Optical switch

An optical switch is a device that selectively switches optical signals on or off or from one channel to another. 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. Since the switching can be temporal or spatial, such switches are analogous to one-way or two-way switches in electrical circuits. In general, optical modulators and routers can be made from each other. An optical switch is a device that selectively switches optical signals on or off or from one channel to another. 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. Since the switching can be temporal or spatial, such switches are analogous to one-way or two-way switches in electrical circuits. 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 apair of port identifiers (i, j ), where i and j are two ports between which theconnection is established. A connection identifies the transmission path betweentwo 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 opticalswitch and the state of the connection. A connection can be in the on state or theoff state. A connection is said to be in the on state if an optical signal applied toone port emerges at the other port with essentially zero loss in optical energy. Aconnection is said to be in the off state if essentially zero optical energy emergesat the other port. Connections established in optical switches can be unidirectional or bidirectional. A unidirectional connection only allows optical signal transmission in one direction between the connected ports. A bidirectional connection allows optical signal transmission in both directions over the connection. Connections in passive and transparent optical switches are bidirectional, i.e., if a connection (i, j ) is set up, optical transmission is possible from i to j and from j to i.