Abstract: An optical submarine communication system has a land cable connected to a terminal apparatus which is installed on land near the seashore for transmitting an optical signal and electric power. The land cable is connected to an optical submarine cable through a beach manhole, and a repeater is connected to the optical submarine cable. The optical submarine communication system has a surge suppressor provided on the land cable, whereby a surge generated from the terminal apparatus side because of a lightning stroke or an insulation failure is suppressed and prevented from reaching and damaging the repeater.

Abstract: First to sixth optical switches 17 to 22 are provided: in event of failure on the part of a third input/output port 33, only the first and second optical switches 17 and 18 turn ON; in the event of failure on the part of a second input/output port 32, only the third and fourth optical switches 19 and 20 turn ON; and in the event of failure on the part of a first input/output port 31, only the fifth and sixth optical switches 21 and 22 turn ON.

Abstract: An optical variable attenuator is provided including polarizers for extracting a predetermined polarized wave component from an input optical signal, an array of Faraday rotators formed of a ferromagnetic material and arranged in series for rotating the plane of polarization of the input signal, electromagnetic coils for supplying magnetic fields to the Faraday rotators, and current supply control circuits for setting the polarization-rotating angle of the array by controlling the intensity of the magnetic fields supplied to the Faraday rotators. The polarization-rotation angle of the array can be finely adjusted and maintained, even when the magnetic fields are not continuously supplied to the Faraday rotators.

Abstract: A plurality of submarine cable transmission paths extending from a plurality of land-based terminal stations are connected with each other in a submarine branching apparatus, and an electric power feeding line is arranged between each land-based terminal station and an electric power feeding line switching unit of the submarine branching apparatus to supply electric power from the electric power feeding line to a communication signal of the corresponding submarine cable transmission path through repeaters. The electric power feeding lines are connected with each other in the electric power feeding line switching unit. A control signal superposed on the communication signal is sent to the electric power feeding line switching unit through one submarine cable transmission path, and the connection of the electric power feeding lines is switched according to the control signal.

Abstract: An optical submarine communication system has a land cable connected to a terminal apparatus which is installed on land near the seashore for transmitting an optical signal and electric power. The land cable is connected to an optical submarine cable through a beach manhole, and a repeater is connected to the optical submarine cable. The optical submarine communication system has a surge suppressor provided on the land cable, whereby a surge generated from the terminal apparatus side because of a lightning stroke or an insulation failure is suppressed from reaching and damaging the repeater.

Abstract: A feed line switching circuit includes a relay connected between feed lines, a normally close contact of the relay, and a resistor that constitutes a series circuit with the normally close contact, which series circuit is connected in parallel with the relay. The resistance of the coil of the relay and the resistance of the resistor are determined to satisfy the condition that the current flowing through the relay after energizing the relay can prevent the chattering of the relay. Thus, the feed line switching circuit can positively carry out the feed line switching.

Abstract: A feed line switching circuit includes a relay connected between feed lines, a normally close contact of the relay, and a resistor that constitutes a series circuit with the normally close contact, which series circuit is connected in parallel with the relay. The resistance of the coil of the relay and the resistance of the resistor are determined to satisfy the condition that the current flowing through the relay after energizing the relay can prevent the chattering of the relay. Thus, the feed line switching circuit can positively carry out the feed line switching.