Interrogation of a large-capacity densely spaced fiber Bragg grating array using chaos-based incoherent-optical frequency domain reflectometry.

An interrogation technique for large-capacity densely spaced fiber Bragg grating (FBG) arrays is demonstrated using incoherent optical frequency domain reflectometry (I-OFDR). A distributed-feedback laser diode under chaotic oscillation, modulated by a frequency-swept microwave, is adopted as the optical source. The reflected sensing signals are converted into electrical signals and subsequently mixed with the original microwave. Fast Fourier transform is applied to the generated beat signal to obtain the position of individual FBGs, while thermal tuning of the lasing wavelength leads to the demodulation of wavelength. By using the chaotic source, interference among the reflected sensing signals is reduced, leading to a significantly improved spatial resolution of 10 cm, with a multiplexing capacity of 3640 and wavelength demodulation accuracy of 15 pm.