| 摘要 |
An optical fiber network of WDM type comprises two fibers (7e, 7w) which carry light signals propagating in opposite direction and which are arranged in a ring configuration. In the ring always one link between two neighbouring nodes is inactive but provides a standby-link which is used for failure in another link, in the case of which the previously inactive link is made active. An add and drop (1) node used in the network for only traffic between neighbouring nodes has band blocking filters (31e, 31w) connected in a fiber (7e, 7w) between a drop coupler (17e', 17w') and an add coupler (23e', 23w'). A drop coupler takes out equal shares of the light power to be received through switches (33e, 33w) and bandpass filters (35e, 35w) in receivers (11e, 11w). The add couplers add new wavelength channels produced in transmitters (13e, 13w) in the node through multiplexers (37e, 37w) and switches (39e, 39w). The switches (33e, 33w; 39e, 39w) are used for receiving and transmitting on the wavelength channels in correct directions depending on the location of the inactive link. Thus, the positions of two of the switches have to be changed when the inactive link is one of the two links directly connected to the node. Such a node has a minimum of in-line components and particularly a minimum of in-line filtering components.
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