Prepared by Ismail Ali Al-Qaram Zeyad Al-Qabbani Ali Kamel Al-Awami
Overview: An optical fiber is a glass or plastic fiber designed to guide light along its length by total internal reflection lighttotal internal reflectionlighttotal internal reflection Optical fibers are widely used in fiber-optic communication, which permits digital data transmission over longer distances and at higher data rates than electronic communication. fiber-optic communicationfiber-optic communication
Optical fiber was developed in 1970 by Corning Glass Works with attenuation low enough for communication purposes (about 20dB/km) Corning Glass WorksCorning Glass Works 1st generation operated at a wavelength 0.8 µm 1st generation operated at a wavelength 0.8 µmµm History 2nd generation 1.3 µm 2nd generation 1.3 µmµm 3rd generation 1.55 µm 3rd generation 1.55 µmµm 4th generation 1.6 µm 4th generation 1.6 µmµm 5th generation extending the wavelength range over which a WDM system can operate. 5th generation extending the wavelength range over which a WDM system can operate.
Types of optical fiber: I.SINGLE-MODE FIBER - narrow core, diameter (8 microns or less). - Light travels parallel to the axis. - little pulse dispersion. Uses: Telephone & cable television networks
II.STEP-INDEX MULTIMODE FIBER - large core, diameter: 100 microns - travel in direct route, other rays zigzag as they bounce off the cladding - pulse, spread out, losing its well-defined shape Uses: short distances, for example an endoscope
III.GRADED-INDEX MULTIMODE FIBER - core has refractive index that diminishes gradually from the center axis out toward the cladding. - the light rays move down the axis advance more slowly than those near the cladding. - shortened path & higher speed less dispersion. - light in the core curves helically.
BASIC CABLE DESIGN Two basic cable designs: Two basic cable designs: 1- Loose-Tube Cable: Uses: Uses: - used in outside-plan installations. - holds up to 12 fibers per buffer tube. - fibers are loosely packaged in gel filled buffer tubes to repel water. - endure outside temperatures and high moisture. - Typically, distance not to exceed 50 feet. Properties: Properties:
2-Tight-Buffered Cable - often used for intra-building -no gel, connectors terminated directly onto the fiber without difficult to use breakout kits less expensive installation less expensive installation - (Temperature rating -40ºC to +85ºC). - Typically, long distance Uses: Uses: Properties: Properties:
Communication Applications Fiber-optic cable is used by many telecommunications companies to transmit telephone signals, internet communication, and cable television signals, sometimes all on the same optical fiber Fiber-optic cable is used by many telecommunications companies to transmit telephone signals, internet communication, and cable television signals, sometimes all on the same optical fiber optical fiber optical fiber
Communication System Using Optical Fiber Components of the Transmission System: Transmitters Transmitters Amplifiers Amplifiers Receivers Receivers
- The most commonly used optical transmitters are semiconductor devices such as Light emitting diodes (LEDs) and laser diodes. I.Transmitters: - A semiconductor laser emits light through stimulated emission rather than spontaneous emission stimulated emissionstimulated emission high output power (~100 mW) high output power (~100 mW) - efficiency (~50%) - wide spectral width of 30-60 nm LEDs: - efficiency (~1%) - Output power 100 microwatts - wide spectral width of 0.81-0.87 µm µm - High data rates, long distances laser diodes:
II. Amplifiers: - Solution for fiber attenuation and fiber distortion. - amplifies the optical signal directly without having to convert the signal into the electrical domain. - Made by doping a length of fiber with an rare-earth mineral (erbium), and pumping it with light from a laser with a shorter wavelength than the communications signal (typically 980 nm) dopingerbiumpumpinglaserdopingerbiumpumpinglaser - The main component of an optical receiver is a photo detector that converts light into electricity through the photoelectric effect. - The main component of an optical receiver is a photo detector that converts light into electricity through the photoelectric effect.photo detectorphotoelectric effectphoto detectorphotoelectric effect - detectors are also used due to their suitability for circuit integration in regenerators and wavelength-division multiplexers circuit integrationcircuit integration Recivers: III. Recivers:
WDM is dividing the wavelength capacity of an optical fiber into multiple channels. Requirements: - multiplixer in the transmition. - demultiplexer in the receiving. -bandwidth can be divided up to 80 channels - carry information at around 14 Terabits/s over 160 km of fiber. Wavelength-Division Multiplexing (WDM) :
- attenuation is caused by a combination of material absorption, and connection losses. material absorptionmaterial absorption -attenuation in modern fiber is about 1000 db/km. about 1000 db/km. - other causes of attenuation are physical stresses to the fiber, microscopic fluctuations in density, and imperfect splicing techniques. Attenuation
Comparison between electrical transmission and fiber optics Electrical Fiber optics Low bandwidth high bandwidth High loss Low loss Easy installation Difficult installation Low cost High cost Affected by electromagnetic interference Not affected by electromagnetic interference Heavy & big cable size Lighter weight & smaller cable size Low electrical resistance High electrical resistance sparks No sparks