a fiber optic interferometric sensor system utilizing a reference transducer and an optical source having a very short coherence length , typically about 80 microns . the optical source is used to activate a remotely located fiber optic sensor which has an optical path defference between two reflecting surfaces such that the reflected optical beams are incoherent for the optical source used . the reflected beams are then coupled to a reference transducer , located remotely from the sensor and preferably near the electronic processing circuitry . the reference transducer is designed with an optical path length difference to produce a coherent combination for the optical path length differences of both the sensor and the reference transducer thereby forming a highly sensitive interferometer .