The field of nonlinear optics is currently producing many eye-catching (sorry) discoveries, such as visible wavelength cloaking devices. A recent paper in Physical Review Letters continues this trend, presenting a mathematical model for a material that light could pass through asymmetrically.
The optical properties of nonlinear materials vary as light travels through them. These effects have previously enabled optical cloaking, but they could now be used to differentiate light that has entered the material from opposite directions.
The model considers two layers of a nonlinear, nonmirror-symmetric lattice whose optical properties vary within it, which is described mathematically. Light incident on the lattice changes the properties of the material, which in turn changes the behaviour of light within the material. This optical dance eventually results in very different transmission coefficients for light arriving from opposite directions.
The paper, co-authored by Italian physicists Giulio Casati and Stefano Lepri, predicts 80 percent transmission for light travelling in the desired direction and 70 percent opacity to light travelling in the other, making the modelled system competitive with photonic crystals. Photonic crystals can also, under the right circumstances, block light travelling in one direction by tuning their crystal lattice structure.
Unidirectional light transmission would be immediately applicable to quantum computing in the form of a wave diode. The wave diode would be analogous to the electrical diode, which conducts electricity in only one direction (It may also be one of the more understandable parts of quantum computing). Further applications could include police observation mirrors that do not require one room to be darkened and, as Lepri suggests, similar systems for sound waves. In fact, it is possible that any system involving waves could be created to have this propagation asymmetry.
Posted on Sunday, 3rd July, 2011