1. Photonic (Optical) Computing Jason Plank

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.