High-resolution interrogation of tilted fiber Bragg gratings using an extended range dual wavelength differential...

An extended range dual wavelength differential detection technique for interrogating fiber Bragg grating sensors is implemented for the measurement of tilted fiber Bragg gratings. The dynamic chirp of a single DFB laser diode modulated with a square wave is used to generate two pairs of wavelengths, in the high and low modulation states, with a separation approximately equal to the bandwidth of the TFBG, resulting in a doubling of the range of the DWDD measurement. A spectral resolution of 0.08 pm and a refractive index resolution of 9.9 × 10^-6 are obtained over a range of refractive index of 3.7 × 10^-2, corresponding to 11.9 bits of resolution.