working wavelength for a fiber optic sensor based on the SPR used in monitoring the water quality

摘要

The optimum working wavelength of a fiber-optic sensor based on the surface plasmon resonance used in monitoring the water quality is studied theoretically and experimentally in this paper. This sensing system was composed of a broad- spectrum source, a fiber sensor head and a micro-optic spectrograph. The sensing fiber adopted was a silica/polymer multi-mode optic fiber, with the 400 um core diameter and 0.36 number aperture. The calculation results showed that there is an optimum working wavelength range corresponding to the given sensor head configuration. Through adjusting the structure parameters the sensing wavelength could be selected to drop into the wavelength range of the commercial semiconductor optical sources, which is beneficial to improving the practicality and the reliability of the sensing system. This system was used to test the impurity of the fresh water and a sensitivity of 8.9 $MUL 10$+$MIN@5$/, corresponding to 10 ppm, was reached.