Optical probe

Optical probe for the detection of the separating interface of two hostile media having different optical indices contained in an enclosure, comprising a cone made from a transparent material and having a predetermined refractive index able to refract an incident light beam if it is located in one of the two media whose refractive index is higher than the predetermined index and is able to reflect an incident light beam if it is located in one of the two media whose index is below the predetermined index, by means of a pair of optical fibres comprising an optical emission fibre for transmitting the incident light beam from a light source to the base of the cone and at least one optical reception fibre for transmitting the optionally reflected beam to an optoelectronic detector, the source and the detector being located outside the enclosure, characterized in that it comprises a tight casing having a reception recess for a base of the cone, said casing being closed by a cover provided with a conical opening for the passage of the cone, the casing having tight passages for the optical fibres and maintaining in a given relative position with respect to the base of the cone two of the respective ends of the two optical fibres of the said pair, two other respective ends of said two fibres being respectively positioned facing the source and facing the detector, the casing and the cone being made from materials able to resist chemical and thermal stresses in the two media.