Multimode Fibre Axial Strain Sensor Utilizing End Reflection Interference

A generic class of single-arm multimode optical fibre sensors based on end reflection interference (ERI) is described and demonstrated. The ERI mechanism provides a simple and viable alternative to the well-established approach of single mode fibre interferometric sensing. A high static phase sensitivity of 3·45 × 107 rad/m, a dynamic phase shifting coefficient of 1·1 rad/Vp − m and a minimum detectable phase shift of 2·3 × 10−5 rad/√Hz have been measured for the reported configuration. Based on theoretical considerations and experimental observations of the periodicity and the magnitude of the intensity fluctuations, it has been unambiguously established that under normal ambient conditions the ERI is the dominant contributor to the intensity changes.