Nanophotonics

Nanophotonics or Nano-optics is the study of the behavior of light on the nanometre scale. It is considered as a branch of optical engineering which deals with optics, or the interaction of light with particles or substances, at deeply subwavelength length scales. Technologies in the realm of nano-optics include near-field scanning optical microscopy (NSOM), photoassisted scanning tunnelling microscopy, and surface plasmon optics. Traditional microscopy makes use of diffractive elements to focus light tightly in order to increase resolution. But because of the diffraction limit (also known as the Rayleigh Criterion), propagating light may be focused to a spot with a minimum diameter of roughly half the wavelength of the light. Thus, even with diffraction-limited confocal microscopy, the maximum resolution obtainable is on the order of a couple of hundred nanometers. The scientific and industrial communities are becoming more interested in the characterization of materials and phenomena on the scale of a few nanometers, so alternative techniques must be utilized. Scanning Probe Microscopy (SPM) makes use of a “probe”, (usually either a tiny aperture or super-sharp tip), which either locally excites a sample or transmits local information from a sample to be collected and analyzed. The ability to fabricate devices in nanoscale that has been developed recently provided the catalyst for this area of study. The study of nanophotonics involves two broad themes 1) studying the novel properties of light at the nanometer scale 2) enabling highly power efficient devices for engineering applications. The study has the potential to revolutionize the telecommunications industry by providing low power, high speed, interference-free devices such as electrooptic and all-optical switches on a chip. Novel optical properties of materials can result from their extremely small size. A typical example of this type of effect is the color change associated with colloidal gold. In contrast to bulk gold, known for its yellow color, gold particles of 10 to 100 nm in size exhibit a rich red color. The critical size where these and related effects take place are correlated with the mean free path of the conduction electrons of the metal. In addition to these extrinsic size effects that determine a material's optical response to incoming light, the intrinsic properties of the material can change. These size effects occur as particles become even smaller. At this stage some of the intrinsic electronic properties of the medium itself change. One example of this phenomenon is in semiconductor nanostructures where the extremely small particle size confines the quantum mechanical wavefunction, leading to discrete optical transitions, e.g., fluorescence colors that depend on the size of the particle. The changing bandgap of the semiconductor is the reason for this color change. This effect, however, since not directly correlated with optical wavelength, is not unanimously included when referring to nano-optics.

Further information:

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6. Article Nanophotonics from Wikipedia, the Free Enciclopedia. Available under the license Creative Commons Attribution-Share Alike.

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