In telecommunication, an optical switch is a switch that enables signals in optical fibers or integrated optical circuits (IOCs) to be selectively switched from one circuit to another.
The word is used 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 physically switching light are often referred to as "photonic" switches, independent of how the light itself is switched. Away from the world of telecom systems, 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 to steer light (i.e., to switch wavelengths or signals within a given fiber).
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 a small number of 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 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 the semiconductor optical amplifiers, which are optoelectronic devices that can be used as optical switches and be integrated with discrete or integrated microelectronic circuits.
A search on “optical switch”  yielded some 8000 patents, roughly categorized as follows:
- MEMS approaches involving arrays of micromirrors that can deflect an optical signal to the appropriate receiver (e.g., U.S. Patent 6,396,976);
- Piezoelelectric Beam Steering involving piezoelctric ceramics providing enhanced optical switching characteristics
- Inkjet methods involving the intersection of two waveguides so that light is deflected from one to the other when an inkjet-like bubble is created (e.g., Patent 6,212,308);
- Liquid crystals (e.g., Patent 4,948,229) that rotate polarized light either 0 degrees or 90 degrees depending on the applied electric field to support switching;
- Thermal methods (e.g., Patent 5,037,169) that vary the index of refraction in one leg of an interferometer to switch the signal on or off;
- Nonlinear methods (e.g., Patent 5,319,492) that vary the diffraction pattern in a medium by taking advantage of the material nonlinear properties to deflect light to the desired receiver;
- Acousto-optic methods that change the refractive index as a result of strain induced by an acoustic field to deflect light (e.g., Patent 6,922,498);
- Amplifiers and attenuators in output fibers that adjust the signal to the digital “0” power range (when the fiber is not switched to) or to the normal power range when it is (e.g., Patent 7,027,211).
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