Technological devices need electricity. This is something most people intrinsically know before anyone tries to teach them the premise. A device such as the wind-up radio doesn’t require batteries or plugging into an electrical grid, but even its muscle-generated power produces electricity in order for the components inside to work. An iron is defined as, “Anappliance with a flat metal bottom, used when heated, as by electricity, to press or smooth clothes.” And yet less than a hundred years ago an iron was essentially a piece of flat iron, heated over a coal or wood burning stove. Electricity has come to represent the future and anything that is not electrically powered in some capacity is viewed as antiquated or obsolete.
It is by challenging the preconceptions that we give rise to the next generation of technology; of alternative fuel cars and solar powered homes. Researchers at the University of Pennsylvania are at present challenging the defining characteristics of circuitry by researching ways of replacing electricity with light. Nader Engheta, a professor in Penn’s School of Engineering and Applied Science, echoes this spirit of challenging preconceptions, “Looking at the success of electronics over the last century, I have always wondered why we should be limited to electric current in making circuits. If we moved to shorter wavelengths in the electromagnetic spectrum, like light, we could make things smaller, faster and more efficient.”
Nanotechnology now allows the construction of structures that have dimensions measured in nanometers. These structures are produced in quantity and are known as metamaterials. They are able to manipulate waves in ways that were previously thought to be impossible. Engheta’s team uses the cross-sections of the nanorods and the gaps between them, to form a pattern that replicates the function of the three most basic circuit elements, resistors, inductors and capacitors. Using nanorods with nine different combinations of widths and heights, the researchers showed that the optical ‘charge’ produced was altered by the optical resistors, inductors and capacitors. Engheta explains, “A section of the nanorod acts as both an inductor and resistor, and the air gap acts as a capacitor.”
Photon-based circuits aren’t a new idea. The problem has always been building logical gates for them to operate. Even electronic gates are imperfect, but these imperfections can be overcome by adding elements that refine the signal, if the signal is low it is boosted and if it is too high it is dampened. In photonics there is no equivalent of these compensations, which means the circuits are restricted to a very small number of chained gates. There is a way of converting photonic input to electrons and then back to photons, but then the benefits of a pure photonic circuit, low power and minute size, are lost.
Even though the end product is still far out of reach, we can already envision a future where light is the driving force behind technology. This isn’t to be confused with solar power, which converts sunlight into electricity, but should be thought of purely in terms of motion. Light represents the pinnacle of speed and by incorporating it into the devices we use, we push our capabilities to the limits of the imagination.