Abstract: A system for locating Fresnel reflections along an optical fiber, including an emission circuit for emitting optical pulses which are coupled into the input face of the fiber; a reception and transformation circuit (20) for receiving signals reflected by the fiber and transforming them into electrical signals; a selection circuit (20) for taking the electrical signals and selecting therefrom only those electrical signals which correspond to Fresnel reflections; a comparison circuit (23, 25, 26) coupled to the selection circuit (20) and receiving a comparison reference signal expressing the rank of an arbitrarily-chosen one of the Fresnel reflections; and an evaluation circuit (13, 21, 22, 24, 26) coupled to the comparison circuit (23,25,26) and to the selection circuit (20) so as to locate the point along the fiber that gave rise to the arbitrarily-chosen Fresnel reflection.

Abstract: The present invention concerns a method for the serial transmission of binary data in which each binary digit is transmitted in the form of an elementary signal occupying a time interval known as the binary interval.In this process a binary 1 is represented alternatively by a pulse or a space occupying the whole of the corresponding binary interval; a binary 0 is normally represented by a pulse occupying a half binary interval, except in the case where it is the first or the last one of a sequence of n+1 successive binary zeroes, the first being represented according to the above rule as a binary 0, except if the binary ones appeared after the preceeding sequence of n+1 successive binary zeros and are an even number, in which case it is represented as a binary 1 following the rule of alternation, the last being represented in accordance with the above rule as a binary 1 contradicting the alternation rule.The invention can be used to advantage in fibre optic links joining junctions encoded in HDB.sub.3.