As computer chips become ever more prodigious in their data-processing capacities, the task of shuttling all those gigabits around inside a chip becomes an increasing challenge. Help may be on the way in the form of photonic components, which deal in pulses of light instead of slower packets of electric charge. For several years researchers have been making so-called silicon optical waveguides, in which light speeds along inside the ridge between two channels as if along an optical fiber.
But such optical interconnects must deliver their data at precise times, which requires delaying the light pulses by controlled amounts. One method is to send the light pulses into microscopic loops made of waveguides where they circulate dozens of times before continuing on their journey. Yurii A. Vlasov and his co-workers at the IBM Thomas J. Watson Research Center in Yorktown Heights, N.Y., sent pulses of light through strings of as many as 100 such loops without suffering prohibitive losses of data.
Another way of delaying light in microscopic devices is to use photonic crystal components, which contain carefully designed arrays of holes whose size and spacing exclude light in a certain frequency band (a so-called photonic band gap). A photonic crystal waveguide can consist of a path without holes running through such an array in a thin slab of silicon. The band gap generated by the holes on each side of the path confines the light to travel that route. Takasumi Tanabe and his colleagues at the NTT Basic Research Laboratories in Japan took this scheme several steps forward by temporarily storing photons in a photonic crystal nanocavity—in this case, a small region where the waveguide is slightly wider.
Whereas some researchers want to delay light, others at the Rensselaer Polytechnic Institute led by E. Fred Schubert have created a coating that reflects almost none of it. The coating, about 600 nanometers thick, consisted of five layers of nanorods—titanium dioxide and silica filaments about 25 nanometers in diameter and up to 300 nanometers long—stacked on a transparent semiconductor wafer. Each layer had a lower refractive index than the one below it. The uncoated semiconductor reflected about 12 percent of light incident on it; when coated, it reflected as little as 0.1 percent. The coating could have applications in photonic components, light-emitting diodes and solar cells.
Other investigators are pursuing the far more speculative goal of building quantum computers, which would exploit weird features of quantum mechanics to achieve unprecedented processing capabilities. One approach involves storing quantum data as long-lived states of atoms and transmitting the information with light waves. But combining those two media requires the transfer of delicate quantum states between matter and light. In 2006 a group of researchers led by experimentalist Eugene S. Polzik of the Niels Bohr Institute at the University of Copenhagen and theorist Ignacio Cirac of the Max Planck Institute for Quantum Optics in Garching, Germany, teleported quantum information from a light pulse to a cloud of atoms.
—Graham P. Collins