Telecom data is transmitted over long distances optically, rather than electronically. It is more efficient, more secure and supports higher data rates than electronic transmission. Telecom networks are therefore made up of fibre-optic cables, or fibres.
Each fibre in the network carries multiple independent signals, to maximise network capacity. Each signal is transmitted on a different wavelength. This is called Wavelength Division Multiplexing, or WDM.
Different fibres meet at junctions in the telecom network, called nodes. At the nodes, Reconfigurable Optical Add-Drop Multiplexers (ROADMs) switch the WDM signals between the different fibres. This enables data to be sent between any two arbitrary points in the telecom network.
Each ROADM uses several Wavelength Selective Switches (WSSs) to steer the WDM signals between the different fibres. A WSS takes the WDM signals from an input fibre, and is dynamically controlled to send each signal to any one of multiple output fibres.
The demand for telecom bandwidth is accelerating rapidly. The number of internet users is increasing, and each user has a growing number of connected devices. These devices are demanding more data to supply bandwidth-intensive services: videos are being streamed and downloaded in ever-higher definitions, and cloud computing is expanding rapidly, for both remote storage and remote processing.
To satisfy this burgeoning demand for bandwidth, the telecom network needs greater switching capacity. This requires greater numbers of WSSs, each with higher performance.