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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 iO 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 106 riu with a proper signal processing scheme.

We propose a model for designing and analyzing rare-earth-doped distributed-feedback (DFB) lasers. The effects of pump depletion and cross-gain saturation are included and shown to be significant for high-efficiency lasers. Our simulations show good agreement with experimental data from an ytterbium-doped fiber laser. We also give some design guidelines for DFB fiber lasers.