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Spotlight on Optics

Spotlight on Optics


  • November 2011

Optics InfoBase > Spotlight on Optics > Nonlinear fiber optics: its history and recent progress [Invited]

Nonlinear fiber optics: its history and recent progress [Invited]

Published in JOSA B, Vol. 28 Issue 12, pp.A1-A10 (2011)
by Govind P. Agrawal

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Spotlight summary: The optical fiber is an amazing tool. Its versatile nature has made it suitable for use in several application fields. In its basic form the fiber can be viewed as an almost transparent, extremely broadband waveguide at near-infrared wavelengths. This has allowed its widespread use in communications, enabling the Internet as we know it today with all its transformational effects in society. But the optical fiber is much more than a standardized low-loss glass cable. For example, when doped with rare earths, it can be used to provide optical gain and form lasers and amplifiers. Through single-mode fiber designs, the beam generated at the output of fiber lasers is usually of a very high quality, whereas the fiber geometry itself allows efficient dissipation of heat, making fiber lasers be, to a great extent, naturally immune to heat generation even when operating at extremely high power levels. In other cases, silica fibers can be designed to exhibit specific dispersion properties over wide spectral regions, maintain the polarization of light along their entire length, or allow light guidance only in certain spectral bands by making use of the bandgap effect. Through suitable choice of materials and waveguide designs, optical fibers have become an enabling technology in diverse areas, ranging for example, from medical imaging to sensing for the construction industry.

What is usually perceived to be one of the main attractions of silica (the most common material for the fabrication of optical fibers) is its high linearity, implying that the interaction of the propagating electromagnetic field with the waveguide material is extremely low. This property of silica is particularly useful in telecommunications, since it allows multiple signals to be simultaneously transmitted over long distances in optical fibers with minimal mixing between them. However, when compared with other optical crystals or liquids, the main feature of the optical fiber is that it allows the field to propagate over extremely long lengths confined in a tiny spot. Therefore, when the power of the field is high, even strong nonlinear effects can be generated. This has been known for more than three decades, and during this period the field of nonlinear fiber optics has experienced significant advances, often fueled by advances in both fiber technology and high power lasers. Today the optical fiber is an important tool for observing supercontinuum spectra (a term used to describe extremely broadband optical spectra, usually generated through the propagation of intense ultrashort pulses under conditions that excite a variety of nonlinear effects), for giving rise to the generation of new wavelengths through parametric effects, or even for controlling the characteristics of one optical beam through another, thereby allowing the all-optical processing of signals at ultrafast speeds.

One could hardly think of a more suitable author for a paper that reviews the basic principles and applications of nonlinear fiber optics. Govind Agrawal’s frequently revised textbooks are the first point of reference for any researcher studying nonlinear effects in fibers, and his name has become synonymous to the basic theory behind the field. Through a brilliantly concise and accessible paper, the nonlinear propagation of short pulses is described within a few pages, and some of the most important applications of the field are presented. This is a thoroughly enjoyable paper, highly recommended to any students starting their journey in the fascinating topic of fiber optics.

--Periklis Petropoulos

OCIS Codes: (130.4310) Integrated optics : Nonlinear
(190.4370) Nonlinear optics : Nonlinear optics, fibers

Posted on November 11, 2011

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