In order to improve the detection distance and the sensitivity, we propose a novel distributed optical fiber sensing system. This system is composed of bidirectional pumping fiber Raman amplifier and unbalanced fiber Mach-Zehnder interferometer. Based on the interference mechanism of phase sensitive optical time domain reflectometer (φ-OTDR), the system can get the sensing information of the whole optical fiber by analyzing the backward scattered light. The interferometer is used as the demodulator of the sensing system, which consists of a 3×3 coupler and two faraday rotator mirrors. By means of the demodulator, the signal light is divided into three beams with fixed phase difference. To deal with these three signals, we can get the vibration information directly on the optical fiber. Through experimental study, this system has a high sensitivity. The maximum sensing length and the spatial resolution of the φ-OTDR system are 100 km and 10 m. The signal to noise ratio about 18 dB is achieved.
We demonstrate a novel distributed optical fiber sensor system based on phase-sensitive optical time-domain reflectometry (Φ-OTDR). Both the phase and the amplitude of the Rayleigh scattering (RS) light can be demodulated based on I/Q demodulation and heterodyne detection using commercial available 100G integrated coherent receiver (ICR). The polarization fading problem in Φ -OTDR can be avoided by considering the RS signal from both polarizations. The dynamic strain sensing with a sensing range of 9.8 km and a spatial resolution of 15 m is experimentally demonstrated.