EKT 442: Optoelectronics EKT 442: Optoelectronics School of Computer and Communication School of Computer and Communication Engineering, Engineering, University Malaysia Perlis (UniMAP) University Malaysia Perlis (UniMAP) Optoelectronics Communications CHAPTER 1 CHAPTER 1
42
Embed
EKT 442: Optoelectronics School of Computer and Communication Engineering, University Malaysia Perlis (UniMAP) Optoelectronics Communications CHAPTER.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
EKT 442: Optoelectronics EKT 442: Optoelectronics
School of Computer and Communication School of Computer and Communication Engineering, Engineering,
University Malaysia Perlis (UniMAP)University Malaysia Perlis (UniMAP)
Chapter 2: Light Propagation & Transmission Characteristics of Optical Fiber
Chapter 3: Optical Components/ Passive Devices
Chapter 4: Optical Sources
Chapter 5: Light Detectors, Noise and Detection
Chapter 6: SYSTEM DESIGN
What are the features of a optical communication system?What are the features of a optical communication system?Why “optical ” instead of “copper wire ”?Why “optical ” instead of “copper wire ”?
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
The Twentieth Century
• 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
cladding
core
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
Short
band
Optical Wavelength Bands
C-band: Conventional Band
L-band: Long Band
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
Military Application
Computer Application
Sensors
Gas sensors
Chemical sensors
Mechanical sensors
Fuel sensors
Distance sensors
Pressure sensors
Fluid level sensors
Gyro sensors
Medical Application
• Endoscope
• Eyes surgery
• Blood pressure meter
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
Fiber Optic Fundamentals
Advantages of Fiber Optics
• Immunity from Electromagnetic (EM) Radiation and Lightning
• Lighter Weight• Higher Bandwidth
• Better Signal Quality• Lower Cost• Easily Upgraded• Ease of Installation
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
Optical power Measurement units:
In designing an optical fiber link, it is of interest to establish, measure the signal level at the transmitter, at the receiver,, at the cable connection, and in the cable.
Power: Watt (W), Decibel (dB), and dB Milliwatt (dBm).
dB: The difference (or ratio) between two signal levels. Used to describe the effect of system devices on signal strength. For example, a cable has 6 dB signal loss or an amplifier has 15 dB of gain.
dBPower
Powerlog10Gain
In
Out
dBm: A signal strength or power level. 0 dBm is defined as 1 mW (milliWatt) of power into a terminating load such as an antenna or power meter.
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.
• 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
• Examples– Interfaces between local area networks and devices– Patch panels– Network-to-terminal connections
Manufacture of Optical Fiber
• 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
Introductions
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
Cont…• Widely adopted to produce very low – loss graded – index fibers.• The glass vapor particles, arising from the reaction of the constituent metal halide
gases and oxygen, flow through the inside of a revolving silica tube.• As the SiO2 particles are deposited, they are sintered to a clear glass layer by an
oxyhydrogen torch which travels back and forth along the tube.
• When the desired thickness of glass has been deposited, the vapor flow is shut off and the tube is heated strongly to cause it to collapse into a solid rod preform.
• The fiber that is subsequently drawn from this preform rod will have a core that consists of the vapor deposited material and a cladding that consists of the original 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 perform is consolidated by heating