ofc

Optical Fibre Cable, Principle and Operation, Fibre construction and Characteristics, OFC Splicing & Overview of PDH Optical

Fibre System

Objective : Introduction to Fibre Optics, theory and principle of Fibre Optics,

propagation of light through fibre, Fibre Geometry, Fibre Types.

FIBRE OPTICS : Optical Fibre is new medium, in which information (voice, Data or Video) is

transmitted through a glass or plastic fibre, in the form of light, following the

transmission sequence give below :

(1) Information is encoded into electrical signals.

(2) Electrical signals are converted into light signals.

(3) Light travels down the fibre.

(4) A detector changes the light signals into electrical signals.

(5) Electrical signals are decoded into information.

ADVANTAGES OF FIBRE OPTICS : Fibre Optics has the following advantages :

(I) Optical Fibres are non conductive (Dielectrics)

- Grounding and surge suppression not required.

- Cables can be all dielectric.

(II) Electromagnetic Immunity :

- Immune to electromagnetic interference (EMI)

- No radiated energy.

- Unauthorised tapping difficult.

(III) Large Bandwidth (> 5.0 GHz for 1 km length)

- Future upgradability.

- Maximum utilization of cable right of way.

- One time cable installation costs.

(IV) Low Loss (5 dB/km to < 0.25 dB/km typical)

- Loss is low and same at all operating speeds within the fibre's

specified bandwidth long, unrepeated links (>70km is operation).

(v) Small, Light weight cables.

- Easy installation and Handling.

- Efficient use of space.

(vi) Available in Long lengths (> 12 kms)

- Less splice points.

(vii) Security

- Extremely difficult to tap a fibre as it does not radiate energy that can

be received by a nearby antenna.

- Highly secure transmission medium.

(viii) Security - Being a dielectric

- It cannot cause fire.

- Does not carry electricity.

- Can be run through hazardous areas.

(ix) Universal medium

- Serve all communication needs.

- Non-obsolescence.

APPLICATION OF FIBRE OPTICS IN COMMUNICATIONS : - Common carrier nationwide networks.

- Telephone Inter-office Trunk lines.

- Customer premise communication networks.

- Undersea cables.

- High EMI areas (Power lines, Rails, Roads).

- Factory communication/ Automation.

- Control systems.

- Expensive environments.

- High lightening areas.

- Military applications.

- Classified (secure) communications.

Transmission Sequence : (1) Information is Encoded into Electrical Signals.

(2) Electrical Signals are Coverted into light Signals.

(3) Light Travels Down the Fiber.

(4) A Detector Changes the Light Signals into Electrical Signals.

(5) Electrical Signals are Decoded into Information.

- Inexpensive light sources available.

- Repeater spacing increases along with operating speeds because

low loss fibres are used at high data rates.

Principle of Operation - Theory • Total Internal Reflection - The Reflection that Occurs when a Ligh Ray

Travelling in One Material Hits a Different Material and Reflects Back

into the Original Material without any Loss of Light.

THEORY AND PRINCIPLE OF FIBRE OPTICS Speed of light is actually the velocity of electromagnetic energy in vacuum

such as space. Light travels at slower velocities in other materials such as glass.

Light travelling from one material to another changes speed, which results in light

changing its direction of travel. This deflection of light is called Refraction.

The amount that a ray of light passing from a lower refractive index to a

higher one is bent towards the normal. But light going from a higher index to a

lower one refracting away from the normal, as shown in the figures.

As the angle of incidence increases, the angle of refraction approaches 90o

to the normal. The angle of incidence that yields an angle of refraction of 90o is the

critical angle. If the angle of incidence increases amore than the critical angle, the

light is totally reflected back into the first material so that it does not enter the

second material. The angle of incidence and reflection are equal and it is called

Total Internal Reflection.

By Snell's law, n1 sin ∅ 1 = n2 sing ∅ 2

The critical angle of incidence ∅ c where ∅ 2 = 90 o

Is ∅c = arc sing (n2 / n1)

At angle greater than ∅c the light is reflected, Because reflected light

means that n1 and n2 are equal (since they are in the same material), ∅ 1 and ∅ 2

are also equal. The angle of incidence and reflection are equal. These simple

principles of refraction and reflection form the basis of light propagation through an

optical fibre.

PROPAGATION OF LIGHT THROUGH FIBRE.

The optical fibre has two concentric layers called the core and the cladding.

The inner core is the light carrying part. The surrounding cladding provides the

difference refractive index that allows total internal reflection of light through the

core. The index of the cladding is less than 1%, lower than that of the core. Typical

values for example are a core refractive index of 1.47 and a cladding index of

1.46. Fibre manufacturers control this difference to obtain desired optical fibre

characteristics.

Most fibres have an additional coating around the cladding. This buffer

coating is a shock absorber and has no optical properties affecting the

propagation of light within the fibre.

Figure shows the idea of light travelling through a fibre. Light injected into

the fibre and striking core to cladding interface at grater than the critical angle,

reflects back into core, since the angle of incidence and reflection are equal, the

reflected light will again be reflected. The light will continue zigzagging down the

length of the fibre.

Light striking the interface at less than the critical angle passes into the

cladding, where it is lost over distance. The cladding is usually inefficient as a light

ø1

Angle of incidence

n1n2

ø2

n1n2

ø1

ø2

n1n2

ø1 ø2

Angle oreflecti

Light is bent away from normal

Light does not enter second material

carrier, and light in the cladding becomes attenuated fairly. Propagation of light

through fibre is governed by the indices of the core and cladding by Snell's law.

Such total internal reflection forms the basis of light propagation through a

optical fibre. This analysis consider only meridional rays- those that pass through

the fibre axis each time, they are reflected. Other rays called Skew rays travel

down the fibre without passing through the axis. The path of a skew ray is typically

helical wrapping around and around the central axis. Fortunately skew rays are

ignored in most fibre optics analysis.

The specific characteristics of light propagation through a fibre depends on

many factors, including

- The size of the fibre.

- The composition of the fibre.

- The light injected into the fibre.

FIBRE GEOMETRY An Optical fibre consists of a core of optically transparent material usually

silica or borosilicate glass surrounded by a cladding of the same material but a

slightly lower refractive index.

Fibre themselves have exceedingly small diameters. Figure shows cross

section of the core and cladding diameters of commonly used fibres. The

diameters of the core and cladding are as follows.

Core (µm) Cladding (µ m) 8 125

50 125

62.5 125

100 140

Jacket

CladdingCore

Cladding

Angle of reflection

Angle of incidence

Light at less thancritical angle isabsorbed in jacket

Jacket

Light is propagated by total internal reflection

Jacket

Cladding

Core

(n2)(n2)

Fig. Total Internal Reflection in an optical Fibre

Fibre sizes are usually expressed by first giving the core size followed by

the cladding size. Thus 50/125 means a core diameter of 50µm and a cladding

diameter of 125µm.

FIBRE TYPES The refractive Index profile describes the relation between the indices of

the core and cladding. Two main relationship exists :

(I) Step Index

(II) Graded Index

The step index fibre has a core with uniform index throughout. The profile

shows a sharp step at the junction of the core and cladding. In contrast, the

graded index has a non-uniform core. The Index is highest at the center and

gradually decreases until it matches with that of the cladding. There is no sharp

break in indices between the core and the cladding.

By this classification there are three types of fibres :

(I) Multimode Step Index fibre (Step Index fibre)

(II) Multimode graded Index fibre (Graded Index fibre)

(III) Single- Mode Step Index fibre (Single Mode Fibre)

(1) STEP INDEX MULTIMODE FIBRE This fibre is called "Step Index" because the refractive index changes

abruptly from cladding to core. The cladding has a refractive index somewhat

lower than the refractive index of the core glass. As a result, all rays within a

certain angle will be totally reflected at the core-cladding boundary. Rays striking

the boundary at angles grater than the critical angle will be partially reflected and

125 8 125 50 125 62.5 125 100

Core Cladding

Typical Core and Cladding Diameters

partially transmitted out through the boundary. After many such bounces the

energy in these rays will be lost from the fibre.

The paths along which the rays (modes) of this step index fibre travel differ,

depending on their angles relative to the axis. As a result, the different modes in a

pulse will arrive at the far end of the fibre at different times, resulting in pulse

spreading which limits the bit-rate of a digital signal which can be transmitted.

The maximum number of modes (N) depends on the core diameter (d),

wavelength and numerical aperture (NA)

( π x d x N A N= 0.5 x (---------------------- ) 2 ( λ ) This types of fibre results in considerable model dispersion, which results

the fibre's band width.

(2) GRADED INDEX MULTI-MODE FIBRE This fibre is called graded index because there are many changes in the

refractive index with larger values towards the center. As light travels faster in a

lower index of refraction. So, the farther the light is from the center axis, the grater

is its speed. Each layer of the core refracts the light. Instead of being sharply

reflected as it is in a step index fibre, the light is now bent or continuously refracted

in an almost sinusoidal pattern. Those rays that follow the longest path by

travelling near the outside of the core, have a faster average velocity. The light

travelling near the center of the core, has the slowest average velocity.

As a result all rays tend to reach the end of the fibre at the same time. That

causes the end travel time of different rays to be nearly equal, even though they

travel different paths.

The graded index reduces model dispersing to 1ns/km or less.

Graded index fibres have core diameter of 50, 62.5 or 85 µm and a

cladding diameter of 125 µm. The fibre is used in applications requiring a wide

bandwidth a low model dispersion. The number of modes in the fibre is about half

that of step index fibre having the same diameter & NA.

πdxNA N= 0.25 x ( ---------------- )2

(λ)

(3) SINGLE MODE FIBRE.

Another way to reduce model dispersion is to reduce the core's diameter,

until the fibre only propagates one mode efficiently. The single mode fibre has an

exceedingly small core diameter of only 5 to 10 µ m. Standard cladding diameter

High orderMode

Dispersion RefractiveIndex Profile

Low Order ModeMulti mode Step Index

InputPulse

OutputPulse

n1

n2

Single Mode Step Index

n1n2

Dispersion

Multi mode Graded Index

n1

n2

is 125 µm. Since this fibre carries only one mode, model dispersion does not

exists. Single mode fibres easily have a potential bandwidth of 50to 100GHz-km.

The core diameter is so small that the splicing technique and measuring

technique are more difficult. High sources must have very narrow spectral width

and they must be very small and bright in order to permit efficient coupling into the

very small core dia of these fibres.

One advantage of single mode fibre is that once they are installed, the

system's capacity can be increased as newer, higher capacity transmission

system becomes available. This capability saves the high cost of installing a new

transmission medium to obtain increased performance and allows cost effective

increases from low capacity system to higher capacity system.

As the wavelength is increased the fibre carries fewer and fewer modes

until only one remains. Single mode operation begins when the wavelength

approaches the core diameter. At 1300 nm, the fibre permits only one mode, it

becomes a single mode fibre.

As optical energy in a single mode fibre travels in the cladding as well as in

the core, therefore the cladding must be a more efficient carrier of energy. In a

multimode fibre cladding modes are not desirable, a cladding with in efficient

transmission characteristic can be tolerated. The diameter of the light appearing at

the end of the single mode fibre is larger than the core diameter, because some of

the optical energy of the mode travels in the cladding. Mode field diameter is the

term used to define this diameter of optical energy.

OPTICAL FIBRE PARAMETERS Optical fibre systems have the following parameters.

(I) Wavelength.

(II) Frequency.

(III) Window.

(IV) Attenuation.

(V) Dispersion.

(VI) Bandwidth.

WAVELENGTH It is a characterstic of light that is emitted from the light source and is

measures in nanometers (nm). In the visible spectrum, wavelength can be

described as the colour of the light.

For example, Red Light has longer wavelength than Blue Light, Typical

wavelength for fibre use are 850nm, 1300nm and 1550nm all of which are

invisible.

FREQUENCY It is number of pulse per second emitted from a light source. Frequency is

measured in units of hertz (Hz). In terms of optical pulse 1Hz = 1 pulse/ sec.

WINDOW A narrow window is defined as the range of wavelengths at which a fibre

best operates. Typical windows are given below :

Window Operational Wavelength

800nm - 900nm 850nm

1250nm - 1350nm 1300nm

1500nm - 1600nm 1550nm

Gamma rays

Rontgen rays

U.V. rays

Visible Light

Infra Red

Thermal Rays

U.H.F.

M.F.

L.F.

Radio Frequencies

10- 12

10 -810

- 610

- 410 0

10 410 6

10 210

- 210

- 10

1Mm

1Km

1m1m

m1µ

m1nm

1pm

WA

VE LENG

TH IN

NM

ATTENUATION Attenuation is defined as the loss of optical power over a set distance, a

fibre with lower attenuation will allow more power to reach a receiver than fibre

with higher attenuation.

Attenuation may be categorized as intrinsic or extrinsic.

INTRINSIC ATTENUATION It is loss due to inherent or within the fibre. Intrinsic attenuation may occur

as

(I) Absorption - Natural Impurities in the glass absorb light energy.

(II) Scattering - Light rays travelling in the core reflect from small

imperfections into a new pathway that may be lost through the

cladding.

(1) Absorption - Natural Impurities in the Glass Absorb Light Energy.

Or

(2) Scattering - Light Rays Travelling in the Core Reflect from small

Imperfections into a New Pathway that may be Lost through the cladding.

LightRay

LightRay

Light is lost

EXTRINSIC ATTENUATION

It is loss due to external sources. Extrinsic attenuation may occur as –

(I) Macrobending - The fibre is sharply bent so that the light travelling

down the fibre cannot make the turn & is lost in the cladding.

(II) Microbending - Microbending or small bends in the fibre caused by

crushing contraction etc. These bends may not be visible with the

naked eye.

Attenuation is measured in decibels (dB). A dB represents the comparison

between the transmitted and received power in a system.

DISPERSION It is defined as the spreading of light pulse as it travels down the fibre.

ecause of the spreading effect, pulses tend to overlap, making them unreadable

by the receiver.

BANDWIDTH

Micro bend

Micro bend

Fig. Loss and Bends

Micro bend

It is defined as the amount of information that a system can carry such that

each pulse of light is distinguishable by the receiver.

System bandwidth is measured in MHz or GHz. In general, when we say

that a system has bandwidth of 20 MHz, means that 20 million pulses of light per

second will travel down the fibre and each will be distinguishable by the receiver.

NUMBERICAL APERTURE

Numerical aperture (NA) is the "light - gathering ability" of a fibre. Light injected into the fibre at angles greater than the critical angle will be propagated.

The material NA relates to the refractive indices of the core and cladding.

NA = n12 - n2

2

where n1 and n2 are refractive indices of core and cladding respectively.

NA is unitless dimension. We can also define as the angles at which rays will be propagated by the fibre. These angles form a cone called the acceptance

cone, which gives the maximum angle of light acceptance. The acceptance cone

is related to the NA

∅ = arc sing (NA) or

NA = sin ∅

where ∅ is the half angle of acceptance

The NA of a fibre is important because it gives an indication of how the fibre

accepts and propagates light. A fibre with a large NA accepts light well, a fibre with a low NA requires highly directional light.

In general, fibres with a high bandwidth have a lower NA. They thus allow

fewer modes means less dispersion and hence greater bandwidth. A large NA

promotes more modal dispersion, since more paths for the rays are provided NA,

although it can be defined for a single mode fibre, is essentially meaningless as a

practical

characteristic. NA in a multimode fibre is important to system performance

and to calculate anticipated performance.

Total Internal Reflection (Summary)

* Light Ray A : Did not Enter Acceptance Cone - Lost

* Light Ray B : Entered Acceptance Cone - Transmitted through the Core

by Total Internal Reflection.

NA = 0.275 (For 62.5 µm Core Fiber)

DISPERSION

Dispersion is the spreading of light pulse as its travels down the length of

an optical fibre. Dispersion limits the bandwidth or information carrying capacity of

a fibre. The bit-rates must be low enough to ensure that pulses are farther apart

and therefore the greater dispersion can be tolerated.

There are three main types of dispersion in a fibre -

(I) Modal Dispersion

(II) Material dispersion

(III) Waveguide dispersion

MODAL DISPERSION Modal dispersion occurs only in Multimode fibres. It arises because rays

follow different paths through the fibre and consequently arrive at the other end of

the fibre at different times. Mode is a mathematical and physical concept

describing the propagation of electromagnetic waves through media. In case of

fibre, a mode is simply a path that a light ray can follow in travelling down a fibre.

The number of modes supported by a fibre ranges from 1 to over 100,000. Thus a

fibre provides a path of travels for one or thousands of light rays depending on its

size and properties. Since light reflects at different angles for different paths (or

modes), the path lengths of different modes are different. Thus different rays take

a shorter or longer time to travel the length of the fibre. The ray that goes straight

down the center of the core without reflecting, arrives at the other end first, other

rays arrive later. Thus light entering the fibre at the same time exist the other end

at different times. The light has spread out in time.

The spreading of light is called modal dispersion. Modal dispersion is that

type of dispersion that results from the varying modal path lengths in the fibre.

Typical modal dispersion figures for the step index fibre are 15 to 30 ns/ km. This

means that for light entering a fibre at the same time, the ray following the longest

path will arrive at the other end of a 1 km long fibre 15 to 30 ns after the ray,

following the shortest path. Fifteen to 30 billionths of a second may not seem like

much, but dispersion is the main limiting factor on a fibre's bandwidth. Pulse

spreading results in a pulse overlapping adjacent pulses as shown in figure.

Eventually, the pulses will merge so that one pulse cannot be distinguished from

another. The information contained in the pulse is lost Reducing dispersion

increases fibre bandwidth.

Model dispersion can be reduced in three ways :

(I) Use a smaller core diameter, which allows fewer modes.

(II) Use a graded -index fibre so that light rays that allow longer paths

also travel at a faster velocity and thereby arrive at the other end of

the fibre at nearly the same time as rays that follow shorter paths.

(III) Use a single-mode fibre, which permits no modal dispersion.

MATERIAL DISPERSION Different wavelengths (colours) also travel at different velocities through a

fibre, even in the same mode, as

n = c/v

where n is index of refraction, c is the speed of light in vacuum and v is the speed

of the same wavelength in the material. The value of V in the equation changes for

each wavelength, Thus Index of refraction changes according to the wavelength.

Dispersion from this phenomenon is called material dispersion, since it arises from

material properties of the fibre.

Each wave changes speed differently, each is refracted differently. White

light entering the prism contains all colours. The prism refracts the light and its

changes speed as it enters the prism. Red light deviates the least and travels the

fastest. The violet light deviates the most and travels the slowest.

The amount of material dispersion depends on two factors :

(I) The range of light wavelengths injected into the fibre. A source does

not normally emit a single wavelength, it emits several. This range of

wavelengths, expressed in nanometer is the spectral width of the

source. An LED has a much higher spectral width than a LASER -

about 35 nm for a LED and 2 to 3 nm for a LASER.

(II) The centre operating wavelength of the sources

Around 850nm, longer (reddish) wavelengths travel faster than the shorter

(Bluish) ones. At 1550nm however the situation is reversed. The shorter

wavelengths travel faster than the longer ones. At some point, the cross over must

occur where the bluish and reddish wavelengths travel at the same speed. This

crossover occurs around 1300nm, the zero-dispersion wavelength. At

wavelengths below 1300nm, dispersion is negative. So wavelengths travel or

arrive later. Above 1300 nm, the wavelengths lead or arrive faster.

This dispersion is expressed in Pico seconds per kilometer per nanometer

of source spectral width (ps/km/nm).

WAVEGUIDE DISPERSION : Waveguide dispersion, most significant in a single- mode fibre, occurs

because optical energy travels in both the core and cladding, which have slightly

different refractive indices. The energy travels at slightly different velocities in the

core and cladding because of the slightly different refractive indices of the

materials. Altering the internal structures of the fibre, allows waveguide dispersion

to be substantially changed, thus changing the specified overall dispersion of the

fibre.

BANDWIDTH AND DISPERSION : A bandwidth of 400 MHz -km means that a 400 MHz-signal can be

transmitted for 1 km. It means that the product of frequency and the length must

be 400 or less. We can send a lower frequency for a longer distance, i.e. 200 MHz

for 2 km or 100 MHz for 4 km.

Multimode fibres are specified by the bandwidth-length product or simply

bandwidth.

Single mode fibres on the other hand are specified by dispersion,

expressed in ps/km/nm. In other words for any given single mode fibre dispersion

is most affected by the source's spectral width. The wider the source spectral

width, the greater the dispersion.

Conversion of dispersion to bandwidth can be approximated roughly by the

following equation.

0.187 BW = --------------------------

(Disp) (SW) (L)

Disp = Dispersion at the operating wavelength in seconds/ nm/ km.

SW = Spectral width of the source in nm.

L = Fibre length in km.

So the spectral width of the source has a significant effect on the

performance of a single mode fibre.

OPTICAL WINDOWS : Attenuation of fibre for optical power varies with the wavelengths of light.

Windows are low-loss regions, where fibre carry light with little attenuation. The

first generation of optical fibre operated in the first window around 820 to 850 nm.

The second window is the zero-dispersion region of 1300 nm and the third window

is the 1550 nm region.

High loss regions, where attenuation is very high occur at 730, 950, 1250

and 1380 nm. One wishes to avoid operating in these regions. Evaluation of

losses in a fibre must be done with respect to the transmitted wavelength.

Figure shows a typical attenuation curve for a low loss multimode fibre.

Making the best use of the low loss properties of the fibre requires that the

sources emit light in the low loss region of the fibre. Plastic fibres are best

operated in the visible light area around 650 nm. One important feature of

attenuation in an optical fibre is that the constant at all modulation frequencies

within the bandwidth. Attenuation in a fibre has two main causes.

(I) Scattering

(II) Absorption

We can obtain losses less than 2.5 dB/km in the first window at 850 nm.

Graded index fibres in the second window with loss below 1 dB/km and in the thrid

window below 0.5 dB/km are obtained. Even lower losses are regarded as

feasible for monomode fibres in all the three windows. Typically minimum loss in

the three windows for the multimode fibre is 2.5 dB/km, 0.44 dB, km and 0.22

dB/km respectively. The corresponding figures for a monomode fibre are 1.9

dB/km, 0.32 dB/km and 0.048 dB/km.

CABLE CONSTRUCTION Cabling is an outer protective structure surrounding one or more fibres.

Cabling protects fibres environmentally and mechanically from being damaged or

degraded in performance. Important consideration in any cable are tensile

strength, ruggedness, durability, flexibility, environmental resistance, temperature

extremes and even appearance. Evaluation of these considerations depends on

the application.

Fibre Optic Cables have the following parts in common ;

(I) Optical Fibre

(II) Buffer

(III) Strength member

(IV) Jacket

Cable Components

Component Function Material

Buffer Protect fibre From Outside Nylon, Mylar, Plastic

Central Member Facilitate Stranding

Temperature Stability Anti-Buckling

Steel, Fibreglass

Primary Strength Member Tensile Strength Aramid Yarn, Steel

Cable Jacket Contain and Protect

Cable Core Abrasion Resistance

PE, PUR, PVC, Teflon

Cable Filling Compound

Prevent Moisture intrusion and Migration

Water Blocking Compound

Armoring Rodent Protection Crush Resistance Steel Tape

Loose Tube Buffering

One way of isolating the Optical Fibre from External Forces is to Place an

Excess Fibre Length within on Oversized "Buffer" Tube.

Siecor/ Optical Cable fills these tubes with a Jollylike Compound to Provide

Additional Cushioning and Prevent the incursion of Moisture.

1. Fibre in Buffer after Manufacturing.

2. Shrinking of Buffer During Temperature Decrease (Different Coefficients of Thermal Expansion Fiber/Plastics)

3. Elongation of Buffer Due to Cable Tensile Stress

NOTE : Additional Excess Length is Achieved when the "Buffered" Fibers are Stranded together during the Cabling Operation.

It is the plastic coating applied to the coating. It protects fibre from outside

stress. The cable buffer is one of two types.

(I) Loose Buffer

(II) Tight Buffer

The loose buffer uses a hard plastic tube having an inside diameter several

times that of the fibre. One or more fibres lie within the buffer tube. As the cable

expands and shrinks with temperature changes, it does not affect the fibre as

much. The fibre in the tube is slightly longer than the tube itself. Thus the cable

can expand and contract without stressing the fibre. The buffer becomes the load-

bearing member.

The tight buffer has a plastic directly applied over the coating. This

construction provides crush and impact resistance. It is more flexible and allows

tighter turn radius. It is useful for indoor applications where temperature variations

are minimum and the ability to make tight turns inside walls is desired.

Types of Fiber Buffering

Tight Buffer Jacket Longitudinal and Transverse Tight

LOOSE BUFFER JACKET

Strength member :

Strength members add mechanical strength to the fibre. During and after

installation, the strength members handle the tensile stresses applied to the cable

so that the fibre is not damaged. The most common strength members are Kevlar,

Armid Yarn, Steel and Fibre glass epoxy rods.

Kevlar is most commonly used when individual fibres are placed within their

own jackets. Steel and fibre glass members find use in multifibre cable. Steel

offers better strength than fibreglass but in some cases it is undesirable when one

wishes to maintain an all-dielectrical cables. Steel attracts lightening whereas

fibreglass does not.

Jacket It provides protection from the effects of abrasion, oil, ozone, acids, alkali,

solvents and so forth. The choice of jacket material depends on degree of

resistance required for different influences and on cost.

The outer layers are often called the sheath. The jacket becomes the layer

directly protecting fibres and the sheath refers to additional layer.

MULTIFIBRE CABLE : It often contain several loose buffer tubes, each containing one or more

fibres. The use of several tubes allows identification of fibre by tube, since both

tubes and fibres can be colour coded. These tubes are stranded around a central

strength member of steel or fibre glass rod. The stranding provides strain relief for

the fibres when the cable is bent.

Typical Mini-Bundle Cable

Description

1 - Blue

2 - Orange

3 - Green

4 - Brown

5 - Slate

6 - White

7 - Red

8 - Black

9 - Yellow

10 - Violet

11 - Blue/ Black

12 - Orange/ Black

THE ENVIRONMENT EFFECT :

1. There are however always small defects at the surface of the fibre, called

microcracks. These cracks grew when water vapour is present and the

fibre simultaneously is under strain, hence shortening the life of the fibre.

2. Another effect ingress of water, which may increase of concentration of

water vapour around the fibre.

3. Temperature variation may cause Expansion/ Contraction of fibres and

affect the performance to some extent. By proper choice of materials and

by adjusting the excess length of fibre in the loose tube, the temperature

variation effect can be neglected.

CABLE DRUM LENGTH : Cables come reeled in various length, typically 1 to 2 km, although lengths

of 5 or 6 kms are available for single mode fibres. Long lengths are desirables for

long distance applications, since cable must be spliced end to end over the run.

Each splice introduce additional loss into the system. Long cable lengths mean

fewer splices and less loss.

METALLIC OR NON-METALLIC CABLES : Fibre optic cables sometimes also contain copper conductors, such as

twisted pair. One use of these conductors is to allow installers to communicate

with each other during installation of the fibre especially with long distance

telephone installation. The other use is to power remote equipment such as

repeaters. Sub-marine cables, cables for overhead mounting, highly, armoured

cables of railways etc are also coming in category of metallic cables. In such

cables strength member will typically be of steel wire and the cable will also

contain one or two copper service pairs. It is also common to include an

aluminium water barrier.

It is possible to construct completely metal free cables, used in areas

suffering from high frequency of lightening. Strength member is made of fibre

glass rod. Induction effect due to lightening or power line parallelism is not at all on

such non-metallic cables.

OFC Splicing

Splices Splices are permanent connection between two fibres. The splicing

involves cutting of the edges of the two fibres to be spliced.

Splicing Methods

Single–Fibre Mechanical Splicing – Single Fibre Capillary – Aligns two fibre ends to a common centerline, thereby aligning

cores. – Clean, cleaved fibres are butted together and index matched. – Permanently secured with epoxy or adhesive.

Examples : Siecor, See Splice GTE Elastomeric Splice.

Fig. SeeSplice Mechanical Splice

Splicing Methods The following three types are widely used :

1. Adhesive bonding or Glue splicing.

2. Mechanical splicing.

3. Fusion splicing.

1. Adhesive Bonding or Glue Splicing This is the oldest splicing technique used in fibre splicing. After fibre end

preparation, it is axially aligned in a precision V–groove. Cylindrical rods or another kind of reference surfaces are used for alignment. During the alignment of fibre end, a small amount of adhesive or glue of same refractive index as the core material is set between and around the fibre ends. A two component epoxy or an UV curable adhesive is used as the bonding agent. The splice loss of this

Splice Location

Uncosted Fibre

Costed Fibre

type of joint is same or less than fusion splices. But fusion splicing technique is more reliable, so at present this technique is very rarely used.

2. Mechanical Splicing This technique is mainly used for temporary splicing in case of emergency

repairing. This method is also convenient to connect measuring instruments to bare fibres for taking various measurements.

The mechanical splices consist of 4 basic components : (i) An alignment surface for mating fibre ends. (ii) A retainer (iii) An index matching material. (iv) A protective housing

A very good mechanical splice for M.M. fibres can have an optical performance as good as fusion spliced fibre or glue spliced. But in case of single mode fibre, this type of splice cannot have stability of loss.

3. Fusion Splicing The fusion splicing technique is the most popular technique used for

achieving very low splice losses. The fusion can be achieved either through electrical arc or through gas flame.

The process involves cutting of the fibres and fixing them in micro–positioners on the fusion splicing machine. The fibres are then aligned either manually or automatically core aligning (in case of S.M. fibre) process. Afterwards the operation that takes place involve withdrawal of the fibres to a specified distance, preheating of the fibre ends through electric arc and bringing together of the fibre ends in a position and splicing through high temperature fusion.

If proper care taken and splicing is done strictly as per schedule, then the splicing loss can be minimized as low as 0.01 dB/joint. After fusion splicing, the splicing joint should be provided with a proper protector to have following protections:

(a) Mechanical protection (b) Protection from moisture.

Sometimes the two types of protection are combined. Coating with Epoxy resins protects against moisture and also provides mechanical strength at the joint.

Now–a–days, the heat shrinkable tubes are most widely used, which are fixed on the joints by the fusion tools.

The fusion splicing technique is the most popular technique used for achieving very low splice losses. The introduction of single mode optical fibre for

use in long haul network brought with it fibre construction and cable design different from those of multimode fibres.

The splicing machines imported by BSNL begins to the core profile alignment system, the main functions of which are :

(1) Auto active alignment of the core. (2) Auto arc fusion. (3) Video display of the entire process. (4) Indication of the estimated splice loss.

The two fibres ends to be spliced are cleaved and then clamped in accurately machined vee–grooves. When the optimum alignment is achieved, the fibres are fused under the microprocessor contorl, the machine then measures the radial and angular off–sets of the fibres and uses these figures to calculate a splice loss. The operation of the machine observes the alignment and fusion processes on a video screens showing horizontal and vertical projection of the fibres and then decides the quality of the splice.

The splice loss indicated by the splicing machine should not be taken as a final value as it is only an estimated loss and so after every splicing is over, the splice loss measurement is to be taken by an OTDR (Optical Time Domain Reflectometer). The manual part of the splicing is cleaning and cleaving the fibres. For cleaning the fibres, Dichlorine Methyl or Acetone or Alcohol is used to remove primary coating.

With the special fibre cleaver or cutter, the cleaned fibre is cut. The cut has to be so precise that it produces an end angle of less than 0.5 degree on a prepared fibre. If the cut is bad, the splicing loss will increase or machine will not accept for splicing. The shape of the cut can be monitored on the video screen, some of the defect noted while cleaving are listed below :

(i) Broken ends.

(ii) Ripped ends.

(iii) Slanting cuts.

(iv) Unclean ends.

It is also desirable to limit the average splice loss to be less than 0.1 dB.

Preconditions for a Splice with a Low Loss

OVERVIEW OF FOTS

1.0 System Composition

1.1 System Configuration Fig.1 shows a simplified and typical block diagram of the FIBRE OPTICS TRANSMISSION SYSTEM (FOTS) that comprises of the following sub systems.

• Digital multiplex sub system • Optical line transmission system • Central supervisory system • Trans multiplexer sub system • Alarm sub system • Power supply sub system

1.1.1 Digital Multiplex Sub System Refer to Fig.2. The digital multiplex system can be divided into three stage second–order multiplexer, third–order multiplexer or second/third order and fourth–order multiplexer. These three–staged multiplexers digitize and multiplex signals into digital bit streams of 2048 kbit/s, 8448 kbit/s, 34368 kbit/s and 139,264 kbit/s.

1.1.2 Second–order multiplexing At transmitting side, the Second–order Digital Multiplexers multiplex four 2048 kbit/s digital bit–streams into one 8448 kbit/s bit stream. Reversely, these multiplexers separate (demultiplex) one 8448 kbit/s digital bit–stream into four 2048 kbit/s digital bit–streams at receiving side.

1.1.3 Third–order multiplexing At transmitting side, the Third–order Digital Multiplexers multiplex four 8448 kbit/s digital bit streams into one 34368 kbit/s stream. Reversely, these multiplexers separate one 34368 kbit/s digital bit stream into four 8448 kbit/s digital bit-streams at receiving side.

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1.1.4 Second/Third–order multiplexing At transmitting side, the Second/Third–order Digital Multiplexers multiplex sixteen 2048 kbit/s or four 8448 kbit/s bit–streams into one 34368 kbit/s bitstream. Reversely, these Multiplexers separate (demultiplex) one 34368 kbit/s bit–stream into sixteen 2048 kbit/s or four 8448 kbit/s bit–streams at receiving side.

1.1.5 Fourth–order multiplexing At transmitting side, the Fourth–order Digital Multiplexer multiplexes four 34368 kbit/s bit–streams into one 139,264 kbit/s bit–stream. Reversely, it separates one 139,264 kbit/s bit–stream into four 34368 kbit/s bit–streams at receiving side.

1.1.6 Optical Line Transmission Subsystem The Optical Line Transmission Subsystem comprises the following sections. (A) Optical Line Transmission Section (B) Line Switching Section (C) Line Supervisory Section (D) Orderwire Section.

2M (1)2M (2)2M (3)2M (4)

8MMUX

34MMUX

8M (1)8M (2)8M (3)8M (4)

34M (1)34M (2)34M (3)34M (4)

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34M 140MTo/FromLineSwitchingSubsystem

DDMDDMDDM

139.264 kbit/s4th order2ndorder/ 3rd order

34368 kbit/s8448 kbit/s2048 kbit/s

Digital Multiplex Subsystem

Fig.2Block Diagram of the Digital Multiplex Subsystem

(A) Optical Line Transmission Section 1.1.7 The Optical Line Transmission Section comprises FD–4013A 140M

Optical Line Terminating Equipment or FD–3019A Optical Line Terminating Equipment and Optical fibre cables (See Fig.3).

1.1.8 Transmit Circuit A 139,264 kbit/s CMI–coded or a 34368 kbit/s CMI or HDB–3 coded signal enters the Optical Line Terminating Equipment and is converted into a unipolar form and, then, converted into a 168,443 kbit/s or 42664 kbit/s signal. After 5B6B–code conversion, frame synchronisation bits, service and remote service data are added as overhead bits. The 168,443 kbit/s or 42664 kbit/s signal is converted from an electrical signal to an optical signal.

1.1.9 Receive Circuit The received 168,443 kbit/s or 42664 kbit/s optical signal enters the Optical Line Terminating Equipment and is converted into an electrical 139,264 kbit/s or 34368 kbit/s unipolar signal according to the following process. Frame synchronisation is established by detecting the frame alignment signal in the received signal. Overheaed bits are decoded into service and remote service data.

The 168,443 kbit/s or 42664 kbit/s signal is converted from 6B to 5B code, decreasing its data rate to 139,264 kbit/s or 34368 kbit/s. The 139264 kbit/s or 34368 kbit/s signal is encoded as a CMI–signal or an HDB–3 signal and sent to the 140M Digital Multiplexer or 34M Digital Multiplexer.

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Fig. 3 Block diagram of a typical Optical Line Transmission System

PCT

1.2.0 Line Engineering Table 1 shows specifications of the system link.

Table 1 System Specification

Sl.No. Items Specification 140M FOTS 34M FOTS

1. Average output power (laser diode) –3.5 dB –3.5 dB

2. Internal wiring and connection loss 2.0 dB 2.0 dB

3. System design 5.0 dB 5.0 dB

4. Optical receive power (BER = 10–9)

–17.5 dBm to –39 dBm

–23 dBm to –43.5 dBm

5. Power penalty 1.0 dB 0.5 dB

6. Maximum line loss (including operating margin)

27.5 dB 32.5 dB

7. Wavelength 1.31 micrometer 1.31 micrometer

8. Optical fibre cable loss (including splicing loss) 0.5 dB/km 0.5 dB/km

The maximum allowable line loss (including splice loss) is obtained by the following formula :

Allowable line loss = (average output power) – (minimum receive level) – (connection loss) – (system margin) – (power

penalty)

1.2.1 Service Data Channel Four streams of 64 kbit/s service data, asynchronous to each other, can be transmitted to the OLT using 5 service data bits within the overhead bit. These 5 bits form a frame having a data of 276 kbit/s as shown in Fig.4. At the transmit side, each stream of 64 kbit/s service data is received by the Service Data Interface, which conforms to the CCITT V.11 Interface format. Four received data streams are multiplexed into a 276 kbit/s signal using bit–interleaving and positive justification technique. The 276 kbit/s signal is inserted into the 168,443 kbit/s main bit stream. At the receive side, the service data bits are extracted from the main bit stream. This 276 kbit/s signal is demultiplexed into four 64 kbit/s data signals with clocks, which are transmitted to the OLT through the V.11 interface.

(B) Line Switching Section 1.2.2 Figs. 6 and 7 show a system block diagram of the FD–00207P 34M/140M

1:N Line Switcher.

1 1 1 0 1 0 0 0 SD1

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SD2

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F: Frame synchronous bitsC1 to C3: Justification control bits# 51: Bits from tributaries available for justification# 1 to 67: Information bitsSD1 to SD4: Service data bits (64 kbit/s each)Bite rate = 276.32 kbit/s

Fig.4Frame Structure of Service Data for

140Mbit/s Fibre Optics Transmission System

SD1

SD2

SD3

SD4

The 1:1 Line Switcher is used to maintain a high service reliability of the 140M Fibre Optics Transmission System (FOTS). If an alarm is generated by any one of eleven regular Fibre Optics Transmission System (maximum), the 1:N Line Switcher quickly restores service by automatically switching the transmission path to a protection system.

1.2.3 Automatic operation of the Line Switcher is performed by logic circuits in both local and remote Line Switchers. Communication between the two Line Switchers is carried out using the overhead bit employed by the Fibre Optics Transmission System. Switching operations are also carried out by manual control in order to ensure system flexibility during maintenance. Note that all manual controls, except for the forced mode that initiates a switching operation immediately, are also accomplished by logic circuits.

1.2.4 The FD–0207P can perform switching operations independently at the transmit and receive sides under automatic, manual, external or forced switching control modes. For an actual switching operation, two system configurations are available : PRE–EMPTIVE and HOT–STANDBY switchings. In this project, HOT–STANDBY switching is employed; restoration can be performed under either the automatic or manual switching control mode.

(C) Line Supervisory Section 1.2.5 The FD–0210 ( ) P Line Supervisory Equipment can monitor operations

of two Line Switchers and upto twelve Optical Line Systems. Each Optical Line System comprises two units of Optical Line Terminating Equipment and a maximum of twenty three units of the Optical Repeater Equipment. As an example, Figs. 8 and 9 shows a simplified diagram of a typical Line Supervisory System comprising two Optical Line Terminating Equipment and one Line Switcher (for two systems).

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Fig. 8Line Supervisory System Configuration for 140M FOTS

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1.2.6 The Line Supervisory Equipment periodically calls the Optical Line Terminating Equipment and Line Switchers (polling operations) in order to obtain alarm and status information. Collected information is processed and stored in memories of the equipment. When the Portable Control Terminal is connected to the Line Supervisory Equipment, the information stored in the memories, including maintenance conditions, can be displayed on liquid crystal display (LCD) of the Portable Control Terminal.

1.2.7 The Line Supervisory Equipment can control the Optical Line Terminating Equipment and the Line Switcher. For example, the Line Supervisory equipment can establish a loopback circuit for an optical transmission line within the Optical Line Terminating Equipment and cause operate the Line Switcher to switch the traffic. These operations are carried out by commands input from the Portable Control Terminal.

1.2.8 An Interface between the Line Supervisory Equipment and the 140M Optical Line Terminating Equipment as well as interface between the Line Supervisory Equipment and the Line Switcher are controlled by the 1200 bit/s basic communication protocol via a common 4–wire multi–drop line.

(D) Orderwire Section 1.2.9 Fig.9 shows a system configuration with the FD–0206A Orderwire

equipment. The orderwire section is useful for achieving easy and prompt maintenance of the Fibre Optics Transmission System. This orderwire section is a 4–wire multi–party telephone system comprising the FD–0206A Orderwire equipment. For orderwire service, the service data channel (SD CH1) of the regular and protection lines of the Fibre Optics Transmission System is employed. The following telephone functions are available.

• Speaker calling telephone • Selective calling telephone • Subscriber telephone • Ringdown telephone

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1.3.0 Central Supervisory Subsystem The C–SV system comprises several kinds of supervisory equipment and associated equipment. A typical configuration is shown in Fig.10. The main equipment comprising the system are as described in the following paragraphs.

A. Central Supervisory Section 1.3.1 Central Supervisory Equipment (C–SV) : The C–SV is installed in the

central station and is a main part of the C–SV system. The C–SV collects all alarm and status information of the FOTS through R–SVs and SUB C–SVs of the C–SV system, displays and prints out the information on real–time basis, and also controls the FOTS remotely. Construction of the supervising displays for the network management can be made by the C–SV with the Subcentral Supervisory Equipment (SUB C–SV). The C–SV consists of FD–0250A Central Supervisory Equipment (C–SV), APC–III Control Terminal (CT) and their peripheral equipment.

1.3.2 The FD–0250A C–SV is a main component of the C–SV and is mounted in a 19–inch rack together with peripheral equipment : printer, V.24 modem and DC–AC inverter. A V.24 modem is used to communicate with the CT.

1.3.3 The CT is set in the maintenance room of the central station together with peripheral equipment such as a printer and V.24 modem. The CT is used as a man–machine interface of the C–SV and management of the supervisory system. A V.24 modem is used to communicate with the FD–0250A C–SV.

B. Subcentral Supervisory Section 1.3.4 Subcentral Supervisory Section (SUB C–SV) : The SUB C–SV is located

in a subcentral station and is a sub–part of the C–SV system. The SUB C–SV collects all alarm and status information of the FOTS through R–SVs of the SUB C–SV system, displays and prints out the information on real–time basis, transfers the information to the C–SV, and also control the FOTS remotely. The SUB C–SV consists of FD–0251A Subcentral Supervisory Equipment (SUB C–SV), CT and their peripheral equipment.

1.3.5 The FD–0251A SUB C–SV is a main component of the SUB C–SV and mounted in a 19–inch rack together with peripheral equipment : Printer,

Prin

ter

Prin

ter

Prin

ter

1 2 3 4

R-S

V

ME

64K

SD

CH

(R

egul

ator

)

64K

SD

CH

(P

rote

ctio

n)

Prin

ter

FD-0

250A

C-S

V

Mai

nten

ance

Roo

m

V.2

4 M

odem

2 3 41

FD-0

251A

SUB

C-S

V

64K

SD

CH

(P

rote

ctio

n)

64K

SD

CH

(R

egul

ator

)

AP

C o

rC

T

AP

C o

rC

T

Prin

ter

Prin

ter

R-S

V

ME

FD-0

251A

SUB

C-S

V

AP

C o

rC

T

Prin

ter

Prin

ter

1 2 3 4

R-S

V

ME

FD-0

251A

SUB

C-S

V

AP

C o

rC

T

1 2 3 4

R-S

V

ME

R-S

V

ME

R-S

V

ME

ME

R-S

V

R-S

V

ME

ME

R-S

V

Rem

ote

Stat

ion

A

Rem

ote

Stat

ion

B

Rem

ote

Sta

tion

C

Rem

ote

Stat

ion

D

ME:

Mai

nten

ance

Ent

ity

m

aint

aine

d by

R-S

V

Sub

cent

ral S

tatio

n B

Sub

cent

ral S

tatio

n A

Cen

tral S

tatio

n

Fig.10Typical Configuration of Central Supervisory System

V.24 modem and DC–AC inverter. A V.24 modem is used to communicate with the FD–0250A C–SV.

1.3.6 The CT is set in the maintenance room of the subcentral station together with peripheral equipment such as a printer and V.24 modem. The CT is used as a man–machine interface of the SUB C–SV and management of the subcentral supervisory system. A V.24 modem is used to communicate with the FD–0251A SUB C–SV.

C. Remote Supervisory Section 1.3.7 Remote Supervisory Equipment (R–SV) : The R–SV is installed in each

remote station where the various equipment to be supervised are installed. The R–SV is at the end of the C–SV system, receives alarm and status information from the supervised equipment of an ME of the FOTS, displays and prints out the information on real–time basis, transfers the information to the SUB C–SV, and it controls the ME of the FOTS remotely. The following two types of the R–SV are provided in accordance with the related MES.

a. R–SV ME FD–0210( ) Line Supervisory Optical line system Equipment (L–SV) b. FD–0144 ( ) Sensor Supervisory Other alarm detectors Equipment (SENSOR SV).

1.3.8 Alarm Subsystem See Fig. 11 for the Alarm Subsystem. All equipment can send a Prompt Maintenance (PM) Alarm, a Deferred Maintenance (DM) Alarm and a Bell and Lamp (BL) Alarm for station use. These station alarms are concentrated at frame–top and are distributed to station alarm facilities. The NE 5586 ( ) Alarm Control Unit (ACU) handles all BL Alarms received from the frame–top and sends AL and AB alarms to station alarm facilities. The ACU also has an alarm lamp(s) on its front for indicating a received BL Alarm.

StationAlarm

Facilities

PM ALM. DM ALM. S ALM. MAINT

AB.AL

PM ALM. DM ALM. MAINT



PM ALM. DM ALM. S ALM. MAINT

ADM

ACU

ADM

ACU

34M/140M/OLT

SV INTF

34M/140M/I : N2-SW

OWSD INTF

TEL(CODEC)

R-SV

CPU

ALM

Fig. 11Block Diagram of the Alarm Subsystem for N 5500S Series Equipment

BM/2M/8M/34M/140M MUX

NCS-4000ClockSupplyEquipment

P-7

DIM-6005CTrans.Multiplexer

X-2

FD 0250ACentralSupervisoryEquipment

II

FD 0251ASubcentralSupervisoryEquipment

AL

AB

MAINTS ALMPWR ALMALABPM ALM

PM ALM

DM ALM

AL

AB

StationAlarm

Facilities(If provided)

Fig.12Block Diagram of Alarm Subsystem

for 19-inch Type Equipment

Power Distribution

See Fig. 13 for the Power supply Subsystem. Station power (–40 V or –64 V DC) is fed to the power terminals at the top of each equipment frame or shelf.

LEGEND

1 2 3 4 5 6 7 8 9 10 11 12

1 2FUSE

PWR 1 PWR 2

PWR GND

Terminal Plate

TerminalX2

DCPowerDistributionBoard

GND

-40 to -64V DC

Frame Top

PWR Terminal X 1GND

3 4

140M OLT/34M OLT

OWSD INTF

ACU

R-SV

2M/8M/34M MUX,8M MUX, 34M MUX,

140M MUX

T-MUX SC-SVC-SV

Shelf Terminal-48V/-64V DC + GND

Fig. 13Block Diagram of the Typical Power Distribution

AB Station Alarm for Audible Alert

ACU Alarm Control Unit

ACU & RMT DATA INTF Alarm Control and Remote Data Interface

ADF Alarm Distribution Frame

ADM Alarm Distribution Modurack

AIS Alarm Indication Signal

AL Station Alarm for Visual Indication

ALM Alarm Unit

BL Station Alarm for Audible Alert and Visual Indication

CONT Control Unit

CMI Code Mark Inversion

CPU Central Processing Unit

C–SV Central Supervisory Equipment

DDM Digital Distribution Modurack

DIG INTF Digital Interface Unit

DM ALM Deferred Maintenance Alarm

E/O CONV Electrical to Optical Converter

FDF Fibre Distribution Frame

FDP Fibre Distribution Panel

GND Ground

LINE INTF Line Interface Unit

LPB Loop Back

L–SV Line Supervisory Equipment

L–SW Line Switch Unit

MAINT Maintenance State Indication Signal

MUX Digital Multiplexer

O/E Optical to Electrical Converter

OLT Optical Line Terminating Equipment

OPT INTF Optical Interface Unit

OW Order Wire Equipment

PCT Portable Control Terminal

PM–ALM Prompt Maintenance Alarm

PWR Power

R–SV Remote Supervisory Unit

RCV–CONT Remote Code Converter

S ALM Service Alarm

SC–SV Sub Central Supervisory Equipment

SD–INTF Supervisory Interface Unit

SV SH ( ) Service Data Channel ( )

TEL Telephone Unit

XMT CONV Transmit Code Converter

1:1 L SW 1:1 Line Switcher

8M MUX 8M Digital Multiplexer

2M/8M/34M MUX 2M/8M/34M Digital Multiplexer



34M HDB3 IN 34M HDB–3 Signal Input

34 M HDB3 OUT 34M HDB–3 Signal Output

34M OLT 34M Optical Line Terminating Equipment

42M OPT IN 42M Optical Signal Input

42M OPT OUT 42M Optical Signal Output

140M OLT 140M Optical Line Terminating Equipment

168M OPT IN 168M Optical Signal Input Adapter

168M OPT OUT 168M Optical Signal Output Adapter

(A) Capacity of Optical Fibre System in PDH (a) Conventional

(i) 8 Mb/s 120 channels (4 PCM) (ii) 34 Mb/s 480 channels (16 PCM) (iii) 140 Mb/s 1920 channels (64 PCM) (iv) 565 Mb/s 7680 channels (256 PCM)

(b) Optimux (i) 2/34 Mb/s optimux (ii) 2/140 Mb/s optimux

(B) Manufacturers of Conventional Optical Fibre Systems (i) OPTEL (ii) I.T.I. (iii) HFCL (iv) Technicom (v) MCE (vi) Natelco (vii) G–Tel (viii) C–DOT (ix) Fujitsu (x) Philips

(C) Manufacturers of Optimux System (i) HFCL (ii) Crompton & Greaves (iii) Technicom (iv) HCL (v) NATELCO

(D) Capacity of SDH O.F. System S.No. Capacity Bit rate 1. STM–1 155.52 Mbit/s 2. STM–4 622.08 Mbit/s 3. STM–16 2488.32 Mbit/s 4. STM–64 9953.28 Mbit/s (E) Manufacturer of SDH O.F. System

(i) FIBCOM (ii) I.T.I. (iii) Siemens (iv) DSC Denmark (v) CIT ALCATEL

Advantage of SDH over PDH The SDH transmission format has been designed to overcome the

limitation of PDH and the present challenge is to migrate from PDH to SDH and the cost constraints of the network.

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