Disclosed is a node structure of an upgradeable wavelength division multiplexing system that can minimize the expense in implementing, maintaining, and upgrading the system. The node structure includes an interleaver for interleaving a plurality of optical signals received therein into a predetermined number of channels; at least one demultiplexer coupled to one of the output channels for demultiplexing the optical signals received thereto into a prescribed number of channels; at least one multiplexer for multiplexing the respective demultiplexed optical signals from the demultiplexer; and, a deinterleaver for deinterleaving the optical signals outputted from the multiplexer to be forwarded to the next node.
The present invention provides a wavelength division multiplexing transmission system for separating wavelength division multiplexing signals, where signal lights with different bit rates are wavelength division multiplexed, according to the bit rate, and processing the separated signals individually. The wavelength division multiplexed signals, where a low-speed bit rate signal is disposed in an odd channel group and a high-speed bit rate signal is disposed in an even channel group, are demultiplexed into a low-speed signal group and a high-speed signal group by an unequal bandwidth interleaver. The low-speed signal group is processed (e.g. demultiplexing, dispersion compensation) by an optical device appropriate for the low-speed signals, and the high-speed signal group is processed by an optical device appropriate for the high-speed signals. By this, a relatively expensive and high function optical device can be applied only for the high-speed signal side, so an increase in the device cost can be kept down. Also a device with specifications appropriate for each signal can be used.
According to the present invention, for example, a WDM light containing 10 Gbit/s signal lights and 40 Gbit/s signal light arranged on wavelength grids at 25 GHz intervals is branched into two by an input side optical coupler to be sent to two routes. In one route side, only the 10 Gbit/s signal lights are demultiplexed by a 10 Gbit/s demultiplexer and a plurality of 1.times.2 optical switches, while in the other route side, only the 40 Gbit/s signal lights are demultiplexed by a 40 Gbit/s demultiplexer and a plurality of 1.times.2 optical switches. Further, the respectively demultiplexed signal lights are multiplexed for each modulating rate by a 10 Gbit/s multiplexer and a 40 Gbit/s multiplexer, and thereafter, further multiplexed by an output side optical coupler to become a WDM light. Thus, it becomes possible to arrange signal lights having different modulating rates at arbitrary wavelengths on wavelength grids at predetermined intervals.
