Abstract: A method of and system for determining a path through which to route a connection in a photonic network in which optically viable photonic paths of one or more physical links are determined and considered as “virtual” links in a “virtual” topology. Routing is then performed using the “virtual” topology rather than the physical topology to compute “virtual” paths of one or more “virtual” links.

Abstract: A compensator for optical transmission systems exploits gain tilt inherent in optical amplifiers. The amount of SRS induced spectral power gradient is determined, and the amplifier gain is changed to cause a compensating gain gradient in the optical amplifier to compensate for the SRS induced spectral power gradient. Fewer components are needed, and so it can be less expensive. It can be implemented as a simple software upgrade to existing systems. Many such compensators can be distributed through the system, without requiring a large inventory of individually specified filters. More accurate compensation can be achieved by making it dependent on the distribution of wavelengths within a band.

Abstract: The invention provides a method of balancing the power level of an optical signal within an aggregate of optical signals in an amplified dense wavelength division multiplexing DWDM optical network, as well as power balancing apparatus therefor.

Abstract: 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.

Abstract: The invention provides a method of balancing the power level of an optical signal within an aggregate of optical signals in an amplified dense wavelength division multiplexing DWDM optical network, as well as power balancing apparatus therefor.

Abstract: A compensator for optical transmission systems exploits gain tilt inherent in optical amplifiers. The amount of SRS induced spectral power gradient is determined, and the amplifier gain is changed to cause a compensating gain gradient in the optical amplifier to compensate for the SRS induced spectral power gradient. Fewer components are needed, and so it can be less expensive. It can be implemented as a simple software upgrade to existing systems. Many such compensators can be distributed through the system, without requiring a large inventory of individually specified filters. More accurate compensation can be achieved by making it dependent on the distribution of wavelengths within a band.

Abstract: An optical link 1 from one terminal A to another B has a series of spans 2 interconnecting nodes between the terminals A, B. Dispersion compensation means applies dispersion compensation to each span 2. Each span 2 contributes noise and the total noise in the link is result of the contributions from each span 2. The spans 2 may be normalised and the total noise in the link the sum of the contributions from each span. The amount of dispersion compensation applied to each span 2 by the dispersion compensation means is determined in accordance with the noise contribution of that span 2.