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Tutorial 1 Optical fiber amplifiers Prof. K Thyagarajan Physics Department, Indian Institute of Technology Delhi, New Delhi 110016 ktrajan@physics.iitd.ernet. Optical amplifiers which amplify information carrying optical signals in the optical domain itself without converting them into electrical signals, have truly revolutionized fiber optic communications and made possible the implementation of dense wavelength division multiplexed (DWDM) systems. This tutorial on Optical Fiber Amplifiers will start with a very brief introduction to single mode optical fibers and their characteristics of specific relevance to optical amplification. Basic working principle and characteristics of optical components such as WDM couplers, tap couplers, polarization combiners, optical isolators, which are used in optical amplifiers, will be covered. We will then discuss the fundamentals of optical amplification by erbium doped fibers and cover various characteristics such as gain spectrum, gain flattening, gain saturation, amplified spontaneous emission noise and transients in EDFAs. Concepts of optical signal to noise ratio (OSNR) and noise figure (NF) of amplifiers as well as issues of limitation due to noise accumulation in a fiber optic system with periodic amplification will also be covered. This will be followed by fundamentals of Raman amplification in optical fibers including gain spectrum, gain flattening and noise and a comparison of the performance of the two types of optical amplifiers with regard to gain and noise. Discussions on discrete and distributed Raman amplifiers and their specific applications will be presented. Examples of link design using EDFA and Raman amplifiers will also be covered. Speaker's biography K. Thyagarajan is currently Professor of Physics at the Indian Institute of Technology, New Delhi. He was a Visiting Scientist at the Ecole Normale Superieure, Paris, France and the Central Research Laboratories (LCR), Thomson-CSF, Orsay, France during 1977-78 and 1983-84 and was a Visiting Professor at the Department of Electrical Engineering, University of Florida, Gainesville, during 1993-1994. Besides several research publications to his credit, Professor Thyagarajan is also co-author (with Professor A. K. Ghatak) of five books: Contemporary Optics (Plenum Press, New York, 1978), Lasers: Theory and Applications (Plenum Press, New York, 1981), Optical Electronics (Cambridge University Press, Cambridge, 1989), Introduction to Fiber Optics (Cambridge University Press, UK, 1998) and Lagrangian Optics (coauthored with V. Lakshminarayanan and Ajoy Ghatak), Kluwer, Boston, 2002. He is also the co-author of a review titled "Graded Index Optical Waveguides: A Review", Progress in Optics (Ed. E. Wolf), Vol. XVIII, 1980. During the period 1988 to 1991, he was an awardee of the Research Fellowship of the Indian National Science Academy. He was the joint awardee (with Prof. B. P. Pal) of the "Fiber Optic Person of the Year 1997" award by Lucent Technologies- Finolex and Voice and Data, India. In 2003 he was given the title of "Officier dans l'ordre des Palmes Academiques" by the French Government. He is currently a consultant to Tejas Networks India Pvt. Ltd., Bangalore specifically looking into advanced issues related to high capacity communication through optical fibers.