Nortel Networks Corporation

Bram Peeters

Nigel Lawrence Bragg

Alan Robinson

James E Whiteaway

James Alexander Shields

Princy Johnson

Friskney Robert

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 &#x201c;virtual&#x201d; topology rather than the physical topology to compute &#x201c;virtual&#x201d; paths of one or more &#x201c;virtual&#x201d; links.

Method of and system for routing in a photonic network

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.

Using gain tilt for local compensation of unwanted power gradients

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. The method involves measuring the power level of the optical signal received at an optical receiver through the optical link and referencing said measured receive power level to a nominal power level in the multiplex immediately preceding the receiver; measuring the power level of the optical signal at an optical transmitter and referencing said measured transmit power level to a nominal power level in the multiplex immediately following the transmitter; calculating a mean power level of the optical signal from said optical measurements, the mean power level of the optical signal being the mean of the power levels of the optical signal at the transmitter and at the receiver referenced to the nominal power levels in the associated multiplexes; and adjusting the mean power level of the optical signal independently of the power levels of other optical signals carried on the same optical link to the receiver so that a desired OSNR at the receiver is achievable.

Power balancing in DWDM optical networks

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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Harlow, United Kingdom

Bram Peeters