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7/29/2019 Tatest Trendsin Fiber Media

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OFC Faculty OF Characteristics 3/12/2013

By

OFC FACULTYALTTC GHAZIABAD

Overview of TransmissionNetwork (ITU standards forOptical Networking Fibers)


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3/12/2013OFC Faculty OF Characteristics

OPTICAL FIBER FOR OPTICALNETWORKING

Deployment of optical fiber in telecommunicationincludes:-

1. Inter office trunking.

2.Terrestrial long haul systems.

3. Loop feeders.

4. Submarine long haul systems.

Requirement of optical networking :-

1.Fiber must be capable of carrying multiple wavelengths over longdistances.

2. Higher bit rates


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3/12/2013OFC Faculty OF Characteristics 3

OPTICAL FIBER PROPERTIES

1. Attenuation :- The components of attenuationdepends on:

A. Rayleighs scattering .

B. Absorption peaks due to hydroxyl ions.

C. Bending induced losses.

D. Silica absorbs light at wavelengths above1.6 m.


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Maximum Span Distance in Kms .

FIBER ATTENUATION

Optical

SignalPowerBudget

Receiver Sensitivity

OpticalSignal

power 0

-10

-20

-28-30

-40

LOSSin

dbm

0 10 20 30 40 50 60 70


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(a) 1st generation of system used multi mode fiber operating at 850 nm.wavelength window.

(b) 2nd generation of optical system used single modefiber operating at 1310 nm. wave length window.

Loss is less than 0.50 db/km

(c) 3rd generation of optical system used single modefiber operating at 1550 nm. wave length window

Loss is less than 0.20 db/km.

APPLICATION OF DIFFERENTWINDOWS IN FIBER


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(d) Todays optical network uses DWDM in 3rd window(the C- band near 1550 nm. )

(e) Future commercial systems are expected to operate in4th window (L-band near 1600 nm. )

CONTINUED ..


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- 190 THz

- OH -

OH-

Cut - off wave lengthfor single - modefibre

- 50 THz

Wavelength ( m.)0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7

0

1

2

3

4

5

First WindowSecond WindowThird Window

Fourth Window

WINDOW CONCEPT IN SPECTRUMOF OPTICAL FIBER


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Dispersion is the effect of widening of pulse width,when the optical pulse is transmitted over long distancein the optical fiber. .

Dispersion determines the maximum1. Available bandwidth

2. Data rate possible in fiber system.

DISPERSION


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DISPERSION

Max. Dis.

Fixed BER

BER

Distance in Km

Disp

er sion


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Time

1 0 1 1

1 1 1

DISPERSION


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TYPES OF DISPERSION

1. Multi-path or Multimode Dispersion2. Material or Chromatic Dispersion3. Wave guide Dispersion or F.S.D.

The 1st two types of dispersion are applicable for MM fiber. While 2nd and 3rd type of dispersion areapplicable for SM fiber.

Chromatic dispersion and wave guide dispersiondepends on the R.I. of the fiber material.


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TOTAL DISPERSION

To minimize the total dispersion it is desirable tooperate at wavelength greater than 1300 nm. Itallows the small positive chromatic dispersion to getcancelled by the small negative wave guide

dispersion. As a result net dispersion becomes zero.However current systems are operating at 1550 nm.Because of:

1. Low attenuation

2.Compatibility with EDFA3.Compatibility with DWDM


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1.20 1.22 1.24 1.26 1.28 1.30 1.32 1.34 1.36 1.38 1.40

Wavelength ( m. )

Material dispersionZero dispersion

Waveguide dispersion

Total dispersion

TOTAL DISPERSION


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ITU RECOGNIZES 4 TYPES OF S.M .FIBERS

1. Dispersion un-shifted fiber (ITU. G-652)

Its chromatic dispersion is minimum at 1310 nm.Its chromatic dispersion at 1550 nm. is high (17-20ps/ nm/km)This is a conventional fiber

Hence dispersion compensation is required at bitrates of above 2.5 Gb/s on long haul systems.


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Ps/nm/-km

260 1280 1300 1340 1340 1360 nm

a) 1330nm region

DISPERSION UN-SHIFTEDFIBER


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When a NRZ signal is generated with an externallymodulated un chirped laser source and transmitted at BGb/s incur a 1-db power penalty.

Then dispersion becomes 104,000/B 2 where B denote thebandwidth in Gb/s .

DISPERSION UN-SHIFTEDFIBER


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At 1550 nm window the dispersion is 17-20 ps/nm-km ondispersion un shifted fiber. So maximum distance is.

Transmission Estimated Maximum

Data Rate Dispersion Distance(Gb/s) (ps/nm) (km)2.5 16,640 98010 1,040 6040 65 4

Dispersion Compensation Management

DISPERSION UN-SHIFTED

FIBER


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DISPERSION SHIFTED FIBER(ITU-RECOMM G-653 )

This fiber shifts the minimum chromatic dispersionwavelength from 1310 TO 1550 nm. It wasconsidered ideal fiber due to its

1. Low dispersion2. Low attenuation3. Compatible with EDFA

It has certain disadvantages due to nonlinear effects.


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DESIGN FEATURES

The level of the dispersion depends on

1. Doping levels of impurities2. The values of Refractive Index Difference ( )3. Core radius (r)

By using various combination between doping level,

doping profiles, and core radius, it is possible toachieve zero dispersion at other wavelengthbetween 1300 nm. to 1600 nm..


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This fiber can operate at minimum attenuationand minimum dispersion.

This fiber is called DSF

Its primary application is for submarinesystems.

DESIGN FEATURES


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1550-nm.LOSS-MINIMIZED FIBER(ITU G - 654)

It has very low loss (0.15db/km) at 1550 nm.wavelength.Low loss is achieved by using pure silica glass in thefiber core and doped silica as fiber cladding.Also maintaining a high cut-off wavelength to reducethe fiber's sensitivity to bending based losses.It is expensive.

Its main application is in repeater less submarine systems.

NONZERODISPERSION


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NONZERODISPERSIONSHIFTEDFIBRE

(ITU G - 655)

This fiber specially designed for use in the latestgeneration of amplified DWDM systems.

Its dispersion can effectively handle the problem of four-wave mixing due to fiber nonlinear effect.

This fiber ensures that individual channel rates of 10Gb/s is maintained upto distance of more than 250km without dispersion compensation.


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POLARIZATION OF LIGHT

Normally Light is unplolarized. Its electric (E) and its magnetic (H) fields have the same strength in all directionsperpendicular to the direction of propagation.

But when light propagates through a medium, it entersthe fields of atoms and ions and field interaction takes place.

This interaction effects the electric dipole moment per unit

volume and the strength of electric/magnetic field of lightin certain directions get changed.


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POLARIZATION OF LIGHT

As a result it may produce an elliptical field distributionand offers birefringence changes properties.

The Optical signal gets separated in two orthogonalpolarized signals. These two polarized signals (Verticalpolarized & Horizontal polarized) travels at differentspeed.

When these two signals (Vertical polarized & Horizontalpolarized) recombined due to variation in time of arrival,a pulse spreading occurs. This phenomenon is known asPolarization Mode Dispersion (PMD).


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PMD value should be less than 140/b, where b isbit rate in Gb/s.

POLARIZATION MODE DISPERSION

Q O


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FIBER REQUIREMENT FOROPTICAL NETWORKING

DWDM System is used for submarine and long - haulterrestrial systems. Due to long distance and highpowered system, the effect of non linearity is needed tobe considered.

Fiber Nonlinear Effects:-This happens in two categories .

1. Stimulated scattering.2. Refractive index fluctuations.

The power level at which these effects appear arecalled thresholds.


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STIMULATED SCATTERING

Some of the forward scattering light is redirected into thebackward propagation light, this reduces the power delivered tothe receiver.

This effect is called Stimulated Brillouin Scattering (SBS). It

has lowest threshold of all nonlinear effect and depend on :

a . Line width of the sourceb . The fiber characteristics.

Typically, (SBS) value is in miliwatts and is independentof the number of channels in DWDM systems

STIMULATED RAMAN


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Light and fiber molecular vibrations can interact toproduce stimulated Raman Scattering (SRS).

The SRS threshold depends ona) Fiber Characteristics.

b) The number of channels loaded.c) The channel spacing.d) The average power per channel.e) The non regenerated system length.

Its typical value is 1 watt. And has very highthreshold. Sophisticated techniques are required totake care of non linearity due to SRS effect.

STIMULATED RAMANSCATTERING (SRS)


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The RI of silica fiber is remarkably constant at lowoptical power levels.But high power from optical amplifiers can modulatethe R.I. Of silica fiber with varying optical intensity of

the transmitted signal. As a result it introduces three types non linearity's.

1. Self Phase Modulation : SPM describes the effect

of a pulse on its own phase.

REFRACTIVE INDEXFLUCTUATIONS


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2. Cross-Phase Modulation (XPM):-XPM describes the effect of a pulse on the phases of pulse in other channels. XPM occurs in multiplechannel systems.


3. Four Wave Mixing (FWM) :-

FWM is the combination of two or more than twowavelength to produce one or more new wavelengths .


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In DWDM systems channels are equally spaced inoptical frequency. Due to their mixing, by productscan fall directly on other channels.



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OTHER PROPRIETY FIBER

All Wave Fiber For Metropolitan Application:

Characteristics of Metropolitan Areas are:Typically metropolitan radius are about 80 km.

Optical amplifiers are not required.Chromatic dispersion is not problem.

1. Some Bell Labs ( Lucent Technology)developed fibers.


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This fiber supports large end users whichrequires frequent bandwidth grooming

management. This can be done by loading100s of wavelengths and also to route, addand drop them.

It can take care of upto125 new wavelength(at 100 Ghz spacing)

OTHER PROPRIETARYFIBER


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2. True Wave RS Fibre For Long Haul TerrestrialApplications :-

Typical distance is between 100 and 1000 km with littleneed to drop and insert traffic.

About 40 wavelength can operate with highest channelpossible bit rate i.e. 10Gb/s.

EDFAs make possible communication in fourth window at1600 nm. Hence, fiber dispersion must be relativelyconstant over broad wavelength region.



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3. True Wave XL Fiber For SubmarineApplications:- Typical span of distance is multiple of 1000s of kilometer

with little or no need to drop or add traffic along the way.

Modal Instability (MI) may appear in the form of spikes. In submarine system, where non regenerative distance is

about 10000 km, the effect of MI may become asignificant problem.

The negative dispersion of true wave XL fiber can over come this potential problem.



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Dispersion management can be used to takecare of dispersion-limited distance.

1. In submarine systems, fiber having negative dispersionare joined with fiber having positive dispersion.

2. In terrestrial systems, dispersion compensating modules(DCM) are inserted at appropriate intervals, thesemodules are made up of several kilometers of dispersioncompensating fiber.

DISPERSION MANAGEMENT


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3/12/2013OFC F l OF Ch i i

for kind suggestion and advice.

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