Fiber Optics Technology
Optical Communication Systems Communication systems with light as the carrier and optical fiber as communication medium o Optical fiber is used to contain and guide light waves n Typically made of glass or plastic n Propagation of light in atmosphere is impractical o o o This is similar to cable guiding electromagnetic waves Capacity comparison n Microwave at 10 GHz n Light at 100 Tera Hz (1014 )
History o 1880 Alexander G. Bell n o 1930: TV image through uncoated fiber cables n o o o Photo phone, transmit sound waves over beam of light Few years later image through a single glass fiber 1951: Flexible fiberscope: Medical applications 1956: The term “fiber optics” used for the first time 1958: Paper on Laser & Maser
History Cont’d o o o 1960: Laser invented 1967: New Communications medium: cladded fiber 1960 s: Extremely lossy fiber: n o o More than 1000 d. B /km 1970: Corning Glass Work NY, Fiber with loss of less than 2 d. B/km 70 s & 80 s : High quality sources and detectors Late 80 s : Loss as low as 0. 16 d. B/km 1990: Deployment of SONET systems
Optical Fiber: Advantages o o o Capacity: much wider bandwidth (10 GHz) Crosstalk immunity Immunity to static interference n n n o Lightening Electric motor Florescent light Higher environment immunity n Weather, temperature, etc. http: //www. tpub. com/neets/book 24/index. htm
Optical Fiber: Advantages o Safety: Fiber is non-metalic n o o o No explosion, no chock Longer lasting Security: tapping is difficult Economics: Fewer repeaters n Low transmission loss (d. B/km) n n Fewer repeaters Less cable Remember: Fiber is non-conductive Hence, change of magnetic field has No impact! http: //www. tpub. com/neets/book 24/index. htm
Disadvantages o Higher initial cost in installation o Interfacing cost o Strength n Lower tensile strength o Remote electric power o More expensive to repair/maintain n Tools: Specialized and sophisticated
Light Spectrum o Light frequency is divided into three general bands o Remember: n When dealing with light we use wavelength: o l=c/f o c=300 E 6 m/sec
Optical Fiber Architecture TX, RX, and Fiber Link Input Signal Transmitter Coder or Light Converter Source-to-Fiber Interface Fiber-optic Cable Fiber-to-light Interface Light Detector Receiver Amplifier/Shaper Decoder Output
Optical Fiber Architecture – Components o Light source: n n o Input Signal Amount of light emitted is proportional to the drive current Two common types: o o LED (Light Emitting Diode) o ILD (Injection Laser Diode) Source–to-fiber-coupler (similar to a lens): n A mechanical interface to couple the light emitted by the source into the optical fiber Coder or Converter Light Source-to-Fiber Interface Fiber-optic Cable Fiber-to-light Interface Light Detector Amplifier/Shaper Decoder Output Receiver Light detector: n n n PIN (p-type-intrinsic-n-type) APD (avalanche photo diode) Both convert light energy into current
Optical Fiber Construction o Core – thin glass center of the fiber where light travels. o Cladding – outer optical material surrounding the core o Buffer Coating – plastic coating that protects the fiber.
Fiber Types Core Cladding o Plastic core and cladding o Glass core with plastic cladding PCS (Plastic-Clad Silicon) o Glass core and glass cladding SCS: Silica-clad silica o Under research: non silicate: Zincchloride n 1000 time as efficient as glass
Plastic Fiber o o o Used for short distances Higher attenuation, but easy to install Better withstand stress Less expensive 60% less weight
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