Optical Coherence Domain Polarimetry (OCDP) Distributed Sensing System

Optical coherence domain polarimetry (OCDP) is one of the white light interferometrictechniques. It’s used to detect the polarization coupling distribution (PCD) along a polarizationmaintaining (such as PANDA) fiber. The PCD is caused by external fields like temperature orstrain. OCDP system consists of a sensing interferometer composed of a PANDA fiberilluminated by a polarized white light source. The optical path difference (OPD) between thepolarization axes from the polarization coupling point to the end of the sensing fiber iscompensated by the processing interferometer (Michelson interferometer) to fall into thecoherence length of the source.The coupling strength has definite relation with strain while the optical path difference has linearrelation with temperature, so distributed sensing can be realized based on OCDP system.In OCDP based sensing system as any polarimetric sensor, the temperature fluctuation modifiesthe birefringence of the PM fiber. So the position and the strength of the polarization couplingwill be distorted.In this thesis, first we study the temperature effect on OCDP system. By measuring the relativeposition of the coupling, the temperature effect on the position can be eliminated.Based on the linearity between the OPD and temperature a distributed temperature sensorconsisting of N PM fiber spliced in series is proposed and demonstrated experimentally.The strain sensor response is expressed as a function of the applied force, the interaction lengthand direction of the force relative to birefringence axis of the fiber. Experimental results agreewell with theoretical predictions and the response can be approximated as linear in a good forcerange.