High Accurate and Stable Demodulation for 3-D Encoded Optical Fiber Sensing Network

An improved demodulation platform for 3-D encoded optical fiber sensing network is proposed with high accuracy and stability. The 3-D encoded optical fiber sensing network, consists of quantities of ultra-weak twin-grating-based microstructures encoded in wavelength, frequency, and time domains, requires high-precise wavelength interrogation due to the complexity of its backscattering spectrum. However, the tunable Fabry–Perot filter (TFF)-based system with high spectrum resolution suffers from nonlinear scanning effect and temperature sensitivity of TFF, which seriously affects the measurement reliability. A wavelength calibration unit composed of multiple fiber Bragg gratings (FBGs), as well as the third-order polynomial fitting, is adopted to establish the accurate wavelength–voltage relationship of TFF, so as to auto-compensate the real-time demodulation deviation. The prototype system is experimentally demonstrated with the wavelength drift of only 6 pm under the temperature change of about 10 °C, as well as the long-term measurement accuracy less than 3 pm. This improved demodulation scheme is universal for all FBGs sensing networks as well.