Surface Plasmon Resonance Tilted Fiber Bragg Grating Refractometer And New Interrogation Technology

A nano-scale gold-coated tilted fiber Bragg grating(TFBG) sensor with clear surface plasmon resonance(SPR) is proposed and experimentally demonstrated. The transmission spectrum of the sensor provides a fine comb of narrowband resonances that overlap with the broader absorption of the surface plasmon and thus provide a unique tool to measure small shifts of the plasmon. The metal film sensing the environment has a very high sensitivity to the change of surrounding refractive index(SRI). Meanwhile, measuring SRI by amplitude modulation is more intuitive and simple than wavelength modulation method, provides a more reliable method for biomass measurement. The experimental results show that sucrose solutions with different SRI ranging from 1.3340 to 1.3410 were measured by wavelength and amplitude methods, obtaining that the wavelength modulation sensitivity is 480nm/RIU, while amplitude modulation sensitivity is 2040dB/RIU.An ultra-thin silver-coated tilted fiber Bragg grating(TFBG) sensor with clear surface plasmon resonance(SPR) together with strong evanescent wave in transmission for "surface" and "bulk" surrounding refractive index(SRI) measurement is proposed and experimentally demonstrated. The thickness of the silver coating over the fiber surface is precisely controlled at 12~16 nm(much thinner than 40~50 nm for traditional SPR excitation). The transmission spectrum of the sensor provides a fine comb of narrowband resonances that overlap with the broader absorption of the surface plasmon and thus provide a unique tool to measure small shifts of the plasmon and identify the "surface" SRI changes with high accuracy. Meanwhile, the ultra-thin nanometric-coating permits part of high-order cladding modes to become leaky modes which have a large sensitivity to variations in the background solution for "bulk" SRI measurement. Experimental results show that above two resonances have an inverse amplitude responses to the SRI changing. Solutions with different RI ranging from 1.3400 to 1.3408 were clearly discriminated in-situ by using the differential amplitude monitoring between “cut-off” cladding resonance and plasmonic resonance, with an amplitude variation sensitivity of ~8100 dB/RIU and a limit of detection of ~10-5 RIU.Combined with nano-scale gold-coated TFBG-SPR sensors, we propose a novel electrochemical surface Plasmon resonance optical fiber sensor for in-situ monitoring EABs. The sensor uses a tilted fiber Bragg grating(TFBG) imprinted in a commercial single mode fiber and coated with nano-scale gold film for high efficiency SPR excitation. The amplitude variation and wavelength shift of the SPR over the fiber surface clearly identifies the electrochemical activity of the surface localized(adjacent to the electrode interface) bacterial cells in EABs, which differs from the “bulk” detections of the conventional electrochemical measurements.