Optical switch  An optical switch is a device that selectively switches optical signals from one channel to another. The switching can be temporal or spatial.The former is known as an optical (time-domain) switch or an optical modulator, while the latter is called an optical space switch or an optical router. In general, optical modulators and routers can be made from each other. The word applies on several levels. In commercial terms (such as "the telecom optical switch market size") it refers to any piece of circuit switching equipment between fibers. The majority of installed systems in this category actually use electronic switching between fiber transponders. Systems that perform this function by routing light beams are often referred to as "photonic" switches, independent of how the light itself is switched. Away from telecom, an optical switch is the unit that actually switches light between fibers, and a photonic switch is one that does this by exploiting nonlinear material properties, such as semiconductor-based materials, to steer light (i.e., to switch wavelengths, intensities, or directions) . Hence a certain portion of the optical switch market is made up of photonic switches. These will contain within them an optical switch, which will, in some cases, be a photonic switch. An optical switch may operate by mechanical means, such as physically shifting an optical fiber to drive one or more alternative fibers, or by electro-optic effects, magneto-optic effects, or other methods. Slow optical switches, such as those using moving fibers, may be used for alternate routing of an optical switch transmission path, such as routing around a fault. Fast optical switches, such as those using electro-optic or magneto-optic effects, may be used to perform logic operations; also included in this category are semiconductor optical amplifiers, which are optoelectronic devices that can be used as optical switches and be integrated with discrete or integrated microelectronic circuits. The functionality of any switch can be described in terms of the connections it can establish. As stated in Telcordia GR-1073,  a connection is the association between two ports on a switch and is indicated as a pair of port identifiers ("i", "j" ), where "i" and "j" are two ports between which the connection is established. A connection identifies the transmission path between two ports. An optical signal can be applied to either one of the connected ports. However, the nature of the signal emerging at the other port depends on the optical switch and the state of the connection.