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Photonic integrated circuit
A photonic integrated circuit (PIC) or integrated optical circuit is a device that integrates multiple photonic functions and as such is analogous to an Electronic Integrated Circuit. However the major difference between the two being that a photonic integrated circuit provides functionality for information signals imposed on optical wavelengths typically in the Visible spectrum or near infrared 850nm-1650nm.
A 2005 development solved a quantum noise problem that prevented silicon from being used to generate laser light, permitting new integrated circuits to use high-bandwidth laser light generated within the circuit itself as a signal medium.
Additional recommended knowledge
Comparison to electronic integration
Unlike electronic integration where silicon is the dominant material system photonic integrated circuits have been fabricated from a variety of material systems including silica on silicon, Silicon on insulator, various polymers and semiconductor materials which are used to make semiconductor lasers such as GaAs and InP. The different material systems are used because they each provide different advantages and limitations depending on the function to be integrated.
The fabrication techniques are similar to those used in electronic integrated circuits in which photolithography is used to pattern wafers for etching and material deposition. Unlike electronics where the primary device is the transistor there is no single dominant device. The range of devices required on a chip includes low loss interconnect waveguides, power splitters, optical amplifiers, optical modulators, filters, lasers and detectors. These devices require a variety of different materials and fabrication techniques making it difficult to realize all of them on a single chip.
Examples of photonic integrated circuits
The primary application for photonic integrated circuits is in the area of fiber-optic communication though applications in other fields such as biomedical are also possible.
The arrayed waveguide grating (AWG) which are commonly used as optical (de)multiplexers in wavelength division multiplexed (WDM) fiber-optic communication systems are an example of a photonic integrated circuit which has replaced previous multiplexing schemes which utilized multiple discrete filter elements.
Another example of a photonic integrated chip in wide use today in fiber-optic communication systems is the externally modulated laser (EML) which combines a distributed feed back laser diode with an electro-absorption modulator  on a single InP based chip.
Advantages of photonic circuits
Photonic integrated circuits can allow optical systems to be made more compact and higher performance than with discrete optical components. They also offer the possibility of integration with electronic circuits to provide increased functionality. 
Photonic integrated circuits should also be immune to the hazards of functionality losses associated with electromagnetic pulse (EMP), though may not be immune to high neutron flux.
Notes and references
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Photonic_integrated_circuit". A list of authors is available in Wikipedia.|