Flat Lenses

We typically think of a lens as having two curved surfaces, the shape of which (also known as the angle of incidence) determines how light passing through it changes direction. A convex shape results in a converging lens, while a concave surface causes the light to diverge. The other factor that determines how the light will behave is the material from which the lens is made. When light slows down (by passing through glass, for example), it also changes direction – a process called refraction.

Now a new class of magnifying lenses has been developed that are flat and thinner than a human hair. They consist of millions of tiny antennae arranged in concentric circles on a substrate using nanolithographic manufacturing techniques. When light falls on them, it is scattered in a way that effectively changes its speed and direction without needing to vary the angle of incidence.

The thin, flat lenses can also be stacked to achieve nearly the same level of control as conventional glass lenses, which are bigger, heavier, and more costly to manufacture. The only drawback is that only about 50 percent of the light traveling through a triplet (three flat lenses sandwiched together) passes through, compared with 90 percent for glass lenses. The researchers are confident, however, that this can be improved by adjusting the shape and position of the antennae.

The new technology will have application in many fields, from eyeglasses to optical radar systems.