Department of Electrical & Electronic Engineering

Assignment onOptical Fiber Communication & Bangladesh

Course Code: EEE-4117Course Title: Optical Fiber Communication

Presented by

Md. Atiqur RahmanDepartment of Electrical & Electronic Engineering

Leading University

Content

sOptical Fiber..........................................................................................................................................3

Evolution of optical fiber......................................................................................................................3

The Nineteenth Century...................................................................................................................3

The Twentieth Century.....................................................................................................................5

The Twenty-first Century and Beyond..............................................................................................7

Types of optical fibers used in commercial applications......................................................................8

Losses in optical fiber link.....................................................................................................................9

Modal and chromatic dispersion......................................................................................................9

Modal Dispersion..........................................................................................................................9

Chromatic Dispersion..................................................................................................................10

Total Dispersion..........................................................................................................................10

Splice...............................................................................................................................................10

Connector........................................................................................................................................11

Fiber Attenuation............................................................................................................................11

Bending Loss................................................................................................................................12

Absorption..................................................................................................................................13

Scattering....................................................................................................................................13

Submarine cable system worldwide...................................................................................................14

First Commercial Cables..................................................................................................................15

Transatlantic Telegraph Cable........................................................................................................15

Cable to India, Singapore, Far East and Australia...........................................................................15

Submarine Cable across the Pacific................................................................................................15

Submarine cable in Bangladesh......................................................................................................15

Synchronous Optical Network (SONET)..............................................................................................16

Fiber optic network backbone in Bangladesh....................................................................................17

Applications of optical fiber in 4G technologies and beyond............................................................18

Reference............................................................................................................................................20

Optical Fiber Optical fiber is a glass/plastic filament or wire which carries light.

It is a cylindrical waveguide that operate at optical frequency. It confines electromagnetic energy in the form of light. It can be used to transfer information (in light form) from one point

to another. Wavelength: 1.7µm – 0.8µm Frequency: 176 THz to 375 THZ

Evolution of optical fiberIn the assignment I divided the evolution of optical fiber in three era

The Nineteenth Century The Twentieth Century The Twenty-first Century and Beyond

The Nineteenth CenturyThe earliest attempts to communicate via light undoubtedly go back thousands of years. Early long distance communication techniques, such as "smoke signals". Larger scale version of this optical communication technique was the "optical telegraph" deployed in France and elsewhere in the late 18th century.

Jean-Daniel Colladon, a 38-year-old Swiss professor at University of Geneva, demonstrated light guiding or TIR for the first time in 1841. He wanted to show the fluid flow through various holes of a tank and the breaking up of water jets. However, in the lecture hall the audience could not see the flowing water. He solved the problem by collecting and piping sunlight through a tube to the lecture table. The light was focused through the water tank and was made to incident on the edge of the jet at a glancing angle. TIR trapped the light in the liquid forcing it to follow the curved path until the water jet broke up. Instead of traveling in a straight line, the light followed the curvature of the water flow. Colladon later on wrote: "I managed to illuminate the interior of a stream in a dark Space. I have discovered that this strange arrangement offers in results one of the most beautiful, and most curious experiments that one can perform in a course on Optics." (Comptes Rendes, 15, 800-802 Oct. 24, 1842).

Colladon sent a paper to his friend Francois Arago who headed the French Academy of Sciences and edited its journal Comptes Renedes. Arago recalled that Jacques Babinet, a French specialist in Optics had made similar demonstrations in Paris. He focused candle light on to the bottom of a glass bottle as he poured a thin stream of water from the top. TIR guided the light along the jet. Arago asked Babinet to write down his work, but Babinet did not think that the work is very important. Yet he made a comment that "the idea also works very well with a glass shaft curved in whatever manner and I had indicated that (it could be used) to illuminate the inside of the mouth (Comptes Rendes 15, Oct. 24, 1842). After sending his letter to Arago, Babinet never returned to guiding of light before he died in 1872.

In 1870, John Tyndall, using a jet of water that flowed from one container to another and a beam of light, demonstrated that light used internal reflection to follow a specific path. As

Jean-Daniel Colladon

Jacques Babinet

John Tyndall

water poured out through the spout of the first container, Tyndall directed a beam of sunlight at the path of the water. The light, as seen by the audience, followed a zigzag path inside the curved path of the water. This simple experiment, illustrated in, marked the first research into the guided transmission of light.

Typical Early TIR (Total Internal Reflection) Demonstration

William Wheeling, in 1880, patented a method of light transfer called “piping light.” Wheeling believed that by using mirrored pipes branching off from a single source of illumination, i.e. a bright electric arc, he could send the light to many different rooms in the same way that water, through plumbing, is carried throughout buildings today. Due to the ineffectiveness of Wheeling’s idea and to the concurrent introduction of Edison’s highly successful incandescent light bulb, the concept of piping light never took off.

That same year, Alexander Graham Bell developed an optical voice transmission system he called the photophone. The photophone used free-space light to carry the human voice 200 meters. Specially placed mirrors reflected sunlight onto a diaphragm attached within the mouthpiece of the photophone. At the other end, mounted within a parabolic reflector, was a light-sensitive selenium resistor. This resistor was connected to a battery that was, in turn, wired to a telephone receiver. As one spoke into the photophone, the illuminated diaphragm vibrated, casting various intensities of light onto the selenium resistor. The changing intensity of light altered the current that passed through the telephone receiver which then converted the light back into speech. Bell believed this invention was superior to the telephone because it did not need wires to connect the transmitter and receiver. Today, free-space optical links find extensive use in metropolitan applications.

Alexander Graham Bell

The Twentieth CenturyFiber optic technology experienced a phenomenal rate of progress in the second half of the twentieth century. Early success came during the 1950’s with the development of the fiberscope. This image-transmitting device, which used the first practical all-glass fiber, was concurrently devised by Brian O’Brien at the American Optical Company and Narinder Kapany (who first coined the term “fiber optics” in 1956) and colleagues at the Imperial College of Science and Technology in London. Early all-glass fibers experienced excessive optical loss, the loss of the light signal as it traveled through the fiber, limiting transmission distances.

Optical Fiber with Cladding

This motivated scientists to develop glass fibers that included a separate glass coating. The innermost region of the fiber, or core, was used to transmit the light, while the glass coating, or cladding, prevented the light from leaking out of the core by reflecting the light within the boundaries of the core. This concept is explained by Snell’s Law which states that the angle at which light is reflected is dependent on the refractive indices of the two materials - in this case, the core and the cladding. The lower refractive index of the cladding (with respect to the core) causes the light to be angled back into the core as illustrated.

The fiberscope quickly found application inspecting welds inside reactor vessels and combustion chambers of jet aircraft engines as well as in the medical field. Fiberscope technology has evolved over the years to make laparoscopic surgery one of the great medical advances of the twentieth century.

The development of laser technology was the next important step in the establishment of the industry of fiber optics. Only the laser diode (LD) or its lower-power cousin, the light-emitting diode (LED), had the potential to generate large amounts of light in a spot tiny enough to be useful for fiber optics. In 1957, Gordon Gould popularized the idea of using lasers when, as a graduate student at Columbia University, he described the laser as an intense light source. Shortly after, Charles Townes and Arthur Schawlow at Bell Laboratories supported the laser in scientific circles. Lasers went through several generations including the development of the ruby laser and the helium-neon laser in 1960. Semiconductor lasers were first realized in 1962; these lasers are the type most widely used in fiber optics today.

Because of their higher modulation frequency capability, the importance of lasers as a means of carrying information did not go unnoticed by communications engineers. Light has an information-carrying capacity 10,000 times that of the highest radio frequencies being used. However, the laser is unsuited for open-air transmission because it is adversely affected by environmental conditions such as rain, snow, hail, and smog. Faced with the challenge of

finding a transmission medium other than air, Charles Kao and Charles Hockham, working at the Standard Telecommunication Laboratory in England in 1966, published a landmark paper proposing that optical fiber might be a suitable transmission medium if its attenuation could be kept under 20 decibels per kilometer (dB/km). At the time of this proposal, optical fibers exhibited losses of 1,000 dB/ km or more. Even at a loss of only 20 dB/km, 99% of the light would still be lost over only 3,300 feet. In other words, only 1/100th of the optical power that was transmitted reached the receiver. Intuitively, researchers postulated that the current, higher optical losses were the result of impurities in the glass and not the glass itself. An optical loss of 20 dB/km was within the capability of the electronics and optoelectronic components of the day.

Intrigued by Kao and Hockham’s proposal, glass researchers began to work on the problem of purifying glass. In 1970, Drs. Robert Maurer, Donald Keck, and Peter Schultz of Corning succeeded in developing a glass fiber that exhibited attenuation at less than 20 dB/km, the threshold for making fiber optics a viable technology. It was the purest glass ever made.

The early work on fiber optic light source and detector was slow and often had to borrow technology developed for other reasons. For example, the first fiber optic light sources were derived from visible indicator LED's. As demand grew, light sources were developed for fiber optics that offered higher switching speed, more appropriate wavelengths, and higher output power. For more information on light emitters see Laser Diodes and LED's.

Fiber optics developed over the years in a series of generations that can be closely tied to wavelength. Figure 6 shows three curves. The top, dashed, curve corresponds to early 1980’s fiber, the middle, dotted, curve corresponds to late 1980’s fiber, and the bottom, solid, curve corresponds to modern optical fiber. The earliest fiber optic systems were developed at an operating wavelength of about 850 nm. This wavelength corresponds to the so-called “first window” in a silica-based optical fiber. This window refers to a wavelength region that offers low optical loss. It sits between several large absorption peaks caused primarily by moisture in the fiber and Rayleigh scattering.

Four Wavelength Regions of Optical Fiber

The 850 nm region was initially attractive because the technology for light emitters at this wavelength had already been perfected in visible indicator and infrared (IR) LED's. Low-cost silicon detectors could also be used at the 850 nm wavelength. As the technology progressed, the first window became less attractive because of its relatively high 3 dB/km loss limit.

Most companies jumped to the “second window” at 1310 nm with lower attenuation of about 0.5 dB/km. In late 1977, Nippon Telegraph and Telephone (NTT) developed the “third window” at 1550 nm. It offered the theoretical minimum optical loss for silica-based fibers, about 0.2 dB/km.

Today, 850 nm, 1310 nm, and 1550 nm systems are all manufactured and deployed along with very low-end, short distance, systems using visible wavelengths near 660 nm. Each wavelength has its advantage. Longer wavelengths offer higher performance, but always come with higher cost. The shortest link lengths can be handled with wavelengths of 660 nm or 850 nm. The longest link lengths require 1550 nm wavelength systems. A “fourth window,” near 1625 nm, is being developed. While it is not lower loss than the 1550 nm window, the loss is comparable.

The Twenty-first Century and BeyondToday, DWDM technology continues to develop. As the demand for data bandwidth increases, driven by the phenomenal growth of the Internet, the move to optical networking is the focus of new technologies. At this writing, over 800 million people have Internet access and use it regularly. That's over 12% of the entire world's population of 6.4 billion people. The world wide web already hosts over 350 million domain names, 8 billion web pages (that's only the visible, indexed, Internet, the invisible Internet is estimated to be up to 100 times larger), and according to estimates people upload more than 3.5 million new web pages every day. The Internet dominates traditional voice communication.

Projected Internet Traffic Increases

The important factor in these developments is the increase in fiber transmission capacity, which has grown by a factor of 200 in the last decade. Figure 8 illustrates this trend.

The Growth of Optical Fiber Transmission Capacity

Types of optical fibers used in commercial applicationsCATV (cable television) services are supplied via a fiber optic network to an optical node, which converts and distributes the electrical signal to subscribers via a coaxial cable connection. CATV applications utilizes both single mode and multimode signals within different areas of the network. Single Mode fiber is used to distribute signal from the central office to optical nodes, where it can be converted to multimode.

Data transmission fiber optics, simply put, is the sending and receiving of data from point-to-point via a network. It ranges from very simple cables connecting servers or storage arrays inside a network or telecommunications system, to large multi-fiber distribution cables supporting intra-building connectivity and beyond.

INTERNET: Bandwidths of up to 10Gbps, Streaming Movies in HD (High Defination), Effortless video conferencing with no lagging, gaming and so on.

The Independent Telecommunication Providers segment is an area of the industry that provides service(s) in rural areas, typically supporting residential and small to medium businesses. The services offered in these areas can range from basic telephone to triple play depending on the provider, subscriber location, and service availability. Expanded service can include television broadcast (high definition in some cases), VoIP (voice over internet protocol) phone service, and security over a single broadband connection. However, more and more of these various services are becoming available in rural locations nationwide.

The most significant and prevalent applications of fiber optics in medicine are in the imaging and illumination components of endoscopes. Flexible and rigid multi-fibers composed of step-index fibers and graded-index imaging rods are extensively used for visualization of internal organs and tissue which are accessible through natural openings or transcutaneous. The design of distinct endoscopes is described with a detailed review of their use in various medical specialties. Low-loss optical fibers are employed to transmit laser energy for surgery and photocoagulation. Multicolor laser light is transmitted through a single thin optical fiber to provide adequate illumination for viewing and color photography. Past attempts to develop plastic imaging multi-fibers and their future potential viewing and color photography. Past attempts to develop plastic imaging multi-fibers and their future potential are discussed. Other uses of fiber optics in medicine include remote spectrophotometry, pressure and position sensing, or scintillation counting. These and other applications, such as intravascular pressure transducers and in vivo ox-meters, are described.

Losses in optical fiber linkLight traveling in an optical fiber loses power over distance. The loss of power depends on the wavelength of the light and on the propagating material. For silica glass, the shorter wavelengths are attenuated the most. The lowest loss occurs at the 1550-nm wavelength, which is commonly used for long-distance transmissions.

Transmission of light by fiber optics is not 100% efficient. There are several reasons for this including absorption by the core and cladding (caused by the presence of impurities) and the leaking of light from of the cladding. When light reflects off the cladding /core interface it actually travels for a short distance within the cladding before being reflected back. This leads to attenuation (signal reduction) by up to 2db/Km for a multi-mode fiber. For example, with this level of attenuation, if light travelled over 10kM of cable only 10% of the signal would arrive at the following end.

The loss of power in light in an optical fiber is measured in decibels (dB). Fiber optic cable specifications express cable loss as attenuation per 1-km length as dB/km. This value is multiplied by the total length of the optical fiber in kilometers to determine the fiber's total loss in dB.

Optical fiber link loss is caused by a number of factors

Higher-order mode losses Modal and chromatic dispersion Connector Splice Fiber attenuation

Modal and chromatic dispersionModal DispersionModal Dispersion is the distortion in fiber or waveguide. Signal is spread due to different propagation velocity of optical signal in different mode.

Intermodal dispersion (also called modal dispersion) is the phenomenon that the group velocity of light propagating in a multimode fiber (or other waveguide) depends not only on the optical frequency (chromatic dispersion) but also on the propagation mode involved.

Intermodal dispersion results from different propagation characteristics of higher-order transverse modes in waveguides, such as multimode fibers. This effect can severely limit the possible data rate of a system for optical fiber communications based on multimode fibers.

Intermodal dispersion

Intermodal dispersion (also called modal dispersion) is the phenomenon that the group velocity of light propagating in a multimode fiber (or other waveguide) depends not only on the optical frequency (chromatic dispersion) but also on the propagation mode involved.

Chromatic DispersionChromatic dispersion (or material dispersion) is produced when different frequencies of light propagate in fiber with different velocities. Chromatic dispersion is larger for the wider source bandwidth. Thus it is largest for LEDs and smallest for LASERs. LED BW is about 5% of λ0, Laser BW about 0.1 % or below of λ0.

In addition to chromatic dispersion, there exists also waveguide dispersion that is significant for single mode fibers in longer wavelengths. Chromatic and waveguide dispersion are denoted as Intra- modal dispersion and their effects cancel each other at a certain wavelength. Total dispersion is determined as the geometric sum of intra-modal and inter-modal (or mode) dispersion with the net pulse spreading.

Chromatic and waveguide dispersion cancel each other at certain wavelength

Total DispersionTotal dispersion is determined as the geometric sum of intra-modal and inter-modal (or mode) dispersion with the net pulse spreading:

2 2 2intermod intramodtot

SpliceSplice loss occurs at all splice locations. Mechanical splices usually have the highest loss, commonly ranging from 0.2 to over 1.0 dB, depending on the type of splice. Fusion splices have lower losses, usually less than 0.1 dB. A loss of 0.05 dB or less is usually achieved with good equipment and an experienced splicing crew. High loss can be attributed to a number of factors, including:

o Poor cleaveo Misalignment of fiber coreso An air gap

o Contaminationo Index-of-refraction mismatcho Core diameter mismatch to name just a few.

ConnectorLosses at fiber optic connectors commonly range from 0.25 to over 1.5 dB and depend greatly on the type of connector used. Other factors that contribute to the connection loss include:

o Dirt or contaminants on the connector (very common)o Improper connector installationo A damaged connector faceo Poor scribe (cleave)o Mismatched fiber coreso Misaligned fiber coreso Index-of-refraction mismatch

Fiber AttenuationAttenuation means loss of light energy as the light pulse travels from one end of the cable to the other. It is also called as signal loss or fiber loss. It also decides the number of repeaters required between transmitter and receiver. Attenuation is directly proportional to the length of the cable.

Attenuation is defined as the ratio of optical output power to the input power in the fiber of length L.

α= 10log10 Pi/Po [dB/km]

Where, Pi= Input Power

Po= Output Power, α is attenuation constant

Fiber Attenuation

The various losses in the cable are due to

Bending Absorption Scattering

Bending LossBend loss occurs at fiber cable bends that are tighter than the cable's minimum bend radius. Bending loss can also occur on a smaller scale from such factors as:

o Sharp curves of the fiber coreo Displacements of a few millimeters or less, caused by buffer or jacket imperfectionso Poor installation practice

This light power loss, called micro-bending, can add up to a significant amount over a long distance. The loss which exists when an optical fiber undergoes bending is called bending losses.

There are two types of bending:

Macroscopic bendingBending in which complete fiber undergoes bends which causes certain modes not to be reflected and therefore causes loss to the cladding.

Macroscopic bending

Microscopic BendingEither the core or cladding undergoes slight bends at its surface. It causes light to be reflected at angles when there is no further reflection.

Microscopic Bending

AbsorptionIn the telecom region of the spectrum, caused primarily by excitation of chemical bond vibrations. Overtone and combination bands predominate near 1550 nm. Low-energy tail of electronic absorptions dominate in visible region. Electronic absorptions by color centers cause loss for some metal impurities.

There are two types of absorption:

o Intrinsic Absorptiono Extrinsic Absorption

Intrinsic Absorption Caused by the interaction with one or more components of the glass Occurs when photon interacts with an electron in the valence band & excites it to a

higher energy level near the UV region.

Extrinsic Absorption Also called impurity absorption. Results from the presence of transition metal ions like iron, chromium, cobalt, copper

& from OH ions i.e. from water.

ScatteringIt occurs due to microscopic variations in the material density, compositional fluctuations, structural in homogeneities and manufacturing defects.

Scattering are two types

o Linear Scattering Rayleigh Scattering losses Mie Scattering Losses Waveguide Scattering Losses

o Non-linear Scattering Stimulated Brillouin Scattering(SBS) Stimulated Raman Scattering(SRS)

Rayleigh scattering Losses These losses are due to microscopic variation in the material of the fiber. Unequal distribution of molecular densities or atomic densities leads to Rayleigh

scattering losses Glass is made up of several acids like SiO2, P2O5, etc. compositions, fluctuations can

occur because of these several oxides which rise to Rayleigh scattering losses.

Mie Scattering LossesThese losses results from the compositional fluctuations & structural in homo generics & defects created during fiber fabrications, causes the light to scatter outside the fiber.

Waveguide Scattering LossesIt is a result of variation in the core diameter, imperfections of the core cladding interface, change in RI of either core or cladding.

SBS Scattering: Stimulated Brillouin Scattering (SBS) may be regarded as the modulation of light

through thermal molecular vibrations within the fiber. Pb = 4.4x10-3d2λ2α dB v watts

Where, λ= operating wavelength (μm)

d= fiber core diameter (μm)

v = source bandwidth in (GHz)

SRS Scattering Stimulated Raman Scattering is similar to SBS except that high frequency optical

phonon rather than acoustic phonon is generated in scattering processes. Pb = 5.9x10-2 d2λα dB watts

Submarine cable system worldwideA massive network of fiber optic cables lies deep under the seas across the Earth. The cables allow us to quickly send our emails and videos, and connect our browsers and phone calls to sites in far-away lands. This network isn’t new. Submarine data cables date back to 1850, when the first international telegraph cable (with a capacity of 10 words per minute) spanned the channel between England and France. As early as 1901, telegraph cables crisscrossed the oceans and connected all the continents except for Antarctica.

Submarine Cable is the cable designed to be placed underwater. Such cables must be specially protected against moisture. At shallow depths on continental shelves, submarine cables commonly are plowed in and armored to protect them against ship anchors, trawler nets, and sharks, which are attracted to the electromagnetic fields and like to gnaw on the cables and repeaters. Submarine Cable was first inaugurated in 1956 containing 4000 voice circuits, termed as TAT-1. Later TAT-8 version, containing 3500 voice circuits was come out in 1983. TAT stands for Trans-Atlantic Telephone.

Subsequent cable generations included upgrades to telephone cables and data communications cables. Analog coaxial cables of steel-wrapped copper were widespread under the oceans beginning in the 1950s. The bandwidth of analog cable increased quickly in the 1960s and 70s, but the highest capacity systems required electrically powered repeaters to boost the signal every 6 to 9 kilometers, making them very expensive to install across oceans.

Starting in 1988, a massive 10-year build-out replaced the vast majority of these copper network cables with long-haul fiber optic cables. Today virtually all of the undersea long-haul communication cables are optical, as are land-based ones. Submarine data cables handle more than 95 percent of IP voice and data traffic between countries and continents, and 100 percent of international Internet traffic. Users in the United States, Europe and other well-connected regions often take for granted the ease of global communications.

The underwater cable network is a critical component to global commerce, and it’s growing. Spurring this growth is ever-increasing IP traffic, demand for higher bandwidth at reduced deployment cost and the need for additional routes and redundant cable systems that ensure resiliency. According to a comprehensive market research report by Global Industry

Analysts, cumulative global installation of submarine optical fiber cable is projected to reach two million kilometers by 2018, up from just over a million kilometers in 2009.

First Commercial CablesIn August 1850, John Watkins Brett's Anglo-French Telegraph Company laid the first line across the English Channel. It was simply a copper wire coated with gutta-percha, without any other protection. The experiment served to keep alive the concession, and the next year, on November 13, 1851, a protected core, or true cable, was laid from a government hulk, the Blazer, which was towed across the Channel. The next year, Great Britain and Ireland were linked together. In 1852, a cable laid by the Submarine Telegraph Company linked London to Paris for the first time. In May, 1853, England was joined to the Netherlands by a cable across the North Sea, from Oxford Ness to The Hague. It was laid by the Monarch, a paddle steamer which had been fitted for the work.

Transatlantic Telegraph CableThe first attempt at laying a transatlantic telegraph cable was promoted by Cyrus West Field, who persuaded British industrialists to fund and lay one in 1858. Subsequent attempts in 1865 and 1866 with the world's largest steamship, the SS Great Eastern, used a more advanced technology and produced the first successful transatlantic cable. The Great Eastern later went on to lay the first cable reaching to India from Aden, Yemen, in 1870.

Cable to India, Singapore, Far East and AustraliaAn 1863 cable to Bombay provided a crucial link to Saudi Arabia. In 1870 Bombay was linked to London via submarine cable in a combined operation by four cable companies, at the behest of the British Government. In 1872 these four companies were combined to form the mammoth global spanning Eastern Telegraph Company, owned by John Pender. A spin-off from Eastern In 1872, Australia was linked by cable to Bombay via Singapore and China and in 1876 the cable linked the British Empire from London to New Zealand

Submarine Cable across the PacificThis was completed in 1902–03, linking the US mainland to Hawaii in 1902 and Guam to the Philippines in 1903. Canada, Australia, New Zealand and Fiji were also linked in 1902.Decades later, the North Pacific Cable system was the first regenerative (repeater) system to completely cross the Pacific from the US mainland to Japan. The US portion of NPC was manufactured in Portland, Oregon, from 1989–1991 at STC Submarine Systems, and later Alcatel Submarine Networks. The system was laid by Cable & Wireless Marine on the CS Cable Venture in 1991.

Submarine cable in BangladeshBangladesh Submarine Cable Company (BSCCL) is a fiber optic submarine cable tele-communications company based in Bangladesh. Emerging in July 2008 from former BTTB (Bangladesh Telegraph & Telephone Board)’s submarine cable project, BSCCL presently handles Bangladesh’s lone submarine cable as a member of the SEA-ME-WE4 international submarine cable consortium that runs a total length of 20,000 km through 17 landing points in Singapore, Malaysia, Thailand, Bangladesh, India, Sri Lanka, Pakistan, United Arab Emirates, Saudi Arabia, Egypt, Tunisia, Italy, Algeria and France.

Synchronous Optical Network (SONET)High-speed (up to 2.5 Gbps) synchronous network specification developed by Bellcore and designed to run on optical fiber. STS-1 is the basic building block of SONET. Approved as an international standard in 1988. On a larger scale, the telecommunications industry uses the SONET standard for optical transport of TDM data. SONET, used in North America, is related standards that specify interface parameters, rates, framing formats, multiplexing methods, and management for synchronous TDM over fiber.

SONET is the American National Standards Institute standard for synchronous data transmission on optical media. The international equivalent of SONET is synchronous digital hierarchy (SDH). Together, they ensure standards so that digital networks can interconnect internationally and that existing conventional transmission systems can take advantage of optical media through tributary attachments.

SONET provides standards for a number of line rates up to the maximum line rate of 9.953 gigabits per second (Gbps). Actual line rates approaching 20 gigabits per second are possible. SONET is considered to be the foundation for the physical layer of the broadband ISDN (BISDN).

Asynchronous transfer mode runs as a layer on top of SONET as well as on top of other technologies. SONET defines a base rate of 51.84 Mbps and a set of multiples of the base rate known as "Optical Carrier levels (OCx)."

SONET

The figure displays an example of statistical TDM. SONET takes n bit streams, multiplexes them, and optically modulates the signal, sending it out using a light emitting device over fiber with a bit rate equal to (incoming bit rate) x n. Thus traffic arriving at the SONET multiplexer from four places at 2.5 Gb/s goes out as a single stream at 4 x 2.5 Gb/s, or 10 Gb/s. This principle is illustrated in the figure, which shows an increase in the bit rate by a factor of four in time slot T.

Fiber optic network backbone in BangladeshEstablishment of fiber optic links in Bangladesh began in 1986, along with the installation of new digital switches. Starting with the optical fiber link between Dhaka’s Maghbazar and Gulshan telephone exchanges, all intra-city inter- exchange connections are now established through short distance fiber-optic links. The intercity portions between the major cities started with the completion of the STM-16 fiber link between Dhaka to Chittagong in 2001. Bogra to Joypurhat to Ragpur and Dinajpur in the north west of Bangladesh is already connected by STM-4 optical link while Dhaka to Bogra optical fiber link via the Jamuna Bridge is currently under construction. In addition, there is a plan to connect Dhaka to Sylhet and Dhaka to Khulna on the optical fiber network.

Bangladesh’s Grameenphone has opened a new fiber optic cable link through the 4.8 kilometer long Jamuna Multipurpose Bridge becoming the first mobile phone operator in the country to do so. The fiber optic cable links Elenga in Tangail and Nolka in Sirajganj and covers a length of about 40 kilometers through the Jamuna Bridge. This link completes the Grameenphone fiber optic transmission backbone between the East and West zones of the country. The fiber-optic transmission backbone will ensure a more secure network providing high quality voice and data services in the Northern and Southern districts.

In the last three years BTTB built about 1375 Km optical fiber network in the country under two projects. The most modern SDH technology was adopted in all these optical fiber links. Dhaka – Comilla – Feni – Chittagong backbone optical link and Feni – Choumuhini – Noakhali, Choumuhini – Lakshmipur, Comilla – B. Baria spur optical links were implemented under Dhaka – Chittagong high capacity optical fiber project. The total length of optical cable laid under this project is about 450 Km. 18 core optical cables were used in backbone link whereas spur links were built with 12 core O.F cables. The transmission capacity of the backbone is 2.5 GB/s (STM-16). Transmission capacity of Feni – Choumihini spur link is 622 MB/s (STM-4) whereas the transmission capacity of Choumuhini – Noakhali, Choumuhini - Lakshmipur and Comilla – B. Baria spur links is 155 MB/s (STM-1). Some short haul optical links like Tongi – Gazipur and B.Baria Microwave Station – B.Baria Exchange of STM-1 capacity were also built under this project. The SDH transmission equipment used in this network are from Alcatel CIT. Under the project entitled “Installation and Expansion of Digital Telephone Exchanges in various District Head Quarters of Bangladesh” which is commonly known as 216 KL project, about 925 Km 12 core optical fiber cable network was built. The SDH transmission equipment used in this network are also from Alcatel CIT. The backbone optical link built under this project is Bogra – Palashbari – Rangpur – Saidpur – Dinajpur – Thakurgaon – Panchagarh. Bogra – Palashbari – Rangpur portion of this backbone is of STM-4 capacity and rest is of STM-1 capacity. Now the present requirement of E1 claims that the Rangpur – Saidpur – Dinajpur section of the link should be upgraded to STM-4. Some spur links also were built in different areas of the country under 216 KL project.

Map of the existing fiber-optic network in Bangladesh

Applications of optical fiber in 4G technologies and beyondIn a world of fast changing technology, there is a rising requirement for people to communicate and get connected with each other and have appropriate and timely access to information regardless of the location of the each individuals or the information. The increasing demands and requirements for wireless communication systems ubiquity have led to the need for a better understanding of fundamental issues in communication theory and electromagnetic and their implications for the design of highly-capable wireless systems. In continuous development of mobile environments, the major service providers in the wireless market kept on monitoring the growths of 4th generation (4G) mobile technology. 2G and 3G are well-established as the mainstream mobile technology around the world. 3G is stumbling to obtain market share for a different reasons and 4G is achieving some confidence.

In 2010, the total mobile subscriber base in North America, Europe and Asia Pacific, is expected to grow up to 2500 million and penetration will be over 50%. This kind of demand growth will require the support of higher capacity networks.

Given the technology at large, 4G mobile technology as an example, will give people a more convenience and ease in lifestyle. With the “anytime, anywhere, anything,” capability, 4G wireless technology will benefit every individual regardless of time and place. Considering global standpoint, this technology stands to be the way to communicate and connect all the time with more ubiquitous means. Therefore, given the ubiquitous networking, e-commerce (or even m-commerce), unified messaging, and peer-to-peer networking, expansion to the mobile and wireless surroundings must reach its maximum possibilities.

The trail going to 4G mobile technology embraces lots of significant trends. Major mobile players have been investing to 2G and the succeeding technology. 4G mobile technologies are perceived to provide fast and high data rate or bandwidth, and offer packetized data communications. Since 4G is still in the cloud of the sensible standards creation, ITU and IEEE form several task forces to work on the possible completion for the 4G mobile standards as well.

Users’ experiences of latest booming Internet forces industry to investigate means to provide high data rate regardless of mobility. 4G is being discussed as a solution to the inquiry and its vision and requirements are being standardized in various standardization bodies. 4G service vision is given from this research. There still have large room for the purpose of service application vision: 3G is being delayed in its commercialization and about a decade of change is left for 4G. However, we believe this paper will promote discussion of 4G services by presenting our vision of 4G services.

In recent years the evolution of mobile communication proceeded mainly under the influence of the 3GPP initiative (3rd Generation Partnership Project). 3GPP is a consortium, or collaboration, of standardization bodies in mobile communications. An important movement is the standardization of advanced mobile communication systems, in particular of the new technologies long term evolution (LTE) and LTE advanced (LTE-A). LTE technologies set new standards in mobile communication concerning band- width. In future, users of one radio cell will share more than 100 Mbit/s of bandwidth. Moreover, on the country- side, where neither appropriate DSL-based technology nor fiber-to-the-home technology is available, LTE offers new possibilities to provide flexible broadband solutions. For instance, in August 2010, Deutsche Telekom turned on the first LTE node in Kyritz, which is located in a rural area approximately 100 km north east of Berlin. To take advantage of next generation mobile networks, an adjustment and optimization of basic transport layers is inevitable. It will be necessary to analyze, which influence LTE and LTE-A take on traffic in access networks and on aggregation is- sues. The recent developments in telecommunication networks show the growing tendency that important network elements are concentrated at few locations. The number of sites with active hardware in access networks is reduced from tens of thousands to a few hundreds, by utilizing the optical transmission technology in combination with the increasing growth of the optical fiber network.

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