System for determining a propagation time of an optical signal in an optical fibre of an optical link, the system comprising: a first item of equipment comprising means for transmitting a measurement optical signal in a propagation direction to a second item of equipment of the system by means of said optical fibre, means for receiving a return optical signal coming from the second item of equipment by means of said optical fibre in the opposite direction to the propagation direction and means for determining said propagation time from an emission time of the measurement signal and a reception time of the return signal; an intermediate item of equipment, the system being configured so that the optical signals transmitted by means of said optical fibre pass through at least said intermediate item of equipment, said intermediate item of equipment comprising at least one amplifier arranged to amplify optical signals received in the propagation direction and block optical signals received in the back propagation direction, and a module for compensating for chromatic dispersion, said module being distinct from the amplifier and introducing a delay; first means for extracting, from the optical fibre, the return optical signal, said first extracting means being located at the output of said intermediate item of equipment; means (45; 52; 61-63; 72-77) for regenerating the return optical signal extracted by the first extracting means; means (11, 37) for injecting the extracted and regenerated return optical signal into the optical fibre, said injecting means being placed at the input of said intermediate item of equipment; and processing means arranged to obtain a reception time of the return signal taking into account said delay introduced by said compensating module. a first item of equipment comprising means for transmitting a measurement optical signal in a propagation direction to a second item of equipment of the system by means of said optical fibre, means for receiving a return optical signal coming from the second item of equipment by means of said optical fibre in the opposite direction to the propagation direction and means for determining said propagation time from an emission time of the measurement signal and a reception time of the return signal; an intermediate item of equipment, the system being configured so that the optical signals transmitted by means of said optical fibre pass through at least said intermediate item of equipment, said intermediate item of equipment comprising at least one amplifier arranged to amplify optical signals received in the propagation direction and block optical signals received in the back propagation direction, and a module for compensating for chromatic dispersion, said module being distinct from the amplifier and introducing a delay; first means for extracting, from the optical fibre, the return optical signal, said first extracting means being located at the output of said intermediate item of equipment; means (45; 52; 61-63; 72-77) for regenerating the return optical signal extracted by the first extracting means; means (11, 37) for injecting the extracted and regenerated return optical signal into the optical fibre, said injecting means being placed at the input of said intermediate item of equipment; and processing means arranged to obtain a reception time of the return signal taking into account said delay introduced by said compensating module.