The Optical Communications Reference

3.1

Chapter 3.1

Optical fibers for broadband

communication

Pal

3.1.1 Introduction

Development of optical fiber technology is considered to

be a major driver behind the information technology

revolution and the tremendou s progress in global tele-

communications that has been witnessed in recent years.

Fiber optics, from the point of view of telecommunica-

tion, is now almost taken for granted in view of its

wide-ranging application as the most suitable singular

transmission medium for voice, video, and dat a signals.

Indeed, optical fibers have now penet rated virtually all

segments of telecommunication networks, whether

transoceanic, transcontinental, intercity, metro, access,

campus, or on-premise. The first fiber optic telecom link

went public in 1977. Since that time, growth in the

lightwave communication industry until about 2000 has

been indeed mind boggling. According to a Luce nt

technology report [1], in the late 1990s optical fibers

were deployed at approximately 4800 km/hr, implying

a total fiber lengt h of almost three times around the globe

each day until it slowed down when the information

technology bubble burst!

The Internet revolution and deregulation of the tele-

communication sector from government controls, which

took place almost globally in the recent past, have sub-

stantially contributed to this unprecedented growth

within such a short time, which has been rarely seen in

any other technology. Initial research and development

(R&D) in this field had centered on achievin g optical

transparency in terms of exploitation of the low-loss and

low-dispersion transmission wavelength windows of

high-silica optical fibers. Though the low-loss fiber with

a loss under 20 dB/km that was reported for the first

time was a single-mode fiber (SMF) at the He–Ne laser

wavelength [2], the earliest fiber optic lightwave systems

exploited the first low-loss wavelength window centered

on 820 nm with graded index multi-mode fibers forming

the transmission media. However, primarily due to the

unpredictable nature of the bandwidth of jointed

multimode fiber links, since the early 1980s the system

focus shifted to SMFs by exploiting the zero material

dispersion characteristic of silica fibers, which occurs

at a wavelength of 1280 nm [3] in close proximity to

its second low-loss wavelength window centered at

1310 nm [4].

The next revolution in lightwave communication took

place when broadband optical fiber amplifiers in the form

of erbium-doped fiber am plifiers (EDFA) were de-

veloped in 1987 [5], whose ope rating wavelengths for-

tuitously coincided with the lowest-loss transmission

wavelength window of silica fibers centered at 1550 nm

[6] and heralded the emergence of the era of dense

wavelength division multiplexing (DWDM) technology in

the mid-1990s [7]. By definition, DWDM technology

implies simultaneous optical transmission through one

SMF of at least four wavelengths within the gain band-

width of an EDFA (Fig. 3.1.1). Recent development of

the so-called AllWaveÔ and SMF-28eÔ fibers 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 transmissi on bandwidth to be poten-

tially tapped through the DWDM technique! These

fibers are usually referred to as enhanced SMF

(G.652.C) and are characterized with an additional low-

loss window in the E-band (1360–1460 nm), which is

about 30% more than the two low-loss windows centered

Guided Wave Optical Components and Devices; ISBN: 9780120884810

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