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.

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