Download Photonic (Optical) Computing

Photonic (Optical) Computing
Jason Plank
Topics to be Addressed




What is photonic computing?
How does it compare to conventional electronic
computing?
How is it done?
What are the challenges imposed by photonic
computing?

What can it do?

What is the current progress of research?
Nomenclature

Electronics – the movement of electrons


Derived from electrons – subatomic particles
which carry electrical charge
Photonics – the movement of light



Derived from photons – the ”units” of light
Photons have properties of both particles and
waves
The term ”photonic computing” is used
interchangeably with ”optical computing”
Current Standards of Computing


Electronic computing is the conventional standard
Today's computers use processors that control and
manipulate the flow of electrons



Signal processing occurs when electrons are sent
through a semiconductive material such as silicon
The semiconductive material controls and
manipulates the flow of electrons
These materials make up what we know as CPUs
Limitations of Electronics and
Electronic Computing

The speed of electrons through electrically
conductive and semiconductive materials

Signal loss and electromagnetic interference

Electrical current generates heat


Greater computational speed requires increased
current, resulting in increased heat
Not well-suited to image processing as opposed to
numerical processing
Advantages of Photonics and
Photonic Computing

In photonic devices, information travels at the
speed of light





Increased throughput over electronic devices
Signal loss is much less significant when
compared to signal loss in electronics
No interference between intersecting beams
Generates insignificant amounts of heat
regardless of how much light is directed through
circuits
Photonic processors are well-suited to image
processing whereas electronic processors are not
Challenges of Photonic Computing


Materials which act as processors for photons are
still in early development and research

Act as an analog to the electronic semiconductor

These materials are called photonic crystals
Without these processors, optical signals need to
be generated and interpreted via electronic means

Example: fiber optics of today
Photonic Crystals

Photonic crystals are structures which control
and/or manipulate the flow of photons

Also known as photonic band-gap structures

Analogous to the electronic transistor

Must be made with extreme precision


Not easily manufactured
Once successfully miniaturized, photonic crystals
may be used as the building blocks of optical
integrated circuits
Photonic Crystals, continued


False-color closeup of a silicon
photonic crystal
Source: Science News

Designed to reflect,
refract, and/or ”bend”
light of a specific
wavelength
Slow or trap light in
specialized
microcavities
May make optical
memory systems
possible
Applications of Photonic Computing

Photonic circuitry may first be used as
replacements for electronic components in
conventional hardware



This results in a hybrid optical/electronic
(optoelectronic) computer system
Seems to be the most likely approach for early
photonic applications
Purely photonic computers

Would be comprised of all-optical components
The von Neumann Bottleneck



The von Neumann Bottleneck refers to the limited
data transfer rate (throughput) resulting from the
separation of CPU and memory
Due to this bottleneck, increases in CPU speed
result in diminishing returns in throughput
Caching and parallel computing reduce the
bottleneck's impact but do not eliminate it
Von Neumann Bottleneck, continued


There is some speculation that photonic
computers may not suffer from this bottleneck
Processors may contain much more memory
Source: cs.cmu.edu
Photonic Crystal Research


A handful of scientists have built photonic
crystals
Currently, research aims to increase efficiency



A technique for building a photon switch which
operates using single photons has been developed
This is an improvement of a technique which used
a burst of photons to operate the switch
Reducing power consumption increases the
feasibility of potential optical components
Topics Discussed

What photonic computing is

How it compares to conventional computing

How it is done

Challenges of photonic computing

The applications of photonic computing

What research has been and is being done in the
field of photonic computing
References





Amato, I. (1992). Designing crystals that say no to photons. Science, New
Series, 255(5051) 1512.
Chang, D. E, Sørensen, A. S, Demler, E. A, & Lukin, M. D. (2007). A singlephoton transistor using nano-scale surface plasmons. Retrieved from
http://arxiv.org/abs/0706.4335v1
Das, S. (2007). Speed-of-light computing comes a step closer. New Scientist,
2613, 28.
Session 13: digital design. Retrieved from http://www.cs.cmu.edu/~ref
/pgss/lecture/11/index.html
Taubes, G. (1997). Photonic crystal made to work at an optical wavelength.
Science, New Series, 278(5344) 1709-1710.

Weiss, P. (2005). Light pedaling. Science News, 168(19), 292.

Weiss, P. (2004). Lighthearted transistor. Science News, 166(21), 324.

Yablonovitch, E. (2000). How to be truly photonic. Science, New Series,
289(5479), 557 + 559.