An optical fiber strain sensor array comprises several sensor support panels spaced in its longitudinal direction and at least one connecting member extending in the longitudinal direction, which mechanically interconnects the sensor support panels. An optical fiber is supported by the sensor support panels and the connecting member. The optical fiber extends with the connecting member between the sensor support panels and forms a curve on the sensor support panel, the curve including at least one portion of the optical fiber that extends in the transverse direction. The width of the connecting member is substantially less than the width of the sensor support panels, such that the connecting member is capable of flexure in the transverse direction. This has the advantage that the connecting member can be flexed to take up any slack during installation of the optical fiber strain sensor array in a wind turbine blade and can be fitted to the turbine blade even if the blade has a conical shape.