Transcript Lecture notes 1 - People @ TAMU Physics

Phys649: Physics of
Optoelectronic Devices
Alexey Belyanin
Room 426 MIST
Office: 845-7785
Cell: 324-3071
Email: [email protected]
Office hours: any time when I am in the office
Textbook:
E. Rosencher, B. Vinter, Optoelectronics, 2002
• Concise presentation of main sub-disciplines
• Emphasis on the key unifying concepts
• Utilitarian approach: useful technique as opposed to
hard-nosed theory
• We won’t cover all chapters (e.g. quantum
mechanics) but you can use them as a reference
Policy
• Attendance is required (20% of the
grade)
– Questions, discussion are encouraged;
– I may adjust the contents of the course as we
go
• Homework assignments every week
(50%)
• Short presentations in the end of the
semester on a topic of your choice
(30%)
Optoelectronics:
•
•
•
•
Studies electronic devices that interact with light
Interact = emit, absorb (detect), modulate, switch
Light = any EM radiation
“Electronic” usually means “made of semiconductors”.
Emerging technologies: plasmonics, graphene, carbon
nanotubes, molecular devices, …
Interplay between quantum electronics, nonlinear
optics, physics of semiconductors, and transport
phenomena
It is important not to get lost and to see coherence
and connections between different subjects
Main devices:
- semiconductor lasers and detectors,
- nonlinear optical systems
- novel devices (carbon-based, plasmonic)
Plan of study for each kind of devices:
• Basic principles and device physics
• Examples of state of the art devices
• Challenges and outlook for the future
Integrated photonics, nanodevices, quantum optical
systems (cryptography, communications, …)
Always with applications in mind, but emphasis on
physics perspective
Physics laid down foundation for the Information Age
• Stone Age
• Bronze Age
• Iron Age
• Ice Age
What is Information Age?
Information Age
The cost of the transmission, storage and processing
of data has been decreasing extremely fast
Information is available anytime, any place, and for
everyone
Information and knowledge became a capital asset
All of this became possible because of several
revolutionary ideas
Transistor
Laser and semiconductor laser
Computer
World-Wide Web
Optical fibers
Integrated circuits
… Are invented by physicists
History of the WWW
History of the WWW
• First proposal: Tim Berners-Lee (CERN)
in 1989
• 1991: First WWW system released by CERN
to physics community; first Web server in the US (SLAC)
• 1993: University of Illinois releases user-friendly
Mozaic server
• Currently: WWW is one of the most popular Internet
applications; >100 million users in the US alone
Invention of Computer
• The first digital electronic computer was invented by
Theoretical Physics Prof. John Vincent Atanasoff
in 1937. It was built by Atanasoff and his graduate
student Clifford Berry at Iowa State College
in 1939 ($650 research grant).
Basement of the Physics Dept. building
where the Atanasoff-Berry Computer
(ABC) was built.
ABC
•Used base-two numbers (the binary system) - all
other experimental systems at the time used base-ten
•Used electricity and electronics as it's principal media
•Used condensers for memory and used a regenerative
process to avoid lapses that could occur from
leakage of power
•Computed by direct logical action rather than by the
enumeration methods used in analog calculators
Implemented principles of modern computers
Only material base has been changed.
ABC Replica
Berry with the ABC
Card punch and reader
The drum – the only surviving fragment of ABC. It
holds 30 numbers of 50 bits each. They are
operated on in parallel. It is the first use of the idea
we now call "DRAM" -- use of capacitors to store
0s and 1s, refreshing their state periodically.
From ABC to ENIAC
• 1940s: J. Mauchly and J. Eckert build ENIAC
(Electronic Numerical Integrator And Computer). All
basic concepts and principles of ENIAC are
“borrowed” from Atanasoff’s papers.
• 1972: U.S. Court voids the Honeywell’s patent on the
computing principles and ENIAC, saying that it had
been “derived” from Atanasoff’s invention.
• 1990: Atanasoff receives the U.S. National Medal of
Technology. He dies in 1995 at the age of 91.
From ENIAC to …
Computers in the future may
weigh no more than 1.5 tons.
(Popular Mechanics, 1949)
1940's - IBM Chairman Thomas
Watson predicts that "there is a world
market for maybe five computers".
1950's - There are 10 computers in the
U.S. in 1951. The first commercial
magnetic hard-disk drive and the first
microchip are introduced. Transistors
are first used in radios.
ENIAC (1946) weighed 30 tons,
occupied 1800 square feet and
had 19,000 vacuum tubes.
It could make 5000 additions per
second
1960's-70's - K. Olson, president,
chairman and founder of DEC,
maintains that "there is no reason why
anyone would want a computer in their
home." The first microprocessor,
'floppy' disks, and personal computers
are all introduced. Integrated circuits are
used in watches.
Impact of semiconductor electronics
Before diodes and transistors: vacuum tubes
1954-1963: SAGE Air Defense Project
• 23 32-bit computers
• Each contains 55,000 vacuum tubes, weighs
250 tons, and consumes 3 Megawatt
• Tracks 300 flights
• Total cost: $60 billion (double the price of
Manhattan Project!)
• Performance equivalent to $8 calculator
built on transistors!
Smaller, Denser, Cheaper
Moore’s Law (1965): every 1.5 years
the number of transistors on a chip is
doubled
Transistor of single-atom size by 2020?
• Limit on the transistor size
• Limit on the manufacturing
technology
Pushing Fundamental Limits:
Challenges and Bottlenecks
 Semiconductors: how small the device can be?
 Memory and data storage: limits on writing density?
 Communications: limits on data rate?
Telecommunications
Shannon-Nyquist Theorem
In a communication channel with bandwidth B,
the data rate (number of bits per second) can
never exceed 2B
Number of channels = Total bandwidth of the medium/B
How it all started …
Samuel Morse's telegraph key, 1844.
Today's information age began with
the telegraph. It was the first
instrument to transform information
into electrical signal and transmit it
reliably over long distances.
Alexander Graham Bell’s
commercial telephone from 1877.
In 1880 patented a “Photophone” (air-based optical telephone)
Alexander Bell, Helen Keller, and Anne Sullivan, 1894
Speaking into the handset's transmitter or microphone makes its
diaphragm vibrate. This varies the electric current, causing the
receiver's diaphragm to vibrate. This duplicates the original sound.
• Telephone connection requires a dedicated wire line;
• Only one communication is possible at a time
Radio: communication through radio waves
1895
www.nrao.edu
Frequency measured in Hertz
1 Hz = 1 cycle/second
1 kHz = 1000 cycles/second
Guglielmo Marconi
How many channels are possible?
How many signals can be transmitted at the same time??
Alexander Popov
Radio stations have to broadcast at different
carrier frequencies to avoid cross-talk
Human ear: 10 Hz-20 kHz
Range of frequencies (Bandwidth) needs to be at least
20 kHz for each station
Frequencies of different stations should be at least 20 kHz apart
About 100 bands
from 0 to 2000 kHz
Even if you transmit only voice, from 0 to 2000 kHz you can
squeeze only 2000 kHz/20 kHz = 100 different “talks”.
What if you want to download data?
Digital transmission: any signal, but
transmission speed is still limited by bandwidth!
Binary code is transmitted: “0s” and “1s” – bits of information
Mega = million, Giga = billion; 1GHz = 1000 MHz = 109 Hz
Want download speed of 2 Mb/sec? Need bandwidth at least 1 MHz
Want 100 Mb/sec? need 50 MHz bandwidth just for yourself
Modern cell phones and GPS use gigahertz (GHz) frequencies
But this is only 1000 MHz/50 MHz = 20 channels at 100 Mb/sec!
Faster, faster, faster
Higher carrier frequencies
Wider bandwidth
Higher data rate
Using optical frequencies?! 100 THz !
What kind of medium can carry
optical frequencies?
Air? Only within line of sight;
High absorption and scattering
Optical waveguides are necessary!
Copper coaxial cable? High absorption,
narrow bandwidth 300 MHz
Glass? Window glass absorbs 90% of light after 1 m.
Only 1% transmission after 2 meters.
Extra-purity silica glass?!
Loss per km, dB
Loss in silica glasses
What is dB?
Increase by 3 dB
corresponds to
doubling of power
Maximum tolerable loss
Wavelength, nm
Transmisson 95.5% of power after 1 km
P = P(0) (0.995)N after N km
P = 0.01 P(0) after 100 km: need amplifiers and repeaters
Total bandwidth ~ 100 THz!!
How to confine light with
transparent material??
n > n’
Total internal reflection!
Dielectric waveguides
n > n’
Optical fiber!
1970: Corning Corp. and Bell Labs
Optical fibers
Made by drawing molten glass from
a crucible
1965: Kao and Hockham proposed
fibers for broadband communication
1970s: commercial methods of
producing low-loss fibers by
Corning and AT&T.
1990: single-mode fiber,
capacity 622 Mbit/s
Now: capacity ~ 1Tbit/s, data rate
10 Gbit/s
Fibers open the flood gate
Bandwidth 100 THz would allow
100 million channels with
2Mbits/sec download speed!
Each person in the U.S. could
have his own carrier frequency,
e.g., 185,674,991,235,657 Hz.
However, we are using less than 1% of available bandwidth!
And maximum transmission speed is less than 0.00001 of bandwidth
Limitations of fiber communications
In optical communications, information is transmitted as light
signal along optical fibers
However, if we want to modify, add/drop, split, or amplify signal, it
needs to be first converted to electric current, and then converted
back to photons
This is a slow process (maximum 10 GHz)
All-optical switches
Micro-Electro-Mechanical Systems (MEMS)
256 micro-mirrors (Lucent 2000)
THE DREAM: could we replace electrons with photons,
and electric circuits with all-optical circuits?
IBM website
Futuristic silicon chip with monolithically integrated photonic
and electronic circuits
wires
waveguides
Possible solutions: photonic crystals, plasmons, etc.
Note T-intersections and
tight bends, as in electric
wires.
You cannot achieve it in
usual waveguides!
Digital Light Processing (DLP)
Texas Instruments 1987
800x600, 1024x768, 1280x720, and 1920x1080
(HDTV) matrices of microscopic mirrors
One mirror is only 16 microns!
Less than 1/5 of human hair width
http://www.dlp.com/includes/demo_flash.aspx
Laser mini-projectors
Need microscopic lasers of all
colors: red, blue, and green
Fiber communications
need mini lasers emitting
in the near-infrared
Smallest lasers are semiconductor lasers!
mini laser projector
Excellent near infrared and
red lasers
Bad blue lasers
Very bad green lasers
Problem of Interconnects
Number of transistors grows, but this does
not improve the performance as much.
Reason?
We use 21-century semiconductor devices and
19-century copper wires connecting them!
Electronic circuits: 45 nm wires, 1 million transistors per mm2
Computing speed is limited by inertia of electrons
The interconnect bottleneck
• 109 devices per chip
• Closely spaced metal wires slow down computation
• Huge heat generated due to electric resistance
Can electronic circuits be replaced by photonic
ones?!
Using photons as bits of information instead of
electrons would speed up the computing
Photons travel much faster and don’t dissipate as much power
However, large size of a photon would make computers
1000 times larger!
Optical computer is still a dream.
Even wilder dream is a quantum computer.
Quantum computer
Bit
Qubit (quantum bit): state of a
single electron or atom
Classical computer: 0 or 1
Quantum computer: 0 or 1 or any mixture of 0 and 1
Quantum computer can perform millions
of calculations in parallel.
Especially good for searching through
huge amount of data or
encoding/decoding secret messages
Extremely fragile, needs low temperature
Conclusions
 Microelectronics is approaching its fundamental limits.
Revolutionary ideas are needed!
- Single-molecule transistors?
- new materials, new fabrication technology?
 Communication: how to increase speed?
- Novel lasers?
- All-optical network?
- How to make photons smaller?
 New principles of computing??