Supervisory apparatus for optical transmission system
First Claim
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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Accused Products
Abstract
A relatively simple, low cost apparatus detects the presence and location of faults in an optical transmission system. It is particularly applicable to underwater optical transmission systems. The optical transmission system contains at least one optical fiber pair extending between two terminals. Optical amplifier based repeaters are located at predetermined positions along fibers. Each repeater has a simple high-loss optical loopback circuit which is used to provide fault identification and location. The loopback circuit couples a portion of the optical signal travelling from a transmitting station through one of the fibers, attenuates that portion of the optical signal, and adds the attenuated signal to the optical signal in the other fiber for return to the transmitting station. Fault location is accomplished by launching a supervisory signal into the fiber from one of the terminals. At each repeater, the loopback circuit causes an attenuated version of the supervisory signal to return to the station from which it was launched, combined with any noise and signal in the return lines. The supervisory signal is a pseudo-random word which can be recovered from the signal and noise in the return line via a correlation technique. The loopback circuit in the repeaters is composed of passive components which may comprise a pair of optical couplers each of which is adjacent one of the two transmission fibers. The optical couplers are connected by a fiber containing a preselected amount of attenuation. There is no need for any sensing circuitry in the repeater to activate the loopback in response to command signals in the supervisory signal. The production of the supervisory signal consequently is simplified because there is no need for command information to be a part of the supervisory signal. Degradation of signals through the optical transmission system is easily detected in a reasonable amount of time at the terminals of the system via the correlation technique. In addition, the correlation technique allows one to easily identify the location of the degradation on the transmission line.
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Citations
11 Claims
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1. An optical transmission system comprising:
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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, and a 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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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Specification