Optical sensor and method of use

  • US 9,140,582 B2
  • Filed: 05/27/2010
  • Issued: 09/22/2015
  • Est. Priority Date: 05/27/2009
  • Status: Active Grant
First Claim
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1. An interferometer apparatus for an optical fibre system, the apparatus comprising:

  • an optical coupler having an input port and first and second ports coupled to optical fibres which define first and second optical paths;

    first and second Faraday rotator mirrors arranged respectively at the ends of the first and second optical paths to reflect light propagating in the first and second optical paths back to the optical coupler to generate an interference signal;

    wherein the optical coupler is configured to direct first and second interference signal components of the interference signal respectively to first and second detector ports, and is configured to direct a third interference signal component of the interference signal towards the input port, and the apparatus comprises means for introducing a phase shift between the first, second and third interference signal components;

    first and second photodetectors connected to first and second detector ports of the optical coupler and configured to measure an intensity of the first and second interference signal components at respective phase shifts;

    a third photodetector connected to a non-reciprocal optical device and configured to measure the intensity of the third interference signal component directed back towards the input port;

    an incoherent light source configured to propagate light in the interferometer apparatus; and

    calibration circuitry configured to;

    determine an electrical offset for each of the photodetectors from the outputs of the photodetectors in a first condition, in which no light is input to the input port and the incoherent light source is switched off so that no light propagates in the interferometer apparatus; and

    determine at least one of a photodetector offset, a relative photodetector gain, and a coupling ratio of the first and second optical paths from the outputs of the photodetectors in a second condition, in which the incoherent light source is switched on such that light propagates in the interferometer apparatus.

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