Photonic integrated circuit
A photonic integrated circuit (PIC) or integrated optical circuit is a device that integrates multiple (at least two) photonic functions and as such is analogous to an electronic integrated circuit. The major difference between the two is that a photonic integrated circuit provides functionality for information signals imposed on optical wavelengths typically in the visible spectrum or near infrared 850 nm-1650 nm.
The most commercially utilized material platform for photonic integrated circuits is indium phosphide, which allows for the integration of various optically active and passive functions on the same chip. Initial examples of photonic integrated circuits were simple 2 section distributed Bragg reflector lasers, consisting of two independently controlled device sections - a gain section and a DBR mirror section. Consequently, all modern monolithic tunable lasers, widely tunable lasers, externally modulated lasers and transmitters, integrated receivers, etc. are examples of photonic integrated circuits. Current state-of-the-art devices integrate hundreds of functions onto single chip. Pioneering work in this arena was performed at Bell Laboratories. Most notable academic centers of excellence of photonic integrated circuits in InP are the University of California at Santa Barbara, USA, and the Technical University of Eindhoven in the Netherlands.
Recently, a large amount of funding has been invested into developing photonic integrated circuits in Silicon.
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.
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 electro-optic crystals such as lithium niobate, 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. For instance, silica (silicon dioxide) based PICs have very desirable properties for passive photonic circuits such as AWGs (see below) due to their comparatively low losses and low thermal sensitivity, GaAs or InP based PICs allow the direct integration of light sources and Silicon PICs enable co-integration of the photonics with transistor based electronics.
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.
Newer techniques using resonant photonic interferometry is making way for UV LEDs to be used for optical computing requirements with much cheaper costs leading the way to PHz consumer electronics.
Examples of photonic integrated circuits
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.
One challenge to achieving this level of integration is the size discrepancy between electronic and photonic components. The emerging field of nanoplasmonics is focused on creating ultracompact components for realizing truly nanoscale photonic devices to match their electronic counterparts.
An example of the new breed of components is a recently proposed novel type of bandpass plasmonic filter that uses a response similar to electromagnetically induced transparency to achieve multichannel filtering. This allows easy control over the filtering wavelengths and bandwidths for applications in wavelength multiplexing systems for optical computing and communications in highly integrated all-optical circuits.
Photonic integration is currently an active topic in U.S. Defense contracts:
Also, it is part of recommendations by the Optical Internetworking Forum for inclusion in 100 gigahertz optical networking standards:
Notes and references
- Larry Coldren; Scott Corzine, Milan Mashanovitch (2012). Diode Lasers and Photonic Integrated Circuits (Second ed.). John Wiley and Sons.
- Rong, Haisheng; Jones, Richard; Liu, Ansheng; Cohen, Oded; Hak, Dani; Fang, Alexander; and Paniccia, Mario (February 2005). "A continuous-wave Raman silicon laser" (PDF). Nature 433 (7027): 725–728. Bibcode:2005Natur.433..725R. doi:10.1038/nature03346. PMID 15716948.
- A. Narasimha et al. (2008). "A 40-Gb/s QSFP optoelectronic transceiver in a 0.13 µm CMOS silicon-on-insulator technology". Proceedings of the Optical Fiber Communication Conference (OFC): OMK7.
- Encyclopedia of Laser Physics and Technology - electroabsorption modulators, electro-absorption modulators
- http://download.intel.com/technology/itj/2004/volume08issue02/art06_siliconphoto/vol8_art06.pdf "Silicon Photonics." Intel Technology Journal, Volume 08, Issue 02. 10 May 2004.
- Rashid Zia, Jon A. Schuller, Anu Chandran, Mark L. Brongersma (2006) "Plasmonics: the next chip-scale technology", Materials Today, Vol 9, Issues 7–8 http://www.sciencedirect.com/science/article/pii/S1369702106715723
- Hua Lu et al 2012 Nanotechnology 23 444003 "Tunable high-channel-count bandpass plasmonic filters based on an analogue of electromagnetically induced transparency" http://iopscience.iop.org/0957-4484/23/44/444003
- Larry A. Coldren, Scott C. Corzine, Milan L. Mashanovitch, "Diode lasers and photonic integrated circuits", Second edition, John Wiley and Sons, 2012
- Alastair D. McAulay: (1999) Optical Computer Architectures: The Application of Optical Concepts to Next Generation Computers
- Architectural issues in designing symbolic processors in optics.
- Brenner, K.-H.; Huang, Alan (1986). "Logic and architectures for digital optical computers (A)". J. Opt. Soc. Am. A3: 62.
- Brenner, K.-H. (1988). "A programmable optical processor based on symbolic substitution". Appl. Opt. 27 (9): 1687–1691.