Arrangement for locating faults in an optical information transmission system

Claim 1

In an arrangement for locating faults in an optical transmission system having forward and return transmission paths, such arrangement comprising: a fault-locating line terminal device (LE1), a repeater (3), and an optical waveguide loop (5) connected betwen the output of the repeater in the forward transmission direction and the input of the repeater in the return transmission direction, so that optical signals coming from the fault-locating terminal device in the forward direction can also be sent in the return direction; the improvement characterized in that: first optical beam splitting means (24) is coupled to said forward transmission path for diverting a small proportion of said optical signals from that path; second optical beam splitting means (26) is coupled in series with said first optical beam splitting means to receive therefrom the diverted optical signals and to further divert a small proportion of the already diverted signals; and said waveguide loop (5) is coupled between said second optical beam splitting means and the input of said repeater (3), whereby only the twice diverted proportion of the optical signals coming from the fault-locating terminal device are branched-off to said loop; and means (33) for selectively connecting the return direction input of the repeater to said loop instead of to the return transmission path.