2008

Nanophotonics Principles and Applications

The term “nanophotonics” is used to encompass the scientific study of the interaction of matter and light at the nanometer scale. It is possible to design nanometer scale devices to slow down, enhance, produce, or manipulate light by understanding how light behaves as it travels through, or otherwise interacts with, materials at the nanometer scale. Two applications where nanophotonics have had an impact on society are devices used in optical switching for telecommunications and Organic Light Emitting Diodes (OLEDs) used in display technology and lighting.

altOrganic Light Emitting Diodes are light emitting diodes that have organic materials as their light emitting layer. The organic materials are generally classified into two categories: small molecule (SMOLED) and polymeric (PLED). In both types, different layers are placed in between a cathode and an anode; when electricity passes through, light is produced. These devices have already been introduced into the commercial market in the form of simple displays on consumer products (Philips electric razor), as well as in both cameras (Kodak) and television sets (Sony).

As the ability to effectively design and manufacture devices at the nanometer scale increases, the applications for nanophotonics grow. There are many industries that benefit from this science and its continued advancement including computer, telecommunication, biotechnology, and sensing.

One way to picture the interaction of light and matter in a nanophotonic material is to consider a photonic crystal. A photonic crystal is a material that has a nanostructure which affects the motion of electromagnetic energy. Photonic crystals can be used in different applications including telecommunications, security dyes and paints. One very colorful example is color changing paints. A small amount of photonic crystals is added to a base paint resulting in a coating that, depending on the type of light shining on it as well as the viewing angle, appears to change colors. As light travels through the crystal it interacts with the matrix of the material. The way that light interacts with the material can be manipulated by changing the surroundings in which the crystal resides. For example, an electric field can be applied to the material to change the speed at which light travels through it. Manipulation of photonic materials can result in changes in frequency/wavelength as well as intensity.

Another more visual, naturally occurring pseudo-example of the interaction of light and matter can be seen in the iridescent opal. The various colors and changes are due to the Bragg diffraction of light on crystal lattice planes. Bragg diffraction involves the penetration of a material by some form of light. If the material is crystalline and has different layers separated by some uniform distance it is possible to measure the distance between the layers using Bragg’s Law. In Bragg’s Law some of the light is reflected by each of the different layers while some light penetrates within the material. By measuring the differences in the reflected light that comes out from different levels it is possible to determine the distance between these levels using geometry and algebra.

While the applications of nanophotonics are broad, the central theme of the production or manipulation of light through a material constructed at nanoscale dimensions is constant. The purpose of the science of nanophotonic devices is to synergistically combine the intimate interaction of matter and light at the nanometer scale. Leading areas of research include optical and electronic devices. A few examples of devices are on-chip and chip-to-chip interconnects, optical switches, optical waveguides as well as the nonlinear electro-optic devices, modulators, and waveguides. Ultimately optical devices are trying to take advantage of the wave type property of light. It is possible to use both constructive and destructive interference to modulate a light signal.