S-72.3310 Transmission Media in Communications Optical … · S-72.3310 Transmission Media in Communications Optical Fibers ... Immunity to electromagnetic interference ... • Gain

S-72.3310 Transmission Media in Communications

Optical Fibers

Dr. Edward MutafungwaDepartment of Communications and Networking, Helsinki University of

Technology (TKK), P. O. Box 2300,

FIN-02015 TKK, FinlandTel: +358 9 451 2318, E-mail: [email protected]

April 08 EMu/S-72.3310/OpticalFibers Slide 2 of 65

Lecture Highlights

� Part I: Overview of the transmission medium

� Introduction

� Comparison of transmission media

� Basics of fiber propagation and impairments

� Wavelength-division multiplexing

� Link and System Design

� Part II: Deployment Considerations

� Introduction

� Fiber in:

• Global, backbone, metro, local access networks

� Fiber deployment options

� Miscellaneous networks

� Conclusions


Part I: Overview of the fiber transmission medium


1. Introduction

�Technology must-haves

� Internet Protocol (IP)

• Inherently connectionless and distributed, seamless flow across multiple media, low overhead

• All-IP, everything over IP etc.

• IP-based service offerings e.g. VoIP, IPTV, VPNs

� Wireless mobility

• The Internet comes to you, any time and any place

� Fiber-optic communications

• Optical networks at the epicenter of the Internet


2. Fiber Transmission Medium

�John Tyndall’s experiment in 1870

� Demonstrated “zigzag” flow of light in a confined medium

Source: D. Goff, Fiber Optic Ref Guide, 3rd ed., 2002.


2.1 Operating Wavelength Bands

�Modern (post 1960) optical communications

� Advent of fibers (for guiding light) and lasers (optical signal source)


2.2 Advantages of Fiber

�Advantages of the fiber transmission media

� Low transmission loss (typically 0.2-0.5 dB/km)

• Allows longer distances between repeaters or amplifiers

• By comparison, Cat. 5 UTP (copper pairs) have loss of 7 dB/km to 220 dB/km in 64 KHz-100 MHz range

600

0.1λ (nm)

0.2

0.5

1.0

2.0

5.0

10

Attenuation (dB/km)

800 1000 1200 1400 1600 1800

Standard fiberLow water-peak fiber



Electrical repeaterMetallic cable

• Copper Links

• Terrestrial radio links

•Satellite links Radio relay stations

Orbiting satellite

•Fiber links

Electrical repeater

Electrical to Optical

converter

O →→→→ E E →→→→ O

Optical to electrical converterFiber



� Larger information carrying capacity

3G/ 3.5G

UWB802.15.3

xDSL

10 Gbps

MM wave communication

1 Gbps

100 Mbps

10 Mbps

1 Mbps

100 Kbps

1 km100 m10 m 10 km1 m

ZigBee802.15.4

WLAN802.11a/b/g

Optical fiber communication

Communication distance

Personal areaCommunicationIrDA

Long distance communication

Data rate

Visible light communications

100 km

iBurst802.20 WiMAX

802.16

Bluetooth802.15.1

SATCOM



� Immunity to electromagnetic interference

• Can be placed alongside powerlines or close to radiative equipment e.g. CAT scanners

� More secure to eavesdropping

� Smaller size and weight

• Example: 700 km of copper cabling weighs 20 tonnes, while same cable run with fiber weighs 7 kg


3. Basics of Fiber Propagation

�An optical fiber is composed of:

� Cylindrical core: refractive index n1 ≅ 1.5

� Cladding: refractive index n2 < n1� Buffer (or primary coating): protects fiber from damage

Core (doped glass)

Cladding (glass)

Buffer (plastic)

Perspective view Transverse section


3.1 Fiber Refractive Index Profile

� Core Refractive Index (n1)

� Cladding Refractive Index (n2)

� Step Index Profile

� Graded (Quadratic) Index Profile

n1n2

n2

Step index

Graded index

n2 n1

x

R.I

n1

x

R.I


3.2 Light Transmission in Fiber

�A simple explanation via Ray Optics

n1

n2

Longitudinal Section

n2

n1


3.3 Modes of a Fiber

�What makes a fiber singlemode or multimode?

Single mode optical fiber

n1

n2

n1

n2n2

n1

•dimension of core

•n1 and n2

•wavelength

Multimode optical fiber

an1

n2


3.4 Fiber Attenuation

�As light travels along a fiber,

Pout = Pin e-ααααL

Pin Pout

Distance

Power

0

Pin

fiber attenuation coefficient

decreases exponentially with distance Lits power



�Attenuation coefficient α preferably expressed in units of dB/km

� dB is logarithmic unit for representing gain or loss

� dBm is logarithmic unit for absolute signal power in mW

αdB =L(km)

| |Pout(dBm)-Pin(dBm) (dB/km)



�What causes fiber loss?� Absorption

� Scattering

� Bending


3.4 Fiber Dispersion

�Dispersion ⇨ different components of the signal travel at different velocities

� Pulses spread in time

� Causes intersymbol interference (ISI) ⇨ more errors

� Limits possible distance and bit rate


�Link performance is limited by:

Loss

Receiver

Spreading

1 0 1 1 1 1 1 1

Receiver

1 0 1 1 1 1 1 1

3.5 Fiber Limitations


3.5 Fiber Limitations

�Graphical representation of fiber limitations

Distance

Bit Rate

Dispersion & Loss LimitedDispersion Limit

Loss L

imit

Costly!

Feasible Regime


4. Wavelength-Division Multiplexing

�Wavelength-division multiplexing or WDM

� Frequency-division multiplexing in the optical domain

� Multiple information-bearing optical signals transported on a single strand of fiber

6 x B bits/s

..

.

B bits/s

..

.

B bits/sMultiplexer

Fiber

Demultiplexer

6 Signals



Optical amplifier

WDM fiber link with optical amplification

Space-division multiplexing fiber link with electrical regeneration

O →→→→ E E →→→→ O

O →→→→ E E →→→→ O

O →→→→ E E →→→→ O

Electrical repeater

Electrical to Optical

converter

Optical to electrical converter

Fiber

O →→→→ E E →→→→ O

O →→→→ E E →→→→ O

O →→→→ E E →→→→ O

O →→→→ E E →→→→ O

O →→→→ E E →→→→ O

WDM fiber link with electrical regeneration



�Current WDM systems

� Dense WDM (DWDM)

• ITU-T G.694.1 grid with channel spacing ≤ 200 GHz

• C- and L-band (1530-1625 nm) operation

� Coarse WDM (CWDM)

• ITU-T G.694.2 grid with 2500 GHz channel spacing

• O-, E-, S-, C- and L-band (1260-1625 nm) operation


5. Link and System Design

�Simple fiber-optic communications link

� Short distance

� Low bit rate

� Point-to-point

�Major concern is to ensure sufficient received power

� Link power budget analysis

Fiber

ReceiverReceiverTransmitterTransmitter


5.1 Link Power Budget

Fiber

ReceiverTransmitter

dB valueValueItem

1a) Average output power

2a) Propagation losses (10 km)

Receiver:3a) Signal power at receiver

3b) Receiver sensitivity

Link Margin (Power Margin)

Transmitter:

Channel:

1.0 mW

0.2 dB/km

= (3a – 3b)

0.0 dBm

-20.0 dB

-20.0 dBm

-30.0 dBm

+10.0 dB


5.1 Link Power Budget

� A power budget for an amplified WDM link more detailed


5.2 Detailed System Design

�In an amplified WDM link, there is more to worry about than just power budget

� Non-ideal optical devices (transmitters, filters etc.)

� Fiber links longer

• Increased transmission loss

• Dispersion and fiber nonlinearity more severe

� Tightly packed wavelength channels

• Interference between different channels

� Cascaded optical amplifiers

• Provide gain but also noise and unequal gain at different wavelengths

• Gain affected by power transients


5.2 Detailed System Design

�Propagation of optical pulse over fiber modeled by the nonlinear Schrödinger equation (NLSE)

� Maxwell’s equations in cylindrical coordinates and with boundary conditions of fiber optic cables

� Also applicable in other areas (e.g. water wave theory)

� Some terms ignored for pulses >10ps (<100 Gbit/s NRZ)

),(),(),(

6),(

2),(

2),( 2

3

33

2

22 tzAtzAi

ttzA

ttzA

itzAz

tzA γββα −∂

∂+∂

∂+−=∂

∂

AttenuationDispersion Dispersion slope Kerr nonlinearities

Pulse shape or envelope at time t and position z along the fiber


5.2 Detailed System DesignSystem Specifications

Distance Bit Rate

Transmitter Type

Fiber Type Receiver Sensitivity

Fiber Loss

FiberDispersion

Transmitter Chirp

Transmitter Output Power

Power Budget

Optical Amplifier

Bit Error Rate

Dispersion Compensator


5.3 Simulation Tools


Part II: Deployment Considerations


1. Introduction

�Optical networks are now widely deployed in different environments

�Special considerations have to be taken when deploying network infrastructure

� Environmental conditions

� Security

� Support facilities

� Cost

� Demand

� Legal considerations


2.1 Intercontinental Optical Networks

� About 70% of earth’s surface covered by water bodies

� For intercontinental (global) connectivity communication links must traverse water bodies

� Overhead in the sky via LEO, MEO or GEO satellites

� Underwater using ”submarine cables”



� Example: TAT-14 fiber cable (2001-present)

� Between USA, UK, France, Netherlands, Germany and Denmark

� Configured as a 4 fiber shared protection ring

� 16 protected WDM channels @ 10 Gbit/s (640 Gbit/s capacity)

Figure: TAT-14 landing points (Source: www.tat-14.com).



� Majority (>75%) of intercontinental traffic now carried on fiber rather than satellite


2.2 Backbone Optical Networks

� Continental backbone network providing connectivity between different countries

Figure: Level 3’s European backbone


2.2 Backbone Optical Networks

� National backbone network interconnecting cities and main towns of a country

Figure: Conceptual backbone networks for Italy (left) and Belgium (right)

*Ref: R. Sabella et al, Journal of lightwave Technology, Vol. 16, No. 11, Nov. 1998


2.3 Optical Metro Networks

�Provide connectivity within a city/metro or region

•San Antonio Metropolitan Fiber Network

•Time Warner Cables

•2400 km of fiber

•Ethernet, IP/MPLS

•Connectivity for corporate customers


2.4 Access Networks

�Access network are “last leg” of telecommunications network

� Between service provider distribution facility and user’s home or business

� Other names:

• last mile

• local loop

• first mile

• etc.

�Fiber is increasingly deployed now in access networks


2.4 Access Networks


2.4 Access Networks

few km

50-70 km


2.4 Access Networks

IP Network

(Internet,

Intranet etc.)

PSTN

1:N Passive

SplitterFeeder

Fiber

Central Office

ONT

ONT

EP2P

PON

OLT

Fiber Access Networks

Distribution

Fibers

Notes: EP2P = Ethernet Point-to-Point, IP = Internet Protocol, MxU = a generic term for Multiple Tenant Unit and Multiple Dwelling Unit, NT = Network Terminal,

OLT = Optical Line Terminal, ONT = Optical Network Termination, ONU = Optical Network Unit, PON = Passive Optical Network, PSTN = Public Switched

Telephone Network, SME = Small and Medium Enterprise.

Residential/SME

Residential/SME

NTs

Enterprise/MxU

ONU

ONT

Residential/SME

Customer Premises


2.5 Fiber Deployment Trends

Figure: Worldwide fiber cable deployment by region expressed in thousands of fiber-km (Source: KMI Research).

Telecomm and dot-com boom

Dot-com bubble burst, “bandwidth glut”

Emerging markets, Fiber access networks deployment


3. Deployment Methods

�Various methods exist for deployment of fibercables

�Selected cable deployment method depends on various factors

� Geographical topography of an area

� Availability of rights-of-way

� Time constraints

� Operator’s business strategy


3.1 Digging Trenches

� Digging trenches specifically for burying fiber Cables

� Well established technique also used for laying other infrastructure (gas pipeline, water pipes etc.)

� Trenches usually 0.5 to 3.0 m deep

� Trenches made using trenchers, ditchers, plows etc.

Figure: Heavy duty ride-on trencher (Source: Vermeer).

Figure: Compact walk-behind trencher (Source: Ditch Witch).


3.1 Digging Trenches

� Digging trenches has many disadvantages� Digging or excavation permits difficult to get and more costly

� Slow cable laying speed e.g. due to boulders encountered in digging

� Unsettling of humans and wildlife in their current habitat

� Possible accidents to passersby due to open trenches

� Damage to existing roads or buried infrastructure (cables, pipes etc.)

Figure: Damage to roads due to trenching


3.2 Trenchless Methods

� Resistance to traditional trenching methods is now widespread

� Magazines (e.g. Trenchless Technology Magazine, Tunneling & Trenchless Construction)

� Conferences e.g. 24th International NO-DIG Conference and Exhibition http://www.nodig06.im.com.au/welcome.html

� Societies e.g. International Society of Trenchless Technology (ISTT)

� Methods such as horizontal directional drilling getting popular� Horizontal holes in the ground drilled using a jet of high pressure fluids

Figure: Non-intrusive deployment of cables under pavements using horizontal directional drilling (Source: Vermeer).


3.3 Utility Fiber

� Collocating cables with other utility infrastructure

� Extensive networks of infrastructure such as:

• Power transmission and distribution lines

• Potable water lines and irrigation pipelines

• Natural gas, petroleum pipelines

• Industrial waste lines, sewage and drainage systems

� Well planned, maintained, almost similar routes to fiber cable routes

� Rights-of-way straightforward using existing utility corridor


3.3 Utility Fiber

Figure: Fiber cables deployed on power transmission lines (source: Alcatel)

Figure: Fiber cables in sewage systems (source: CityNet, CableRunner)

Figure: Installation of fiber cables in natural gas pipes (Source Sempra Fiber Links).


3.4 Along Transport Networks

�Placing fiber on transport networks� Networks for various transport modes for people and freight• Railway lines (e.g. VR/Corenet)

• Alongside motorways/freeways

• Underground rail or road tunnels

� Simplified rights-of-way and ready made routes

Figure: Corenet (VR Group) fiber backbone.


3.6 Underwater Fiber

� Underwater or submarine fiber cabling

� For cable deployments in oceans, seas and inland waterways

� Avoid over digging in developed urban areas

� Provide nationwide connectivity for countries made of many Islands

Figure: Japan Information Highway (JIH) cable.

Figure: Neuf Cegetel has 200 km of underwater fiber in the River Seine waterway that runs through Paris.


4. Miscellaneous Networks

�Optical networking technologies now used for various non-conventional applications

�Introduce high-capacity and low signal lossadvantages to new application environments

�Need for some device modifications from traditional optical networks

� Different operating environment

� Unfamiliar traffic types


4.1 Intelligent Transportation Systems

� Optical technologies now used for on-board vehicles networks� Assisted driving, increased safety, entertainment and navigation purposes

� Networking cables and devices adapted for vehicular environment � Rugged (vibrations, dirt, moisture, chemicals etc.)

� Unpredictable (e.g. large temperature variation)


4.1 Intelligent Transportation Systems

� Various standards for optical on-board vehicle communications� FlexRay, MOST (Media Oriented Systems Transport), IDB-1394

(automotive version of IEEE-1394 or FireWire)� Mostly use plastic optical fibers� Peak rates: Flexray (10 Mb/s), MOST (24.8 Mb/s), IDB-1394 (400

Mb/s)� Flexray for vehicle control, MOST and IDB-1394 for multimedia

applications

2006 BMW X5 Mercedes E-Class Saab 9-3 Audi A8

Flexray MOST


4.2 Avionics Fiber-Optics

� Fiber networks on planes

� High capacity ⇒ in-flight entertainment, internet, control etc.

� Long reach to various parts all plane sizes

� Low weight ⇒ less fuel

� Small size

� Challenges

� ”New technology” for flight critical systems

� Vulnerability of fiber connectors in extreme environments (temperature, vibrations etc.)

� Example: Avionics Full-Duplex Ethernet/ARINC 664 standard

� 10 Mb/s (Copper), 100 Mb/s (Copper or Fiber), GbE (future)

� Planned for A380s, 787s

Airbus A380

Boeing 787


4.3 Fiber Transmission for RF Networks

� Fiber connecting distributed antenna systems

� Improved indoor coverage in malls, underground parking, high-rise buildings etc.


4.3 Fiber Transmission for RF Networks

� Backhaul links for signal transfer between base stations and switching centers� Leased lines, digital microwave or satellite links � About 25% of operator’s OPEX and expensive to scale� 3.5G networks could require up to 15 times more backhaul capacity

compared to 2G/2.5G networks� 4G networks (LTE, IMT-Advanced) will increase requirements even

further

� Now use of fiber backhaul links increasingly attractive


4.4 Optical Wireless

�Transmission of infrared beams (optical signals) in free space (fiberless)� Also known as free space optics (FSO)

� Utilize conventional optical 1300/1550 nm transmitters and receivers with some slight modifications



�Advantages of FSO over fiber communications

� Tetherless flexibility

� Cost-effectiveness

�Advantages of FSO over RF wireless communications

� Availability of large unregulated unlicensed bandwidth

� Data rates up to a several Gbit/s possible

� Links usually not affected by multipath fading



� Disadvantages of optical wireless

� Obstructed by opaque objects ⇒ stringent line-of-sight requirement

� Maximum transmitter power limited by eye safety regulations

� Ambient noise due to sun-light, light-bulbs etc.

� Variable signal loss due adverse weather conditions e.g. fog, snow

Attenuation 0.19 dB/km

Sources: K. Kazaura (Waseda University)

Attenuation 2.58 dB/km Attenuation 12.65 dB/km

Figure: Example path attenuation for various weather conditions (visibility levels)



� Disadvantages of optical wireless

� Need for transmitter-receiver tracking alignment due to moving buildings (wind, thermal expansion etc.), turbulence etc.



�Most applications have been for indoor systemswith coverage limited to a few meters

� Billions of products shipped with infrared ports

� “Point-and-shoot” inter-connection of laptops, PDAs, phones etc.



� Outdoor terrestrial FSO systems also gaining popularity

� Advances in beam tracking and acquisition

� Rapid provisioning of multi-Gbit/s links for post-disaster recovery, major sporting events, cellular back haul etc.

Sources: Waseda University, Hamamatsu Photonics, IEEE/ConTEL conference

Figure: Rooftop FSO installation



� Inter-satellite links also increasingly using optical wireless technologies

� Orbiting satellites for broadband services require multi-Gb/sinterconnections

Earth

RF linkRF link

Optical/infrared link

Satellite Satellite

Earthstation

Earthstation


6. Conclusions

�Optical networks are now an integral part of manycurrent systems

�Fiber likely to get even closer to the user e.g. fiber-to-the-desk


Thank You!

Documents

S-72.3310 Transmission Media in Communications Optical … · S-72.3310 Transmission Media in Communications Optical Fibers ... Immunity to electromagnetic interference ... • Gain