Litton Systems, Inc.

Eugene L Ferraro

Lawrence J Hershman

James D Green

William Christopher Knaack

John Thomson Douglass, Iv

An optical receiver system for processing signals output from a polarization diversity detector that includes a plurality of photodetector cells. Each cell provides an signal that includes a phase generated carrier signal having a modulation frequency &#x3c9; and a sensor signal that has an in-phase component I and a quadrature phase component Q superimposed on the phase generated carrier signal. A plurality of variable gain amplifiers are arranged to produce a plurality of amplified signals. A feedback circuit is connected to the plurality of variable gain amplifiers for controlling the gains thereof. A plurality of demodulator circuits are arranged to receive the amplified signals. The demodulator circuits are arranged to provide for each photodetector cell an I signal output that indicates an amplitude of the in-phase component I and a Q signal output that indicates an amplitude of the quadrature phase component Q.

Multi-channel optical receiver for processing tri-cell polarization diversity detector outputs

A calibration technique for a signal processing system, wherein a digital down converter is selected by a system controller for calibration. The digital down converter's settings are copied into a calibration digital down converter which mimics the operation of the selected digital down converter. A best polarization diversity detector signal path, an optimal phase offset value for an in-phase data signal, an optimal phase offset value for a quadrature phase data signal, and a normalized gain value for the in-phase and quadrature phase signals of the selected digital down converter are determined. The system controller updates the selected digital down converter with the determined optimal settings. This procedure is repeated for each digital down converter in the signal processing system, while the signal processing occurs simultaneously.

Method and apparatus for calibration of a signal processing system

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.

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Simi Valley, CA, United States of America

Eugene L Ferraro