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Supervisory apparatus for optical transmission system

  • US 5,825,515 A
  • Filed: 05/22/1996
  • Issued: 10/20/1998
  • Est. Priority Date: 09/03/1991
  • Status: Expired due to Term
First Claim
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1. An optical transmission system comprising:

  • a first optical fiber extending between first and second terminals for carrying optical signals from the first terminal to the second terminal;

    a second optical fiber extending between first and second terminals for carrying optical signals from the second terminal to the first terminal;

    at least one optical repeater coupled to the first and second optical fibers between said first and second terminal, said repeater for optically amplifying signals in the first and second optical fibers, said repeater having a permanently connected passive high loss loopback circuit between the first and second optical fibers, the loopback circuit including;

    a first optical coupler having an input responsive to optical signals in the first optical fiber and an output producing optical signals related to the optical signals in the first optical fiber;

    an attenuator having an input responsive to the optical signals output by the optical coupler for attenuating by a predetermined amount the signals output by the optical coupler, anda second optical coupler responsive to the attenuated optical signals from the attenuator for returning the attenuated signals to the first terminal via the second optical fiber; and

    wherein said first terminal includes a transmitter and receiver, said transmitter for launching an optical signal on the first optical fiber and said receiver for detecting variations in the returned attenuated optical signal on the second optical fiber to identify the existence and location of a fault in the optical transmission system.

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