From Physics to From Physics to Optoelectronics TechnologyOptoelectronics Technology

Alexey BelyaninTAMU-Physics

Physics in the Information Age

Laser

Transistor

Computer

World Wide Web

… Are all 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; 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 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. buildingwhere 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 computersOnly 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 1951. 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 GHzMfg. Process: 0.13-micronNumber of transistors: 178 million2 MB L3 cache; 512 KB L2 cacheBus 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

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!

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: 1947John Bardeen, Walter Brattain, and William Shockley Nobel Prize in Physics 1956

Background: SemiconductorsMetals

Semiconductors

Insulators

Conduction Band

Conduction Band

Conduction Band

Valence Band

Valence Band

Valence Band

Eg

Eg

• 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!

Vol

tage

Time

Vol

tage

Analog-to-digital conversion

Time

Analog radio broadcasting: Low-frequency audio signal modulates the amplitudeof 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(2f t)

1 kHz = 1/ms

Sound waves: 30 Hz-20 kHz

Spectral window (Bandwidth) needs to be at least 30 kHz Spectral window (Bandwidth) needs to be at least 30 kHz for each stationfor 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(220t) + sin(219t)- cos(219t)+ (1/3) sin(217t)-(1/3) cos(217t)+…

Time, ms

Frequency, kHz

Time, ms

Max Data rate = one pulse per 0.25 ms = 4 kHz = 4000 bit/s

Bandwidth B = 4 kHzPulse 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?!

Lo

ss p

er k

m

Wavelength, nm

Maximum tolerable loss

Transmisson 95.5% of power after 1 km P = P(0) (0.995)N after N kmP = 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 gateBandwidth 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??