Abstract: In an optical fiber network bidirectional WDM traffic is sent on one optical main transmission fiber (1) between two nodes (A, B) connected in the path of the transmission fiber. The bidirectional traffic between a pair of nodes is carried on two different wavelength channels (Nos. 1, 2), one for each direction. The two wavelength channels are added to/dropped from the traffic in the ring fiber (1) in each node using a two-channel add/drop filter (5e1-2, 5w1-2), e.g. a band add/drop filter. In this way the number of add/drop filters connected in the path of the transmission fiber can be kept as small as possible.

Abstract: An optical WDM ring network includes at least two add/drop nodes connected in a ring path. The ring path comprises only a single optical fiber arranged for bidirectional traffic between the nodes. A 2×2 switch is used in one of the add/drop nodes for switching signals forwarded from the node to the other node to travel either on a first segment of the ring path or on a second, complementary segment of the ring path when required for protection purposes. Signals from the other node to the first node are issued to travel on both segments but the switch selects the actual segment from which the signals are received in the first node. The signals switches by the switch can be high priority signals used in protected channels communicated between the node and another node. On the segment from which the high priority signals are not received, low priority signals in non-protected channels can be communicated between the nodes, these channels also passing the switch.

Abstract: A broadcast and select ring network for optical WDM communication includes two parallel fiber rings (1a, 1b) carrying traffic in opposite directions between nodes (3; A, B, C, D). The nodes comprise on their receive side selecting means such as a cross connect device (21) or similar means allowing a flexible selection of the wavelength channels which are to be received by each node. Thereby, any WDM channel in the rings can be selected and received in the nodes. For example, all nodes can receive signals in the same channel for e.g. set up or reconfiguration purposes. Furthermore, the number of receivers in a node can be small but still all channels can be received. The number of transmitters in each a node can also be small since every transmitter can reach every receiver.