A “SEMINAR ON ”

Submitted to:-

Ravi Goyal Sir

Submitted by:-

Ram Niwas Bajya

OPTICAL FIBER

Contents

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Optical fibre

Basic physics of OFC

Merits & Demerits of OFC

Nomenclature of OFC

Absorption & attenuation

Jointing & termination of OFC

Optical sources & Detectors

FBG & Applications

OPTICAL FIBER OFC have Fibres which are long, thin strands made

with pure glass about the diameter of a human hair

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Total internal reflection At some angle, known as the critical angle θc, light traveling from a higher

refractive index medium to a lower refractive index medium will be refracted at 90° i.e. refracted along the interface.

If the light hits the interface at any angle larger than this critical angle, it will not pass through to the second medium at all. Instead, all of it will be reflected back into the first medium, a process known as total internal reflection

Incident angle =

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Optical fiber mode

Fibbers that carry more than one mode at a specific light wavelength are called multimode fibres. Some fibres have very small diameter core that they can carry only one mode which travels as a straight line at the centre of the core. These fibres are single mode fibres.

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Optical fiber's Numerical Aperture(NA)

Multimode optical fiber will only propagate light that enters the fiber within a certain cone,known as the acceptance cone of the fiber. The half-angle of this cone is called the acceptance angle θmax. For step-index multimode fiber, the acceptance angle is determined only by the indices of refraction:Where

n is the refractive index of the medium light is traveling before entering the fibernf is the refractive index of the fiber corenc is the refractive index of the cladding

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Medium / Link Carrier Information Capacity

Copper Cable

(short distance)

1 MHz 1 Mbps

Coaxial Cable (Repeater every 4.5 km)

100 MHz 140 Mbps (BSNL)

UHF Link 2 GHz 8 Mbps (BSNL), 2 Mbps (Rly.)MW Link

(Repeater every 40 km)

7 GHz 140 Mbps (BSNL), 34 Mbps (Rly.)

OFC 1550 nm 2.5 Gbps(STM-16 – Rly.)

10 Gbps (STM-64)

1.28 Tbps (128 Ch. DWDM)

20 Tbps (Possible)RAM NIWAS BAJIYA

Frequency Vs Attenuation In Various Types of Cable

• More information carrying capacity fibbers can handle much higher data rates than copper. More information can be sent in a second

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Limitations of OFC Difficulty in jointing (splicing)

Highly skilled staff would be required for maintenance

Precision and costly instruments are required

Tapping for emergency and gate communication is difficult.

Costly if under- utilised

Special interface equipment’s required for Block working

Accept unipolar codes i.e. return to zero codes only.

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Nomenclature for Optical Interface

X can be I or S or L or V or U & denotes haul I for intra station (up to 2 km)

S for short haul (15 km)

L for long haul (40 km at 1310 nm & 80 km at 1550 nm)

V for very long haul (60 km at 1310 nm & 120 km at 1550

nm)

U for ultra-long haul (160 km at 1550 nm)

Optical Interface specified as X.Y.Z

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• Y can be 1 or 4 or 16 or 64 & denotes STM Level

– 1 for STM-1

– 4 for STM-4

– 16 for STM-16

– 64 for STM-64

• Z can be 1 or 2 or 3 & denotes fibre type – 1 for 1310 nm over NDSF (G.652 fibre)

– 2 for 1550 nm over NDSF (G.652 fibre)

– 3 for 1550 nm over DSF (G.653 fibre)

– 5 for 1550 nm over NZDSF (G.655 fibre)

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Examples of Nomenclature for Optical Interface

I.16.1 – Intra station STM-16 link on 1310 nm fibre

S.16.2 – Short haul STM-16 link on 1550 nm fibre (G.652)

L.16.2 & L.16.3 – Long haul STM-16 link on 1550 nm fibre (G.652 &

G.653)

S.4.1 – Short haul STM-4 link on 1310 nm fibre

L.4.1 – Long haul STM-4 link on 1310 nm fibre (40 km)

S.1.1 – Short haul STM-1 link on 1310 nm fibre

L.1.1 – Long haul STM-1 link on 1310 nm fibre (40 km)RAM NIWAS BAJIYA

Absorption & Attenuation

Scattering of light due to molecular level irregularities in the glass

Light absorption due to presence of residual materials, such as

metals or water ions, within the fiber core and inner cladding.

These water ions that cause the “water peak” region on the

attenuation curve, typically around 1380 nm.

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• Three peaks in attenuation 

a). 1050 nm b). 1250 nm c). 1380 nm 

• Three troughs in attenuation (Performance windows)

a.) 850 nm: 2 dB/km b). 1310 nm: 0.35 dB/km c). 1550 nm: 0.25 dB/km

Absorption loss & Scattering loss

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JOINTING AND TERMINATION OF OFC

There are two methods for jointing Optical fibre cable.

a). splicing b.) connectors

a). splicing1.Fusion Splicing-

• Fusion splicing provides a fast, reliable, low-loss, fibre-to-fibre connection by creating a homogenous joint between the two fibre ends.• The fibres are melted or fused together by heating the fibre ends, typically using an electric arc.• Fusion splices provide a high-quality joint with the lowest loss (in the range of 0.01 dB to 0.10 dB for single-mode fibres) and are practically non-reflective.RAM NIWAS BAJIYA

2. Mechanical Splicing-

• Mechanical splicing is of slightly higher losses (about 0.2 db) and less-reliable performance• System operators use mechanical splicing for emergency restoration because it is fast, inexpensive, and easy.• Mechanical splices are reflective and non-homogenous

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b). Basics about connectors-• Fibre optic connector facilitates re-mateable connection i.e. disconnection / reconnection of fibre• Connectors are used in applications where – Flexibility is required in routing an optical signal from lasers to receivers

– Reconfiguration is necessary– Termination of cables is required

• Connector consists of 4 parts:– Ferrule– Connector body– Cable – Coupling device

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Optical sourcesAn optical source is a major component of optical transmitters. Fiber optic communication systems often use semiconductor optical sources such as Light emitting diodes ( LEDs) and semiconductor lasers.

Some of the advantages are:

Compact in size

High efficiency

Good reliability

Right wavelength range

Small emissive area compatible with fibre core

dimensions

Possibility of direct emulation at relatively high

frequencies

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Optical Detectors

The role of an optical receiver is to convert the optical signal back into electrical signal and recover the data transmitted through the optical fibre communication system. Its vital component is a photo detector that converts light into electricity through the photoelectric effect.

Some the advantages are:

· high sensitivity· fast response· low noise· low cost· high reliability

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FBG and ApplicationsThe Filter that Bragg Grading

Fiber Grating Fiber grating is made by periodically changing the refraction

index in the glass core of the fiber. The refraction changes are made by exposing the fiber to the UV-light with a fixed pattern.

Glass core

Glass cladding Plastic jacket Periodic refraction index change(Gratings)

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Fiber Grating Basics When the grating period is half of the input light wavelength, this

wavelength signal will be reflected coherently to make a large reflection. The Bragg Condition

r = 2neff

in

Reflection spectrum

reflect

Transmission spectrum

trans.

n (refraction index difference)

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Creating Gratings on Fiber One common way to make gratings on fiber is using Phase Mask

for UV-light to expose on the fiber core.

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Characteristics of FBG

It is a reflective type filter Not like to other types of filters, the demanded

wavelength is reflected instead of transmitted It is very stable after annealing

The gratings are permanent on the fiber after proper annealing process

The reflective spectrum is very stable over the time It is transparent to through wavelength signals

The gratings are in fiber and do not degrade the through traffic wavelengths, very low loss

It is an in-fiber component and easily integrates to other optical devices

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Temperature Impact on FBG The fiber gratings is generally sensitive to temperature change

(10pm/°C) mainly due to thermo-optic effect of glass. Athermal packaging technique has to be used to compensate the

temperature drift

1533.8

1534.0

1534.2

1534.4

1534.6

1534.8

1535.0

1535.2

-5 15 35 55 75

Temperature (℃)

Cen

ter W

avel

engt

h (n

m)

Athermal

Normal

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Types of Fiber Gratings

TYPES CHARACTERS APPLICATIONSSimple reflective gratings

Creates gratings on the fiber that meets the Bragg condition

Filter for DWDM, stabilizer, locker

Long period gratings

Significant wider grating periods that couples the light to cladding

Gain flattening filter, dispersion compensation

Chirped fiber Bragg gratings

A sequence of variant period gratings on the fiber that reflects multiple wavelengths

Gain flattening filter, dispersion compensation

Slanted fiber gratings

The gratings are created with an angle to the transmission axis

Gain flattening filter

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Typical FBG Production Procedures

SelectProperfiber

H2loading

Laserwriting Annealing Athermal

packaging Testing

Different FBG requires different specialty fiber

Increase photo sensitivity for easier laser writing

Optical alignment & appropriate laser writing condition

Enhance grating stability

For temperature variation compensation

Spec test

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Current Applications of FBG FBG for DWDM FBG for OADM FBG as EDFA Pump laser stabilizer FBG as Optical amplifier gain flattening filter FBG as Laser diode wavelength lock filter FBG as Tunable filter FBG for Remote monitoring FBG as Sensor ….

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Possible Use of FBG in System

MultiplexerDispersion control EDFA

OADMSwitchEDFADemux

ITU FBG filterDispersion

compensation filterPump stabilizer &

Gain flattening filter

ITU FBG filter

Tunable filter

ITU FBG filterPump stabilizer &

Gain flattening filter

E/O

Wave locker

Monitor

Monitor sensor

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ITU FBG Filter for DWDM

1, 2 … nFBG at 1

1 2

Circulator CirculatorFBG at 2

3

CirculatorFBG at 3

...

1, 2 … nFBG at 1

1 2

Circulator CirculatorFBG at 2

3

CirculatorFBG at 3

...

Multiplexer

De-multiplexerRAM NIWAS BAJIYA

ITU FBG Filter for OADM

Circulator CirculatorFBG

Through signal

Dropped signal Added signal

Outgoing signalIncoming signal

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Dispersion Compensation Filter

Dispersedpulse

circulator

Chirped FBG

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Pump Laser Stabilizer

980spectrum

Focal lens

Fiber 980 Stabilizer

+

-Pump Laser

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Gain Flattening Filter

1 5 0 0 1 5 2 0 1 5 4 0 1 5 6 0 1 5 8 0 1 6 0 0W av e len g th (n m )

-1 5

-1 0

-5

0

5

1 0

1 5

2 0

Gai

n (d

B)

Gain profileGFF profileOutput

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