Fiber Optics: Engineering from Global to Nanometer Dimensions Prof. Craig Armiento Fall 2003 1
Optical Fiber Communications What is it? Transmission of information using light over an optical fiber Why use it? 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 Fall 2003 2
Electromagnetic Spectrum and Communication Services 0.8 1.6 µm Fall 2003 3
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! Fall 2003 4
Basic Optical Link Design Electrical-to-Optical Conversion Optical-to-Electrical Conversion Fall 2003 5
Using Wavelengths to Increase Capacity 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 Fall 2003 6
Information Capacities in Optical Fiber Each wavelength can carry a signal operating at 10 gigabits/sec (10 10 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 Fall 2003 7
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 Fall 2003 8
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 Fall 2003 9
Optical Fiber is Everywhere! Fall 2003 10
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 Fall 2003 11
Managing Global Networks Network Operations Center Fall 2003 12
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 Fall 2003 13
Manufacturing Fiber: Draw Tower Fall 2003 14
Fiber Cables Multi-purpose Cable Submarine Cable Telephone Pole Mounted Cable Fall 2003 15
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 CO 2 and HeNe lasers Fall 2003 16
Diode Lasers are Small! Laser Fall 2003 17
Component Manufacturing for Fiber Optics Semiconductor devices such as ICs and lasers are produced in clean rooms 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 Fall 2003 18
Materials Engineering Thin layers of semiconductor materials are grown on an atomic level using MBE Example of layers grown with a spacing of 1.2 nm (10-9 m) Fall 2003 19
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 Fall 2003 20
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 Fall 2003 21
Optical Switch Fall 2003 22
Optical Switching Route optical communication signals without conversion to the electronic domain using microscopic mirrors based on MEMS technology Fall 2003 23
MEMS: Miniature Motors Fall 2003 24
MEMS Mirror Array for Projectors Digital Light Processing (DLP) Texas Instruments Fall 2003 25
Engineering on a Global to Nano Scale 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 10 6 meters 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 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 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 That s a range of 10 15! Fall 2003 26