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Short Description of Optical sources and detectors.
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PRESENTATION
TOPIC: FIBER OPTICS CONTEMPORARY STUDENT. NAME: AZIZ ZOAIB ID: FA06-BS-0013 COURSE: TELECOM INFRASTRUCTURE
TOPICS IN PRESENTATION
History Intro about Optical fiber. Advantages and Disadvantages of Optical fiber. Optical fiber link. Types of Fiber. Losses in Optical fiber cables. Light sources and light detectors. Amplification.
HISTORY
Optical communication: Transfer of
information from source to destination in the form of light signals.
1968 NIPPON co. developed graded index fiber with lot of impurities. (about 100 dB/km)
1970 CORNING GLASS WORKS (USA) fabricated single mode fiber with losses less than 20 dB/km
CONTD.
1977 BELL LAB based fiber optic in PCM format at 44.7 mbps for VOICE, VIDEO & DATA.
1978 instead of lab trials field trials were done. 1982 40000 km of optical fiber were in
operationA MERGER OF:• Semiconductor technology.• Optical fiber (medium).
OPTICAL FIBER
The thin glass center of the fiber where the light travels is called the “core”.
The outer optical material surrounding the core that reflects the light back into the core is called the “cladding”.
In order to protect the optical surface from moisture and damage, it is coated with a layer of buffer coating.
OPTICAL FIBER
ADVANTAGES:
Much wider bandwidth of 10 GHz Fiber optic cables weigh less than a copper wire cable Data can be transmitted digitally. Lower-power transmitters can be used instead of the high-
voltage electrical transmitters used for copper wires. Unlike electrical signals in copper wires, light signals from
one fiber do not interfere with those of other fibers in the same cable.
Impossible to tap into a fiber optics cable, making it more secure
OPTICAL FIBER
DISADVANTAGES:
Higher initial cost in installation.
They are more fragile than coaxial cable.
More expensive to repair and maintain.
OPTICAL FIBER LINK
FIBER USED
Glass core with plastic cladding PCS (Plastic-clad silicon)
Glass core and glass cladding SCS (Silica-clad silica)
Under research (non silicate zinc-chloride)
OPTICAL FIBER
Losses in Optical Fiber Cables:
Absorption due impurities in the fiber material Rayleigh scattering due microscopic irregularities in the
Fiber Radiation losses caused by kinks and bends Of fiber Coupling losses due to misalignment and imperfect
surface finish
ABSORPTION LOSSES IN OPTICAL FIBERL
oss
(dB
/km
)
1
00.7 0.8
Wavelength (m)0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7
2
3
4
5
6
Peaks causedby OH- ions
Infraredabsorption
Rayleigh scattering& ultravioletabsorption
LIGHT SOURCES
LED (Light emitting diode): Made from material such as AIGaAs and GaAsP Light is emitted when holes and electrons recombine
ILD (Injection Laser diode): Similar in construction as LED but ends are highly
polished to reflect photons back and fourth
LIGHT EMITTING DIODE
Basic LED operation:
The normally empty conduction band of semiconductors populated by electron injected into it by the forward current through the junction, and the light is generated with electrons recombine with holes. This the
mechanism by which light is emitted from LED.
LIGHT EMITTING DIODE For fiber-optics, the LED should have a high radiance
(light intensity), fast response time and a high quantum efficiency.
LED Structures: Planar LED Dome LED Surface emitter LED Edge emitter LED
LASER
Light Amplification by ‘Stimulated Emission' and
Radiation (L A S E R) Coherent light (stimulated emission) Narrow beam width (very focused beam) High output power (amplification) Narrow line width because only few wavelength will
experience a positive feedback and get amplified (optical filtering)
LASER Absorption: An atom in the ground state might
absorb a photon emitted by another atom, thus making a transition to an excited state.
Spontaneous Emission: Random emission of a photon, which enables the atom to relax to the ground state.
Stimulated Emission: An atom in an excited state might be stimulated to emit a photon by another incident photon.
LIGHT DETECTORS
PIN diode: Photons are absorbed in the intrinsic layer Sufficient energy is added to generate carriers in the depletion
layer for current to flow through the device
LIGHT DETECTORS
APD (Avalanche photo diode): Photo generated electrons are accelerated by relatively large
reverse voltage and collide with other atoms to produce more free electrons
Avalanche multiplication effect makes APD more sensitive but also more noisy than PIN diode.
OPTICAL AMPLIFIERS
With the demand for longer transmission lengths,
optical amplifiers have become an essential
component in long-haul fiber optic systems which
lessen the effects of dispersion and attenuation
allowing improved performance of long-haul optical
systems.
Types of optical amplifiers
Semiconductor optical amplifiers (SOA)
Erbium doped fiber amplifiers (EDFA)
Semiconductor Optical Amplifiers
Semiconductor optical amplifiers (SOA) are essentially laser diodes, without end mirrors, which have fiber attached to both ends. They amplify any optical signal that comes from either fiber and transmit an amplified version of the signal out of the second fiber.
SOA are typically constructed in a small package, and they work for 1310 nm and 1550 nm systems.
The drawbacks to SOA include high-coupling loss, polarization dependence, and a higher noise figure
EDFA
EDFA allow information to be transmitted over longer distances without the need for conventional repeaters. The fiber is doped with erbium, a rare earth element, that has the appropriate energy levels in their atomic structures for amplifying light.
Functioning like a laser without mirrors, the EDFA uses a semiconductor pump laser to introduce a powerful beam at a shorter wavelength into a section of erbium-doped fiber several meters long. The pump light excites the erbium atoms to higher orbits, and the input signal stimulates them to release excess energy as photons in phase and at the same wavelength. EDFAs boost wavelengths in the 1550 nm range, and the pump light is typically 1480 nm or 980 nm.
THANKS
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