Fiber Optics:
Engineering from Global to Nanometer Dimensions
Prof. Craig Armiento
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Intro to E.E.
Fall 2003
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Optical Fiber Communications
What is it?
Transmission of information using light over an optical fiber
Why use it?
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Extremely high data rate and wide bandwidth
Low attenuation (loss of signal strength)
Longer distance without repeaters
Immunity to electrical interference
Small size and weight
Longer life expectancy than copper or coaxial cable
Bandwidth can be increased by adding wavelengths
Intro to E.E.
Fall 2003
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Electromagnetic Spectrum and Communication Services
0.8 – 1.6 µm
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Intro to E.E.
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What is an Optical Fiber?
• Made from silica glass
• Light is contained in an
inner core which is only
9 µm in diameter
• Very low loss of signal
strength (0.3 dB per
kilometer - which is
7%/km)
• Despite being made of
glass, fiber is strong and
bendable!
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Intro to E.E.
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Basic Optical Link Design
Electrical-to-Optical Conversion
Optical-to-Electrical Conversion
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Using Wavelengths to Increase Capacity
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Intro to E.E.
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Engineers can increase the information
capacity between two locations by using
extra wavelengths
All of the wavelengths are added to a
single fiber
This is called Dense Wavelength
Division Multiplexing (DWDM)
Eliminates the need for multiple fibers
Each wavelength is generated by a
different source and carries it’s own
data
The wavelengths don’t interfere with
each other when in the same fiber
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Information Capacities in Optical Fiber
• Each wavelength can carry a signal operating at 10
gigabits/sec (1010 bits/sec)
• A fiber can transport up to 64 different wavelengths
– Each wavelength can carry 10 Gb/s
– Unlike electrical signals, optical signals inside the same fiber at
different wavelengths don’t interfere with each other
• Each fiber can have an aggregate data rate of 640 Gb/s
– This is 640,000,000,000 bits per second!
• This rate translates to:
– 10 million simultaneous telephone calls (64 kb/s each)
– Download the contents of the Library of Congress takes:
• 84 years using a 56 kp/s modem
• 0.22 seconds using the aggregate fiber rate
• These rates can go much higher!
– Researchers have developed operation of 40 Gb/s per wavelength
– A fiber cable can contain as much as a hundred fibers
– Researchers are working towards hundreds of wavelengths
Armiento
Intro to E.E.
Fall 2003
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Cable Size Comparison: Copper vs. Fiber
This is a standard
copper cable used for
telephone service.
This carries about 300
phone calls
One of these fibers can
carry up to 10 million
telephone calls
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Intro to E.E.
Fall 2003
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Fiber Optics Engineering Disciplines
• Network Design
– Optical power levels, routing and switching
• Communications Theory
– Multiplexing multiple data streams
• Optical Physics
– Fiber design, optical component design
• Material Science
– Fiber manufacturing, new materials for sources, detectors
• Semiconductor Physics
– Designing lasers, photodetectors
• Electronics
– High speed IC design for transmitter and receiver
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Intro to E.E.
Fall 2003
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Optical Fiber is Everywhere!
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Optical Network Design
Engineering on a Global Scale
• Designing fiber optic networks that carry
information over thousand of miles
– How to get the photons to travel that far
– How to keep the bits of information intact
– Protocols to use – analog or digital?
• Designing fiber networks for different applications
– Telecommunications and data
– Cable TV
– Local Area networks – e.g., campus network
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Managing Global Networks
Network
Operations
Center
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Attenuation vs. Wavelength
Optical fiber systems
use sources and
detectors that work in
the near infrared
wavelengths because
fiber has the lowest
losses
Fiber has losses as low
as 0.2 dB/km. Coaxial
cable has losses as high
as 60 dB/km
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Intro to E.E.
Fall 2003
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Manufacturing Fiber: Draw Tower
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Fiber Cables
Multi-purpose
Cable
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Submarine
Cable
Fall 2003
Telephone Pole
Mounted Cable
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Optical Sources
• Lasers are used as optical sources
– Sufficient power for long distances
– Pure optical spectrum - single wavelength
– Can be modulated at high data rates (gigabits per
second)
• Designed to emit at infrared wavelengths – from
1.3-1.55 µm where fiber has the lowest loss
• Made from semiconductor materials and are
designed to couple light into the fiber core
• Semiconductor lasers are very different from more
conventional lasers such as CO2 and HeNe lasers
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Diode Lasers are Small!
Laser
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Component Manufacturing for Fiber Optics
Semiconductor devices such as
lasers are often made with very thin
layers (<1 µm) using sophisticated
equipment such as this Molecular
Bean Epitaxy (MBE) system
Semiconductor devices such as
ICs and lasers are produced in
clean rooms
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Materials Engineering
Thin layers of semiconductor
materials are grown on an
atomic level using MBE
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Example of layers grown
with a spacing of 1.2 nm
(10-9 m)
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Packaging a Laser
Laser packaging requires submicron
accuracy to align a micron size
emitting spot to the core of a fiber.
These parts must be soldered in place
and keep their alignment for 20 years
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Microelectromechanical Systems (MEMS)
• There is a new class of components micro-sized
moving components for different applications
• MEMS are fabricated in silicon using processes
used in IC manufacturing
• MEMS are used in many applications
– Air bags, biological analysis, fiber optics, etc
• MEMS have been used to create tiny mirrors that
can be used to switch and deflect light
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Optical Switch
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Optical Switching
Route optical communication signals
without conversion to the electronic
domain using microscopic mirrors
based on MEMS technology
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MEMS: Miniature Motors
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MEMS Mirror Array for Projectors
Digital Light Processing (DLP)
Texas Instruments
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Engineering on a Global to Nano Scale
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Global Optical Networks
– A network engineer designs optical networks that transmit high speed data over
thousands of kilometers across continents and oceans
– The physical scale is 106 meters
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Communication Equipment Design
– An equipment engineer must integrate high speed electronic ICs and optical
components into subsystems that are used in telecom centers
– The physical scale in on the order of a meter
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Fiber and Laser Packaging
– A packaging engineer must design alignment accuracy on a scale of a micron
between the fiber core and laser emission spot
– The physical scale is 10-6 meters
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Optical Component Design
– A component engineer can design quantum well lasers with device dimensions
of 1 nanometer (2 atoms thick!)
– The physical scale is 10-9 meters
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That’s a range of 1015 !
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Intro to E.E.
Fall 2003
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