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Multi-point refractometry using tilted fiber Bragg gratings interrogated by a time-domain technique

Tilted fiber Bragg gratings (TFBGs) have been demonstrated to be accurate refractometers. Because they require spectral measurements over several tens of nanometers, most demodulation techniques reported so far are not suited for quasi-distributed refractive index sensing with TFBGs cascaded along an optical fiber. In a recent work, we demonstrated that an optical time domain reflectometer (OTDR) can be used to multiplex identical TFBGs refractometers. Based on this principle, we present here a quasi-distributed refractive index sensor with improved dynamic range where a long-period grating stops the TFBGs Bragg reflections going back to the OTDR.