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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.
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
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
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
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
Applications of Fiber Optics • Military • Computer • Medical/Optometric • Sensor • Communication
Sensors Gas sensors Chemical sensors Mechanical sensors Fuel sensors Distance sensors Pressure sensors Fluid level sensors Gyro sensors
Endoscope Eyes surgery Blood pressure meter Medical Application
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
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
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.
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.
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.
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.
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.
Principles of Fiber Optic Transmission • Electronic signals converted to light • Light refers to more than the visible portion of the electromagnetic (EM) spectrum
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.
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
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
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)
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
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
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)
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
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
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
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
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
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
