Light is the ultimate escape artist. Scientists have spent centuries trying capture it, most recently building nanoscale materials that screen, absorb, and reflect its waves. Yet some light always seems to elude capture, either leaking out or fading away. Now, scientists have devised minuscule chambers that can theoretically hold precise quantities of light forever, a discovery that could hasten the development of light-based computers.
The ability to carefully control and confine light in small spaces is a key goal for scientists developing technologies like ultrafast optical computers, which use photons—rather than electrons—to process information. When light enters a cavity, its interaction with the container typically gives rise to microscopic oscillations that fritter energy away. But here Silva et al. present a way to prevent this decay, using nanoscopic, plasma-covered chambers called meta-atoms.
The team’s first successful meta-atom—modeled using a computer program that simulates electromagnetic (EM) waves—was a spherical dielectric cavity surrounded by an electron-gas shell. When light enters the spherical cavity, it squeezes the wavelength to fit within the walls of the chamber, ensuring that the trapped light energy has a precise value that can be contained by its plasma-filled shell. Typical material structures are intrinsically bidirectional, so if one wishes to pump the nanosized chamber from the outside, then the cavity walls will necessarily leak some of the energy contained in it. To solve that problem, the team used a nonlinear mechanism that enables an EM wave to pump just enough energy into the container to keep the oscillations under control and the light contained.
Next, they used a similar approach to produce 2-D square and kite-shaped chambers, which may be easier to stack on computer chips than spheres. In this manner, they demonstrated that it is possible to confine the light in nanosized chambers of arbitrary geometry. Similar to their spherical counterparts, the 2-D chambers can trap light if zapped with a precisely titrated EM wave. In addition to optical computers, these nanoscale light trappers could potentially be used for chemical and biological sensors. (Radio Science, https://doi.org/10.1002/2017RS006381, 2018)
—Emily Underwood, Freelance Writer