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Gujarat Technological University

Birla Vishvakarma MahavidyalayaEngg. College

Subject :- Optical Fiber Communication

(2161006)

Prepared by:-Kashyap Mandaliya

(140083112008)

Guided by:-Prof. Rajvirsinh Rana

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MEASUREMENT OF DISPERSION,

NA AND EYE DIAGRAM

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WHAT IS ABOUT ?➤ Optical power measurement is the most basic function

in fiber optics metrology.➤ Parameters such as time, distance, wavelength, phase

and polarization vary ( not fixed quantity ).

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TYPES :-➤ Dispersion➤ NA➤ Eye diagram

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DISPERSION➤ Pulse broadening of light wave signals .➤ Intermodal dispersion :- In multimode fibers,

Intermodal dispersion arises from that each mode in optical pulse travels a slightly different distance and thus arrives at fiber end at slightly offset times.

➤ Chromatic dispersion :- In chromatic dispersion ( probably in singlemode ) stems from the variation in propagation speed of individual wavelength components of optical signal.

➤ Polarization mode dispersion :- It arises from splitting of polarized signal into orthogonal polarization mode, each has different propagation speed.

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TIME DOMAIN ANALYSIS OF INTERMODAL DISPERSION

Laser diode is used to inject narrow pulse of optical energy.Output pulse of laser diode is coupled through mode scrambler into test

fiber.Output of fiber is measured by optical sampling oscilloscope ( uilt in

optical receiver, photo diode)Variable delay line is used to offset the difference in delay.

Fig 1

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MATHEMATICAL FORMULAE➤ RMS pulse width is given by :-

Where center t bar is determined by :-

CHROMATIC DISPERSION :-The chromatic dispersion of an optical medium is the phenomenon that the phase velocity and group velocity of light propagating in a transparent medium depend on the optical frequency.

Electric signal generator modulates the output of TNOS by intensity modulator.A vevtor voltmeter is used to measure the phase of the modulation related to

electrical modulation source and this Phase measurements is repeated at wavelength intervals by ∆.lambda across spectral band.

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Fig 2

POLARIZATION DISPERSION :-

A polarizer or polariser is an optical filter that passes light of a specific polarization and blocks waves of other polarizations. It can convert a beam of light of undefined or mixed polarization into a beam with well-defined p -olarization, polarized light.

An Optical Spectrum Analyzer (or OSA) is a precision instrument designed to measure and display the distribution of power of an optical source over a specified wavelength span.

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Polarization mode dispersion (PMD) is a form of modal dispersion where two different poloarization of light in a waveguide, which normally travel at the same speed, travel at different speeds due to random imperfections and

asymmetries, causing random spreading of optical pulses. Unless it is compensated, which is difficult, this ultimately limits the rate at which data

can be transmitted over a fiber.

Fig 3

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In the three types of dispersion in optical fiber, components of the signal are delayed differentially, broadening the pulse.

Fig 4

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EYE DIAGRAM TEST :-

An eye diagram is a common indicator of the quality of signals in high-speed digital transmissions. An oscilloscope generates an eye diagram by overlaying sweeps of different segments of a long data stream driven by a master clock. , so called because the resulting image looks like the opening of an eye.

Fig 5

Diagrams illustrate how an eye diagram is formed.

The bit sequences 011, 001, 100, and 110 are superimposed over one another to obtain the final eye diagram.

Fig 6

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NUMERICAL APERTURENumerical aperture refers to the maximum angle at which light incident on the fiber end is very internally reflected and is transmitted properly along the fiber.

NA decides - Normalized frequency of fiber and no of modes propagating through the fiber.

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THANKYOU

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