Delay Calibration Method for Wavelength-Swept Laser-Based FBG Demodulation System

A remote fiber optical sensors network which uses optical fiber to connect the fiber Bragg grating sensors network and demodulation system has been widely applied in the industrial monitoring field. Due to the long distance and hence large delay between the sensing grating and the swept laser, the wavelength of the returned light is different from that of the launching light. Such wavelength mismatch will cause demodulation error. In this letter, we propose a novel autocalibration method. By switching the swept laser between two different scanning rates, the delay-caused error can be estimated and hence compensated. Experimental results show that the wavelength demodulation error can be reduced from over 20 nm to 10 pm only. The method reported here is autoadaptive to different fiber lengths, which leads to much faster response time, and the nonlinearity during wavelength scanning is suppressed, which enables an accuracy as high as 10 pm.