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Optical Concepts
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Milestones in Optics
Laser development Fiber optics development First fiber production with attenuation of dB/km
Production of fiber with attenuation of dB/km Mass production of fiber with attenuation of .
dB/km for nm First field trial using fiber optics in Chicago Production of Single Mode fiber
with attenuation of .dB/km for nm Mass production of Single Mode Fiber Development of
optical amplifiers
.
Optical Concepts
and data over substantial distances between customer and network sites . Reliability
Microwave Fiber Optics A communications network is one that conveys / transports
information audio. Optical Concepts .Why Fiber Optics Capacity. video. Twisted Pair Coax
Networks Distance.
Mbps Mbps . Mbps Kbps Network Providers combine the signals from different users and
send them over a single transmission Optical Concepts . .Basic Network Information Rates
Examples of information rates for some typical voice. Mbps . video and data services Video
on demand/interactive TV Video games Remote education Electronic shopping Data transfer
Videoconferencing Voice . Mbps Mbps .
Optical Concepts .The Optical Fiber Very thin strands of pure silica glass through which
laser light travels in optical networks .
Optical Concepts .The Optical Fiber .
. Optical Concepts .
The wavelength nature Of light . Optical Concepts .The Light Theory The Quantum nature
Vs.
The Quantum Nature of Light When a photon insides on an atom. Optical Concepts . exciting
it to a higher energy level Photon E E E Energy levels E. E. it transfers its energy to an
electron within this atom.E .
with exactly the same energy This energy equals h. to be absorbed Conversely. photon
frequency . an electron in an excited state can drop to a lower energy state by emitting a
photon.Photon Absorption and Emission Energy Spontaneous emission E Excited State
Level EE h E Absorption E Ground Level The energy of the photon must be exactly equal to
that required to excite the electron to a higher energy level. Optical Concepts . h Plank
constant.
In spontaneous emission the high energy state lifetime is between nanoseconds to
milliseconds In stimulated emission the emitted photon is identical in wavelength. phase and
direction to the incident photon Optical Concepts .Photons Behavior Spontaneous emission
Stimulated emission Photon Photon E E E E E E .
Optical Amplification Energy Population Inversion E gt E Stimulated emission amplification E
Amplification E E The amount of electrons in stimulated level must be higher than those in
ground level . Optical Concepts .
Optical Concepts .The Wavelength Nature Wavelength is the distance between identical
points in the adjacent cycles of a waveform signal propagated in space or along a wire
Wavelength is specified in nanometers units of meter .
Electromagnetic Spectrum . Optical Concepts .
the shorter its wavelength c / f c .Wavelength Vs Frequency The higher the frequency of the
signal. m/s The standard unit of frequency is Hertz If a wave completes one cycle per
second.. then f Hz THz cycles per second . Optical Concepts .
sometimes called loss A natural consequence of signal transmission over long distances
The extent of attenuation is usually expressed in dB dB a common unit of measurement for
the relative difference between two power levels dB logPout / Pin log Pout .Optical
Parameters Attenuation refers to any reduction in the strength of a signal Attenuation occurs
with any type of signal. log Pin dBm a measure of absolute power dBm log Pmw . Optical
Concepts .
Characteristics of Different Wavelengths in Pure Silica Fiber Beginning of the s Beginning of
the s Today . Optical Concepts .
Optical Concepts .Optical Parameters Dispersion refers to the expansion or widening of the
signal by the time it reaches the receiving end Dispersion is due to the fact that different
wavelengths propagate in different velocities Dispersion does not alter the wavelength
frequency but it directly affects the bit rate Measured as the amount of delay in picoseconds
seconds per km of fiber per nm change in the wavelength .
Optical Concepts Distance along fiber .Dispersion Pulse Shape and Amplitudes Input pulses
Output pattern Intersymbol interference .
Dispersion Types Modal dispersion Material dispersion Waveguide dispersion Polarization
dispersion Chromatic Dispersion Before After t t . Optical Concepts .
Modal Dispersion Depends on the diameter of the core and the critical angle Significant in
Multimode fibers and not in Singlemode fibers l l Input Surface Refraction Jacket t l l t t Core
Pulse entering the fiber Cladding t Pulse exiting the fiber . Optical Concepts .
Optical Concepts .Chromatic Dispersion Material dispersion Effect of the fiber material on
the propagation velocity of the wave Waveguide dispersion relates to the ratio between core
radius and wavelength Input Surface Refraction Jacket Core Cladding .
Chromatic Dispersion Material dispersion and Waveguide dispersion may act in opposite
ways Fiber is engineered in order to give a resultant chromatic dispersion near to zero .
Optical Concepts .
Gps . Optical Concepts .Dispersion Penalty Dispersion Penalty The dispersion of the signal
causes attenuation dB per km for .
Optical Concepts . older fibers etc. external stress. . material properties. the noncircular core
of the fiber may contribute to cause PD Caused by several sources core shape.Polarization
Dispersion This kind of dispersion is significant in higher bitrates. from Gbps Due to
manufacturing imperfections.
G.Wavelength Vs Dispersion G. lt . G. lt . ZeroDispersion Optical Concepts . / G. Fiber
ZeroDispersion NonZeroDispersion ITUT Standard G. . l nm Dispersion ps/nm km
Attenuation dB/ km lt . G. G.
Optical Concepts .Limits How Far dB/km Dispersion .km The How far and How fast are not
only fiberdependent .Limits How Fast ps/nm.Optical Parameters Attenuation .
Light Amplification by Stimulated Emission of Radiation Typical Transmittance Profile of a
Laser Diode Transmittance f f f f The frequencys lasers output is uniform . Optical Concepts
.LASER .