Design and experiment study of solution refractive index sensor based on TFBG-SPR

摘要

The core and cladding modes exhibit different refractive index sensitivities, while temperature and stress sensitivities are approximately equal. Because of the characters of cladding mode, the solution refractive index(SRI) sensor is designed and studied. In order to increase the sensitivity of SRI sensor, 45nm thick gold film is deposited on the surface of cladding of TFBG to excite surface plasmon resonance(SPR). The quality and uniformity of gold surface were investigated with aid of a thermal field scanning electron microscopy and the effect is satisfactory. After that, the refractive index(RI) sensing characteristics of both bare and gold deposited TFBGs were studied by experiments of different concentration solutions of NaCl、 MgCl_2 and CaCl_2 respectively. The result proved that the TFBG-SPR increase the RI sensitivity dramatically by 1.5 nm/RIU to 500 nm/RIU. And SRI of TFBG-SPR is 250 to 400 times larger than that of the bare-TFBG. The linear fittings of the center wavelength of cladding modes and SRI of bare and gold-coating deposited SPR sensor are good when refractive index is changed from 1.333 to 1.3941. Meanwhile, the influence of temperature on SPR was taken in consideration and compensated.