Regulating the flow of energy is integral to electronics engineering. When it comes to light communication, several diode options are available (e.g. thin film). Another option includes gallery microcavities that may translate or “whisper” light in between doughnut shaped optical resonators (one with gain and the other with loss) on a silicon chip to different ports.
Second harmonic generation by micro-disks has recently come into realization. The breakthrough made it possible to use GaAs as a “whisper” gallery to strongly interact with the passing light and double its frequency. Energy and momentum are conserved in the frequency-doubling process through a fundamental constant and quasi-phase matching respectively.
A femtosecond pulsed laser creates nanostructured dots on glass. This information is encoded in 5D space: size, orientation and 3 normal directions of the nanostructure. The polarization of light passing through a 3 layer crystal with 5um separation can then be read by a combination of an optical microscope and a polarizer. The result is an ultra-high data capacity, thermal stability up to 1000 degC and practically an unlimited data lifetime.
In another application, optical lattice clocks loose one second every 300 million years which makes them three times as accurate as current atomic clocks. Light is used to excite strontium atoms and the atomic vibration measurements are taken. An ion clock is also under development. Dependence on a single atoms reduces its relative stability, but the accuracy is deemed to be loosing only one second every few billion years.
Electrical switching may also be induced by a laser light source. Magnetite’s electronic structure breaks down into conducting and non-conducting regions in the first 1 trillionth of a second. The switch occurs between non-conducting and conducting states.
Propagation of EM waves along a surface due to incident light has applications in electrical switching, solar cells, LEDs etc. Even though Au or Ag is typically required, polymer composites can also be engineered to sustain cheaper and more flexible devices.
Repeatability of a structure allow for better engineered devices with better consistency. Pillars are popular due to the ease of synthesis, usually by standard MEMS techniques. LSPR with this structure is also possible at IR wavelengths in heavily silicon (Si) doped indium arsenide (InAs) microparticles. In other cases, ordered Au NPs can produce low-energy photons in the visible spectrum when energized with a beam of electrons.
Single molecule detection may also be possible with plasmonic arrays. An array of Au hills folded into a spherical NP shape promote local electromagnetic enhancement regions. The detection of a single thyroid cancer marker (Thyroglobulin, Tg) and bovine serum albumin (BSA) proteins was made possible with such NPs and with tracking the variation in surface plasmon resonance upon irradiation with 780nm wavelength excitation.
Features smaller than a wavelength of light have astonishing properties. For example, plasmonic nanoparticles may aggregate to for a wave mixer. This means that it is possible to mix colors in a very general way. One can send beams of two different colors and get a third color for example.