An optical wdm network having an efficient use of wavelengths and a node therefor

摘要

An optical fiber network of WDM type comprises two fibers which carry light signals propagating in opposite directions and which are arranged in a ring configuration. One standby link between two neighboring nodes is inactive but is made active if an active link fails. An add and drop node used in the network has band blocking filters connected in a fiber between a drop coupler and an add coupler, taking out a share of the light power in each direction to be received through bandpass filters in receivers and adding new wavelength channels produced in transmitters, respectively. Switches are used for receiving and transmitting on the wavelength channels in correct directions. The positions of the switches can be changed when the inactive link has to become one of the two active links directly connected to the node. A very efficient use of the wavelength channels in the network can then be achieved for nodes having a minimum of in-line components, and particularly, a minimum of in-line filtering components.