Transmission of data

With the increasing quest for transporting large amounts of data at a fast speed along with miniaturization both electronics and photonics are facing limitations. Photonic components such as fiber optic cables can carry a lot of data but are bulky compared to electronic circuits. Electronic components such as wires and transistors can be incredibly small but carry less data. A problem holding back the progress of computing is that with mismatched capacities and sizes, the two technologies are hard to combine in a circuit. Researchers can cobble them together, but a single technology that has the capacity of photonics and the smallness of electronics would be the best bridge of all. Researchers are pioneering just such a technology called -plasmonics.Plasmonics, sometimes called "light on a wire”, would allow the transmission of data at optical frequencies along the surface of a tiny metal wire, despite the fact that the data travels in the form of electron density distributions rather than photons. Plasmonics refers to the investigation, development and applications of enhanced electromagnetic properties of metallic nanostructures. The term plasmonics is derived from "plasmons", which are the quanta associated with longitudinal waves propagating in matter through the collective motion of large numbers of electrons

.

Plasma

Plasma is a medium with equal concentration of positive and negative charges, of which at least one charge type is mobile. In a solid the negative charges of the conduction electron (i.e., electron gas) are balanced by an equal concentration of positive charge of the ion cores. A plasma oscillation in a metal is a collective longitudinal excitation of the conduction electron gas against a background of fixed positive ions with a plasma frequency. Surface plasmons are density waves of electrons—picture bunches of electrons passing a point regularly—along the surface of a metal. Plasmons have the same frequencies and electromagnetic fields as light, but their sub-wavelength size means they take up less space. Plasmonics, then, is the technology of transmitting these light-like waves along nanoscale wires. With every wave we can in principle carry information. Plasmon waves are interesting because they are at optical frequencies. The higher the frequency of the wave, the more information we can transport. Optical frequencies are about 100,000 times greater than the frequency of today's electronic microprocessors. The research is a prime example of work at the forefront of strategic initiatives in information technology and photonics, and nanoscience and nanotechnology. The key is using a material with a low refractive index, ideally negative, such that the incoming electromagnetic energy is reflected parallel to the surface of the material and transmitted along its length as far as possible. There exists no natural material with a negative refractive index, so nanostructured materials must be used to fabricate effective plasmonic devices. For this reason, plasmonics is frequently associated with nanotechnology.

Plasmonics

Plasmonics describes how ultrasmall metal structures of various shapes capture and manipulate light and provides a practical design tool for nanoscale optical components. The fact that light interacts with nanostructures overcomes the belief held for more than a century that light waves couldn't interact with anything smaller than their own wavelengths. Research has shown that nanoscale objects can amplify and focus light in ways scientists never imagined. The "how" of this involves plasmons, ripples of waves in the ocean electrons flowing across the surface of metallic nanostructures. The type of plasmon that exists on a surface is directly related to its geometric structure. When light of a specific frequency strikes a plasmon that oscillates at a compatible frequency, the energy from the light is harvested by the plasmon, converted into electrical energy that propagates through the nanostructure and eventually converted back to light. The new findings offer a new understanding of plasmonics, an emerging field of optics aimed at the study of light at the nanometer scale -- at dimensions far smaller than a wavelength of light, smaller than today's smallest electronic devices. The field of plasmonics, which has existed for only a few years, has already attracted researchers from industry and government. According to new research scientists studying the way light interacts with metallic nanostructures will make it easier to design new optical materials and devices "from the bottom up," using metal particles of specifically tailored shapes. One primary goal of this field is to develop new optical components and systems that are the same size as today's smallest integrated circuits and that could ultimately be integrated with electronics on the same chip.

The research show that the equations that determine the frequencies of the plasmons in complex nanoparticles are almost identical to the quantum mechanical equations that determine the energies of electrons in atoms and molecules called “plasmon hybridization”. Just as quantum mechanics allows scientists to predict the properties of complex molecules research shows how the properties of plasmons in complex metallic nanostructures can be predicted in a simple manner. The findings are applicable not only to nanoshells, but to nanoscale wave guides and any other nanophotonic structures. The ultimate goal of R & D is to demonstrate plasmonics in action on a standard silicon chip and have made working plasmonic components. The next step will be to integrate the components with an electronic chip to demonstrate plasmonic data generation, transport and detection. Plasmon waves behave on metals much like light waves behave in glass, meaning that plasmonic engineers can employ all the same ingenious tricks—such as multiplexing, or sending multiple waves—that photonic engineers use to cram more data down a cable. Meanwhile, because plasmonic components can be crafted from the same materials chipmakers use today, engineers are hopeful they can make all the devices needed to route light around a processor or other kind of chip. These would include plasmon sources, detectors and wires as well as splitters and even transistors.

Applications

The potential of plasmonics right now is mainly limited by the fact that plasmons typically can travel only several millimeters before they peter out. Chips, meanwhile, are typically about a centimeter across, so plasmons can't yet go the whole distance. The distance a plasmon can travel before dying out is a function of several aspects of the metal. But for optimal transfer through a wire of any metal, the surface of contact with surrounding materials must be as smooth as possible and the metal should not have impurities. For most wavelengths of visible light, aluminum allows plasmons to travel farther than other metals such as gold, silver and copper. It is somewhat ironic that aluminum is the best metal to use because the semiconductor industry recently dumped aluminum in favor of copper—the better electrical conductor—as its wiring of choice. Of course, it may turn out that some kind of alloy will have even better plasmonic properties than either aluminum or copper. Another classic semiconductor industry issue the researchers will have to address is heat. Chipmakers are constantly battling to ensure that their electronic chips don't run too hot. Plasmonics also will likely generate some heat, but exactly how much is not yet known. Even if plasmonics run as hot as electronics it will still have the advantage of having a higher data capacity in the same space.

Before all-plasmonic chips are developed, plasmonics will probably be integrated with conventional silicon devices. Plasmonic wires will act as high-bandwidth freeways across the busiest areas of the chip. Plasmon printing is a new approach to lithographic printing that takes advantage of the resonantly enhanced optical intensity in optical near field of metallic nanoparticles, and which could enable printing of deep subwavelength features using conventional photoresist and simple visible or ultraviolet light sources. Plasmonics has also been used in biosensors. When a particular protein or DNA molecule rests on the surface of a plasmon-carrying metallic material, it leaves its characteristic signature in the angle at which it reflects the energy. In the field of chemical sensing, plasmonics offers the possibility of new technologies that will allow doctors, anti-terror squads and environmental experts to detect chemicals in quantities as small as a single molecule.