From Physics to Optoelectronics Technology Alexey Belyanin TAMU-Physics

Physics in the Information Age Laser Transistor Computer World Wide Web … Are all invented by physicists

History of the WWW

First proposal: Tim Berners-Lee (CERN) in : 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; 60 million users in the US alone

Invention of Computer The first digital electronic computer was invented by Theoretical Physics Prof. John Vincent Atanasoff in 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.

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.

ABC Replica 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. Card punch and reader Berry with the ABC

From ENIAC to … ENIAC (1946) weighed 30 tons, occupied 1800 square feet and had 19,000 vacuum tubes. It could make 5000 additions per second 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 The first commercial magnetic hard-disk drive and the first microchip are introduced. Transistors are first used in radios. 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.

Intel Pentium 4 Processor Extreme Edition (Nov. 3, 2003) Clock speed: 3.20 GHz Mfg. Process: 0.13-micron Number of transistors: 178 million 2 MB L3 cache; 512 KB L2 cache Bus speed: 800 MHz The electronics and semiconductor industries account for around 6.5% of the gross domestic product, representing over $400 billion and 2.6 million jobs. The telecommunications industry earns $1.5 trillion each year and employs 360,000 Americans.

Moore’s Law (1965): every 2 years the number of transistors on a chip is doubled Smaller, Denser, Cheaper

Pushing Fundamental Limits: Challenges and Bottlenecks  Semiconductors: how small the transistor can be?  Memory and data storage: limits on writing density?  Communications: limits on data rate?

Limit on the transistor size Limit on the manufacturing technology

Before transistors: vacuum tubes : SAGE Air Defense Project 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!

Diode: one-way valve for electrons Triode: controllable valve

Semiconductor Diodes and Transistors “ One should not work on semiconductors, that is a filthy mess; who knows whether they really exist.” Wofgang Pauli 1931 Transistor invention: 1947 John Bardeen, Walter Brattain, and William Shockley Nobel Prize in Physics 1956

Background: Semiconductors Metals Semiconductors Insulators Conduction Band Valence Band EgEg EgEg Electron energies are grouped in bands Exclusion Principle: Only one electron per state allowed No current at all Just right! Current flows, but no control

Doping hole P-type N-type

P-N junction and diode effect

Forward bias: Current flows Reverse bias: No current

Bipolar junction transistors

FET: Field-Effect Transistor

Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET)

MOSFET: the workhorse of Integrated Circuits Jack Kilby: Nobel Prize in Physics 2000 How thin can be the gate oxide?

Fabrication Limits Photolithography

Rayleigh Resolution Limit Best spatial resolution is of the order of one wavelength of light

Telecommunications

Analog system: high-quality sound, but limited speed and apps Digital system: any signal, high speed, but sound quality is lower Voltage variations repeat sound wave variations Binary code is transmitted Remember Atanasoff!

Voltage Time Voltage Analog-to-digital conversion Time

Analog radio broadcasting: Low-frequency audio signal modulates the amplitude of high-frequency carrier wave Amplitude Modulation (AM) AM Station frequencies (in kHz): f = 1050, 1120,1240, 1280,… Stations broadcast at different carrier frequencies to avoid cross-talk Sin(2  f t) 1 kHz = 1/ms Sound waves: 30 Hz-20 kHz Spectral window (Bandwidth) needs to be at least 30 kHz for each station

Modulating a carrier wave with digital data pulses How large is data rate? It is limited by bandwidth! Time

Synthesizing digital data packet Data rate = 1/1ms = 1kHz = Distance between side-bands! 4 sin(2  20t) + sin(2  19t)- cos(2  19t)+ (1/3) sin(2  17t)-(1/3) cos(2  17t)+…

Time, ms Frequency, kHz Time, ms Max Data rate = one pulse per 0.25 ms = 4 kHz = 4000 bit/s Bandwidth B = 4 kHz Pulse duration ~ 1/B

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

Sharing the bandwidth (multiplexing)

Higher carrier frequencies Wider bandwidth Higher data rate Faster, faster, faster Using optical frequencies?! 1000 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 Wavelength, nm Maximum tolerable loss 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 Total bandwidth = 400 THz!! Loss in silica glasses

How to confine light with transparent material?? Total internal reflection! n > n’

Dielectric waveguides n > n’ Optical fiber! 1970: Corning Corp. and Bell Labs

Fibers open the flood gate Bandwidth 400 THz would allow 400 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.

Present-day WDM systems: bandwidth 400 GHz, Data rate 10 GBits/sec Limits and bottlenecks

What’s Wrong? Modulation speed of semiconductor lasers is limited to several Gbits/sec Electric-to-optical conversion is slow and expensive

All-optical switches Micro-Electro-Mechanical Systems (MEMS) 256 micro-mirrors (Lucent 2000)

Conclusions  Microelectronics is approaching its fundamental limit. Revolutionary ideas are needed! - Organic semiconductors? - Single-molecule transistors?  Communication: how to increase data rate? - Novel lasers? - All-optical network?  New principles of computing??