Abstract
An integrated vibration measurement scheme with wide dynamic range, high frequency response and multi-points accurate location is proposed by combining unidirectional Mach-Zehnder interferometer (MZI) and phase sensitive optical time domain reflectometer (φ-OTDR). Using a wavelength division multiplexing (WDM) scheme, the φ-OTDR and the MZI are merged together into one novel system successfully. An improved 3 × 3 coupler-based demodulation method is proposed to demodulate the interference signal produced by the MZI. The vibration frequency is obtained by analyzing the demodulated phase difference. Meanwhile, the vibration position is obtained by analyzing the backscattering signals produced by the φ-OTDR. Experimental results demonstrate that the spatial resolution is 20 m at the sensing length of 4 km and the frequency response reaches up to 10 MHz. Compared with the previous merged systems, this system detects the frequency without dead zone. The MZI part does not affect the φ-OTDR part. The vibration frequency can be obtained accurately with no limitations of π radians phase difference jumps, which means the detectable dynamic range is expanded.
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