The document discusses fiber optic transmission systems (FOTS). It describes how FOTS uses optical fibers to transmit information over long distances using light signals. It discusses the key components of a FOTS including transmitters, optical fibers, optical receivers, and how total internal reflection allows fibers to transmit signals. The document also covers fiber types, advantages of FOTS over copper wire, components in DMRC's network, and technologies like SDH used for optical communication.

1. Delhi Metro Rail Corporation
Training Institute
ISO 9001:2008
ISO 9001:2008
FIBER OPTIC TRANSMISSON SYSTEM

2. Fiber Optics Transmission system FOTS
 FOTS stands for Fiber Optics Transmission system. It is
the transmission system that uses optical fiber as
communication media. Thus optical fiber communication
is the method of transmitting information through optical
fibers.
 Optical fibers can be used to transmit light and thus
information over long distances.
 They are largely used for telephony, but also for Internet
traffic, long high-speed local area networks (LANs),
cable-TV, and increasingly also for shorter distances.
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3. Parts of a single optical fiber
Fiber optics (optical
fibers) are long, thin
strands of very pure
glass about the
diameter of a human
hair.
They are arranged
in bundles called
optical cables and
used to transmit light
signals over long
distances.
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4. Optical fiber types
 Single mode fibers
Single-mode fibers have small cores and transmit
infrared laser light. Some optical fibers can be made
from plastic. These fibers have a large core and transmit
visible red light from LEDs.
 Multimode fibers
Multi-mode fibers have larger cores and transmit infrared
light from light-emitting diodes (LEDs).
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5. Total Internal Reflection:
 Total internal reflection is the principal on
which optical fibers work
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6. Fiber optic relay system
 Fiber optic relay system consists of the following:
 Transmitter - Produces and encodes the light signals
 Optical fiber - Conducts the light signals over a distance
 Optical regenerator - May be necessary to boost the
light signal (for long distances)
 Optical receiver - Receives and decodes the light
signals
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7. Advantages of Fiber Optics:
Compared to conventional metal wire (copper wire), optical fibers are:
1.Less expensive
Several miles of optical cable can be made cheaper than equivalent
lengths of copper wire. This saves your provider (cable TV, Internet)
and your money.
2.Thinner
Optical fibers can be drawn to smaller diameters than copper wire.
3.Less signal degradation
The loss of signal in optical fiber is less than in copper wire.
ISO 9001:2008
4.Non-flammable
Because no electricity is passed through optical fibers, there is no
fire hazard.

8. 5.Higher carrying capacity
Because optical fibers are thinner than copper wires, more fibers
can be bundled into a given-diameter cable than copper wires. This
allows more phone lines to go over the same cable or more
channels to come through the cable into your cable TV box.
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6.Light signals
Unlike electrical signals in copper wires, light signals from one fiber
do not interfere with those of other fibers in the same cable. This
means clearer phone conversations or TV reception.
7.Low power Transmitters
Because signals in optical fibers degrade less, lower-power
transmitters can be used instead of the high-voltage electrical
transmitters needed for copper wires. Again, this saves your
provider and you money.

9. ISO 9001:2008
8.Digital signals
Optical fibers are ideally suited for carrying digital information,
which is especially useful in computer networks.
9.Lightweight
An optical cable weighs less than a comparable copper wire cable.
Fiber-optic cables take up less space in the ground.
10.Flexible
Because fiber optics are so flexible and can transmit and receive
light, they are used in many flexible digital cameras for the
following purposes:
 Medical imaging - in bronchoscopes, endoscopes, laparoscopes
 Mechanical imaging - inspecting mechanical welds in pipes and
engines (in airplanes, rockets, space shuttles, cars)
 Plumbing - to inspect sewer lines

10. Losses in Optical Fiber Cable
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 Attenuation loss
Attenuation loss takes place due to coupler, splices, connectors,
fiber itself. Attenuation varies with the wavelength of the light
850 nm- 2.5 to 3.0 dB/km
1310 nm- 0.4 to 0.5 dB/km
1550 nm- 0.25 to 0.3 dB/km
 Absorption
Absorption is a natural property of glass itself. Losses due to
absorption are very large in UV and infra red regions.

11. ISO 9001:2008
 Scattering
Loss of the optical energy is due to imperfections in the fiber. Light
is scattered in all directions, which causes the loss of power in
forward direction, known as Rayleigh scattering loss, takes place
due to variations in the density and composition of glass material in
the fiber. Rayleigh scattering loss is inversely proportional to four
power of wavelength, i.e., for high wavelength, losses will be small.
 Macro and Micro bending
i) Macro bending: Loss is caused due to deformation of fiber axis
during cabling process.
ii) Micro bending: Excessive bending of the cable or fiber may
result in loss known as micro bend loss. For single mode fiber
attenuation at longer wavelength like 1550 nm is sensitive to
bending.


12. Fiber Optics Transmission System (FOTS) in DMRC
 FOTS can be termed as the backbone of DMRC
telecommunication network.
 Fiber optics eases up the data and voice communication
or access to various systems at different stations.
 This network is based on fiber optical cables on both
sides of the track.
 The number of fibers is determined in order to comply
with redundancy. The fiber is redundant for security and
protection.
 In case of fiber optic failure, communication can take
place via spare fiber while the fiber that is down may be
fixed.
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13. The main components of the fiber optic transmission
system are:
1. Optical fiber cables
2. Synchronous Digital Hierarchy (SDH)
3. Digital Distribution Frame (DDF)
4. Flexible Multiplexer (FMX)
5. Optical Distribution Frame (ODF)
 1. Optical fiber cables are used for the transmission of
the data from one station to the other station. Mainly the
clock signal from the master clock is transmitted as it
helps in the synchronization so that it does not cause
any delay in the data transmission and hence the metro
trains can run in their required time.

ISO 9001:2008

14.  SDH:
SDH i.e synchronous digital hierarchy is the technique used for the
optical communication. Before knowing in depth about the SDH we
should know about the PDH, which was used before the advent of
SDH.
 PDH (Pleisochronous Digital Hierarchy):
PDH uses copper wire to transmit information from one
station to other hence, increased I2R losses, eddy current losses,
current and voltage range limitations and need of repeaters after
very small distance, all these factors discouraged the use of PDH.
One major drawback is multiplexing and demultiplexing at all
stations through which information passes. Troubleshooting is
rigorous task due to increased complexity. Due to above mentioned
factors, we have switchover from PDH to SDH technology.
ISO 9001:2008


15.  Pliesochronous means ‘just synchronous’. In PDH technique
different clocks were used and all the clocks cannot be same at
same time or synchronous. Also in PDH system, while sending E1
channel, 64kbps additional bits are sent called the stuffing bits and
the pointer associated tells whether bits in 64kbps are data or just
stuff. If bits are stuff then they are not demultiplexed at the
destination.
Limitations of PDH:
 Not manageable from central network
 Not completely synchronized
 Not standardized
 Less Bandwidth (due to physical media)
Thus to overcome the above limitations we use SDH technique.
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16. SDH(Synchronous Digital Hierarchy):
In SDH, information is transferred through optical fiber. Through
this technology we are able to transmit data in terabytes using
wavelength 1310 nm.
There is no need to demultiplex whole information coming from
side by stations. Information to side by stations is passed using
STM-4 (Synchronized Transport Module) at 622.08 Mbps.
4 STM1 multiplexed in TDM (Time Division Multiplexing) forms
STM-4. In this technology repeaters are required at comparatively
larger distances.
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 E2=4 E1
 E3=4 E2=16 E1
 E4=4 E3=16 E2= 64E1
 STM1=63 E1

17. Formation of E1 channel
E1 is the tributary signal for SDH to work.
0 1 2 3 4 5 ……………… 16 ………………… 31
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1::
7
256 such data packets give 65536 bps, approx. 64 kbps. 32 time slots
of 64 kbps give E1 signal transmitting @ 2.048Mbps. E1 is bi-directional
signal Out of these 32 channels 30 are used as voice channel while 2
are used for control and signaling information.
0 16 31
0 – Control data
16 - Signaling data: Carries information about the path E1 goes through.

18. DDF (Digital Distribution Frame).
 The DDF basically provides a flexible way of
connecting equipment side to cable side. From
the DDF the system working at 2 Mbps rate is
directly provided the connections with required
number of E1 lines.
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19. ISO 9001:2008
FMX/Access MUX:
If data rate is less than 64 Mbps then, it is termed as
sub-rate. If data rate is more than 64 Mbps then it is
termed as super rate.
Access-MUX is used for systems requiring transfer
rate below 2.048 Mbps. It multiplex the data from the
systems operating at the data rates lower than 2 Mbps
into E1 lines.
Since no single node will be able to use all the
bandwidth therefore, all the data i.e. audio and video
signals are multiplexed in order to make maximum use
of available bandwidth.
FMX is interfaced with Clock system, Cameras, Radio,
NP-SCADA, etc.

20.  Optical Distribution Frame (ODF):
GSS and FPS together forms ODF (Optical Distribution Frame). At
each node (or station), optical fiber cables are terminated in the
GSS (Generic Splicing Self) and are distributed to the system
through FPS (Fiber Patching Shelf).
 From the FPS patch cords, both ends have connectors for
connection, are sent to the SDH where apart from being converted
to electrical signal, the signals required at the particular node
dropped (or extracted) and multiplexed into E1 lines at 2.048 Mbps
which are terminated at DDF (Digital Distribution Frame).
 The DDF basically provides a flexible way of connecting equipment
side to cable side. From the DDF the system working at 2 Mbps rate
is directly provided the connections with required number of E1
lines. The systems working with lower rates than 2 Mbps access the
network through FMX.
 The FMX demultiplexes the E1 lines coming from DDF to the lines
at the lower rates for use of various systems.

ISO 9001:2008

21.  There are two GSS, one for up (in Depot direction) and other for
down (opposite to Depot). There are 48 trays in each GSS. All fibers
coming from and going to adjacent stations are passing through
GSS. Fibers needed at particular station are connected to FPS in
zero dB connector (0.3dB loss) through pigtail cords, connector at
one end only. These fibers are then passed to SDH. And fibers not
needed at particular station are spliced through.
 Splicing is a technique for joining together individual fiber or optical
cable sections to forms continuous lines for these long distant links.
Splicing can be done in two ways:
 Mechanical Splices: This aligns the axis of the two fibers to be joint
and physically hold them together.
 Fusion Splices: This is accomplished by applying localized heating
(i.e. by electric arc or flame) at the interface between two butted,
pre-aligned fiber ends, causing them to soften and fuse together.
In DMRC fusion splicing is used. Splicing loss is around 0.1dB
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22. In DMRC only 2 fibers for each side are used for transmission in
both directions. 24 fibers optical cable is used at elevated stations,
36 fibers optical cable at underground stations and 48 fibers cable
at OCC. These figures are selected on the basis of need of
information to be received or passed.
Equipments used for testing of optical fiber cables are:
 OTDR (Optical Time Domain Reflectometer)
 Optical Power Source Meter
OTDR (Optical Time Domain Reflectometer): It is used to calculate
the distance between one and other end. Also gives account of
attenuation loss (per km loss) and cumulated (or total) loss.
Optical Power Source meter: Used for point to point testing and total
losses also.
In case of any short distance breakage, spull (1km long optical fiber
cable) is used for connection through splicing. Each station is
provided with 4 O-drums to extend the fiber cable in case of any
breakage.
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23. Any Questions?
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24. THANK YOU
ISO 9001:2008