A Investigation of Optical Fibre Interferometric Vibration and Rotation Measurement Techniques.

Available from UMI in association with The British Library. The use of fibre optic sensors for the measurement of several physical variables is introduced with a particular emphasis on noncontact vibration and rotation sensing with large dynamic range. The general principles of interferometric displacement sensors are outlined and the established signal recovery schemes are briefly described. Novel signal recovery techniques which are more specifically suited to all-fibre sensors are introduced and applied to vibration sensing and also to the fibre optic gyroscope. A new pseudo-heterodyne signal processing system based upon sinusoidal phase modulation is developed and the theoretical performance characteristics are experimentally verified. Operation of the system using direct phase modulation (p.m.) with a piezo-electric fibre stretcher and indirect p.m. via modulation of a laser diode's emission frequency are demonstrated. Operational limitations and detection capabilities are discussed and compared to the active homodyne technique. This new approach for signal recovery is shown to be well suited to the fibre gyroscope application and solves the ambiguity problem encountered at high rotation rates with the dynamic phase bias technique. Detection sensitivities of the order of 1^circ /minute are achieved with the test system, 1 ^circ/hour being achieved with an improved optical configuration. An alternative approach, suitable for passive operation of the Sagnac interferometer, is also described. Quadrature outputs are derived using a polarisation based technique and superimposed onto an electronic carrier to allow large dynamic range operation.