Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

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.

Abstract: 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.

Abstract: 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.

Abstract: 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.