ICM2014Dr Paul S. SpencerModule consists of: 20 Lectures 4 TutorialsOptoelectronicsRecommended text: W.B. Jones Introduction To Optical Fibre Communication Systems, Oxford Uni. Press. J. Gower Optical Communication Systems, Prentice Hall. J. Wilson & J.F.B.Hawkes Optoelectronics: An Introduction, Prentice Hall.( www.britneyspears.ac/lasers.htm)

Optical CommunicationHistory: Long and Illustrious Waving arms, Beacons Coded Messages Flags, Flashing lights Navigation Starlight Time travel Age of the Universe, Space-Time

Science: Descartes - corpuscular nature Newton Dispersion, Snells Law Huygens wave nature: Interference, Diffraction, Polarisation Maxwells Equation Einstein Photoelectric effect, Relativity, LASER Planck Blackbody Radiation: Quantum Mechanics: QED

Technology: Coherent Sources Bandwidth Compact, Robust and Cheap

Coherent Electro-Magnetic SourcesThe total power, PT , of N coherent sources of equal amplitude is equal to the power of a solitary source, P0 , multiplied N2 !!!! Incoherent Electro-Magnetic SourcesThe total power, PT , of N incoherent sources of equal amplitude is equal to the power of a solitary source, P0 , multiplied N. Examples: Lasers, Microwave (Masers) and Radio Sources. Microwave oven. Examples: Almost everything else, domestic and commercial lighting, electric cookers and fires. Barbecues. Strictly speaking no source is complete coherent or incoherent

Casimir Effect

It was the Dutch theoretical physicist Hendrik Casimir (1909-2000) who first realized that when two mirrors face each other in a vacuum, fluctuations in the vacuum exert "radiation pressure" on them. On average the external pressure (red arrows) is greater than the internal pressure (green arrows). Both mirrors are mutually attracted to each other by what is termed the Casimir force. The force F ~ A/d4, where A is the area of the mirrors and d is the distance between them.

While the Casimir force is too small to be observed for mirrors that are several metres apart, it can be measured if the mirrors are within microns of each other. For example, two mirrors with an area of 1 cm2 separated by a distance of 1 m have an attractive Casimir force of about 10-7 N - roughly the weight of a water droplet that is half a millimetre in diameter. Although this force might appear small, at distances below a micrometre the Casimir force becomes the strongest force between two neutral objects. Indeed at separations of 10 nm - about a hundred times the typical size of an atom - the Casimir effect produces the equivalent of 1 atmosphere of pressure.

The Casimir force, which is most noticeableat submicron distances, and can affectmicroelectromechanical systems, or MEMS. This MEMS device consists of a polysilicon plate suspended by a torsional rod only a few micrometres in diameter. When a metallized sphere (purple) approaches the plate, the attractive Casimir force between the two objects causes the plate to rotate around the rod.

(b) An electron micrograph of the device that shows the polysilicon plate.

(c) A close-up of the rod.