[attachment=3071]

Technical Seminar on Optical Computing Technology






Introduction

Optical computing is the science of making computing work better using optics and related technologies
Some researchers use optoelectronic computing


Why Do We Need Optical Computers?
Rapid growth of the Internet
Network speeds currently limited by electronic circuits
Terabit speeds are required
Traditional silicon circuits have a physical limit


Silicon Machines¦

Types of Optical Computer
Optical Analog

These include 2-D Fourier transform or optical correlators, and optical
matrix-vector processors. 
Optoelectronics

In this type of computing device would be to shorten the pulse delay
in chips and other logic elements by using optical interconnections. 

MATERIALS FOR OPTICAL COMPUTER
Materials belong to the classes of phthalocyanines and polydiacetylenes. are used.
Phthalocyanines are large ring-structured porophyrins for which large and ultrafast nonlinearities have been

observed. These compounds exhibit strong electronic transitions in the visible region and have high chemical and

thermal stability up to 400C.
Subsequently, polydiacetylenes are among the most widely investigated class of polymers for nonlinear optical

applications. Their subpicosecond time response to laser signals makes them candidates for high-speed

optoelectronics and information processing.

MATERIALS FOR OPTICAL COMPUTER
How Does It Work?
Devices used for optical computing
Logic gates :
Logic gates are implemented optically by controlling the population inversion that occurs to produce lasing. A

controlling laser is used to control the population inversion thus causing switching to occur.
Holographic truth table
“ Destructive interference will light to be emitted or not based on phase relationship
Logic based on gratings
“ 1 is represented by vertical grating causing light
“ 0 is represented by horizontal grating causing darkness1



Devices used for optical computing
Holographic storage :
Holographic data storage has 4 components
Holographic material; thin film on which data is to be stored
Spatial Light Modulator (SLM); 2D array of pixels, each of which is a simple switch to either block or pass

light
Detector array; 2D array of detector pixels, either as Charge-coupled device (CCD) camera or CMOS detector

pixels to detect existence of light
Reference arm; arm carrying the laser source to produce the reference beam


Devices used for optical computing
Interconnections in optical computing
Optical interconnection technologies arerelatively mature
Fiber optic cables and optical transceivers are widely used
Applications of optical communications like fiber channel and computer networking are already being used.
Although there is a basic speed limitation is optoelectronic conversion delays
WDM is used to get around this limitation
Chip to Chip and On-Chip interconnection possibilities are still being examined
Promising but there are problems regarding dense organization of optical processing units

Devices used for optical computing

Devices used for optical computing
Smart Pixel Technology 
Different Approaches to Smart Pixels
Monolithic integration:
§         Materials incompatibility (III-V™s and Si)
§         Si-SiGe-Ge-GaAsto lattice matching and strain relief 

Hybrid integration:
§         Flip-chip bonding
§         Difficulty of optical access
§         Remove substrate prior to (epi-lift-off) or after integration
§         Use transparent substrate (Silicon-on-Sapphire)o
§         Use longer wavelengths (980 nm, 1310 nm)



Application of Optical Computing
Optical Computing In Communication
Wavelength division multiplexing
Optical Amplifiers & DWDM
Storage area network
Fiber Channel Topologies
Basic topologies
F C-AL (Fiber Channel Arbitration Loop):
Cost effective, low performance solution
Switched:
Better performance, more expensive
Hybrid topologies
Uses loops and switches as building blocks
Any interconnection network scheme can be realized



Application of Optical Computing
Optical Computing In VLSI Technology
Many researchers have been investigating suitable optical logic devices, interconnection schemes, and

architectures. Furthermore, optics may provide drastically new architectures to overcome some architectural

problems of conventional electrical computers.
Optical computing as expanders
The optical expander described utilizes high-speed and high-space-bandwidthproduct connections that are

provided by optical beams in three dimensions.


Whatâ„¢s Beyond the Optical Limit?
Quantum computing
Allows particles to be in more than one state at a time
Each particle in a quantum computer to hold more than one bit of information.
A quantum computer is, thus far, only a hypothetical machine
Expected between 2030 and 2050

CONCLUSION
Optics has been used in computing for a number of years but the main emphasis has been and continues to be to

link portions of computers, for communications, or more intrinsically in devices that have some optical

application or component.
Optical digital computers are still some years away, however a number of devices that can ultimately lead to

real optical computers have already been manufactured, including optical logic gates, optical switches, optical

interconnections, and optical memory.
The most likely near-term optical computer will really be a hybrid composed of traditional architectural design

along with some portions that can perform some functional operations in optical mode.