Abstract
In this article, we propose a hybrid time and wavelength division multiplexed (TWDM) active quadrature demodulation technique for fiber-optic Fabry–Perot acoustic sensor network. A modulated grating Y-branch (MG-Y) laser is utilized to achieve fast and programmable wavelength tuning. For each sensing channel, two operating wavelengths with quadrature phase difference are determined by the initial cavity length of the sensor. According to the DC voltages of the detected signal, the operating wavelength is feedback-controlled to locate on the spectral slope, maintaining the high sensitivity of the sensing system. Compared with traditional passive quadrature demodulation and quadrature point intensity demodulation methods, the feedback control logic is simple and flexible. Moreover, the proposed active quadrature demodulation scheme is easily applicable to sensors with different cavity lengths. Combined with a hybrid TWDM technology, simultaneous multi-point acoustic detection can be achieved, requiring only one tunable laser and one photodetector. A two-point sound velocity sensing system and a four-point sound source localization system are constructed. Experimental results show that different sensing channels can work effectively without crosstalk.
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