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Chapter 1 Introduction

Chapter 1 Introduction. Introduction.

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Chapter 1 Introduction

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  1. Chapter 1 Introduction

  2. Introduction For years fiber optics has been merely a system for piping light around corners and into in accessible places so as to allow the hidden to be seen. But now, fiber optics has evolved into a system of significantly greater importance and use. Throughout the world it is now being used to transmit voice, video, and data signals by light waves over flexible hair-thin threads of glass or plastics. Its advantages in such use, as compared to conventional coaxial cable or twisted wire pairs, are fantastic. As a result, light-wave communication systems of fiber optics communication system are one of the important feature for today’s communication.

  3. A History of Fiber Optic Technology The Nineteenth Century • John Tyndall, 1870 • water and light experiment • demonstrated light used internal reflection to follow a specific path • William Wheeling, 1880 • “piping light” patent • never took off • Alexander Graham Bell, 1880 • optical voice transmission system • called a photophone • free light space carried voice 200 meters • Fiber-scope, 1950’s Light

  4. The Twentieth Century core cladding • Glass coated fibers developed to reduce optical loss • Inner fiber - core • Glass coating - cladding • Development of laser technology was important to fiber optics • Large amounts of light in a tiny spot needed • 1960, ruby and helium-neon laser developed • 1962, semiconductor laser introduced - most popular type of laser in fiber optics

  5. The Twentieth Century (continued) • 1966, Charles Kao and Charles Hockman proposed optical fiber could be used to transmit laser light if attenuation could be kept under 20dB/km (optical fiber loss at the time was over 1,000dB/km) • 1970, Researchers at Corning developed a glass fiber with less than a 20dB/km loss • Attenuation depends on the wavelength of light

  6. Fiber Optics Applications • Military • 1970’s, Fiber optic telephone link installed aboard the U.S.S. Little Rock • 1976, Air Force developed Airborne Light Fiber Technology (ALOF) • Commercial • 1977, AT&T and GTE installed the first fiber optic telephone system • Fiber optic telephone networks are common today • Research continues to increase the capabilities of fiber optic transmission

  7. Applications of Fiber Optics • Military • Computer • Medical/Optometric • Sensor • Communication

  8. Military Application

  9. Military Application

  10. Computer Application

  11. Sensors Gas sensors Chemical sensors Mechanical sensors Fuel sensors Distance sensors Pressure sensors Fluid level sensors Gyro sensors

  12. Endoscope Eyes surgery Blood pressure meter Medical Application

  13. The Future • Fiber Optics have immense potential bandwidth (over 1 teraHertz, 1012 Hz) • Fiber optics is predicted to bring broadband services to the home • interactive video • interactive banking and shopping • distance learning • security and surveillance • high-speed data communication • digitized video

  14. Fiber Optic Fundamentals

  15. Immunity from Electromagnetic (EM) Radiation and Lightning Lighter Weight Higher Bandwidth Better Signal Quality Lower Cost Easily Upgraded Ease of Installation Advantages of Fiber Optics The main advantages: Large BW and Low loss

  16. Immunity from EM radiation and Lightning: - Fiber is made from dielectric (non-conducting) materials, It is un affected by EM radiation. - Immunity from EM radiation and lightning most important to the military and in aircraft design. - The fiber can often be run in same conduits that currently carry power, simplifying installation.

  17. Lighter Weight: • Copper cables can often be replaced by fiber optic cables that weight at least ten times less. - For long distances, fiber optic has a significant weight advantage over copper cable.

  18. Higher Bandwidth • Fiber has higher bandwidth than any alternative available. • CATV industry in the past required amplifiers every thousand feet, when copper cable was used (due to limited bandwidth of the copper cable). • A modern fiber optic system can carry the signals up 100km without repeater or without amplification.

  19. Better Signal Quality - Because fiber is immune to EM interference, has lower loss per unit distance, and wider bandwidth, signal quality is usually substantially better compared to copper.

  20. Lower Cost • Fiber certainly costs less for long distance applications. • The cost of fiber itself is cheaper per unit distance than copper if bandwidth and transmission distance requirements are high.

  21. Principles of Fiber Optic Transmission • Electronic signals converted to light • Light refers to more than the visible portion of the electromagnetic (EM) spectrum

  22. The Electromagnetic Spectrum • Light is organized into what is known as the electromagnetic spectrum. • The electromagnetic spectrum is composed of visible and near-infrared light like that transmitted by fiber and all other wavelengths used to transmit signals such as AM and FM and television.

  23. Principles of Fiber Optic Transmission • Wavelength - the distance a single cycle of an EM wave covers • For fiber optics applications, two categories of wavelength are used • visible (400 to 700 nanometers) - limited use • near-infrared (700 to 2000 nanometers) - used almost always in modern fiber optic systems

  24. Fiber optic links contain three basic elements • transmitter • optical fiber • receiver Optical Fiber Transmitter Receiver User Input(s) User Output(s) Electrical-to-Optical Conversion Optical-to-Electrical Conversion

  25. Transmitter (TX) • Electrical interface encodes user’s information through AM, FM or Digital Modulation • Encoded information transformed into light by means of a light-emitting diode (LED) or laser diode (LD) Optical Output Electrical Interface Data Encoder/ Modulator Light Emitter User Input(s)

  26. Receiver (RX) • decodes the light signal back into an electrical signal • types of light detectors typically used • PIN photodiode • Avalanche photodiode • made from silicon (Si), indium gallium arsenide (InGaAs) or germanium (Ge) • the data decoder/demodulator converts the signals into the correct format User Output(s) Light Detector/ Amplifier Data Decoder/ Demodulator Electrical Interface Optical Input

  27. Transmission comparison • metallic: limited information and distance • free-space: • large bandwidth • long distance • not private • costly to obtain useable spectrum • optical fiber: offers best of both

  28. Fiber Optic Components

  29. 2.3.1 Fiber Optics Cable • Extremly thin strands of ultra-pure glass • Three main regions • center: core (9 to 100 microns) • middle: cladding (125 or 140 microns) • outside: coating or buffer (250, 500 and 900 microns)

  30. A FIBER STRUCTURE

  31. Light Emitters • Two types • Light-emitting diodes (LED’s) • Surface-emitting (SLED): difficult to focus, low cost • Edge-emitting (ELED): easier to focus, faster • Laser Diodes (LD’s) • narrow beam • fastest

  32. Detectors • Two types • Avalanche photodiode • internal gain • more expensive • extensive support electronics required • PIN photodiode • very economical • does not require additional support circuitry • used more often

  33. Interconnection Devices • Connectors, splices, couplers, splitters, switches, wavelength division multiplexers (WDM’s) • Examples • Interfaces between local area networks and devices • Patch panels • Network-to-terminal connections

  34. Manufacture of Optical Fiber

  35. Introductions • 1970, Corning developed new process called inside vapor deposition (IVD) to first achieve attenuation less than 20dB/km • Later, Corning developed outside vapor deposition (OVD) which increased the purity of fiber • Optical fiber was developed that exhibits losses as low as 0.2dB/km (at 1550nm). This seemed to be adequate for any application. • As the Internet expanded, more capacity was needed. Electronics can handle about 40Gbps, but not much more. Researchers developed Dense Wavelength-Division Multiplexing (DWDM) - 80 or more simultaneous data streams can now be combined on a single fiber, each being transmitted at a slightly different color of light

  36. Manufacture of Optical Fiber - MCVD • Modified Chemical Vapor Deposition (MCVD) • another term for IVD method • vaporized raw materials are deposited into a pre-made silica tube

  37. Manufacture of Optical Fiber - OVD • Outside Vapor Deposition (OVD) • vaporized raw materials are deposited on a rotating rod • the rod is removed and the resulting preform is consolidated by heating

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