Improvement of Dynamic Range in a Time-Division Multiplexing-Based Linear Sagnac Interferometric Sensor System

An auxiliary optical structure and an improved 3 x 3 fiber coupler phase demodulation algorithm are proposed to enhance the dynamic range (DR) of a time-division multiplexing (TDM)-based linear Sagnac interferometer (LSI) sensing system. The auxiliary optical structure is constructed to remove dc pulses caused by time delay fiber (TDF) in the LSI system, resulting in a 5.5-dB improvement in the system's DR. Based on this, the demodulation algorithm is improved by considering the characteristics of the new system, allowing for the real-time acquisition of the difference between the maximum and minimum values of the two interfering signals. The small-signal phase demodulation distortion problem present in traditional algorithms is overcome, leading to a further 9-dB improvement in DR. In addition, the frequency response of different branches is tested, and the experimental results show that consistent frequency responses are observed across all branches. The proposed new TDM interferometric system can be further integrated with wavelength-division multiplexing (WDM) technology, offering potential application prospects in acoustic source localization, multibranch perimeter security, and oil pipeline leakage monitoring.