At&t Bell Laboratories

Tyco Telecommunications (us) Inc.

Tyco Submarine Systems Ltd.

Lucent Technologies Inc.

Tycom (us) Inc.

Tyco Electronics Subsea Communications LLC

Cleo D Anderson

Neal S Bergano

Robert L Lynch

Richard L Maybach

William W Patterson

Francis C Bekampis

David Gunderson

Joel Schesser

The position and amount of localized polarization dependent anomalies such as polarization mode dispersion and/or polarization dependent loss may be measured by applying a polarization modulated probe signal to an optical transmission line. The polarization modulated probe signal is returned via optical feedback paths positioned along the line, and is detected by a probe signal receiver to identify the position and strength of the anomaly.

Method and apparatus for detecting localized polarization dependent anomalies on optical transmission lines

A powering arrangement for an undersea cable system provides that each branch of the system is supplied with a current equal to half of the current in the trunk. By coupling both branches to the trunk, the current adds at the branching unit. Upon occurrence of a power path fault in any branch, a virtual ground moves to the site of the fault. In addition, an image virtual ground moves to a similar point in the branch that does not have the cable fault. As a result of this implementation, the cable power system is able to tolerate at least one fault in a branch without necessitating repair, and can tolerate some multiple branch faults depending upon their location. In contrast to the operation of existing power-switched branching units, the fault-tolerant branching unit does not require down-powering and re-powering in order in order to change the power configuration, e.g., to allow a virtual ground to be re-located at shunt fault sites that occur in either trunk or branches. Moreover, even with a branch shunt fault or cable break, the fault-tolerant branching unit allows for power to be removed from the faulted branch for repair without having to first power down the other two legs. And finally, at the completion of a branch repair, power to the repaired branch can be restored without first powering down the other two legs.

Method and apparatus for operating cabled-fiber undersea network, and fault-tolerant branching unit for use therein

An optical transmission system allows for the remote determination of the output power of each carrier for each repeater. The optical transmission system includes two terminals, an optical path that transmits a plurality of optical signals between the two terminals, and a plurality of repeaters spaced along the optical path. At least one of the terminals generates a first line monitor signal and a second line monitor signal. The second line monitor signal is delayed by a round trip delay from the terminal to a repeater at which the output power is desired to be measured. The terminal then transmits the first line monitor signal on the optical path. Each repeater in the transmission system generates a return line monitor signal in response to receiving the first line monitor signal and transmits the return line monitor signal on the optical path.

Remote monitoring of an optical transmission system using line monitoring signals

An optical transmission system allows for the remote determination of the total output power of each repeater. The optical transmission system includes two terminals, an optical path that transmits a plurality of optical signals between the two terminals, and a plurality of repeaters spaced along the optical path. In each of the repeaters, pilot signals are inserted by impressing them upon the amplified optical signals output from the repeater. The pilot signals are derived from an oscillator whose frequency is unique to the repeater in which the pilot signals are inserted. The magnitude of each pilot signal is proportional to the output power of its associated repeater. Each terminal provides a measurement of the total power output from each repeater using a receiving device. The receiving device selects the unique oscillator frequency for each of the repeaters desired to be measured, and measures the pilot signals at the selected frequency.

Line monitoring of an optical transmission system using pilot signals

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.

Supervisory apparatus for optical transmission system

An optical transmission system, especially useful in undersea applications, includes an optical path between two terminals with one or more repeaters located between the terminals for amplifying optical communications signals flowing in the optical path. The repeaters contain optical fiber amplifiers driven by pump lasers. The average optical power produced by the pump lasers is controlled in proportion to the magnitude of electrical line current produced by a controllable constant current source located in one of the terminals. This is achieved by regulator circuits which are responsive to a signal related to the magnitude of the line current and signals related to the actual optical output of the pump lasers. The magnitude of the line current may be conveniently set at the terminals so that the lowest bit error rate is achieved in the transmission system. Alternatively, the magnitude of the line current may also be set to at some minimum level to achieve an acceptable bit error rate and low pump laser and fiber amplifier aging.

Pump laser control circuit for an optical transmission system

A control signalling arrangement for a pulse transmission system uses a main data stream including a block parity channel. Control signals are transmitted from an end terminal to a repeater by inserting the control signals in periodically spaced bit positions of the block parity channel. At the repeater, the control signals are separated from the block parity channel for controlling the circuits or devices for maintenance operations.

Control signalling arrangement for a digital transmission system

A maintenance response signalling arrangement for a digital transmission system transmits response signals from a repeater to an end terminal. From the repeater, response information is modulated onto a subcarrier which is superimposed as a jitter signal on the main data stream. At the end terminal, the response information is recovered from the jitter signal on the main data stream.

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Cleo D Anderson