Study of optical fiber sensor tip based on surface plasmon resonance

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European Optical Society
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Optical fiber sensors based on surface plasmon resonance (SPR) has been widely studied for the last 20 years using several configurations mostly with multimode optical fibers combining large cores and plastic claddings. Sensors based on this physical phenomenon present very high sensitivity to the refractive index variations. SPR can be defined as a charge-density oscillation that in certain conditions exist at the interface of two media excited by the evanescent wave of the propagated light. The proposal is a SPR sensor in a single mode fiber end chemically etched by emersion in a 48% hydrofluoric acid solution with a Titanium mirror. The result is a tip on a single mode fiber with the cladding removed and a mirror perpendicular to the light path at the end, allowing operation in reflection mode. Although only 9 m in diameter the sensor has high robustness. A set of thin films were then deposited around the cylindrical fibers. The etched region was coated with 2nm of Ti to improve the adhesion of a 20nm thick gold film followed by a 100nm thick layer of a dielectric material. Thin metal and dielectric films were produced by electron beam evaporation. The equipment is fitted with a homemade rotary system to produce homogeneous films around the cylindrical fibers. It was found that a velocity of around 5rpm improves the film homogeneity. Simulations were performed in order to determine the optimal thicknesses of the thin films to create a resonance dip in the 1550nm wavelength.
Almeida, José Manuel Marques Martins de; Coelho, Luís; Paulo André; Santos, José Luís; Diana Viegas; RAS Ferreira. STUDY OF OPTICAL FIBER SENSOR TIP BASED ON SURFACE PLASMON RESONANCE, Trabalho apresentado em Reunião Ibero Americana de Óptica (RIAO) / Encontro Latino Americano de Óptica, Lasers e Aplicações (OPTILAS), In Reunião Ibero Americana de Óptica (RIAO) / Encontro Latino Americano de Óptica, Lasers e Aplicações (OPTILAS), Porto, 2013