A fiber optic switch is a module or device that switches optic fiber signals between circuits. Although this can refer to a wide range of devices that exist in telecom optical infrastructure, most utilize electronic circuits to provide multiplexing, enabling or switching between fiber transponders. These are referred to as photonic switches, but the process can also be called lambda switching or wavelength switching. These switch individual wavelengths onto specific fiber optic paths and may be incorporated with dense wavelength division multiplexing (DWDM) to enable multiple light wavelengths to coexist and provide concurrent data transfer on a single optical fiber. Light paths can then operate in an information network as a virtual circuit.

A type of switch is an optical cross-connect (OXC). An OXC can split off a single modulated wavelength beam from a fiber optic strand and retransmit this onto another different strand. Multiprotocol lamda switching can be used to replace the generic labeling in the multiprotocol label switching (MPLS) standard to effectively replace labels  which are used by routers and switches for high speed networking with specific wavelength IDs.

Modern fiber optic switches are MEMs devices employing micro mirrors, refractive mediums or diffraction gratings to steer and separate signals along with integrated electronic control circuitry. Wavelength specific signal splitters can also be implemented using interference filters. These optic devices all have the characteristic of being able to be controlled in some way by an electric field. This control can be by a number of mechanisms including electro-mechanical, electro-optic, acousto-optic and thermo-optic effects.  Each potential mechanism has different characteristics like switching times and attenuation or loss of signal level.

Modules tend to be defined in a similar way to electronic switches, for example, 1x2, 2x2,1x4,1x8, referring to the number of inputs and the number of outputs that can be switched to. Bidirectional switches are available. There is typically a control port for remote control of these devices that complies to a standard interface like USB. Card versions are available for rack-mounted installations.