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A reconfigurable optical add drop module has a coarse demultiplexer, for outputting sub bands of wavelengths, a fine mux/demux, for adding and/or dropping wavelengths, a coarse multiplexer, for remultiplexing the sub bands, an optical switch in between the coarse demultiplexer and the fine mux/demux

A reconfigurable optical add drop module has a coarse demultiplexer, for outputting sub bands of wavelengths, a fine mux/demux, for adding and/or dropping wavelengths, a coarse multiplexer, for remultiplexing the sub bands, an optical switch in between the coarse demultiplexer and the fine mux/demux, to switch the sub bands for pass through, or for add/drop. Reconfiguration can be remote, automatic, with less interruption to traffic. By switching sub bands rather than individual wavelengths, the number of switches can be reduced, and consequently losses, and space requirements can be reduced. Also, upgrading from pass through to add drop, of one or more sub bands is easier. Hence initial capital cost of nodes and the cost of upgrading can be reduced, since there is less need to provide redundant add drop capacity initially. Mid stage access enables external components to be added to the optical path for the sub bands.

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1. A reconfigurable optical add drop module having:a coarse demultiplexer, for outputting sub bands of wavelengths, a fine mux/demux, for multiplexing to create at least one sub band and/or demultiplexing at least one of the sub bands, a coarse multiplexer corresponding to the coarse demultiplexer,

1. A reconfigurable optical add drop module having:a coarse demultiplexer, for outputting sub bands of wavelengths, a fine mux/demux, for multiplexing to create at least one sub band and/or demultiplexing at least one of the sub bands, a coarse multiplexer corresponding to the coarse demultiplexer, for remultiplexing at least some of the sub bands, a plurality of optical switches, each on an optical path of a different one of the sub bands between the coarse demultiplexer and the coarse multiplexer, and wherein each of the plurality of switches are arranged to switch the respective sub band either for pass through from the coarse demultiplexer to the coarse multiplexer, or for coupling the respective sub band optical path with said fine mux/demux for adding or dropping at least one of the wavelengths of the respective sub band. 2. The module of claim 1 having a middle mux/demux stage in between the fine demux and the plurality of switches.3. The module of claim 2 having a second set of one or more switches in between the middle mux/demux stage and the fine demux for selectively passing through one or more of the demultiplexed sub bands.4. The module of claim 2, the middle mux/demux stage or the fine mux/demux comprising a number of multiple input arrayed waveguide devices arranged on a common substrate.5. The module of claim 1, the coarse demultiplexer comprising two stages of demultiplexing.6. The module of claim 1, at least the plurality of switches and the fine mux/demux being arranged in the same component, the component having at least part of an optical path for the respective sub band between the switch and the fine mux/demux, the optical path having an interface to allow another optical component to be inserted in the optical path.7. The module of claim 1, arranged as two complementary components, one being a multiplexing half, the other being a demultiplexing half, with optical path interfaces for optical coupling of pass through sub bands between the two complementary components.8. The module of claim 1 having one or more amplifiers for amplifying one or more of the sub bands individually.9. The module of claim 1, comprising a hybrid package having at least the coarse demultiplexer, one or more of the plurality of switches, and a demultiplexer part of the fine mux/demux.10. The module of claim 1, the coarse demultiplexer or the coarse multiplexer being formed using a different technology to that used for the fine mux/demux.11. The module of claim 10, the coarse demultiplexer or coarse multiplexer comprising a dielectric film type filter.12. A node for an optical network, having one or more of the modules of claim 1.13. A method of operating an optical network using a remote network management or control system to reconfigure the node of claim 12, having the steps of receiving a prompt to reconfigure, and sending a command to the module to control one or more of the switches.14. A single wafer component having a fine mux/demux element and a middle mux/demux element, suitable for the module of claim 1 and having at least part of an optical path for coupling between the middle and the fine elements, the optical path having an external interface to allow another optical component to be inserted in the optical path.15. The wafer component of claim 14 having an optical switch for switching between a pass through and an add/drop state.16. The module of claim 1, wherein said fine mux/demux comprises a plurality of inputs, wherein each of said plurality of switches couples to a different one of said plurality of inputs and wherein said fine mux/demux is arranged to demultiplex different sub bands depending on the input used.17. A method of adding or dropping sub bands of wavelengths, having the steps of:coarsely demultiplexing a wavelength multiplexed optical signal to output sub bands of wavelengths, remultiplexing at least some of the sub bands, using a plurality of optical switches, each on an optical path of a different one of the sub bands to switch the respective sub band either for pass through to the remultiplexing step, or for coupling the respective sub band optical path with a same fine mux/demux for adding or dropping, and using the fine mux/demux to multiplex to create the sub band for adding, and/or demultiplexing the sub band for dropping. 18. A method of offering a data transmission service by operating an add drop module using the steps of claim 17.19. The method of claim 17, wherein said fine mux/demux comprises a plurality of inputs, wherein each of said plurality of switches couples to a different one of said plurality of inputs and wherein said fine mux/demux is arranged to demultiplex different sub bands depending on the input used.20. A component for a reconfigurable optical wavelength add drop module, the component having:a coarse demultiplexer, for outputting sub bands of wavelengths, a fine mux/demux, for adding and/or dropping wavelengths from one or more of the sub bands, a coarse multiplexer corresponding to the coarse demultiplexer, for remultiplexing the sub bands, and a plurality of optical switches each on an optical path of a different one of the sub bands between the coarse demultiplexer and the coarse multiplexer, wherein each of said plurality of switches is arranged to switch the respective sub band either for pass through to the coarse multiplexer, or for coupling the respective sub band between the coarse demultiplexer and said fine mux/demux via an optical path having an interface to allow another optical component to be inserted in the optical path. 21. The component of claim 20, wherein said fine mux/demux comprises a plurality of inputs, wherein each of said plurality of switches couples to a different one of said plurality of inputs and wherein said fine mux/demux is arranged to demultiplex different sub bands depending on the input used.22. A hybrid packaged component suitable for an optical add drop module, the component having a coarse mux/demux element, a fine mux/demux element of a different type having a plurality of inputs, and a plurality of optical switches for coupling between the coarse mux/demux and the inputs of said fine mux/demux via optical paths having an external interface to allow another optical component to be inserted in the optical path.23. The component of claim 22, having an optical switch for switching between a pass through and an add/drop state.24. The component of claim 22, the coarse mux/demux element comprising a dielectric filter.25. A node for an optical network having the component of claim 22.26. The component of claim 22, wherein said fine mux/demux is arranged to demultiplex different sub bands depending on the input used.