Evanescent field refractive index sensor utilizing a narrow fibre Bragg grating and a tunable DBR laser

We have demonstrated an evanescent field refractive index fibre sensor comprising a 42 mm Bragg grating in an etched fibre together with a tunable DBR laser. Characterization of different aqueous sucrose solutions resulted in a resolution of roughly 10mM sucrose. The sensor in the presented form has a theoretical sensitivity of higher than 10(-5) refractive index units (riu) in a refractive index region close to the cladding index of the fibre. However, the technique allows for an even higher sensitivity than 10(-6) riu with a proper signal processing scheme.