The present invention relates to a head (500) for a sensor comprising two sections of optical fiber enabling the propagation of infrared light having at least one infrared wavelength and generating evanescent waves toward the outside in order to detect infrared signatures of an external medium, said head (500) comprising: an optical fiber forming a curved portion (15) for connecting the two sections of fiber, and for coming into contact with the external medium so as to detect the infrared signatures interfering with the propagation of the evanescent waves propagating along the fiber, and means (504, 506) for protecting the curved portion (15) against external mechanical stress, while ensuring that a contact area (30) exists between the external medium and said curved portion (15).