TABLE OF CONTENTS

Abstract …............ ….... ........ ...... ..... ....... …..... ..... ..... ..... ........ .... .... 3 Introduction...... …........ …......... …........ …........... …............ …........ … 3-4 What is Optical Networking........... .......... ......... ........ ............ ................ 4 Standards........ ….... ….............. …........... …......... …........... ….......... .. 4 Historical Milestones........ …... …... …...... ….... …......... …....... …....... 4 Optical Networking why......... ….......... …..................... …................ …. 5 Principles and Operation............... …................. …........ ….............. …... 5-8 Single Mode Fiber............ …........................ ….................. …...... 6 Multimode Fiber................. ….................. ….............. …........ … 6-7 Optical Networking Tools.............. …............... …............. …............ ….. 8-10 Fiber Optic Splicers................. …............. ….... …........... …........ 8-9 Fiber Optic connectors.................. …............... …................. ….... 9 Fiber optic couplers........... …................. …............. …............ …. 9 Fiber Optic Transmitters................ ….................. …............ …...... 9 Fiber Optic Receivers............ ….................. …............ …..... ….... 10 Types Of Optical Networks.............. …........................... …............. …..... Optical Network Architecture............... …............... …............ ….......... ... Optical Networking vs Other Technologies................. …............ …......... Optical Networking Advantages........ …................ …................. ….. …. Optical Networking disadvantages....... …........... …......... …............ ….. Business Implications and Applications....... …........... …............... ….... Conclusion............. …........................... …............. …...... ….......... …... References............... …................... …....................... …................. …....

Optical Fiber Networking

Abstract:

Today bandwidth, reliability, resiliency, performance, redundancy, cost efficiency and security are some of demands placed on telecommunications. Since fiber optics initial development, it fulfilled all the requirements over wireless and copper based telecommunications solutions. Largest obstacle implementing fiber optics by most businesses was cost. With advancements in fiber optics and ever growing demand for bandwidth, cost of installation and maintenance of optical fiber systems has been reduced dramatically with many advantages like cost efficiency will continue to be increase of optical fiber systems replacing copper based communications.

1. Introduction:

One of major issues in networking industry today is demand for more bandwidth. Before the introduction of optical networks, reduced availability of the fibers became a big problem for network providers. With the development of the optical networks a new probably very crucial milestone is reached in network evolution. Optical fiber is plastic or glass fiber designed to guide light. Optical fiber is overlap of engineering and applied science concerned with application and design of optical fibers. Optical fibers are used in communication that permits transmission at higher rates and over long distances then other forms of communication. optical Fibers are used cause signals travel through them with low loss and are immune to electromagnetic interference. Fibers are also used to form sensors and other applications.

Fiber optics consists of core, cladding and protective outer coating that guides light along core by total internal reflection. Core and cladding are made of the high quality silica glass. Optical fibers are can break if bent sharply. Connecting 2 optical fibers done by mechanical spicing or fusion splicing requires interconnection technology and special skills.

This paper will briefly discuss history of fiber optics and types of optical networks and principle and operation of optical networks. It covers optical network architecture and comparison of optical

networks with other networking technologies and applications of optical networks and business implications. It also discusses the advantages and disadvantages of optical networking.

2. What is Optical Networking ?

As name suggests optical network is a class of network where optical components are building blocks of network. Communication between telephones, computers and other electronic devices using the light When compared to metallic cables fiber optics offer lower attenuation, greater bandwidth, and no interference or crosstalk. These advantages led to dramatic growth of optical fiber systems worldwide. Nearly all long haul communications today depend on use of optical networks for their robust performance and large capacity. Fiber Optical network is far more greater potential transmission and reliable than networking in electrical domain.

3. Standards:

Standards for optical fiber cable and other fiber components have been developed over last 20 years by American National Standard Institute(ANSI) and International Telecommunication Union(ITU). Standards are initially developed in North America under Synchronous Optical Network(SONET) and lately by ITU using the name Synchronous Digital Hierarchy.

4. Historical Milestones:

1958: Discovery of laser Mid-60's: Demonstration of wave optics 1970: The production of low loss fibers that made long distance transmission through fiber possible 70's – 80's : Use of fiber in Telephony Mid 80's: LAN/MAN broadcast and select architecture Late 80's: Development of optical amplifier Mid/late 90's: DWDM system explode Late 90's: Intelligent optical network 20: Soliton transmission with TDM

5. Optical networking: Why?

Traditional Network consists of collection of electronic switches which are interconnected by point to point fiber optic links which can span metropolitan, local or wide area networks. For accommodating continually increasing demand for flexibility and bandwidth, that type of networks are enhanced by adding more switches and fibers and increasing bit rate per fiber and upgrading the size of the switches functionality and throughput. Such type of enhancements lead to very complex and large networks that are expensive and difficult to construct,maintain and operate. Recent and emerging advances in technology promises all optical networks capable of providing improved flexibility, economy and robustness while still using large existing fiber base.

6. Principles and Operation:

An Optical fiber is cylindrical waveguide made up of two transparent materials with different index of refraction. Two materials are arranged concentrically to form inner core and outer cladding. Different entry angles of light source result in multi modes of wave propagation. It can be restricted to single mode by smaller diameter core. The light source can be laser or light emitting diode.

6.1. Single Mode Fiber:

Single mode fiber has relatively narrow diameter. It carries higher bandwidth then the multi mode

fibers and requires a light source with narrow spectral width. Single mode fiber gives a higher transmission rate and 50 times more distance than the multi mode and also costs more. It has much smaller core then multimode. The single light wave and small core virtually eliminate distortion which may result from overlapping light pulses which provides highest transmission speeds and least signal attenuation of any fiber.

6.2. Multimode Fiber:

Multimode fibers has bigger diameter than single mode. Most applications where multi mode fiber is used uses 2 fibers. Multimode fibers gives high bandwidth with high speeds. The light waves are dispersed in numerous paths as they travel through cable path. In long cables, multiple paths of light cause distortion of signal at receiving end, resulting in unclear, incomplete transmission of data, so designers call for single mode in new applications

Choice between single mode and multi mode fibers depend on desired transmission rate or spacing. The single mode fibers are preferred choice for high data rate systems or haul. Earliest form of multi mode fiber is step index, where core has uniform index refraction and concentric cladding has uniform

but lower index. Such case has propagation velocity in core is constant, so rays traveling shorter distance arrive before the rays traveling long distance producing dispersion or pulse spreading. These effects may be remedied by constructing fiber whose refractive index increases towards axis resulting in refractive index which is parabolic. With graded index fiber, rays traveling long paths have great velocity than rays traveling short paths due to decrease in refractive index with radial dist. Various modes tend to have same arrival time so dispersion is minimized. So great bandwidths are possible for multi mode fibers.

With the spectrum available in optical fiber system, there are 3 low loss windows at wave lengths 1300,1550 and 850nm. The early applications of optical fibers applications are based on short wave length of roughly 800 to 860nm. Operations at long wavelengths particularly at 1300 to 1550 nm is attractive due to dispersion and attenuation characteristics at the wavelengths. Today short wave length bands are used for low data rate systems and short haul.

Longer wave length bands are for high data rates and for long haul. Special fibers have developed which shifts minimum dispersion to 1550nm to take adv of minimum dispersion and lower attenuation.

These fibers are dispersion shifted fibers which are important in single mode applications.

Low data rate and short haul optic systems tend to multi mode cable, PIN diode and LED transmitter. High data rate and long haul systems tend to laser diode, single mode cable and avalanche receivers. Latest fiber optic systems have significantly improved and bandwidth and repeater spacing possible. Several wavelengths can be transmitted in wavelength division multiplexing. Optical amplifiers that are available eliminate electronics instead use semi conductor devices or doped fiber. The use of amplifiers allow optical fiber system to bit rate with out replacing repeaters. Amplifiers have also used to achieve ultra long distance which is transmission of idealized pulse with out any loss of pulse shape.

7. Optical Network Topologies

All networks involve same basic principle i.e. information can be shared with, send to, bypassed, passed on within number of the computer stations and master computer. The network applications include LANs, WANs, MANs, SANs, interbuiding and intrabuilding communications, intelligent transportation systems, broadcast distribution, telecommunications. In addition to so many advantages like bandwidth, durability, immunity the optical fiber better accommodate today's complex network architectures than the copper alternatives. Picture below explains interconnection between networks.

Networks are configured in number of topologies which includes bus network with or without backbone, ring network, which is redundant or self healing, star network or combination of all these networks. In these each topology has strengths and weaknesses. Some networks works better for some applications and some works better for other. Local, wide area or metropolitan networks normally use mesh technology or combination.

Bus Network:

Bus network topology or daisy chain topology which has each computer connected directly on main

communication line. The one end has controller other end has terminator. Computer that want to talk to main computer has wait till its turn for accessing transmission line. In straight network only one computer can be able to communicate at time. When computer uses network, information is sent to controller which in turn sends information to line of computers until reaches terminating computer. Each computer receives same information.

A bus network with backbone operates same fashion but every computer is separately connected to network. This offers great reliability than simple bus topology.

Ring Network

In the configuration the computers in ring link to main communication line. Network receives information via token consists of information requested by computers in the network. The token passed around ring until requesting computer received data. Token uses packet of information that serves as address for computer that requested information. Computer than empties token and token continues to travel until another computer requests information to put in token.

Advanced version of ring network use two communication cables sending that sends information in both directions which is known as counter rotating ring which creates fault tolerant network that redirects transmission in other direction, should node on network detect disruption. In this network uses optical fiber transceivers. In this one controlling unit is set in master mode along several nodes that are remote units. First remote transceiver receives transmission from master unit and then retransmits to next remote unit and at the same time transmitting it back to master unit. Interruption in signal line on first ring bypassed via second ring allowing network to maintain integrity. The following picture shows configuration as it might used in ITS installation.

Star Network

The star network incorporate the multi port star coupler to achieve topology. Main controlling computer interconnects with all computers in network. Failure of one computer doesn't cause failure in network. Picture below illustrates star network.

Both star and bus networks use central computer that controls system inputs and output.

7.Optical Networking tools:

Tools we use for Optical networking are below.

7.1. Fiber Optic Splicers:

Fiber optic spice is permanent fiber joint to establish optical connection between two fibers. System design requires fiber connections have particular optical property such as low loss that are met with only by fiber spicing. Optic splicers also permit repair of fibers damaged during accident, installation or stress. Generally fiber splicing is used whenever disconnection or repeated connection is not necessary.

Mechanical and fusion splicing are techniques in fiber splicing. Mechanical splice is used where materials and mechanical fixtures perform fiber connection and alignment. Fusion spice is used where localized fuse melts or fuses 2 fibers together. Each technique seeks to optimize performance, reduce splice loss.

7.2. Fiber Optic Connectors:

Connector is demateable device which permits coupling of the optical power between two fibers or 2 groups of fibers. Optic connectors must maintain optic alignment and will provide repeatable losses measurement during numerous number of connections. Connectors are easy to assemble and cost effective and reliable. Connectors are insensitive to environment conditions like temperature, moisture , dust. Butt jointed connectors and the expanded beam connectors are 2 types of connectors. Butt jointed connectors bring and align two fiber ends to close contact. End faces some times touch others do not. Expanded beam connectors use 2 lens to expand and refocus the light from transmitting fiber to the receiving fiber. Connector consists of 2 plugs and adopter as coupling device.

7.3. Fiber Optic Couplers:

Some optic data links need more than simple point to point connection. Optic coupler is a device that distribute signal from one fiber to two or more. It also combines two or more signal into single. Optical couplers attenuate signal much more than splice or connector cause input signal divided among output ports.

Optic couplers can be active or passive devices. Passive coupler redistribute optical signal not using optical to electrical conversion. The active couplers combine or split signal electrically and use detectors and sources for input and output. 7.4. Fiber Optic Transmitters:

Transmitter is hybrid optic electrical device, converts electrical signal to optic signals and launches them into optical fiber. Transmitter consists an interface circuit, optical source and source drive circuit. Interface circuit accepts incoming signal and process it to make compatible with source drive circuit, it in turn modulate optical source by varying current through it.

7.5. Fiber Optic Receivers:

In fiber optics the signals that reach optic receivers are attenuated and distorted. Receiver must convert input and amplify resulting electrical signal with out distorting it to point where other circuitry can not use it.

8. Types of Optical Networks:

Fiber optic networks may classified into several types. Opaque optical network include the optical electronic optical conversion. All optical networks each connection is transparent except end nodes.
Optical networks are single wavelength or multi wavelengths. Use of SONET with single carrier is typical example of single wavelength, opaque optical network.

Passive Optical Networking:

Type of networking where only single strand of optical fibers can take part and build connection between multiple computer networking clients from the different areas called as passive optical networking. Some times customers complain lower rate of the internet connection with this type of networking.

Synchronous Optical Networking:

This type optical networking deals with data transmission. Optical networks monitor all data related to information can pass smoothly from through network from one pace to the other. It is more effective to physical networking, also observes type of data. Type of data should be in one form and be relayed properly.

Star Networking:

Networking carried out with help of star networks called as star networking. It deals with connection between main computer systems to other computers in the network. They are able to enhance performance of connection san network.

9. Optical Network Architecture:

There are 2 standard fiber optic architectures they are ring and linear. Both provide restoration and network protection services. SONET rings are most widely deployed architecture. They are thought as linear network folded back for creating ring or loop. Unlike linear architecture rings were designed to guarantee the automatic restoration of the services when cables fail by using loops around failed component. Because of this protection against failures those rings are self healing. Here there are several SONET(synchronous optical networking) ring architectures which depends on number of fibers level of protecting in switching and transmission direction.

SONET originally developed in US, SONET standard is adopted by ITU but renamed as SDH(synchronous digital hierarchy). The standards provide complete set of the specifications to allow the national and international in connections at various levels. Optical fiber interfaces are are defined to provide universal fiber interface and to permit mid span interconnection of the different vendor equipment. Optical fiber interfaces are are defined to provide universal fiber interface and to permit mid span interconnection of the different vendor equipment .Standardized signal structure existing

hierarchical rates to be accommodated. The overhead with in SONET signals facilitate synchronization, electronic switching, add and drop multiplexing, network management and performance monitoring of composite and tributary signals. SONET hierarchy built on synchronous multiplexing of basic SONET rate 51.84 Mb/sec. Higher SONET rates are N*51.84Mb/sec. Basic signal structure providing sufficient flexibility in carrying variety of lower rate with in 51.84Mb/sec.

10. Optical Networking vs Other Technologies:

10.1. Size and Weight: Individual optical fibers are 125 μm in diameter, multiple fiber cables made smaller than corresponding metallic cables.

10.2. Bandwidth: Optical fiber cables have bw's that are order of magnitude greater to metallic cables. The low data rate system can easily be updated to higher data rates with out need of replacing fibers. The upgrade can be done by changing LED to laser, improving receiver, improving modulation techniques or using wavelength division multiplex(WDM).

10.3. Repeater Spacing: With low loss optical fiber cables distance btw repeaters be significantly greater than metallic cable systems. Losses in fiber optics are independent of the band width. But with twisted or coaxial pair the losses increase with bandwidth. Thus advantage in the repeater spacing increases with system bandwidth.

10.4. Electrical Isolation: Optical fiber cable is nonconducting electrically, which eliminates all the electrical problems that are in metallic cable. Optical fiber systems are immune to lightning induced currents, power surges, short circuits and ground loops. Optical fibers are non susceptible to the electro-magnetic interference from radio signals,adjacent cable systems, power lines or other electromagnetic source.

10.5. Crosstalk: Cause there is no optical fiber coupling from to the another fiber with in the cable, optical fiber systems are free from the crosstalk. In the metallic cable systems crosstalk is the common problem and often the limiting factor in the performance.

10.6. Environment: Proper designed optical fiber systems are relatively not affected by the adverse temperature, moisture conditions therefore have application to the under water cable. For metallic cable moisture is the problem particularly in under ground applications resulting in attenuation, short circuits, increased crosstalk and corrosion.

10.7. Reliability: Reliability of the optical drivers, optical receivers and optical fibers has reached point where limiting factor is usually associated electronic circuitry.

10.8. Cost: Numerous advantages that are listed here for optical fiber systems resulted in dramatic growth of application with reductions in cost due to the technological improvements and the sales volume.

10.9. Frequency Allocations: Metallic and fiber cable systems does not require frequency allocations from already crowded spectrum. Cable systems do not have multipath fading, interference problems and terrain clearance common to radio systems.

11. Advantages of Optical networking:

Extremely High bandwidths Easy to accommodate the increasing bandwidths Resistance to the electro magnetic interference Early detection of the cable damage and secure transmissions

12. Disadvantages of Fiber Optics:

It is very expensive to construct fiber optics for optical networks Installing costs though dropping are still high Special test equipments is often required Susceptibility to physical damage It is very difficult to join fiber optic cables than copper cables

13. Business implications and Applications:

Today optical fibers are much more cost effective than the metallic cable, radio for long haul, high bit rate and satellite applications. Optical fibers also expected to eventually overtake metallic cables in the short haul applications including local networks and metro facilities. The one final cost factor of optical fibers is choice of material such as silicon, is of course one of earths most abundant elements compared to copper which someday be in short supply. The other material ie radio spectrum already in short supply.

14.Conclusion:

As the demands on modern networks rise, security, reliability and speed become more of a necessity as opposed to a feature. Fiber optical networks can help deliver those requirements in harsher environments with additional benefits. Modern fiber cables can contain up to thousand fibers in single cable, the performance of the optical networks easily accommodates even the today's demands for the bandwidth on point-to-point basis. However, the unused point-to-point potential bandwidths does not translate to the operating profits, and is estimated that no more than 1% of the optical fiber buried in the recent years is actually 'lit' .

15. Reference:

[1] Alberto Bononi, Optical Networking(Springer, 1999)
[2] http://www.martindalecenter.com/Calculators4_F_Opt.html. This site has numerous calculators and animations for optical communications.
[3] Optical Networks by Ramaswami and Sivarajan
[4] Goff, David R. “A Brief history of Fiber Optic Technology”, Fiber Optic Reference
Guide, 3rd ed. Focal Press: 2002. URL: www.fiber-optics.info/fiber-history.htm