For decades scientists have been trying to build computers that process information using light rather than electric currents. One of the biggest stumbling blocks has been finding a suitable nonlinear process to carry out the optical equivalent of a transistor’s switching. But now a U.S.–Canadian research collaboration believes it may have the answer—a specially-designed gel that allows quite weak laser beams to guide themselves and interact with other beams some distance away.
Nonlinearity is central to digital computing as it allows transistors to act as switches—to transmit an electrical current when activated by a much smaller (electrical) signal. Unlike electrons, however, photons don’t naturally interact with one another. To get around this problem in their attempt to build an all-optical computer—one which would store, transmit and process data in the form of photons—researchers have been developing materials that serve as intermediaries between laser beams.
In the latest work, scientists at Harvard University, MA, USA, and McMaster University, Ontario, Canada, fired laser beams at a water-filled polymer network known as a hydrogel that also contained light-sensitive molecules. The idea was to optically induce a chemical reaction that would expel water from the material, causing the polymer network to shrink and become more dense. This would yield a higher refractive index in the path of the beam, and a lower one outside it, creating a waveguide that would in turn concentrate the beam and boost its intensity—a positive feedback loop initiated simply by switching the beam on.