OPTICAL FIBER COMMUNICATION

Submitted By:Umang BhatiaRoll No: 12450

OUTLINE

• Summer Training at Signal and Telecommunication Department

North Eastern Railways, Izatnagar, Bareilly from 15th June, 2015

to 11th July, 2015.

• An amazing experience as I got to see, how exactly the

communication system works for Indian Railways.

• Main Objective was to learn Optical Fiber Communication In

Railways.2

OPTIC FIBER • An optical fiber is a cylindrical

dielectric waveguide made of low-loss materials such as silica glass.

• It has two main component layers: A Core & A Cladding.

• It has a central core in which the light is guided, embedded in an outer cladding of slightly lower refractive index.

• It works on the principle of total internal reflection

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INSIDE OPTICAL FIBER CABLE

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• Core – thin glass center of the fiber where light travels.• Cladding – outer optical material surrounding the

core• Buffer Coating – plastic coating that protects the fiber.

TYPES OF OPTICAL FIBER

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OPTICAL FIBERS

MULTIMODE FIBERS

STEP INDEX GRADED INDEX OM1/OM2/OM3

SINGLEMODE FIBERS

STEP INDEX

TYPES OF OPTICAL FIBER(conti…) SINGLE MODE FIBER• Used to transmit one signal per

fiber.• Used in telephone and cable TV.• They have small cores(9 microns

in diameter) .• Transmit infra-red light from

laser.

MULTI MODE STEP INDEX FIBER • Used to transmit many signals

per fiber.• Used in computer networks. • They have larger cores(62.5/50

microns in diameter) • Transmit infra-red light from LED.

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MULTI MODE GRADED INDEX FIBER • Core diameter : 50/62.5 microns.• Cladding size: 125-140 microns.• Refractive index changes

continuously.• Low dispersion.• Core refractive index is made to vary

as a function of the radial distance from the center of the fiber

OM1: refer to the commonly used 62.5/125 multimode fiber.OM2: refer to the commonly used 50/125 cable.Both OM1 and OM2 easily supports applications ranging from Ethernet to gigabit Ethernet.OM3: Typically this fiber optic patch cable is with 50/125 multimode fiber, with aqua jacket.They support bandwidth up to 10GB upto 300 meters.

PROPAGATION IN OPTICAL FIBER

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COLOR COATING

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Fiber geometry parameters• The three fiber geometry

parameters that have the greatest impact on splicing performance include the following:• Cladding diameter• Core/clad concentricity

(or core-to- cladding offset)• Fiber curl

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LOSS MECHANISMS

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24 fiber cable used in Indian Railways

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COMPARATIVE STATEMENTADVANTAGES

• Wide bandwidth• Light weight and small size• Immunity to

electromagnetic interference

• Lack of EMI cross talk between channels

• Lack of sparking• Compatibility with solid

state sources• No emission licenses

DISADVANTAGES• High investment cost• Need for more

expensive transmitters and receivers

• Fragility • Opaqueness• Requires special skills

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AREAS WHERE WE CAN USE IT• Medical

Used as light guides, imaging tools and also as lasers for surgeries • Defence/Government

Used as hydrophones for seismic and SONAR uses, as wiring in aircraft, submarines and other vehicles and also for field networking

• Data StorageUsed for data transmission

• TelecommunicationsFiber is laid and used for transmitting and receiving purposes

• NetworkingUsed to connect users and servers in a variety of network settings and help increase the speed and accuracy of data transmission

• Industrial/CommercialUsed for imaging in hard to reach areas, as wiring where EMI is an issue, as sensory devices to make temperature, pressure and other measurements, and as wiring in automobiles and in industrial settings 13

JOINING OF FIBER- SPLICING

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Mechanical splicing Fusion splicingReflection losses(-45 db to -55 db)

No reflection losses

Insertion loss(0.2 db)

Very low insertion loss(0.1 db to .15 db)

cost – high Comparatively less

Possible Alignment Error During Splicing

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OPTICAL COMMUNICATION SYSTEM

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PULSE CODE MODULATION

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TIME DIVISION MULTIPLEXING• Time on the information channel, or fiber, is shared among the many

data sources• The multiplexer MUX can be described as a type of ―rotary switch,

which rotates at a very high speed, individually connecting each input to the communication channel for a fixed period of time

• The process is reversed on the output with a device known as a demultiplexer, or DEMUX

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WAVELENGTH DIVISION MULTIPLEXING

• Data from each TDM channel is loaded on one optical frequency (or wavelength, λ) of a particular wavelength band

• These wavelengths are then multiplexed onto one fiber with the help of WDM multiplexers

• Other side of the network these wavelengths are demultiplexed by using either optical filters, gratings or WDM demultiplexer

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PLESIOCHRONOUS DIGITAL HIERARCHY (PDH)

• In Europe a standard was adopted where thirty-two, 64kbit/s channels were combined to produce a structure with a bit rate of 2.048 Mbit/s (usually referred to as 2 Mbit/s)

• Four, 2 Mbit/s signals were combined together to form an 8 Mbit/s signal (actually 8.448 Mbit/s).

• As the need arose further levels of multiplexing structure were added to include rates of 34 Mbit/s (34.368), 140 Mbit/s (139.264) and 565 Mbit/s (564.992).

• These transmission speeds are called Plesiochronous Digital Hierarchy or PDH rates

• Although each of the systems works fine as a stand-alone hierarchy, it does make international inter-connection very difficult and costly

• This was the major reason for the development of a new internationally agreed standard 20

PDH (conti..)

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DEMISE OF PDH

1. Bit interleaving multiplexing

2. Lack of Flexibility

3. Lack of consensus on standards

4. Limited Network

Management/debugging

5. Defined for selected topologies

6. Mode of Transmission

7. Less bandwidth compared to

SDH22

SYNCHRONOUS DIGITAL HIERARCHY (SDH)

• SYNCHRONOUS :ONE MASTER CLOCK & ALL ELEMENTS SYNCHRONISE WITH IT.

• DIGITAL: INFORMATION IN BINARY.• HIERARCHY: SET OF BIT RATES IN A HIERARCHIAL ORDER

At each hierarchical level, synchronous transport module is formed with information pay-load and overhead bits and a synchronizing mechanism is in-built to ensure all network elements work to a master clock referenceAll the limitations of PDH are removed in SDH • High transmission rates• Simplified add & drop function• High availability and capacity matching• Reliability• Future-proof platform for new services• Interconnection

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Building Block of SDH

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SDH Transport Rates

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Signal Level

STM-1

STM-4

STM-16

STM-64

Rate (Mbps)

155.52

622.08

2488.32

9953.28

Capacity Voices

63 E13 E31 E4

252 E112 E3 4 E4

1008 E148 E316 E4

4032 E1192 E364 E4

189014401920

756057607680

302402304030720

12096092160

122880

ADVANTAGES OF SDH

• SDH permits the mixing of the existing European and North American PDH bit

rates

• All SDH equipment is based on the use of a single master reference clock source &

hence SDH is synchronous

• Compatible with the majority of existing PDH bit rates

• SDH provides for extraction/insertion, of a lower order bit rate from a higher

order aggregate stream, without the need to de-multiplex in stages.

• SDH provides for a standard optical interface thus allowing the inter-working of

different manufacturer’s equipment26

Any Questions or Comments?

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THANK YOU