Delay-disorder fiber Bragg grating recognition and calibration method for a Fourier domain mode-locked wavelength-swept laser-based interrogation system.

Fourier domain mode-locking has been used in fiber Bragg grating interrogation for high-speed and long-distance measurement. But the delays induced by long fiber between multisensors and interrogation systems result in nonneglected wavelength error in this high-speed wavelength-swept system. More seriously, the cross-sweep cycle and different distance delays may cause the delay-disorder problem which makes the system unable to determine the order of the delayed peaks and unable to address the location of sensors with corresponding wavelength-encoding characteristics. This paper proposes a novel delayed-peak recognition and calibration method in which the laser works at four different scanning rates. We confirm the relationship between delayed peaks and sensors with recognition parameters at two low rates and eliminate wavelength error at two high rates. Experimental results show that this method recognizes the delayed peaks correctly and calibrates wavelength accurately with error below 10 pm.