Method and apparatus for interrogation of fiber optic interferometric

Abstract

A technique for interrogation of fiber optic interferometric sensors wherein an optical signal is modulated by an array of fiber optic sensors in response to acoustic pressure. Modulated signals (channels) from each sensor are multiplexed onto a single fiber optic cable and the multiplexed signal is input to a polarization diversity detector having at least two outputs. The optical signal is converted into a digital, electrical signal. A plurality of digital down converters demultiplex and demodulate the separate channels and output in-phase data and quadrature phase data for each of the signal channels. A system controller connects to the digital down converters and to a calibration digital down converter. The calibration digital down converter, controlled by the system controller, mimics an operation of each digital down converter in turn in order to determine optimal digital down converter settings for each digital down converter. The system controller updates the optimal settings for each digital down converter such that the digital down converters are dynamically calibrated according to the optimal settings. The in-phase and quadrature phase data output of the digital down converters are then processed with an acoustic signal processor.