Wavelength division multiplex (WDM) optical network
A wavelength division multiplex (WDM) optical network comprises a ring configuration of optical fiber links connecting a plurality of nodes and add and drop filters at each node connected in series within the ring. One or more of the filters are arranged to add or drop at least two selected adjacent wavelength channels of the WDM optical signal while allowing the remainder of the channels within the WDM signal to pass substantially unattenuated. The wavelength channels of each node are selected such as to maximize the number of adjacent wavelength channels at each node.
1 . A wavelength division multiplex (WDM) optical network, comprising: a plurality of nodes serially connected in a ring by optical waveguiding means; add and drop optical filters at each node and connected in series within the ring; WDM optical signals being routed between node pairs in dependence upon a respective wavelength channel ascribed to each node pair; at least one of the filters being configured to add/drop at least two selected adjacent wavelength channels of a WDM optical signal to/from the ring while allowing a remainder of the channels of the WDM optical signal to pass substantially unattenuated; and the respective wavelength channels for each node pair being ascribed such as to maximize a number of adjacent wavelength channels at each node.
2 . The WDM network according to claim 1 , in which the ring is passive and does not include optical amplifying means for optically amplifying the WDM optical signals passing around the ring.
3 . The WDM network according to claim 1 , in which the network is fully meshed, and each node includes the add and drop filters such that every node is connectable to every other node by a respective wavelength channel.
4 . The WDM network according to claim 1 , in which a single wavelength channel defines a connection between a respective pair of nodes.
5 . The WDM network according to claim 1 , in which each filter adds or drops either a single or two adjacent wavelength channels.
6 . The WDM network according to claim 1 , in which the optical waveguiding means comprise an optical fiber.
7 . The WDM network according to claim 1 , in which the add and drop filters comprise a dielectric filter stack.
8 . The WDM network according to claim 1 , in which the add and drop filters comprise a resonant cavity.
9 . The WDM network according to claim 1 , in which the add and drop filters comprise a fiber Bragg grating.
10 . An optical filter for use in a wavelength division multiplex (WDM) optical network, comprising: a plurality of nodes serially connected in a ring by optical waveguiding means; the filter being connected in series within the ring; WDM optical signals being routed between node pairs in dependence upon a respective wavelength channel ascribed to each node pair; the filter being configured to add/drop at least two selected adjacent wavelength channels of a WDM optical signal to/from the ring while allowing a remainder of the channels of the WDM optical signal to pass substantially unattenuated; and the respective wavelength channels for each node pair being ascribed such as to maximize a number of adjacent wavelength channels at each node.
11 . The optical filter according to claim 10 , the filter having an insertion loss of at most 0.5 dB.
12 . The optical filter according to claim 10 , the filter having a figure of merit of at least 0.7.