Multiresonant analysis improves the limit of detection of tilted fiber Bragg grating refractometers

A multiresonant approach based on tracking 27 cladding mode resonances of tilted fiber Bragg grating refractometers is shown to improve the limit of detection by a factor of 3 to 4 relative to the conventional approach of tracking the single-most sensitive resonance. Limits of detection below 2 × 10-5 in index change are achieved for dilutions of ethanol in water in repeated experiments. In all cases, wavelengths are referenced to the core mode resonance which eliminates the effect of small temperature changes during and between experiments.