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Optical fibre sensors are essentially a means whereby light guided within an optical fibre can be modified in response to an external physical, chemical, biological, biomedical or similar influence. They are the subject of intense interest for detecting various types of damage in composite materials. This study is focused on the use of a polarimetric sensor to monitor damage accumulation under quasi-static loading. In the polarimetric sensor, the optical core of the high-birefringence (Hi-Bi) fibre transmits orthogonally polarised components of light with different velocities. A change of strain state in the host material will affect the strain state in the fibre core and hence the relative phase of the orthogonally polarised optical signals. The interference of these signals results in a dynamic change in the output signal, which can be used for damage detection. The polarimetric sensor is an integrating sensor (hence potentially detecting changes over long lengths) and it also has a high lateral strain sensitivity, as well as it is relatively cheap and simple to manufacture. Thus polarimetric sensors have the potential to detect damage development within large composite structures. In this study, the sensors have been arranged with the detecting length either completely within the coupon or extending throughout the whole length of the coupon. The transparent nature of the composite specimens used in the work enables the propagation of cracks to be recorded directly with a video camera. It is shown that the polarimetric sensor can be made either to be sensitive to matrix cracking damage over a particular, short length of the composite or to be sensitive throughout the complete length of the composite.