Lens makers go flat out

Optics researchers in Canada have made a liquid-crystal lens with a focal length that can be adjusted by applying a voltage. The lens, which is flat, could have applications in mobile phones, laser cavities and surveillance equipment.

Vladimir Presnyakov and Tigran Galstian of the University of Laval in Quebec made their lens by adding a small amount of a light-sensitive monomer to a liquid crystal in a commercially available electro-optic cell and irradiating it with a laser beam.

The laser caused the monomers to form a polymer network, and since the intensity of the laser beam varied with position, the density of the network also varied with position. This in turn influenced the orientation of the liquid crystal molecules in the cell and the refractive index at different positions. Therefore, by carefully controlling the intensity profile of the laser, it is possible for the cell to act as a lens.

It is also possible to change the profile of the refractive index across the lens, and therefore the focal length of the lens, by applying a voltage. For instance, the Laval team was able to vary the focal length by a factor of five (from 1.6 to 8 metres) in a few milliseconds by increasing the applied voltage from 1.5 to 4.5 volts.

Presnyakov and Galstian say that their device is a good alternative to other prototype liquid lenses because it has no moving parts. Furthermore, they claim that their lens is simpler, more robust and more cost-effective than other lenses.