OFC

BSNL Junior Engineer Introduction to OF Communication

INDEX

SI. No. Content Page No.
L-1 Introduction to optical fiber Communication 1 to 15
L-2 Construction of OF Cables 16 to 30
L-3 Introduction of OFC System 31 to 41

JOB AIDs FOR PRACTICAL

P-1 Identification of optical fibre pairs, study of

construction of different types of cables Job_Aids_1 Page 42

P-2 Fibre splicing Job_Aids_2 Page 43 to 45
P-3 Fault localization using OTDR/ Job_Aids_3 Page 46 to 47

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Module - 5

Lesson - 1

Introduction to Optical Fibre Cable

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Introduction to Optical fibre cable

OBJECTIVE:-This lesson provides the insight into Fibre Optics introduction , theory

and principle of Fibre Optics, propagation of light through fibre, Fibre Geometry, Fibre
Types.

1.1 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.

1.2 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, Lightweight 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.

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- Does not carry electricity.
- Can be run through hazardous areas.

(ix) Universal medium
- Serve all communication needs.
- Non-obsolescence.

1.3 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.

1.4 TRANSMISSION SEQUENCE:

(1) Information is Encoded into Electrical Signals.
(2) Electrical Signals are Converted 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 : Fibre Optic

communication

Figure. 1 Page 4 of 48

1.5 PRINCIPLE OF OPERATION - THEORY

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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.

Figure. 2: Total Internal Reflection

1.6 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 sin  2

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

Is c = arc sin (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.

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Angleofincidence ø1 Angleof
reflection
ø1 ø1 n1
n2 ø2
n1 n1
n2 n2 ø2
ø2

Lightisbentaway Lightdoesnotenter
fromnormal secondmaterial

Figure. 3: Refraction & Reflection

1.7 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 traveling 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 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.

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Jacket
Jacket
Cladding

Core

Cladding(n2) Cladding

Core(n2) Jacket
Lightatlessthan Angleof Angleof
criticalangleis incidence reflection
absorbedinjacket

Lightispropagatedby

total internal reflection

Fig. Total Internal Reflectioninanoptical Fibre

Figure. 4: Total Internal Reflection in an optical Fibre

1.8 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 (m) Cladding (m)
8 125
50 125
62.5 125
100 140

Table. 1: Core and Cladding Diameters

Figure. 5: Typical Core and Cladding Diameters

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Fibre sizes are usually expressed by first giving the core size followed by the
cladding size. Thus 50/125 means a core diameter of 50m and a cladding diameter of
125m.

1.9 FIBRE TYPES

The refractive Index profile describes the relation between the indices of the core
and cladding. Two main relationships 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)

1.10 OPTICAL FIBRE PARAMETERS

Optical fibre systems have the following parameters.

(I) Wavelength.
(II) Frequency.
(III) Window.
(IV) Attenuation.
(V) Dispersion.
(VI) Bandwidth.

1.11 OPTICAL TRANSMITTERS

In optical line systems we need light sources in the infra–red spectrum part. The
wavelengths used are in one of the following windows of optical fibres, i.e. 850 nm, 1300
nm or 1550 nm.

The features of an ideal source for fibre optic communication systems are as follows
 High brightness
 Small emission area (< Fibre Core).
 Small emission cone angle (< Fibre Numerical Aperture (NA)).
 Fast response to electrical modulation.
 Long life

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 Emission wavelength compatible with fibre.

Only 2 semiconductor devices approach these ideals:

 Light emitting diode (LED)
 Semiconductor LASER (Light amplification by stimulated emission of

radiation).

1.12 LED'S (LIGHT EMITTING DIODE)

 LED's are generally manufactured from crystalline materials such as Gallium–Arsenide.

 The LED has a relatively wide lobe of radiation.

 The transfer characteristic of the LED is linear.

 The LED has a bandwidth of approximately 10.000 GHz (= 20 nm).

 The LED represents in most respects a good compromise between performance and cost.

Light emitting diodes are composed of a P–N junction with "doped" semiconductor
layers. Injected electrons will recombine with "holes" in the P–layer where this

phenomenon results in the emission of photons.

There are two types of LEDs :

a. Surface emitting LED's
b. Edge emitting LED's.

The edge emitting LED has more or less a similar composition as a LASER. The
beam is relatively directed and thus the efficiency of the coupled light into the fibre is
higher than the surface LED. The light generated by LED's is incoherent. The photons are
neither in phase with each other nor do they possess the same frequency. This fact limits the
application possibilities of LEDs.

In optical line systems not using monomode fibres, the transmitted pulses from

LED sources suffer from pulse broadening, caused by chromatic dispersion. The bandwidth
of LED–light pulses depends on the DC current supply. The optical power of a LED can be

controlled by an external current producing the injection electrons. The relation between

optical power P and controlling current is given in figure 6.

Figure. 6: Power Characteristic of a LED

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The linearity of LEDs is fairly good. There is no threshold. The temperature range
is rather wide and the curves show little influence of temperature variations (0 ...... 80o).

The modulation frequencies are limited to about 100 MHz due to the delay in
recombination time of the carriers in the active area.

The lifetime of LEDs is rather long = 106 working hours (110 years), but their
output power is low as compared to LASER.

1.13 LASERS

In LASERS, spontaneous photon emission is generated between 2 parallel
reflecting surfaces. Since the dimensions of this device are very small, the beam is not so
well collimated as in a HENE gas LASER.

However, the external beam is quite narrow and is generated within such a small
area that very high power levels can be launched into even the smallest optical fibre.

The LASER has a bandwidth of approximately 1000 GHz ( = 2 nM). The transfer
characteristic of a LASER is non linear (see figure), so a LASER needs a more complicated
stabilizing of the working point, which changes with temperature and aging, etc.

LASERS working in the windows 850 nM and 1.3 M are usually made from Al
Ga AS material. LASER for 1.55 M are made of quaternary compound in Ga AS P.

A LASER has a threshold phenomenon in its light/current response. For that reason
a bias current must be supplied to make the LASER work, in the linear slope region. Also,
feedback must be adopted to keep both output power and variations in temperature between
certain limits.

In a LASER's life time the optical power and the light/current characteristic shows a
gradual degradation of the performance (see figure).

In practical systems the bias current is controlled automatically to obtain an optical
output power. By observing the value of the bias current and comparing this value with a
chosen alarm threshold value, a laser can be replaced in. Whenever there is an increase in
the biasing current by more than 50% of the initial value, the laser is said to have lived its
life. An alarm is initiated to indicate end of laser's lifetime in system.

1.13.1 LASER SAFETY

The high degree of collimation and brightness of some LASER beams makes them
a serious hazard to the human eye and, therefore, suitable safety precautions have to be
taken in their operation.

Semiconductor LASERS for optical transmissions generally have a lower
brightness and poor collimation, can also be a hazard if viewed under particularly
unfavourable conditions.

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With certain exceptions the radiation from LEDs is quite safe to the naked eye.
Optical line equipments have a laser safety switch off function, to switch off the LASER
during break in fibre somewhere on route.

However, no energized optical source or illuminated Fibre should be viewed
through a naked eye or microscope.

1.14 TYPICAL CHARACTERISTICS OF LIGHT SOURCE

PROPERTY LED LASER SINGLE LASER
Spectral width (nm) 200–100 1–5 0–2
Rise time (ns) 0.1–1
Modulation B.W (MHz) 2–250 0.1–1 ~ 2000
Coupling efficiency Moderate
Compatible fibre mode < 300 < 2000 Single
Temperature sensitivity High
Circuit Complexity Very low Moderate Complex
Lifetime (hours) 104–105
Costs M.M. (Si and GI) M.M. GI & SM Highest
Path length Very long
Data rate Low High Very high

Simple Complex
5 104–105

10

Low High

Moderate Long

Moderate High

Table. 2: Characteristics of Light Source

Figure. 7: Laser Light/Current Characteristic

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Figure. 8

Figure. 9: LASER Transmitter

1.15 LASING SPECTRUM

When the drive current is near threshold, lasers produce multimode spectra. As the
current increases, total line width decreases and number of longitudinal modes decreases.
At sufficiently high currents, the spectrum contains just one mode. The light from LASER
beam is confined to a narrow angular region.

Spectral width : laser produce range of wavelengths called spectral width, usually
quoted as FWHM (Full width at half maximum power ) or 3 db point. Wider the spectral
width more is the dispersion.

Line width : semiconductor laser produces a series of lines at a number of discrete
wavelengths. Width of these lines is called line width.

Figure. 10: Spectral Width and Bandwidth Page 12 of 48

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1.16 APPLICATIONS OF LED AND LASER

For low data rates and for shorter routes, LEDs are a good choice for the transmitter
because the driving circuitry needed is very simple. On the other hand, for high speed data
and long haul systems, LASERS are selected for transmitters. The driving circuitry is quite
complex, but LASER sources have the following advantages.

 Larger output power.
 Narrow spectral width
 Suitable emission geometry.

The disadvantage with laser is that they require large driving and modulating
currents. Their lifetime is shorter as compared to LEDs. The output power varies with time
and temperature. This necessitates the use of feed back and regulation circuitries for
maintaining output power constant.

1.17 LASER TYPES:

 Fabry-Perot (FP) :- Generates many wavelengths (MLM = multi Longitudinal mode ).
Linewidth 2 nm. Spectral width 5-8 nm used in PDH.

 Distributed Feed Back (DFB):- All Other wavelengths are reduced (more than 30 db
except one (SLM = single longitudinal mode). Linewidth is 5x10-6 nm. Spectral width
0.4 nm. They are used in SDH.

 Distributed Bragg Reflector (DBR) :- Mostly used as Tunable Laser for WDM
working.

1.18 CHIRP:

Chirp is a gradual shift in frequency as shown in figure.

Figure. 11: Optical Field with and without Chirp

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When input power is applied , there is an abrupt change in carriers (electron-holes)
flux density in the cavity resulting change in Refractive Index of cavity, causing change in
central wavelength . Central wavelength shifts towards longer wavelength. DFB lasers have
less chirp problem than FP lasers. Modulating signal also spreads the spectral width of laser
by twice the frequency of modulating signal. Laser chirp can be reduced by using external
modulator.

1.19 OPTICAL DETECTORS

A Photo-detector converts light into an electric current. In a fibre optic
communication system, detectors received the transmitted pulses and convert them, with as
little loss as possible into electronic pulses that can be used by a telephone, computer, other
terminal at the receiving end or at an intermediate repeater. In this role the detector must
have -

 High efficiency.
 Fast response.
 Low noise.
 Small size and light weight.
 Long life and reliability.
 Low cost.
1.19.1 Important detector properties:

 RESPONSIVITY – It is the ratio of the output current of the detector to the optic
input power. Responsivity p = i/P i.e. Amp/Watt

 SPECTRAL RESPONSE – This refers to the curve of the detector responsivity as
a function of wavelength. Different detectors must be used in different optical
windows.

 RISE TIME – the rise time (Tr) is the time for the detector output current to
change from 10 % to 90 % of its final value when the optic input power variation is
a step. The 3 db modulation bandwidth of the detector is :

 F3 db = o.35/Tr

 QUANTUM EFFICIENCY – Efficiency n is defined as the ratio of number of
emitted electron to the number of incident photons.

 Two types of Photodiodes most nearly meet the above requirements:

a. Pin photodiode.

b. Avalanche photodiode

1.20 PIN PHOTODIODES

Pin photodiode is relatively easy to fabricate, highly reliable, has low noise and is
compatible with low voltage amplifier circuits. In addition, it is sensitive over an extremely
large bandwidth because there is no gain mechanism. PIN photodiodes have resistance
intrinsic layer, sandwiched between P and N layers, the depletion layer spread over intrinsic

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layer under influence of high field due to reverse bias. The device operates under reverse

bias, meaning that in the absence of light, only a small leakage current will flow. Under
reverse bias, a moderate electric field of about 105 volts per cm exists in the vicinity of the

junction that depletes the region of all free carriers.

When a photon enters the depletion region, it is absorbed and generates an electron
and a hole, both of which are rapidly drawn to the opposite electrodes. Then they are
collected and appear as a current in the external circuit. Because there is no gain mechanism
in a PIN photodiode, the maximum efficiency of the device is unity and the gain bandwidth
product is equal to the bandwidth itself. The ultimate bandwidth of a PIN photodiode is
limited by the time, it takes to collect the charge. This time is inversely proportional to the
width of the depletion region and directly proportional to the velocity of the charge carriers
in the region of high electric field. PIN photodiodes have lower capacitance, high quantum
efficiency and high speed of response.

1.21 AVALANCHE PHOTODIODES (APD)

APDs are operated at reverse voltage high enough so that when the carriers are
separated in the electric field, they collide with the atoms in the semiconductor crystal
lattice. The collisions ionize the lattice atoms, generating a second electron–hole pair. Each
of the secondary carriers, along with the initial carrier, also collides with the lattice and
large numbers of carriers are eventually collected at the electrodes. This gives the device
internal gain. The principal source of noise in APDs is the avalanche process that gives the
APD gain. An existing transmission system can often be upgraded simply by a change in
optical detectors (receivers), i.e. from PIN to APD. The detectors, in general, must have a
good sensitivity, which is limited by noise and is influenced by :

(i) Thermal noise from the input resistance to the pre amplifier.

(ii) Short noise from the photo diode.

(iii) Noise from the first stage of the amplifier.

(iv) Dark current noise.

The actual output of a detector depends on the quantum efficiency. For the same
quantum efficiency, an APD has better sensitivity than PIN diode. Silicon detectors are
useful only up to 1.1 M. For longer wavelength, germanium based devices are used. The
Ge–APD is useful in the 1.0–1.5 M range. In GaAS PIN diodes in conjunction with a low
noise FET amplifier offer sensitivity of the order of –65 dBM. In contrast to APDs, PIN
diodes offer inferior sensitivities. They are mainly useful for low bit rate and of short route
length.

1.22 COMPARISON OF DETECTORS (OPTICAL)

Characteristic PIN(Si) APD (Si) APD (Ge)

Detection range (m) 0.4–1.1 0.4–1.1 0.4–1.6

Wavelength of peak sensitivity 0.8–0.9 0.5–0.9 1.1–1.4

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Quantum efficiency (%) 6.0–8.0 4.0–8.0 4.0–5.0
Dark current (nA) 0.82 (m) 0.82 (m) 1.15 (m)

0.1–5.0 0.02–15 10–200

Rise time (ns) 0.5–3.0 0.1–0.5 0.1–0.2

Detecting area 4–6 1–15 50–70

Table. 3: Optical Detectors Comparison

1.23 MATERIAL FOR SOURCES AND DETECTORS

High capacity communication system operates at 1.3 and 1.55 micrometers. Such
systems employ Indium gallium arsenide (In Ga As) or germanium as the detecting semi–

conductor.

1.24 BIT ERROR RATE (BER)

In a digital optical communication system, the sensitivity can be determined by
calculating how often a transmitted digital 1 will be mistakenly identified by the receiver as
a zero or vice versa. This is known as Bit Error Rate. For most signal applications a bit
error rate of 10–9, i.e., one mistake per 109 transmitted bit is sufficiently low. The

sensitivity of all optical detectors decreases, however, with increasing bit rate, because the
total noise also depends increasingly on bandwidth – a characteristic of white noise source
that is intrinsic to these detectors.

CONCLUSION:-From this lesson trainee is able to understand Fibre Optics, theory

and principle of Fibre Optics, propagation of light through fibre, Fibre Geometry, Fibre
Types etc.

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Module - 5

Lesson - 2

Construction of OF Cables

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2. CONSTRUCTION OF OPTICAL FIBRE CABLE

OBJECTIVE:- This lesson provides the insight into Fibre cable construction , cable

components, Multifiber cable , The environment effect, metallic or non metallic cables,
connectors, Optical Fibre Connector Techniques, Type of Connectors, Digital Distributing
Frame (DDF), Fibre Distribution Frame (FDF) etc.

2.1 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 considerations 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

2.2 CABLE COMPONENTS

Component Function Material

Buffer Protect fibre From Outside Nylon, Mylar, Plastic

Central Member Facilitate Stranding Steel, Fibreglass
Temperature Stability
Anti-Buckling

Primary Strength Member Tensile Strength Aramid Yarn, Steel

Cable Jacket Contain and Protect PE, PUR, PVC, Teflon
Cable Core
Cable Filling Abrasion Resistance Water Blocking
Compound Compound
Prevent Moisture
Intrusion and Migration

Armoring Rodent Protection Steel Tape
Crush Resistance

Table. 1: Cable Component Material & Functions
2.2.1 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.

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Siecor/ Optical Cable fills these tubes with a Jollylike Compound to Provide
Additional Cushioning and Prevent the incursion of Moisture.

Figure. 1: Fibre in Buffer after Manufacturing.

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

Figure. 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.

2.2.2 Types of Fiber Buffering

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 Tight Buffer Jacket

Figure. 4: Longitudinal and Transverse Tight Buffer Jacket
2.2.3 Loose Buffer Jacket

Figure. 5: Loose Buffer Jacket
2.2.4 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.

2.2.5 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.

2.3 MULTIFIBRE CABLE:

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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.

Figure. 6: Typical Mini Bundle Cable

Figure. 7: Multi Fibre Cable Identification

2.3.2 Description

1 - Blue 5 - Slate 9 - Yellow
2 - Orange 6 - White 10 - Violet
3 - Green 7 - Red 11 - Blue/ Black
4 - Brown 8 - Black 12 - Orange/ Black

2.4 THE ENVIRONMENT EFFECT :

 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.

 Another effect ingress of water, which may increase of concentration of water
vapour around the fibre.

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 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.

2.5 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.

2.6 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.

2.7 CONNECTORS

Connectors, splices and couplers are vital elements in the Fibre Optics Technology.
Connectors can be defined as a remittable means of arranging transfer of optical energy
from one fibre optic component to another in an optical fibre system. These components
include Fibres, Couplers and Filters and Opto–Electronic devices. The couplers are
multiport devices which permit transfer of optical power from one port to all other
simultaneously or vice–versa. Splices are permanent joints between two fibres.

These devices providing interconnection inevitably introduce a loss at the
interconnect point. The loss at these joints can be broadly categorised in mainly two areas:

 Intrinsic losses and

 Extrinsic losses

These losses are common to both the connectorised or spliced joint.

2.7.1 CONNECTORS

The connectors are rematable interconnect devices which provide flexibility
required in a Fibre Optic Transmission system. The basic function required of connectors
is to allow transfer of optical power from one fibre component to another with minimum

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loss and possibility of disconnection and remating number of times with minimum insertion
loss.

2.7.2 Connector Requirement
 The attenuation in optical fibre connectors should be less than 1 dB.
 The connector must provide consistent performance on each remating.
 The connector must provide protection to the fibre so that it does not break
while being handled.
 The connectorisation technique should be simple.
 The connector size should not be very much bigger than the fibre size and it
should not be too small.
 Connector must be cost effective.

2.7.3 Connector Composition

Connector fundamentally consists of two parts, a plug and an adapter. For fibre to
fibre connections, the fibres are terminated in individual plugs and mated in the adapter.

Figure. 8; Plug & Adaptor

For fibre to device connection, the devices may be housed in the adapter part and
the fibre in the plug part. The fixing of the fibre in the plug may be achieved directly or by
using sleeves commonly known as ferrules. The proper centering in these ferrules could be
achieved by using precision drilled holes, jewels or rods depending on the arrangement.
The adapter provides the alignment mechanism.

The performance of the connectors depends on the accuracy of the alignment of the
optical elements to be connectorised. The basic elements in the connectors are fibre fixing
mechanism and the alignment mechanism. The alignment accuracies required are of very
high to avoid losses and are consequently quite costly.

2.8 OPTICAL FIBRE CONNECTOR TECHNIQUES

Optical fibre connectors are made by the following techniques :

 Geometric techniques:
a. 3–Rod connectors.
b. 3–Sphere connectors
c. V–grove connectors.

 Precision techniques:

a. Ferrule connectors.
b. Bi–conical connectors.

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c. Core–centered connectors.
d. Core–aligned connectors.
e. Precision moulded connectors.

 Optical techniques:

a. Optically focussing connectors.
b. Optically collimating connectors.
c. Fibre Taper connectors.

2.9 TYPE OF CONNECTORS

Following types of practical connectors are available in the market.

(1) Amphenol Fibre Optic Connectors:
 Based on precision plug concept.

(2) The Radial Connectors
 Based on core aligned concept

(3) OCN Connectors:
 Based on precision ferrule concept.

(4) The FC, D3 and D4 connectors:

The connectors are primarily precision plug connectors, which are being used in
Japan. These connector have notches and pin arrangement to maintain angular alignment
for a repeatable insertion loss performance. The FC type of connector has been approved by
the NITC, Japan and is similar in construction to D4 connector, D3 connector is slightly
bigger in dimensions.

These connectors consist primarily of precision plugs and coupler body. The fibres
are fixed in the plugs and the plug ends polished. The fixing of plug to the coupler is
through screw on top or BNS arrangement is also available.

(5) Precision moulded Connectors:

These connectors are exactly similar in construction to FC, D3 etc. (metal type of
connectors), but made of plastic and are light weight, easy to handle and interchangeable.

(6) Philips Connectors:

These are core centred connectors used by M/s Philips, Holland.

(7) Bare Fibre Adaptors:

These are primarily optical connectors in which the fibre can be fixed for
measurements purpose and removed after the measurement is over. The connector uses
mechanical force for holding the fibre in the connector. The fibre can be released by release
of the mechanical pressure.

2.10 FC DESIGN

The FC design is a ferrule–in–sleeve concept but is designed so that the plug
housing screws onto sleeve housing. As shown in the Figure given below, the plug is keyed
and the sleeve housing notched so that the ferrule does not rotate. The ferrule and fibre can
come with an end finish that permits contact of the fibres, thus reducing insertion loss and
reflection dramatically.

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Figure. 9: FC Connector Design

This is known as Physical connect (PC) connector or simply as FCPC connector.
Because the ferrule is keyed, it cannot rotate such that he contacting fibres scratch each
other.

For single mode fibre the insertion loss is typically 0.4 to 0.7 dB with maximum
loss variations between 0.8 and 1.0 dB depending on the manufacturer. With the Pc type,
mean loss can be reduced to 0.15 dB.

Connectors have to be especially selected to guarantee low reflection. They should
satisfy two criteria.

 Physical contact
 Angled contact
Connectors with high–return–loss connectors are good choice. Additionally, all
connectors have to be cleaned carefully to avoid breaks in the physical contact. Some
connectors are shown in the Fig. given below which are used in LAN, WAN and CATV
networks.

Figure. 10 Different Types of Connectors Page 25 of 48

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Figure. 11: Different Types of Connectors

2.11 DIGITAL DISTRIBUTING FRAME (DDF)

The Digital Distributing Frame (DDF) is a 75-ohm frame system that serves as an
equal level cross-connect point for signals conforming to the following signal formats:

• 2.048 Mb/s
• 8.448 Mb/s
• 34.368 Mb/s
• 139.264 Mb/s
• 155.52 Mb/s

The modules allow test access to all equipment terminated at the frame and provide
flexible cross-connects between Network Elements (NEs). Alternatively, the DDF can be
set up as an interconnect point, typically as a point of interface between the DSX of a Local
Exchange Carrier (LEC) and connecting MUXes.

The DDF system consists of individual DDF modules mounted in a panel. There are
three types of modules:

The Rear/Front DDF-Dual Monitor Module (R/F DDF-DM), the Rear/Rear DDF-
DM Dual Moniotr Module (R/R DDF-DM), and the DDF-Performance Module (DDF-
PM). For testing purposes, each DDF-PM module is equipped with a single MONITOR
port on the front that provides a –20 dB signal level for the transmit and receive signal of
the NE terminated on the rear of the module. Each DDF-DM is equipped with two

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MONITOR ports on the front that provide a –20 dB signal level for the transmit and receive
signal of the Network Element (NE) terminated on the rear of the module.

The R/F DDF-DM, shown Figure 11, is equipped with six BNC connectors. Four
BNC connectors are located on the front of the module: MON-O (Monitor Out), MON-I
(Monitor In), OUT, and IN. Two BNC connectors are located on the rear of the module:
TX and RX (Out transmit and In receive, respectively).

The R/R DDF-DM, shown in Figure 12 is equipped with six BNC connectors. Four
BNC connectors are located on the rear of the module: OUT, IN, TX (Out Transmit), and
RX (In Receive). Two BNC connectors are located on the front of the module: MON-O
(Monitor Out) and MON-IN (Monitor In).

The DDF-PM is equipped with five BNC connectors. Three BNC connectors are
located on the front of the module: MON, OUT, and IN. Two BNC connectors are located
on the rear of the module: TX and RX (Out Transmit and In Receive respectively).

The panels are available in 32-(R/F and DDF-PM only), 24-, 10-, and 8-module
arrangements, which are designed to mount horizontally in either a 23-inch (600 mm) wide
bay frame (10-, and 32-module version) or a 19-inch (500 mm) wide bay frame (8-, and 24-
module version). The 24-module panel can also be mounted vertically (typically, this will
be a cabinet application). In the 8-, and 10-module versions, the modules mount
horizontally in a 2-inch (50 mm) high panel in four or five rows (respectively) of two
modules per row.

Additionally, an 8-module panel designed for wall mount applications is also
available. The DDF system may be configured for front or rear cross-connect and
interconnect applications. A complete line of network bay frames, framework hardware,
and patch and test cords are available to support installation, cable management, and
operations.

2.11.1 Features
 Incorporates world wide standard BNC connectors, thus making the DDF system

compatible with most applications.

 The DDF system is compatible with DS3, E1, E2, E3, E4 and STM-1 signal rates.

 The BNC connectors are equipped with a locking mechanism for the patch cords (in
cross-connect arrangements).

 The front and rear cross-connect arrangements allow easy access for patching around
faulty equipment.

 Excellent transmission performance characteristics which allow the DDF to be used as
an interconnect point in conjunction with a separate DSX system.

 The DDF system has ground-isolated modules, thus no separate grounding required.

 Test cords are equipped with easy-to-use, push-on BNC connectors. Patch cords are
equipped with locking BNC connectors.

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 Standard BNC connectors are available from a variety of sources for any coaxial cable
type.

 The DDF can be configured to use different connectors other than BNCs.like 120 ohms.

 Each 24 and 32-circuit R/F DDF-DM and DDF-PM panel includes a heavy-duty hinge
on the bottom, which allows the panel to swing forward for easy access to the rear of
the panel. This feature is especially useful when mounting in a cabinet.

Figure. 12: Rear/Front Digital Distributing Frame-Dual Module (R/F DDF-DM)

Figure. 13: Rear/Rear Digital Distributing Frame-Dual Monitor (R/F DDF-DM) Module

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2.12 FIBRE DISTRIBUTION FRAME (FDF)

 Distribution frame includes metallic casing, adaptor plate, splice tray and other
necessary Materials for the termination of optical fiber cables

 Frame has fiber splicing and distribution function
 Optical fiber distribution frame can be installed in the 19 inches rack
 Environment:
 Environmental temperature: -25 to 55 degrees Celsius
 Relative humidity: below 85% (when the temperature is below 30 degrees Celsius)
 Atmospheric pressure: 70 to 106kPa
 Main technical indexes:
 Insulation resistance: >=2 x 10,000mΩ/500V DC
 Voltage strength: non-puncture, no arcover under 15kV DC/min
 Good cold rolled steel material
 Weight: 3.4kg
 Dimensions: 485 x 300 x 52mm
 Slide type, easy to pull out for management
 Different front plates can be choosed for SC, FC, ST and LC
 Capacity: 1U24 Core, 2U48 Core, 3U72 Core and 4U 96 Core

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Figure. 14: Fiber Distribution Frame (FDF)

2.12.2 Features:

This product is used as the terminal ending and distribution of the main optical fiber
cable of the central office in the optical fiber cable, communication system. It can realize
the connection, distribution, and dispatching of the fiber circuit. And it is the distribution
connection equipment between the optical fiber cable and the fiber cable communication
system

 Electrolysis sheet frame, electrostatic spraying in the whole

 Front input and all front operation

 Flexible installation, wall type or back type, and can be installed in large groups

 Modular structure can adjust the splicing and distribution units

 Suitable for ribbon and non-ribbon optic fibers

 Suitable for inserting installation of SC, FC, ST (additional flange)adapters

 30C oblique installation of adapters, preventing eyes from laser's hurts and ensuring the
fiber bending radius

 Reliable fiber introduction, protecting, grounding and fixing

 The bending radii in any place are ensured to be more than fixing

 Realize the scientific management of the patch cords by using many groups of fiber unit

 Realize up or down input by the simple adjustment of units, and clear identify

 Applications:

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City and country cable network, the data and graph transfer system, the CATV wired TV
series

CONCLUSION:- From this lesson trainee is able to understand Fibre cable

construction , cable components, Multifiber cable , The environment effect, metallic or non
metallic cables, connectors, Optical Fibre Connector Techniques, Type of Connectors,
Digital Distributing Frame (DDF), Fibre Distribution Frame (FDF) etc.

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Module - 5

Lesson - 3

OFC System

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3. INTRODUCTION TO OFC SYSTEM

OBJECTIVE:- This lesson provides the insight into OFC System Configuration,

Digital Multiplex Sub System, Optical Line Transmission Subsystem, Capacity of Optical
Fibre System in PDH, OFC Splicing, laying of cable etc.

3.1 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

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Figure. 1: Simplified Block Diagram of Fibre Optics Transmission System

3.2 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.

3.2.1 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

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separate (demultiplex) one 8448 kbit/s digital bit–stream into four 2048 kbit/s digital bit–
streams at receiving side.

3.2.2 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.

Figure. 2: Block Diagram of the Digital Multiplex

3.2.3 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.

3.2.4 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.

3.3 OPTICAL LINE TRANSMISSION SUBSYSTEM

The Optical Line Transmission Subsystem comprises the following sections.

 Optical Line Transmission Section
 Line Switching Section
 Line Supervisory Section
 Orderwire Section.

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3.3.1 Optical Line Transmission Section

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).

Figure. 3: Block diagram of a typical Optical Line Transmission System

LEGEND

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

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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 MUX 34M Digital Multiplexer
140M MUX 140M 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

3.3.2 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.

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3.3.3 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.

3.4 CAPACITY OF OPTICAL FIBRE SYSTEM IN PDH

3.4.1 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)

3.4.2 Optimux
(i) 2/34 Mb/s Optimux
(ii) 2/140 Mb/s Optimux

3.5 MANUFACTURERS OF CONVENTIONAL OPTICAL FIBRE
SYSTEMS

(1) OPTEL
(2) I.T.I.
(3) HFCL
(4) Technicom
(5) MCE
(6) Natelco
(7) G–Tel
(8) C–DOT
(9) Fujitsu
(10) Philips

3.6 MANUFACTURERS OF OPTIMUX SYSTEM

(1) HFCL
(2) Crompton & Greaves
(3) Technicom
(4) HCL

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(5) NATELCO

3.7 OFC SPLICING

3.7.1 Splices

Splices are permanent connection between two fibres. The splicing involves cutting
of the edges of the two fibres to be spliced.

3.7.2 Splicing Methods

The following three types are widely used:

3.7.3 a. Adhesive bonding or Glue splicing.
b. Mechanical splicing.
c. Fusion splicing.
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 Single Model(SM) 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:

a. Auto active alignment of the core.
b. Auto arc fusion.
c. Video display of the entire process.
d. 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

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under the microprocessor control, 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.

Figure. 4: Preconditions for a Splice with a Low Loss

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3.8 LAYING OF CABLE

It is as per letter no DOT. 352/91 TPL (OP) dated at ND- 08-04-1992
3.8.1 Soil categorization: (for depth of trench)

(A) Rocky: Cable trench, where cannot be dug without blasting and/or chiseling.

(B) Non-Rocky: Other than ‘A’ above including murram and soil mixed
with stone and soft rock.

3.8.2 Pipes for cable laying and protection
(A) HDPE pipe 75 mm (diameter) length 5m. (approx 18 to 20’ ) phase I
(B) HDPE pipe 50 mm (diameter) length 5m. (approx 18 to 20’ ) phaseII
(C) PLB pipe (40 mm. outer diameter) length 1km/200m (town limits with rope)
phase III
(D) GI pipe for PLP 50 mm dia length 6 meter

3.8.3 Measurement of cable depth
(All depth should be measured from the top of pipe. However it is acceptable if it is

less by more then eight cms. from the specified.

(A) Cross country rout (normal soil)
 Above HDPE pipe 1.5 meter
 Trench depth 1.65 meter
 in rocky area minimum depth 0.9 m ( where dug is not possible more then 1 meter

above pipe due to any obstruction should be consider) and all cables having depth
less then 1.2 meter should be protected by RCC/GI pipes

(B) In built up area (city/town/urban area)
i. OF cable should be laid through exiting duct.
ii. GI pipe or RCC pipe at the entry of duct.

iii. In non duct area it should be laid through HDPE pipe/PLP pipe at dept 1.5
meter using RCC/GI pipe for protection.

iv. Depth in rocky soil may be consider as 0.9 to 1.0 meter

(C) On culvert/bridge over river and nallah.
i. At the depth of 1.5 meter below the bed throw HDPE/ RCC Pipe. Pipe
length should be 2 meter extended at both ends.
ii. This should be fixed along the parapet wall/bridge wall when
the river or nalla full of water through out year, through fixed GI pipe on
wall at suitable height above the water level.

(D) Along rail bridge or crossing

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Through HDPE pipe/PLP pipe protected by RCC or iron pipe as per the prescribed
by railway authority.

(E) On road crossing

At a depth of 1.5 meter through HDP pipe enclosed in RCC pipe extended by 3.0
meter to the side end of the read.
3.8.4 Indicators along route

(A) Route indicator

At every 200 m route length of showing name of route & no of indicators.

(B) Joint indicator
At every joint (Splice) generally it is placed at every 2/4 Km(Drum length)

(C) Branch (Root diversion) indicator
Provided at route diversion or branching from the main root.

CONCLUSION:-From this lesson trainee is able to understand OFC System

Configuration, Digital Multiplex Sub System, Optical Line Transmission Subsystem,
Capacity of Optical Fibre System in PDH, OFC Splicing, laying of cable etc.

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Job Aid No. 1
Identification of optical fibre pairs, study of construction

of different types of cables

1. Objective:-
After completion of this session trainee will be able to identify different
component parts of optical fibre cable(Siecor) and their functions.

2. Tools/items required:-
1. Piece of Siecor make O.F. cable.
2. Tight buffer cable (pig tail)

3. Test Set up:- -----------

4. Procedure:-
Siecor make O.F. cable(12 fibre)

Item no. Name of the component Functions & Specifications
1 ------------------------------- --------------------------------------

2 --------------------------------- ---------------------------------------

3 -------------------------------- --------------------------------------

4 --------------------------------- ---------------------------------------

5 ---------------------------------- -----------------------------------------

6 --------------------------------- ---------------------------------------

Module 5: OF cables & installation Page 43 of 48
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BSNL Junior Engineer OFC System

Job Aid No. 2
Fiber Splicing

1. Objective:-

After completion of this session, trainee will be able to prepare cable end for
splicing operations.

2. Procedure :- (for Siecor makes O.F.cable)

1. Mark a point at appropriate distance as shown above from the cable end.
2. Remove outer (orange) jacket 1.90 metres by jacket remover.
3. Remove inner (black) jacket 1.90 meters by hook knife, rip cord.
4. Cut the rip cord & aramid yarn by scissor at the mark point and remove it.
5. Using sheath ripper cut the two binders every 6” apart.
6. Push the cut binders away from the mark point, until all binders removed.
7. Unwind the buffer tubes from around the centre member.
8. Flush (cut) the central member and dummy tubes (filters) by using the diagonal

cutter pliers.
9. Using gel off paper, wipe the jelly over the buffer tubes. Use dry towel cloth/tissue

paper for final cleaning.
10. Using second notch from top (1 mm size) of buffer tube stripper, remove the buffer

tubes, leaving 55 cm from flush end of cable, in instalment of 9’’ length.
11. Clean jelly over the fibre bunch by gel off paper & finally by dry towel cloth.
5. Observations: - Cable end is ready for splicing.
6. Precautions:-
1. Buffer tubes off fibres should not get kinked during sheath removal procedure.
2. Some tools are sharp. Normal care should be observed.

Module 5: OF cables & installation Page 44 of 48
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(Fusion Splicing)

1. Objective
After completion of these sessions, trainee will be able to splice two fibre ends by
Fusion Splicing Machine.

2. Tools / Items required :-
1. Auto Fusion Splicing Machine
2. AC/DC Converter with power supply cords.
3. T.V. Monitor with video cord & power supply cord.
4. Standby battery (chargeable with supply cord & charger).
5. Manual operation box.
6. Fibre stripper.
7. Acetone
8. Tissue papers
9. Fibre Cutter (Cleaver)
10. Insulation tape
11. Two fibre pieces

3. Test Set up :-

4. Procedure :-
1. After connecting the AC/DC converter, TV monitor with Fusion Splicing
Machine & after making necessary power cord connections as shown in test
set up, make power ON and wait for Return Origin Complete display on TV
screen. Press Reset button. Reset Complete is displayed on TV screen and
beep sound is heard. Machine is ready for splice operation.

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2. Using Fibre Stripper, remove 5cm. (approximately) plastic colour coating of
fibre.

3. Clean the bare fibre with Tissue paper soaked in Acetone.
4. Cut the bare fibre end with the cleaver so that end is perpendicular to the fibre

axis and length is 16+/- mm.
5. Open the hood. Open the clamp by pulling the lever towards you. Keep the

bare fibre on V groove mirror surface through V notch guide to stop the colour
coated fibre. Push the lever away to close the clamp.
6. Prepare the other fibre end in the same way. Repeat the steps (2) to (5).
7. Close hood (see that the fibres are not pressed under the hood). Press Set and
observe T.V. screen. If fibre ends are accepted, Set complete will be
displayed. Otherwise Error will be displayed on screen with beep sound.
8. If Set Complete is displayed, press once again Set for splicing operations.
Once the fibres are spliced, loss is displayed. Press Reset. After Reset
Complete, open hood and remove the splice.
9. If Error is displayed, wait for beep sound. Press Reset. After Reset Complete
is displayed, open the hood and correct the error as per display or cut the fibre
end again with cleaver and repeat the process (consult the hand book for detail
error correction).
10. If the appearance of the fibre splice is not good, press Arc manually. Again
fibres are fused once more. (sometimes after re-fusion, splice loss is
increased).

5. Observations :- Fibre loss should be <=0.1db, with good appearance.

Fibre loss=---------------------------

6. Precauations :-

1. Fusion splicing is recommended in air-conditioned environment to avoid dust.

2. Never touch the electrodes, because a high voltage of 6000V is developed

during fusion.

3. Make sure to ground the unit.

4. Make sure that the splicing machine is completely dry before use.

Module 5: OF cables & installation Page 46 of 48
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BSNL Junior Engineer OFC System

Job Aid No. 3
Fault Localisation using OTDR

1. Objective:
After completion of this session, trainee will be able to-
1. Operate Optical Time Domain Reflectometer.
2. Measure fibre Loss, Fibre Length, Fibre attenuation, Splice Loss, Connector
Loss etc.
3. Localize Break in Fibre.

2. Tools/ Items Required :
1. OTDR
2. Fibre spools containing 1 KM length of Fibre -2 Nos.
3. Pig tail -1 No

3. Test Set Up:

4. Procedure:
A. Optical Fibre Transmission Loss Measurement:

1. Display the waveform for which loss is to be measured on the CRT.
B. Splice loss measurement

1. Display the waveform for the splice measurement on the CRT.
2. For more accurate measurement, set the LSA/2 POINT key to LSA.
3. The measured results are automatically displayed at the lower left side of the
CRT.
C. Auto splice Loss Measurement
1. Display the waveform for the splice loss measurement on the CRT.
2. Read the displayed value of splice loss.
D. Distance measurement
1. Display the waveform at the distance between two points to be measured.

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2. Set the SPLICE/LOSS key to LOSS.
3. Set the X and * markers to the points to be measured.
4. The result of the distance measured between the two markers is displayed at the
lower left side of the CRT.

5. Observation:- ------- db.
Fibre loss -------- db/Km.
Fibre Attenution --------- db.
Splice Loss ----------Km.
Distance to break

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