Lambda switching (sometimes called photonic switching, or wavelength switching) is the technology used in optical networking to switch individual wavelengths of light onto separate paths for specific routing of information. In conjunction with technologies such as dense wavelength division multiplexing (DWDM) - which enables 80 or more separate light wavelengths to be transmitted on a single optical fiber - lambda switching enables a light path to behave like a virtual circuit.
Although the ability to redirect specific wavelengths intelligently is, in itself, a technological breakthrough, lambda switching works in much the same way as traditional routing and switching. Lambda routers - which are also called wavelength routers, or optical cross-connects (OXC) - are positioned at network junction points. The lambda router takes in a single wavelength of light from a specific fiber optic strand and recombines it into another strand that is set on a different path. Lambda routers are being manufactured by a number of companies, including Ciena, Lucent, and Nortel.
Multiprotocol Lambda Switching is a variation of Multiprotocol Label Switching (MPLS, confusingly, the abbreviation for both variants) in which specific wavelengths serve in place of labels as unique identifiers. The specified wavelengths, like the labels, make it possible for routers and switches to perform necessary functions automatically, without having to extract instructions regarding those functions from IP addresses or other packet information.
Lambda switching gets its name from lambda, the 11th letter of the Greek alphabet, which has been adopted as the symbol for wavelength. In networking, the word is used to refer to an individual optical wavelength.