Introduction Basic properties of light Optical Fiber Characteristics Optical fiber cables Optical fiber connectors Optical fiber directional couplers Fusion splicing of fiber optics Transmission attenuation Dispersion Optical fiber link Modes Light sources Detectors Optical measurements Fiber networks

There are 3 transmission media • Electric Current via copper cables ( twisted pairs- coaxial cables)

• Electromagnetic waves space

• Optic Waves via optical fiber cables

1880 Alexander G. Bell, Photo phone, transmit

sound waves over beam of light . 1930 TV image through uncoated fiber cables. Few years later image through a single

glass fiber. 1951 Flexible fiberscope: Medical applications. 1956 The term “fiber optics” used for the first time. 1958 Paper on Laser . 1960 Laser invented . 1967 New Communications medium: cladded

fiber. 1960s Extremely lossy fiber: more than1000 dB

/km.

1970 Corning Glass Work NY, Fiber with loss of less than 2 dB/km.

70s & High quality sources and detectors 80s Late 80s Loss as low as 0.16 dB/km.

1990 Northern and western Europe has completed the installation of fiber optic long distance networks, now it is time for the second run.

1992 Field test for fiber optic networks to the homes, FTTH in Europe.

2000 SDH, SONET and ISDN-B .

2009 14 th October , First FTTH to katamia (Cairo )

Small size and light weight . much wider bandwidth (10 GHz) . Crosstalk and interference immunity . Immunity to static interference . Safety: Fiber is nonmetallic . Longer lasting (unproven) . Security: tapping is difficult . Economics: Fewer repeaters, low cost . Low transmission loss . System reliability and ease of

maintenance . Ruggedness and flexibility .

Higher initial cost in installation .

Interfacing cost .

Strength: Lower tensile strength .

more expensive to repair/maintain .

Tools: Specialized and sophisticated

Difficult jointing of individual fiber segments (improving continuously by new developments) .

Limited life-time of light sources .

Need for control of production parameters to obtain ideal fiber dimensions and index profile

The need for additional copper energy cables may become a necessity. (New developments increased the distance between repeaters tremendously: in the year 2000 working systems containing repeater fields of 140km at 2.1 Gbit exist)

InputSignal

Coder orConverter

LightSource

Source-to-FiberInterface

Fiber-to-lightInterface

LightDetector

Amplifier/ShaperDecoder

Output

Fiber-optic Cable

Transmitter

Receiver

Economical light source emits at defined wavelength.

Fiber optical cable of small loss .

Fusion machine for stable splices .

Detector of high sensitivity and high responsibility .

Electric circuits deal with the optical components .

• Junction Cables

• Transmission Cables

• International CablesSEA ME WE 2SEA ME WE 3SEA ME WE 4South East Asia Middle East West Europe

•Local CablesFTTCFTTHControl NetworksComputer Networks ( LAN , WAN )

The route of the submarine cable (black); the blue segment is terrestrial

SeaMeWe-3

• SeaMeWe-3 is a submarine cable that connects Karachi, Pakistan to Middle East, Africa and Europe. A major bulk of our trade happens through Karachi and a major bulk of the internet traffic in Pakistan, India and Bangladesh is routed through this cable.

• The SeaMeWe is owned by consortium of companies. A satellite up link would at least ensure a plan B, a fall back plan without having to worry about the maintenance of this under water cable.

• Major Arab countries like Saudi Arabia, UAE, Kuwait already have a satellite system in place that helps them redirect their internet traffic when this cable starts to malfunction. As a rising regional economy, its time we put some thought to this.

The route of the submarine cable (red); the blue segment is terrestrial

• South East Asia–Middle East–Western Europe 4 (SEA-ME-WE 4) is an optical fibre submarine communications cable system that carries telecommunications between Singapore, Malaysia, Thailand, Bangladesh, India, Sri Lanka, Pakistan, United Arab Emirates, Saudi Arabia, Sudan, Egypt, Italy, Tunisia, Algeria and France.[1]

• It is intended to be a complement to rather than a replacement for the SEA-WE-ME 3 cable.

• The cable is approximately 18,800 kilometres long, and provides the primary Internet backbone between South East Asia, the Indian subcontinent, the Middle East and Europe

•S1 - Tuas to Mumbai

•S2 - Mumbai to Suez

•S3 - Suez to Cairo

•S4 - Cairo to Marseille

1. Marseille, France

2. Annaba, Algeria

3. Bizerte, Tunisia

4. Palermo, Italy

5. Alexandria, Egypt

6. Cairo, Egypt (overland)

7. Suez, Egypt (overland/return)

8. Jeddah, Saudi Arabia

9. Fujairah, United Arab Emirates

10. Karachi, Pakistan

11. Mumbai, India

12. Colombo, Sri Lanka

13. Chennai, India

14. Cox's Bazar, Bangladesh

15. Satun, Thailand

16. Melaka/Malacca, Malaysia

17. Tuas, Singapore

• The SEA-ME-WE 4 system is divided into four segments with seventeen landing points:[3]

Landing points

Segments

•The SEA-ME-WE 4 cable system was developed by a consortium of 16 telecommunications companies which agreed to construct the project on 27 March 2004.[2]

•Construction of the system was carried out by Alcatel Submarine Networks (now Alcatel-Lucent Submarine Networks, a division of Alcatel-Lucent) and Fujitsu.[2]

•The eighteen month construction project was completed on 13 December 2005 with a cost estimate of US$500 million.[4][2]

•Segment 1 construction, running 8,000 kilometres from Singapore to India, was done by Fujitsu, which also provided the submarine repeater equipment for Segment 4.[4]

•The SEA-ME-WE 4 cable system was proposed and developed by the SEA-ME-WE 4 Consortium. The Consortium continues to maintain and operate the system. It comprises 16 telecommunications companies:[18][4]

Algérie Télécom ,Algeria Bharti Infotel Limited ,India

Bangladesh Submarine Cable Company Limited (BSCCL) ,Bangladesh CAT Telecom Public Company Limited ,Thailand

Emirates Telecommunication Corporation) ETISALAT ,(UAE France Telecom - Long Distance Networks ,France

MCI ,UK Pakistan Telecommunication Company Limited ,Pakistan

Singapore Telecommunications Limited) SingTel ,(Singapore Sri Lanka Telecom Limited) SLT ,(Sri Lanka

Saudi Telecom Company) STC ,(Saudi Arabia Telecom Egypt) TE ,(Egypt

Telecom Italia Sparkle S.p.A. ,Italy Telekom Malaysia Berhad) TM ,(Malaysia

Tunisie Telecom ,Tunisia Tata Communications previously Videsh Sanchar Nigam Limited (VSNL) ,

India

•SEA-ME-WE 4 is used to carry "telephone, internet, multimedia and various broadband data applications".[2]

•The SEA-ME-WE 3 and the SEA-ME-WE 4 cable systems are intended to provide redundancy for each other.[2]

•The two cable systems are complementary, but separate, and 4 is not intended to replace 3.[2]

• Both derive from the same series of projects (SEA-ME-WE), but have different emphases. SEA-ME-WE 3 is far longer at 39,000 kilometres[21] (compare to SEA-ME-WE 4's 18,800 kilometres) and extends from Japan and Australia along the bottom of the Eurasian landmass to Ireland and Germany.[22]

•SEA-ME-WE 4 has a faster rate of data transmission at 1.28 Tbit/s against SEA-ME-WE 3's 10 Gbit/s.[21]

•SEA-ME-WE 4 has a faster rate of data transmission at 1.28 Tbit/s against SEA-ME-WE 3's 10 Gbit/s.[21]

•SEA-ME-WE 3 provides connectivity to a greater number of countries over a greater distance, but SEA-ME-WE 4 provides far higher data transmission speeds intended to accommodate increasing demand for high-speed internet access in developing countries .

•The cable uses dense wavelength-division multiplexing (DWDM),[1] allowing for increased communications capacity per fibre compared to fibres carrying non-multiplexed signals and also facilitates bidirectional communication within a single fibre.

• DWDM does this by multiplexing different wavelengths of laser light on a single optical fibre so that multiple optical carrier signals can be concurrently transmitted along that fibre.

• Two fibre pairs are used with each pair able to carry 64 carriers at 10 Gbit/s each.[4] This enables terabit per second speeds along the SEA-WE-ME 4 cable,[2] with a total capacity of 1.28 Tbit/s.[4]

The telecommunications industry differentiates between several distinct configurations. The terms in most widespread use today are:

FTTN - Fiber-to-the-node - fiber is terminated in a street cabinet up to several kilometers away from the customer premises, with the final connection

being copper.

FTTC - Fiber-to-the-cabinet or fiber-to-the-curb - this is very similar to FTTN, but the street cabinet is closer to the user's premises; typically within 300m.

FTTB - Fiber-to-the-building or Fiber-to-the-basement - fiber reaches the boundary of the building, such as the basement in an multi dwelling unit, with the final connection to the individual living space being made via

alternative means .

FTTH - Fiber-to-the-home - fiber reaches the boundary of the living space, such as a box on

the outside wall of a home .

FTTP - Fiber-to-the premises - this term is used in several contexts: as a blanket term for both FTTH and FTTB, or where the fiber network includes both homes and small businesses

C = λ f

λ = C / f

f = C / λ

• Frequency (f) is the number of complete oscillations in

• one second .

• Wavelength (λ) is the distance between two consecutive

• tops or bottoms (nm) .

• The optical fiber wavelength ranges from 820- 1600 nm .

In free space (vacuum) C° = 3 × 108 m/sec .

Glass is more dense than air . Speed of light in air is more than the

speed of light in any other material .

2.2 Speed of Light

Examples

1 -λ = 1 µ m , f? =

2 -f = 300 GHz , λ? =

Solution

1- f = C / λ = 3× 108 / 1× 10-6

= 3 × 1014 Hz = 300 T Hz

2- λ = C / f = 3× 108 / 300× 109

= 1× 10-3 = 1 m m

2.3 The Electromagnetic Spectrum

In the field of optical communications, (λ) is indicated instead of the frequency (f). Visible light occupies the wavelength range from 380 nm (violet) to 780 nm (red). Optical telecommunications uses the near IR range around the wavelength 1μm. This corresponds to a frequency in the order of magnitude of 1014 Hz.

When light falls to the interface of two media , there will be penetration or reflection or both .

2.4 Reflection & Penetration

Reflection depends on the surface .

If the surface is smooth , there will be “ regular reflection “.

2.4.1 Regular reflection

If the surface is rough , then there will be

“ diffuse reflection “ .

2.4.2 Diffuse reflection

2.4.3 Total reflection

LAW OF REFLECTION

2.4.4 Law of reflection

2.5 Refraction

Penetration of light ray from one medium to another.

Speed of light differs from medium to another.

Angle of refraction depends on the optical dense of the second medium.

REFRACTED RAY OF SPEED

2.5.1 Refraction index The speed of light in any other medium except vacuum is less than Co

The ratio between the speed

of light in free space and in a medium is called the refractive index (n) .

n = Co / C = speed of light in free space / speed of light in the medium .

The less the speed the more the refractive index .

MEDIUMREFRACTION INDEX

(n)

AIR1.00

WATER1.33

FUSED QUARTZ1.46

GLASS1.5-1.9

OPTICAL FIBER1.5

2.5.2 Comparison between (n) in different media

n is always > 1

Examples

Calculate the refractive index (n) if

1 -C = 2× 105 Km /s

2 -C = 0.5 C0

Solution

1- n = Co / C = 3× 108 / 2× 108 = 1.5

2 -n = Co / C = Co / 0.5 Co = 2

Example

Calculate the speed of light in a medium of refractive

Index 1.48

Solution

C = Co / n = 3× 108 / 1.48

= 2.027 × 108 m /s

2.5.3 Snell’s law ( Law of refraction )

Where

α = incident angle

Θ = refraction angle

n1 = refractive index of

the first medium

n2 = refractive index of

the second medium

Θ = sin-1 [ sin α . n1/n2 ]

Example

n1 = 1 , n2 = 1.5 , α = 30 0

Θ? =

solution

Θ = sin-1 [ sin α . n1/n2 ]

Θ = sin-1 [ sin 30 . 1/1.5 ]

Θ = sin-1 [ 0.5 * 0.66 ]

Θ = sin-1 0.33 = 19.47 0

2.6 Total Internal Reflection

TOTAL INTERNAL REFLECTION

At a certain angle of incidence the angle of reflection becomes 90o

(total internal reflection)

Total internal reflection occurs only when the medium of incidence is optically denser and at certain incidence angle (critical angle)

EXAMPLE

n1 = 1 .5 , n2 = 1 , Θ = 90 0

α c? =

SOLUTION

sin α c / sin Θ = n2 / n1

sin α c = 1 / 1.5 = 0.67

Snell’s law

α c = 42 0

2.7 Reflection Cases

Incident ray may:

Reflect

Have total internal

reflection

Refract

Law of Refraction

When light falls perpendicularly to a surface , it will not fully penetrate the surface but a small part of this light will be reflected .

It is called Fresnel reflection .

2.8 Fresnel Loss

Reflection Factor = ρ = ( ) 2

ρ = ( ) 2 = 0.04

n2-n1

n2+n11.5-1

1.5+1

2.8.1 Reflection factor

2.9 Rayleigh scattering

results from the existence of small

particles and inhomogeneties which are

illuminated and thereby emit light in all

directions.

The emitted light is called Tyndall-light

This scattering is proportional to λ-4 .

Example:

By what percentage is the tyndall-light increased when the wavelength is decreased 10% ?

Solution

B1 = k / λ4 B2 = k / (0.9 λ)4 = k / λ4 * 1 / (0.9)4

B2 = 1.52 B1

The increase = 52%

Rayleigh scattering limits the shorter wavelength

Core – thin glass center of the fiber where light travels.

Cladding – outer optical material surrounding the core .

Buffer Coating – plastic coating that protects the fiber.

• Materials for cladding and core :

- glass cladding/glass core . - plastic cladding/glass core . - plastic cladding/plastic core.

Core cladding jacket

Multicore

Single core

Minimum dispersion: all rays take same path, same time to travel down the cable. A pulse can be reproduced at the receiver very accurately.

Less attenuation, can run over longer distance without repeaters.

Larger bandwidth and higher information rate .

Disadvantages:

Difficult to couple light in and out of the tiny core .

Highly directive light source (laser) is required. Interfacing modules are more expensive .

Multimode step-index Fiber: inexpensive; easy to couple light into

Fiber result in higher signal distortion;

lower TX rate.

Multimode graded-index Fiber: intermediate between the other two

types of Fibers.

3.6 Light Propagation

Light propagates only in the core of the fiber.

All light that will not propagate in the core in the direction of propagation is a loss .

If there will be scattering due to impurities some of the light will not propagate in the output direction .

The cladding is manufactured in the way to prevent light from penetrating it .

3.6.1 Propagation in Step Index fiber

The core is consisted of only one layer .

)by reflection (Step index fiber)

Light will propagate in a straight line till reaching the surface of another medium with different n .

Light propagates by reflection in step index fiber .

by refraction (Graded index fiber)

In graded index fiber ,

the core is consisted

of many layers (30-50)

each of different n .

PROPAGATION BY REFRACTION

GRADED INDEX FIBER

Light is refracted as it goes from layer to

another layer .

3.7 Light Propagation in the Core

Minimum incident angle which makes light propagates in the core

α should be ≥ α c

α decreases with the increase of θ (launch angle) .

Θ has a maximum value after which α

will be less than α c

3.8 launch Angle

Maximum ACCEPTANCE Angle

3.9 Numerical Aperture (NA)

NA is the light gathering of an optical fiber.

NA is a function of the refractive indeces of the fiber.

NA is Less than 1.

NA is Indicates the efficiency of source to fiber

coupling.

NA has major importance in launching light into the Optical fiber .

When NA is large the accepted amount of light will be great and then the possible transmission distance will be great .

=0.242 =√1.482 -1.462 sine Θ = √n1

2- n2

2

sine Θ = NA NA = 0.24

14o = Θ = sin-1 0.24

•For larger NAs, the OF accepts more of the beam and the cone of light at the other end is correspondingly wider

However, a greater acceptance angle also results in greater dispersion effects .This applies to all fibres, even single-mode OFs.

Examplen1 = 1.48 , n2 = 1.46

Calculate NA and Θ

Solution

:Typical values far NAs

Single-mode fibres = 0.13 = 7.47°(Multi-mode fibres = 0.20 = 11 .54°(

The acceptance angle is in relation to the axis of incidence. To obtain the complete cone angle, the acceptance angle must be multiplied by 2

:Example

NA=0.13 :Acceptance angle

sin 0.13 = 7.47° :Cone angel

2× 7.47°= 14.94o

Example:

n1 (Core) = 1.469 , n2 (Cladding) = 1.45

n1(Core) = 1.469 , n2 (Cladding) = 1.464

Calculate NA for the following cases

1 -Multimode Fiber

2-Single mode Fiber

Solution

1 -For Multimode Fiber

14

24.045.147.1

max

2222

21

nnNA

2 -For Single mode Fiber

NA = sin Θ max

22

21 nn =

95.6

121.0465.1469.1

max

22

76

2

10log10)(

source

fiberNAl NA

NAP

2

10log10)(

source

fiberdl d

dP

dBLogLogP dl 1.4)39,0(10)100/5.62(10)( 102

10

(Pl )NA 10Log10 (0.275 / 0.30) 10Log10 (0.94) 0.8dB

A source, with an output diameter of 100m and an NA of 0.30 is connected to a fiber with a core diameter of 62.5m and NA of 0.275. The ( P ) NA and the ( P ) d are as follows:

Sources of losses of light power due to mismatches:

In the transmission of light through an

optical waveguide (fiber) there will only exist

a specific number of energy paths

(N ) .

These paths are called modes and may be

calculated.

In case of step index fiber

22

2

1

2

aNAV

N

In case of graded index fiber

22

4

1

4

aNAV

N

Example :

A graded- index fiber with a core diameter d

=50 μm and NA = 0.2 is to be operated at a

wavelength of λ = 1 μm . How many modes

are capable of propagation in this fiber ?

Solution

V = (d.π.NA ) / λ = 50*10-6 * 3.14 * 0.2 / 1*10-6 = 31.4

N = V2 / 4 = (31.4)2 / 4 = 247 modes

Such a fiber is called a multi mode fiber.

To obtain a single mode fiber, one must

reduce the number of modes by reducing the

V parameter. To do this:

- The core diameter or NA must be reduced

- The wavelength must be increased

Example

Calculate N for MMSI if NA = 0.2 , d = 50 µm ,

= 800 nm

22

2

1

2

aNAV

N

esmod800800

2.0*10*50*14.3

2

123

Solution

Example

Calculate N for MMGI if NA = 0.2 , d = 50 µm ,

= 800 nm

Solution22

4

1

4

aNAV

N

mod400800

2.0*10*50*14.3

4

1

4

232

VN

Example

Calculate N for SMSI if NA = 0.11 , d = 9 µm ,

= 1310 nm

Solution

=1550 nm

22

1310 2

1

2

NAaV

N

esmod311.0*1310

10*9*14.3

2

123

esV

N mod211.0*1550

10*9*14.3

2

1

2)(

232

1550

Example : A fiber with a core diameter d = 9 μm and

N=0.11 is to be operated at a wavelength of 1.3 μm .How large is the V parameter of this fiber?

Solution

V = (d.π.NA ) / λ = 9*10-6 * 3.14 * 0.11 / 1.3*10-6

=2.39 (<2.405)

In this condition the fiber is a single mode fiber.

The result shows 2 polarization modes oscillating rectangular to each other

propagate with single mode fiber, These 2 polarization modes are handled as a single mode .

3.11 Fiber Attenuation

Fiber Attenuation in (dB/km)

The attenuation tells how the light is attenuated

along the fiber and is normally measured in

(dB/Km) for a certain wavelength .

Scattering

Rayleigh-ScatteringInhomogeneities

FlawsIrregularities in core

diameter

3.11.1 Scattering

Scattering of the light in the fiber is caused by the

variation in the molecular density and composition

of the fiber .

3.11.2 Absorption

As compared to ordinary glass, optical fiber core remarkably free from impurities.

Through careful processing, for instance , silicon has been kept to a purity of 99.999% .

However though the impurities are only a few parts per billion, they absorb some of the light and convert it to heat.

Factors affecting the absorption :

• The kind of impurity Metal ions (iron, copper, cobalt,

nickel or manganese) and water in the form of OH

Hydroxide.

• Wavelength Absorption happens at certain

wavelengths or in absorption bands.

Los

s (d

B/k

m)

1

00.7 0.8

Wavelength (m)0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7

2

3

4

5

6

Peaks causedby OH- ions

Infraredabsorption

Rayleigh scattering& ultravioletabsorption

3.12 Dispersion As light pulses travel along an optical fiber, they tend to become wider, often to the point that they will overlap other pulses.

The spreading is called dispersion .

Dispersion makes it hard for the receiver to tall one pulse from another. It is a form of signal distortion which effectively limits the information carrying capacity of an optical system.

WIDTH OF

INPUT PULSE

WIDTH OF

OUTPUT PULSE

in (ns)

To measure dispersion we calculate the difference in width (in nanoseconds) between the input pulse and the output pulse .

Monochromatic Light

One

Wavelength

λ

3.12.1 Monochromatic Light

No dispersion for monochromatic .

3.12. 2 Polychromatic Light

Polychromatic light is composed of many different

wavelengths

EACH

IS

MONOCHROMATIC

Light can be separated into individual wavelengths by

glass prism through the process of dispersion .

http://upload.wikimedia.org/wikipedia/commons/f/f5/Light_dispersion_conceptual_waves.gif

Different

Speeds

Time Shift

Different wavelengths propagate with different speeds in the same medium .

They will not reach at the far end at the same time (there will be time shift) .

Multimode Step Index Fiber

INPUT PULSE

OUTPUT PULSE

REFRACTIVE INDEX PROFILE

SLOWEST MODE

FASTEST MODE

MODAL DISPERSION DIFFERENCE IN HOW FAR

MODES TRAVEL IN GIVEN TIME

3.12.3 Types of Dispersion

Modal dispersion (Ψmod )

In step index multimode fiber, light rays that travel parallel to the axis will have a shorter path length than rays that zigzag down the fiber.

Therefore some rays will take longer to reach the output .

Ψmod = Tkm * Δ / 2 ns / km

Where

Tkm = traveling time per (fiber km)

Δ = n1-n2 / n1

ExampleIn step index multimode fiber

Δ = 0.01 , n = 1.5

CALCULATE Ψmod

SolutionΨmod = Tkm * Δ / 2

= n / c0 * Δ / 2 = 1.5 / 3 × 105 *

0.01 / 2

= 25 ns / km

Input pulse

Output pulse Refractive

index

Modal dispersion in graded-index fiber is less than

that of the step index fiber .

Ψmod = Tkm * Δ2 / 2

Example :

In graded-index fiber

Δ = 0.01 , n = 1.5

CALCULATE Ψmod

Solution

Ψmod = Tkm * Δ2 / 2 = 1.5 / 3 × 105 * (0.01) 2 / 2

= 0.25 ns / km

Single-Mode Step Index Fiber

Only One Mode:

No Modal Dispersion

Output Pulse

Refractive Index Profile

Input Pulse

In the single mode fiber (monomode fiber) There

is only one mode propagation.

No modal dispersion.

The width of input pulse is the same like that of the output pulse.

Material dispersion

Material Dispersion

All light sources for an optical fiber emit light not only in one single wavelength (λ) but rather in a spectral width distributed around the wavelength (λ) .

The light pulse is composed of light of different wavelengths depending on the spectral width of light source.

This means that different wavelengths will have different velocities in glass, therefore they will not arrive simultaneously at the same output.

• Patch Cables

• Aerial Cables

• Conduit Cables

• Buried Cables

• Submarine Cables

Patch Cables

Figure 8 (aerial/self-supporting) fiber cables

Conduit Cables

Armored Fiber Optic Cable for direct buried

Fiber optic cable for submarine use

• Secondary Protection with Loose Tube

Secondary Protection with Loose Tube

Long Haul Networking

Building Interconnections (Campus LAN)

Trunking Lines Direct to Telecommunications Closet

Local Loop

Distance Learning

Intrabuilding Backbones

• Tight Secondary Protection Fiber

Tight Secondary Protection Fiber

nearly all commercial communications applications demanding the high

performance of optical fibers.

Such applications include moderate distance transmission for telco local loop, LANs, and point-to-point links in cities, buildings, factories, office parks and on campuses.

Tight-buffered cables offer the flexibility, direct connectability and design versatility necessary to satisfy the diverse requirements existing in high performance fiber optic applications.

Typical applications include central-office

switches, parallel computing clusters, LANs,

remote testing, and under-carpet cabling.

• Fiber Optic Ribbon

4.3 Optical Fiber Cable Structure

Tubes

Outer Sheath

Strength Member

Fiber Optics

Aramid Yarn (Kevler)

Inner Sheath

Aluminum Tapeا

Strength member

Tubes

Fiber Optics

Aramid Yarn

(Kevler) )

Copper Conductors

Aluminum Tape

5 * 4* 50 µ m + 1 * 2 * 0.65 mm , 1300 nm

1234567891011121314

4.4 Type Codes

Product designationA-Outdoor cable

H Single-fiber loose buffer, unfilledW Single-fiber loose buffer, filledB Multi-fiber loose buffer, unfilledD Multi-fiber loose buffer, filled

S Metal element in cable core

F Filling compound for filling the stranding interstices in the cable core

2Y PE sheath)L(2Y Laminated sheath

)ZN(2Y PE sheath with nonmetallic strength member)L)(ZN(2Y Laminated sheath with nonmetallic strength member

b Armoring bY Armoring with PVC protective coverb2Y Armoring with PE protective cover

Number of fibers or number of multifiber loose buffers x number of fibers per buffer tube

Type of fiberG Graded indexE Single mode

Core diameter (μm) Cladding diameter (μm)

Attenuation coefficient (dB/km)

WavelengthB 850 nmF 1300 nmH 1550 nm

Bandwidth in MHz for 1 km

Lg stranded layers

Example:

A-WSF(ZN)2Y -12 *1G 50/125- 3.0 B 600

The cable is an outdoor cable (A) with loose buffer

jackets filled (W), metallic element in the cable

centre (S) and filling between the buffer jackets (F).

Laminated sheath with non-metallic strength member

(ZN) 2Y. Furthermore the cable contains 12 graded

index fibers (G) with the diameters 50 µm for the

core and 125 µm for core and cladding. The

attenuation coefficient is 3 dB and a bandwidth of

600 MHz for 1 Km by a wavelength of 850 nm (B).

During the installation the cable should be handled with care, especially concerning bends.

The bending radius must not be less than the diameter of the cable multiplied by 20: Bending radius = 20 x diameter of cable

Optical fibers are used in pairs, one for Transmit (TX) and one for Receive (RX). A new technology, the wave division multiplex (WDM), reduces this to one fiber for Transmit and Receive.

The economics of cable construction are such that the cable sheath for damage protection and the strength members for increased pulling tensions are the expensive factor in fiber cable production. Therefore, it has to be calculated correctly, whether using more fibers in the cable or higher level equipment for more capacity.

4.5 Cable Installation

• An optical fiber connector terminates the end of an optical fiber, and enables quicker connection and disconnection than splicing.

• The connectors mechanically couple and align the cores of fibers so that light can pass.

• Most optical fiber connectors are spring-loaded: The fiber endfaces of the two connectors are pressed together, resulting in a direct glass to glass or plastic to plastic contact, avoiding any glass to air or plastic to air interfaces, which would result in higher connector losses.

• A variety of optical fiber connectors are available.

optical fiber connector

• Generally, organizations will standardize on one kind of connector, depending on what equipment they commonly use, or per type of fiber (one for multimode, one for single mode).

• In data com and telecom applications nowadays small form factor connectors (e.g. LC) and multi-fiber connectors (e.g. MTP) are replacing the traditional connectors (e.g. SC), mainly to pack more connectors on the overcrowded faceplate, and thus reducing the footprint of the systems.

5-1 D4 connector

• It was widely used in telcom. networks in the

80s to early 90s and some may still be in use.

• Used in Multi and single mode

5-2 SMA connector

• These connectors are still in use on some military and industrial systems.

• Used in Multimode only

5-3 FC Connector

• FC was one of the most popular single mode connectors for many years

• It's been mostly replaced by SCs and LCs.

5-4 BICONIC connector

• The yellow body indicating a SM version - MMs were usually black.

• Usually MM Biconics had losses of 0.5-1 dB and SM 0.7 dB or higher.

5-5 ST Connector

• ST (an AT&T Trademark) is probably still the most popular connector for multimode networks (ca. 2005), like most buildings and campuses.

• And because they are spring- loaded, you have to make sure they are seated properly

5-6 SC Connector

• It is widely used for it‘s excellent performance

• It was not widely used at first because it was twice as expensive as a ST. Now it's only a bit more expensive and much more common

General representation of an N× M optical coupler

6-1 Optical Coupler Usage

• fiber coupler is an optical fiber device with one or more input fibers and one or several output fibers.

• Light from an input fiber can appear at one or more outputs, with the power distribution potentially depending on the wavelength and polarization.

• Fiber optic couplers should prevent the transfer of optical power from one input fiber to another input fiber.

• Directional couplers are fiber optic couplers that prevent this transfer of power between input fibers.

• Many fiber optic couplers are also symmetrical. A symmetrical coupler transmits the same amount of power through the coupler when the input and output fibers are reversed

Examples of complex system architectures.  

Beside simple point to point links, optical

fiber communications often makes use of more

complex topologies (e.g., ring, star, bus) mainly in LANs

This can be carried out directly avoiding any optical to electrical conversion by making use of passive optical devices known as optical directional couplers.

Optical couplers are usually provided with connectors to allow any easy connection to optical fiber lines and to active or passive devices .….. ……..

For these applications, special functions are needed such as distribution of the same signal to several subscribers, insertion of many signals into one line .

Twisted Fiber-Optic Coupler

• Such couplers can be fabricated in different ways, for example by thermally fusing fibers so that their cores get into intimate contact .

Fabrication of a fused biconical taper coupler (star coupler).  

6-2 Optical Coupler Fabrication

• Passive fiber optic coupler fabrication techniques can be complex and difficult to understand.

• Some fiber optic coupler fabrication involves beam splitting using microlenses or graded-refractive-index (GRIN) rods and beam splitters or optical mixers.

• These beamsplitter devices divide the optical beam into two or more separated beams.

• Fabrication of fiber optic couplers may also involve twisting, fusing, and tapering together two or more optical fibers. This type of fiber optic coupler is a fused biconical taper coupler.

•Fused biconical taper couplers use the radiative coupling of light from the input fiber to the output fibers in the tapered region to accomplish beam splitting. coupler). 

• Most Couplers and Splitters are designed bi-directionally, enabling the same product to be used as a coupler or a splitter.

• Single Mode, multimode, and PM fiber

types

• Multiple port configurations

• Compact size

• Various coupling ratios, 50 : 50 to 1 :

99

• Multiple packaging options

• PC, UPC, and APC connector polish

types

• Available with FC, SC, ST, LC, and MU

terminations

6-3 Optical Coupler Features

6-4 Typical Applications of Fiber Couplers

Some typical applications of fiber couplers are:

•In a cable TV system, the powerful signal from one transmitter is sent in to a fiber splitter, which distributes the power over a large number of output fibers for different customers.

•Within the resonator of a fiber laser, a dichroic fiber coupler can be used to inject pump light, and another fiber coupler can be used as the output coupler. This technique is used particularly in fiber ring lasers, having no resonator ends where light could be injected.

6-5 Passive and Active Couplers• The difference between active

and passive couplers is that a passive coupler redistributes the optical signal without optical-to-electrical conversion. Active couplers are electronic devices that split or combine the signal electrically and use fiber optic detectors and sources for input and output.

6-6 Coupling Loss• Fiber optic couplers attenuate the

signal much more than a connector or splice because the input signal is divided among the output ports. For example, with a 1 X 2 fiber optic coupler, each output is less than one-half the power of the input signal (over a 3 dB loss). • If all fibers involved are single-mode (i.e., support only a single mode per polarization direction for a given wavelength), there are certain physical restrictions on the performance of the coupler .

• In particular, it is not possible to combine two or more inputs of the same optical frequency into a single-polarization output without significant excess losses, except if the optical phases of the input beams are precisely adjusted and stabilized .• This means that the two inputs to be combined would have to be mutually coherent .

• However, such a restriction does not occur for different input wavelengths: there are couplers which can combine two inputs at different wavelengths into one output without exhibiting significant losses. Such dichroic couplers are used e.g. in fiber amplifiers to combine the signal input and the pump wave.

• Other wavelength-sensitive couplers are used as multiplexers in wavelength division multiplexing )WDM( telecom systems to combine several input channels with different wavelengths, or to separate channels .

• Multimode fiber combiners allow e.g. the powers of two mutually incoherent beams to be combined without a power loss. However, this will cause some loss of brightness .

6-7 Bandwidth of Coupler

• Most types of couplers work only in a limited range of wavelength (a limited bandwidth), since the coupling strength is wavelength-dependent (and often also polarization-dependent).

• This is a typical property of those couplers where the coupling occurs over a certain length.

• Typical bandwidths of fused couplers are a few tens of nanometers.

Y Coupler (optical splitter )

Schematic representation of a Y coupler

( or optical splitter )

A Y coupler (optical splitter) is a device that divides

the optical power carried by one input fiber sharing

it between two output fibers .

It can be used as a monitor of the power level that is

carried by the main line.

6-8 Types of fiber optic couplers

• However, an optical splitter may distribute the optical

power carried by input power in an uneven manner. An

optical splitter may split most of the power from the

input fiber to one of the output fibers.

•Only a small amount of the power is coupled into the

secondary output fiber.

•This type of optical splitter is known as a T-coupler, or

an optical tap.

Optical Combiner

Schematic representation of an optical combiner

When the devices are used to combine the signals

carried by two fibers into one, they are sometimes

referred as optical combiners.

Optical x Coupler

Schematic representation of an optical × coupler

( or 2 × 2 directional coupler ) .

Both functions, combining and splitting are carried out

by the so called X coupler (2X2 directional coupler).

Optical Star Coupler

Schematic representation of an N × M star coupler

Multiport devices having input (or output) ports in excess of 2 are usually called star couplers . A star coupler is a passive device that distributes optical power from more than two input ports among several output ports .

Optical Tree Couplers

Schematic representation of a 1 × M tree coupler

• A tree coupler is a passive device that splits the optical power from one input fiber to more than two output fibers

•A tree coupler may also be used to combine the optical power from more than two input fibers into a single output fiber

• Star couplers and tree couplers are mainly

used in LANs and usually are supposed to

produce uniform division of the input power to

the output ports.

• Star and tree couplers distribute the input

power uniformly among the output fibers.

7-1 Fusion Splicer of Fiber Optics

Fujikura FSM-60S Fusion Splicer

A fusion splice is a way of joining two fiber cores by melting the ends together using an electric arc.

A splicing machine is used because an extremely high degree of accuracy is needed, the machine first has to align the cores and then apply the exact amount of heat to melt the ends before pressing them together.

Splicing can be carried out using a mechanical splice but these only hold the fiber ends together, precisely aligned but not permanently joined

There are four basic steps to fusion splicing

1 - Strip back all coatings down to the bare fibers

and clean using isopropyl alcohol.

2 - Cleave the fibers using a precision cleaving tool and

put the heat shrink tube on to one of the ends.

3 - Fuse the fibers together in the fusion splicer.

4 - Put the heat shrink protector on the fiber joint .

7.3 Fusion Splicing Preparation

Stripping Strip back the external sheathing of the cable using a rotary stripping tool.

Cut back the aramid strength member using ceramic or kevlar scissors. Strip the primary buffer from the fiber using fiber strippers not ordinary wire strippers.

Cleaving

The cleaver first scores the fiber and then pulls the fiber apart to make a clean break.

It is important that the ends are smooth and perpendicular to get a good joint.

Cleavers vary from manufacturer to manufacturer and you should read the instructions for the one you are using.

Basically the operation consists of putting the fiber into the groove and clamping, then close the lid and press the lever.

7.4 The Fusion Process

The Fusion Process

Once the fiber ends are prepared they are

placed in the fusion splicer. Press the button

and the machine takes care of the rest of the

fusion process automatically.

First the two fibers are aligned, you can see

this on the photo where a much magnified

image shows the two fiber ends. The display

also shows how well the cleaver does its job

of producing a perfect 90 degree cut

Once the fibers are aligned the splicer fires an electric arc between the two ends which melts them immediately and pushes them together, or fuses them into one piece of fiber.

The fusion splicer then tests for dB loss and tensile strength before giving the "OK" beeps for you to remove the splice from the machine.

7.5 Protection

The splicer has a built in heat shrink oven, so when the fiber is taken out of the machine the protective tube is slid into place and the whole assembly is put into the oven to shrink the tube on to the splice.

The protective tube gives physical protection to the splice .

Once all of the fibers have been joined the whole tray is then fixed into a splice box which protects the cable joint as a whole and the cable clamps are then tightened to prevent any external forces from pulling on the splices.

Splice attenuation < 0.1 db

7.6 Splice Attenuation

For the good splice , the attenuation will be

less than 0.1 db per splice.

Causes of bad splices

Probable faults in splicing:

• Radial faults

• Angle faults

• Axial faults

These faults will cause arise

in attenuation.

• optical fiber closure provide reliable, stable

and flexible protection for the direct, terminal

or branching connection of fiber.

7-7 Optical Fiber Closure

• Sealing system consist of cable clamps, cable gaskets

and a case gasket provide proven watertightness and

great deal of flexibility.

• It's very convenient especially for branch cable

splices.

• Diameter of 8mm to 17mm cables are available .

• series of Fiber Optic Splice Trays offers a

unique and flexible splice and storage system.

• Available in three industry standard config

urations (mechanical, fusion or ribbon) or as a

totally universal kit.

• Telecommunications Fiber Optic Splice Trays

provide the most flexible and universal fiber

storage system available .

• Pivoting splice trays maximize density and

maintain sufficient bend radius.

Fiber Optic Splice Trays

Splice Closure containing trays

Mechanical Splice employs V-groove butting technology, which is applicable

for connecting singlemode and multimode optical fibe ...

Applications: fast fiber conection outside application

no polishing and no epoxy hand operation ...

Splice L925BP 1.It is applicable for connecting

singlemode and multimode optical fibers. 2.Excellent in

quality(ISO9001:2008) ...

Mechanical Splice employs V-groove butting technology, which is

applicable for connecting singlemode and multimode optical fibe ...

After the fibers are inserted into the splice, the cap is depressed with the Assembly Tool. The motion of the cap

squeezes the "legs" of the element such that the "legs" come together. The fibers are permanently aligned and

gripped in the fiber holding region of the splice when the cap is actuated.

The Fibrlok has an insertion loss of <0.2dB with a minimum tensile load of 4.4N (1.0lb-f) and splice reflection no greater

than -40dB

2612 ) 3M 2612 Fibrlok 12 Fiber Ribbon Optical Splice

The Fibrlok 2612 12 Fiber Ribbon Optical Splicing System provides permanent mechanical splices for 12 single mode or multimode optical fibers with a nominal cladding diameter of 125um.

This splice is yellow color coded for easy recognition.

This 12 fiber mechanical splice can be used with either fiber optic ribbon cable or individual 250um coated fibers which have been organized into a ribbon structure (i.e. "ribbonized"). For additional information concerning the use of 250um fiber, refer to the Fibrlok 2670 Multi-Fiber Ribbon Construction Tool.

8 .Optical Fiber Link

ELECRICAL

CIRCUITS

Electrical

Interface

Code Converter

OPTICAL

TRANSMITTER

LED

LD

FIBRE CABLE OPTICAL

RECEVIER

ELECTRICAL

CIRCUITS

Avalanche photo

Diode (APD)

PIN-diode

Step index

Graded index

Single mode

Electrical interface

Clock regeneration

Code conversion

Fiber optical link

Connectors

Splice

block diagram of an optical fiber transmission line

8.1 Fundamental Mode of Operation of an Optical Transmission Plant

In such a plant an analog telephone signal with a frequency band of 300 - 3,40Q Hz is converted by means of an analog/digital (AID) converter to a digital signal.

This consists of electrical pulses. With these pulses you now steer a semi-conductor laser, which is able to produce light pulses of high intensity (brightness) within a small frequency band.

The laser is now switched on and off by the frequency of the incoming electrical pulses and thus produces optical signals.

These optical signals are transmitted to a photodiode, the receiver, via an optical fiber line, which is connected to the laser and the photodiode .

The photodiode converts the optical signal back to an electrical one, which is also converted back to an analog one by means of a digital/analog converter (D/A) to achieve the original telephone signal.

Optical fibers are suitable for transmission of digital signals, since only ‘ON and ‘OFF’ signals have to be detected by the receiver.

Thus mainly PCM- or similar systems are connected to optical fiber lines.

Transmission Attenuation in

Optical Fiber System

8-2 Transmission Attenuation

The transmission attenuation is the total attenuation

(in dB) between two given interfaces

A = PT – PR dB

A = ATF + n1Ac + n2As + l Af + n3 AT + AFR dB

WhereATF = Insertion loss transmitter to fiberAc = Connector AttenuationAs = Splice AttenuationAf = Fiber attenuationAT = Branching attenuationAFR = Insertion loss fiber to receiverPT = Output Power of transmitterPR = Receiver input powern = Number of connectors , splices and branching

8-3 System Margin (M)

M = PM – PM min (dB)

Where PM min = limit sensitivity of the receiver

M = (PT – PR min ) – A

M is for :

Attenuation due to temperature variations Ageing of cable and devices

Maintenance

Example

PT = 0 dBm

A = 36 dB dB 6 M=

Calculate the sensitivity of the receiver

Solution

PR min = PT – A – M

= 0 – 36 – 6 – = 42 dBm

Problem 1

An Optical Fiber Cable System has :

• 60 km length

• Splice Loss = 0.3 db /splice

• Connector Loss = 0.2 db /connector

• Cable attenuation coefficient = 0.5 db /km

• The available cable lengths = 5km / reel

• System Margin = 5 dbCalculate :

1- Number of Splices

2- Total Loss

3- Receiver Sensitivity if transmitted power = o dbm

Problem 2

For an Optical Fiber Cable System ,

• Total loss between transmitter and receiver stations = 30 db

• Span = 50 km

• Splice loss = 0.1 db / splice

• Connector Loss = 0.3 db /connector

• The available cable lengths = 2 km / reel

• System Margin = 0.2 db /kmCalculate :

The maximum attenuation coefficient of the cable used .

In the transmission of light through an optical waveguide (fiber) there will only exist a specific number of energy paths .

These paths are called modes and may be calculated.

a = core radius NA = numeric aperture λ = frequency to be used

V = 2π (a / λ) NA

An optical fiber will guide any number of modes but under specific conditions it will guide only one single mode.

For a specified NA and core diameter a, the wavelength (cut off wavelength) when the fiber turns into a single mode fiber may be calculated through the formula below.

λ= π (2a / V) NA = π (2a / 2.405) NA

The number of modes can be calculated as follows:

- For graded index profiles

N = V2 / 4

- For step index profiles

N = V2 / 2

Example :

A graded- index fiber with a core diameter d =

50 μm and NA = 0.2 is to be operated at a

wavelength of λ = 1 μm . How many modes are

capable of propagation in this fiber ?

Solution

V = (d.π.NA ) / λ = 50*10-6 * 3.14 * 0.2 / 1*10-6

= 31.4

N = V2 / 4 = (31.4)2 / 4 = 247 modes

Such a fiber is called a multi mode fiber.

To obtain a single mode fiber,

one must reduce the number of modes by reducing the V parameter.

To do this:

- The core diameter or NA must be

reduced

- The wavelength must be increased

Example : A fiber with a core diameter d = 9 μm

and N=0.11 is to be operated at a wavelength of 1.3 μm How large is the V parameter of this fiber?

SolutionV = (d.π.NA ) / λ = 9*10-6 * 3.14 * 0.11 / 1.3*10-6

=2.39 (<2.405)

In this condition the fiber is a single mode fiber.

The result shows 2 polarization modes oscillating rectangular to each other

propagate with single mode fiber, These 2

polarization modes are handled as a single mode .

Light-Emitting Diodes (LED)

made from material such as AlGaAs or GaAsP.

light is emitted when electrons and holes recombine .

either surface emitting or edge emitting . Injection Laser Diodes (ILD)

similar in construction as LED except ends are

highly polished to reflect photons back & forth .

Advantages:

more focussed radiation pattern; smaller Fiber

much higher radiant power; longer span

faster ON, OFF time; higher bit rates possible

monochromatic light; reduces dispersion

Disadvantages:

much more expensive higher temperature; shorter lifespan

Directional size and configuration with the

launching of light into the fiber.

Linear Accurately track the electrical input signal.

Minimize dispersion Emit light at wavelength to suit the fiber attenuation and

receiver.

Extreme bandwidth Capable of modulating from audio to GHz.

Low couple attenuation Good coupling into the fiber

High output power Enough power to drive detectors

far away

Minimize dispersion Narrow spectral bandwidth

Unaffected by Capable of maintainingambient conditions a stable output

Cheap and reliable Complete with other transmission

techniques

10.4 Spectral Width For different light sources

10 20 30 40

10

8

6

4

2

Output power ]mW[

Current ]mA[

Threshold

LED

LED

LDt=20o

LDt=50o

LDt=70o

Light-emitting diode

Red, green and blue LEDs of the 5mm type

TypePassive, optoelectronic

Working principleElectroluminescence

InventedNick Holonyak Jr. (1962)

Electronic symbol

Pin configurationAnode and Cathode

modern versions are available across the visible, ultraviolet and infrared wavelengths, with very high brightness

The LED is based on the semiconductor diode. When a diode is forward biased (switched on), electrons are able to recombine with holes within the device, releasing energy in the form of photons

This effect is called electroluminescence and the color of the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor

LEDs present many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved robustness,

Laser diodes find wide use in telecommunication as easily modulated and easily coupled light sources for fiber optics communication

These devices are sometimes referred to as injection laser diodes

LASER means Light Amplification by Stimulated Emission of Radiation

PIN Diodes photons are absorbed in the intrinsic layer.

sufficient energy is added to generate carriers in the depletion layer for current to flow through the device.

Avalanche Photodiodes (APD)

Photo generated electrons are accelerated by relatively large reverse voltage and collide

with other atoms to produce more free electrons .

avalanche multiplication effect makes APD more sensitive but also more noisy than PIN diodes.

Strength of the light pulse Sensitivity of detector Noise Signal to noise ratio (SNR) Bit error rate (BER) Response Quantum efficiency Bandwidth

12.1 Units

dB = 10 log Po / Pi

dBm = 10 log Po / 1 mw

dBr = 10 log Po / Pr

dB = dBm1 – dBm2

1 - Pi = 10 mw , Po =10 nw

2 - Pi = 10 mw , Po = 1 mw

Calculate the loss or the gain

Solution1- A = 10 log Po / Pi = 10 log 10 × 10-6 / 10 × 10-3

= 10 log 10-3 = -3 × 10 =-30 dB ( loss )

2 - A = 10 log Po / Pi = 10 log 1 × 10-3 / 10 × 10-3

= 10 log 10 = 1 × 10 = 10 dB ( gain )

Optical power measurement .

Bandwidth measurement .

Total loss measurement.

( db/ km ) measurement

Splice Loss measurement

Connector Loss measurement.

Distance and fault location

measurement

Optical time domain reflectometry consists of injecting a light pulse down the optical fiber to be analyzed and observing, at the point of injection, the intensity of the light reflected back in the opposite direction to the pulse propagation.

The detected backscattered (or retro diffusion) signal is a decreasing exponential, to which peaks caused by reflection from fiber connectors, splices or faults are added .

  The measurement result should provide :

• the attenuation .

• the location of faults in terms of

distance from defined point .

• the attenuation versus

distance( dB/km(.

• the reflectance of an event or an

optical link.

12.4 OTS Measurement Principles

The attenuation measurement in power of a complete link or elements such as fiber sections, connections, optical components, requires a calibrated laser light source and a power meter.

This is generally deducted from the optical power measurement at two points :

dB = dBm1 – dBm2

To make accurate measurements the following conditions are required;

• Use a light source that is stable in time and in respect to the temperature.

• Verify that the connections, the fibers and the receiving cell are perfectly clean.

• Use a reference link between the laser source and the element under test.

• To make several measurements with the same light injection conditions, the reference fiber must not be disconnected during the measurement period.

Optical Time Domain Reflectometer ( OTDR ) module.

Visual Fault Locator (VFL) module .

Optical Transmitter System ( OTS ) module .

Fault Locator module .

Wavetek device contains many modules

13.1 Local Area Network and Subscriber Loops

In a local network optical fiber cables are often installed as overlay networks which are added to the existing old cable network, without replacing it.

New networks are making use of the optical fiber technology partly or completely.

We distinguish three different types of applications:

13 .Fiber Networks

13.1.1 Fiber to the Curb (FTTC)

Means a fiber optic cable is installed between the exchange and the cabinet, now called optical line unit. From here the secondary network remains like before. The advantage is that primary capacity can be increased easily, quick and at low cost.

.13.1.2 Fiber to the Building (FTTB)Has one great advantage over “Fiber to the urb”. This is the power supply and the accessibility of fibers for the subscriber. Power supply can be provided within the building since the ONU is pushed forward there.The outside network is similar but with the difference that the ONU’s are placed inside of buildings.

13.1.3 Fiber to the Home The entire connection between the exchange and he subscriber is realiseci by optical fiber . No network part is copper wire any more. The speed which can be used for data communication and of course normal telephone service can be as much as 2 Mbits per subscriberThis technology is until now mainly used for commercial areas to connect companies with high-speed communication.

.13.2 Fiber Trunk Networks In former times exchanges were connected by copper cables (often coaxial cables) or by means of microwave links.

With the introduction of digital switching systems (e.g. EWSD) a need of connection with high capacity and speed became necessary.

As the copper cables and microwave links proved to be not reliable enough and also to very costly, fiber optic cables were installed instead.

Often the network is laid out as a ring. In case of a failure the traffic can be easily routed via the cable section which is still functioning.