Consequent to the mind boggling progress in high-speed optical telecommunication witnessed in late 1990s, it appeared that it would only be a matter of time before the huge theoretical bandwidth of 53 THz, offered by low-loss transmission windows in low water peak high-silica optical fibers would be tapped for telecommunication through dense wavelength division multiplexing techniques! In spite of this possibility, there has been a considerable resurgence of interest amongst researchers to develop application-specific specialty fibers, e.g. fibers in which transmission loss of the material would not be a limiting factor and in which nonlinearity and dispersion properties could be conveniently tailored to achieve transmission characteristics that are otherwise almost impossible to realize in conventional high-silica fibers. Research targeted at such fiber designs in the early 1990s gave rise to a new class of fibers, known as microstructured optical fibers (MOFs), which are characterized with wavelength scale periodic refractive index features across its cross-section. The periodicity could be realized by having a two-dimensional periodic array of low and high refractive index regions e.g. air holes embedded in a solid dielectric like fused silica glass. These structures exhibit photonic bandgaps i.e. they forbid propagation of a certain band of wavelengths within them. If the frequency of incident light happens to fall within the photonic bandgap, which is characteristic of these fibers, then propagation of light is forbidden inside it. In contrast to the electronic bandgap, which is the consequence of a periodic arrangement of atoms/molecules in a semiconductor crystal lattice, a photonic bandgap arises due to a periodic distribution of refractive index in a PCF. However by introducing in the central region a defect to an otherwise periodic structure, light (within the bandgap) could be localized in the defect region thereby mimicking a fiber core. The defect region could be a medium of refractive index higher or lower (e.g. air) than the average refractive index of the surrounding layers. In the former case, light is guided by modified total internal reflection due to the average refractive index of the cladding being lower than the central defect region. In case of lower refractive index defect, the corresponding MOFs are known as photonic bandgap fibers (PBGFs). In contrast to a conventional optical fiber, in which light is guided by total internal reflection, Bragg scattering is responsible for effective wave guidance in such fibers, which led to the christening of these fibers as photonic bandgap guided optical fibers. In 1987 in the same issue of Physical Review Letters, Eli Yablonovitch and Sameer John independently proposed for the first time the possibility of controlling properties of light through the photonic bandgap effect in man-made photonic crystals. Microstructured optical fibers have been a fall out of that research. The talk would focus on basic functional principle of optical wave guidance in such fibers vis-a-vis conventional fibers. Details of propagation and design & technology of 1D photonic band gap Bragg fibers would be described, in which we have recently made some research contributions and our collaborators in Russian Academy of Science have succeeded in fabricating some of our designed fibers. Discussions on applications would include designs of dispersion compensating fibers, fibers for metro networks, nonlinear spectral broadening in them and generation of supercontinuum light.

Bishnu P. Pal obtained M.Sc. and Ph.D. degrees in Physics from Jadavpur University (Kolkata) and IIT Delhi in 1970 and 1975, respectively as a National Science Talent Search Scholar. In late 1977 he joined the academic staff of IIT Delhi as a specialist on Fiber Optics, where he is a Professor of Physics since 1990. He has worked as Visiting Professor at the Norwegian Institute of Technology, Trondheim (Norway), University of Strathclyde, Glasgow (UK), Optoelectronics Research Center at City University of Hong Kong, and Universities at Nice and Limoges (France), the Fraunhofer Institute für Physikalische Messtechnik, Freiburg (Germany) as Alexander von Humboldt Fellow, and the National Institute of Standards and Technology, Boulder (USA) as a Fulbright Scholar, for various periods. He has been a founding member of International Journal of Optoelectronics (Taylor & Francis, UK) and he is currently a Member of the Editorial Advisory Boards of the journals: J. Elect. Engg. & Tech. (Korea), Optoelectron. Letts. (China), and IETE Students Journal (India). Prof. Pal has extensive teaching, research, sponsored R&D, and consulting (for Indian and US industries) experience on various aspects of Fiber Optics and related components and he has published and reported over 130 research papers and research reviews in international journals and conferences and has coauthored one each Indian and US patents. He is co-author of the book entitled Fiber Optics and Instrumentation (in Russian, Mashinostroenie Publishing House, Leningrad, 1987) and has edited the books: Fundamentals of Fiber Optics in Telecommunication and Sensor Systems (New Age Publications, New Delhi and John Wiley, New York, 1992, 4th reprint 2006) and more recently “Guided Wave Optical Components and Devices: Basics, Technology, and Applications (Academic Press/Elsevier, Burlington, 2006). He has also contributed 11 chapters in other books and monographs. He has been deeply involved with the conception and development of the Fiber Optics Laboratory at IIT Delhi in late 1970s. Prof. Pal is a Fellow of IETE (India) and Optical Society of India, Foreign Member of the Royal Norwegian Society of Sciences and Letters Academy (Norway), and is a Member of the Optical Society of America and IEEE/Laser and Electrooptics Society (USA). He has been an invited speaker at over 24 international conferences and he has been a member of the Technical/Advisory Committees of over 15 International Conferences. He is a co-recipient (with K. Thyagarajan) of the First Fiber Optic Person of the Year award in 1997 instituted by Lucent Technology in India for his significant contributions in all-fiber branching components for optical networks and also the Gowri Memorial Award for the year 1991 of IETE (India) for his paper (co-author B.D. Gupta) on fiber optic biosensors. He is currently a Distinguished Lecturer of IEEE/LEOS for 2005-2007 for his significant contributions to Guided Wave Optical Components and Devices. His current research interests concern guided wave optical components for DWDM and optical networks, gain flattening in EDFAs, specialty fibers like dispersion compensating fibers, and microstructured optical fibers, and also fiber optic sensors, optrodes, and near field fiber probes. Prof. Pal is running a 3-year term as a Member of the International Council of the Optical Society of America effective January 2007.