An edge wavelength-switching system includes an optical switch and a wavelength selective switch. The optical switch includes a west hub-side port, an east hub-side port, a west local-side port, and an east local-side port. The wavelength selective switch includes (i) a multiplexed port optically coupled to the west local-side port and (ii) a bypass port optically coupled to the east local-side port, and (iii) a plurality of demultiplexed ports. An optical network includes a network hub including an M-by-N.sub.1 wavelength-selective switch, N.sub.1>M≥1, a first network node, and a second network node. Each of the first and second network nodes includes a respective edge wavelength-switching system. The network hub, the first network node, and the second network node are optically coupled.

A power over fiber system includes a power sourcing equipment, a powered device, optical fiber cables, optical switches, a detector and a control device. The power sourcing equipment includes a semiconductor laser that oscillates with electric power, thereby outputting feed light. The powered device includes a photoelectric conversion element that converts the feed light into electric power. The optical fiber cables transmit the feed light. The optical switches selectively connect the optical fiber cables. The optical fiber cables and the optical switches can form at least two transmission routes of the feed light. The detector detects a poor transmission point on a transmission route among the transmission routes of the feed light. The control device controls the optical switches so as to form another transmission route among the transmission routes of the feed light in accordance with the poor transmission point, the transmission route bypassing the poor transmission point.

A node (10) includes multiplexing unit (11) that multiplexes a plurality of subcarrier signals for performing optical wavelength multiplexing communication into a wavelength group signal; output unit (12) that outputs the multiplexed wavelength group signal to an optical transmission line; pre-multiplexing level correction unit (13) that corrects a level deviation between the subcarrier signals before the multiplexing based on an optical level of the wavelength group signal in the output unit (12); and post-multiplexing level correction unit (14) that corrects a level deviation of the wavelength group signal after the multiplexing including the corrected subcarrier signals based on the optical level of the wavelength group signal in the output unit (12).

Disclosed is a solution for monitoring an operation of an optical fiber. An arrangement for the purpose includes: an indicator device arranged to: receive, from an optical component, a sample of a signal conveyed in the communication channel; determine an indicator value indicative of an amount of light in the sample of the signal; and a computing device arranged to compare the indicator value to a reference value, and set a detection result to express either that the sample of the signal carries a predefined amount of light or the predefined amount of light is absent from the sample. Also disclosed is a method, a computing device, a computer program product and a communication system thereto.

Disclosed is a solution for monitoring an operation of an optical fiber. An arrangement for the purpose includes: an indicator device arranged to: receive, from an optical component, a sample of a signal conveyed in the communication channel; determine an indicator value indicative of an amount of light in the sample of the signal; and a computing device arranged to compare the indicator value to a reference value, and set a detection result to express either that the sample of the signal carries a predefined amount of light or the predefined amount of light is absent from the sample. Also disclosed is a method, a computing device, a computer program product and a communication system thereto.

A polarization recovery device comprises an input that receives a first optical signal with unknown polarization and with at least one signal parameter at an initial value, a first output that outputs a second optical signal with known polarization and with the at least one signal parameter at or near the initial value, and a recovery block that generates the second optical signal based on the first optical signal.

A polarization recovery device comprises an input that receives a first optical signal with unknown polarization and with at least one signal parameter at an initial value, a first output that outputs a second optical signal with known polarization and with the at least one signal parameter at or near the initial value, and a recovery block that generates the second optical signal based on the first optical signal.

In an optical communication system, an optical communication device and a plurality of optical transmission devices are loop-connected via transmission line. An optical signal transmission unit of the optical communication device, when no communication interruption occurs in the transmission line, outputs an optical signal addressed to a communication destination device that communicates with the own device to a transmission line connected to either one of two neighboring optical transmission devices. The optical signal transmission unit outputs, at the time of communication interruption occurring in the transmission line, an optical signal addressed to the communication destination device to both of transmission lines connected to respective two neighboring optical transmission devices. A branch unit of the optical transmission device branches the optical signal input from a neighboring device, and outputs branched optical signals to another neighboring device and a subordinate communication destination device of the own device.

In an optical communication system, an optical communication device and a plurality of optical transmission devices are loop-connected via transmission line. An optical signal transmission unit of the optical communication device, when no communication interruption occurs in the transmission line, outputs an optical signal addressed to a communication destination device that communicates with the own device to a transmission line connected to either one of two neighboring optical transmission devices. The optical signal transmission unit outputs, at the time of communication interruption occurring in the transmission line, an optical signal addressed to the communication destination device to both of transmission lines connected to respective two neighboring optical transmission devices. A branch unit of the optical transmission device branches the optical signal input from a neighboring device, and outputs branched optical signals to another neighboring device and a subordinate communication destination device of the own device.

Provided is a multiplex transmission system capable of achieving a redundant configuration for coping with a failure while reducing useless resources. A multiplex transmission system includes a first multiplex transmission apparatus 100, a second multiplex transmission apparatus 200, a resource pool 130 having resources capable of selectively constructing one or more functions among a plurality of functions, and a management control unit 140 for controlling the resource pool 130. The first multiplex transmission apparatus 100 includes a plurality of client ports. During normal time, a function associated with each of the plurality of client ports is constructed in the resource pool 130. When a failure occurs, the management control unit 140 controls the resource pool 130 so as to release a resource in which is constructed a function associated with a port with a low priority among the plurality of client ports and to construct, in the resource, a function necessary for restoring signal transmission associated with a port with a high priority among the plurality of client ports.