Abstract: The invention relates to a fibre sensor that enables the propagation of infrared light at at least one wavelength of 0.8 to 25 micrometres, the fibre successively comprising along its length a first infrared waveguide section (23), a second detection section (25) intended to come into contact with an external environment in order to detect infrared signatures interfering with the propagation of the evanescent waves propagating along the fibre (2), and a third infrared waveguide section (27). The invention is characterized in that, in the second fibre section (25) that has the detection role, the fibre (2) is constituted of a curved part, the radios of curvature of which is locally less than 2.3 millimetres.