1 Application Specific Optical Fibers Bishnu P. Pal Indian Institute of Technology Delhi Physics Department New Delhi: 110016 India 1. Introduction Optical fiber technology was considered to be a major driver behind the information technology revolution and the huge progress on global telecommunications that has been witnessed in recent years. Fiber optic telecommunication is now taken for granted in view of its wide-ranging application as the most suitable singular transmission medium for voice, video, and data signals. Indeed, optical fibers have now penetrated virtually all segments of telecommunication networks - be it trans-oceanic, transcontinental, inter-city, metro, access, campus, or on-premise [Pal, 2006]. Initial R&D revolution in this field had centered on achieving optical transparency in terms of exploitation of the low-loss and low-dispersion transmission wavelength windows of high-silica optical fibers. The earliest optical fiber communication systems exploited the first low loss wavelength window centered on 820 nm of silica with graded index multimode fibers as the transmission media. However, primarily due to unpredictable nature of the bandwidth of jointed multimode fiber links, since early- 1980s the system focus had shifted to single-mode fibers. This was accentuated by the discovery of the zero material dispersion characteristic of silica fibers, which occurs at a wavelength of 1280 nm [Payne & Gambling, 1975] in close proximity to its second low loss wavelength window centered at 1310 nm. The next revolution in lightwave communication took place when broadband optical fiber amplifiers in the form of erbium doped fiber amplifiers (EDFA) were developed in 1987 [Mears et al, 1987], whose operating wavelengths fortuitously coincided with the lowest loss transmission window of silica fibers centered at 1550 nm [Miye et al, 1979] and heralded the emergence of the era of dense wavelength division multiplexing (DWDM) technology in the mid-1990s [Kartapoulos, 2000]. Recent development of the so-called low water peak fibers like AllWave™ and SMF-28e™ fibers, which are devoid of the characteristic OH − loss peak (centered at 1380 nm) extended the low loss wavelength window in high-silica fibers from 1280 nm (235 THz) to 1650 nm (182 THz) thereby offering, in principle, an enormously broad 53 THz of optical transmission bandwidth to be potentially tapped through DWDM technique! State-of-the-art technology has already demonstrated exploitation and utilization of 25 ~ 30 THz optical bandwidth. The emergence of DWDM technology has also driven the development of various specialty fibers and all-fiber components for seamless growth of the lightwave communication technology. These application-specific fibers were required to address new issues/features such as broadband dispersion compensation, realization of specialized components such as Source: Frontiers in Guided Wave Optics and Optoelectronics, Book edited by: Bishnu Pal, ISBN 978-953-7619-82-4, pp. 674, February 2010, INTECH, Croatia, downloaded from SCIYO.COM www.intechopen.com