Interrogation of a Sensor Array of Identical Weak FBGs Using Dispersive Incoherent OFDR

Incoherent optical Fourier-domain reflectometry (OFDR) incorporating a dispersive delay line is used for the interrogation of an array of three identical fiber Bragg gratings with a Bragg wavelength of 1552.81 nm, reflectivity of -19.3 dB, and 10-cm separation. The dispersive delay line induces different delays in the wavelengths reflected by each grating, thus being sensitive to Bragg wavelength shifts. Compared with the conventional incoherent OFDR, dispersive effects decrease the spatial resolution, which in our experiments reached a value of 1.2 cm in fiber at a measurement bandwidth of 10 GHz. As a quasi-distributed temperature sensor, the array shows an accuracy of ±0.5 °C for temperatures up to 100 °C, and an estimated total measurement range of 540 °C. Tradeoffs among bandwidth, scan time, dispersion-dependent spatial resolution, and accuracy are also analyzed.