Photonic (Optical) Computing

1. Jason Plank Photonic (Optical) Computing

2. 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?

3. 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”

4. 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

5. 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

6. 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

7. 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

8. 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

9. Photonic Crystals, continued • 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 False-color closeup of a silicon photonic crystal Source: Science News

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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 single-photon 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.