Credit: © 2007 AIP

A photonic crystal is a periodic structure that can used to manipulate the flow of electromagnetic radiation, such as light. The spacing inside the material does not allow certain wavelengths of light to propagate, the range of which is known as the photonic band gap. This gives rise to novel optical properties that can be used to make devices such as low-loss fibres. Although one-dimensional photonic crystals are already in widespread use and two-dimensional materials are nearing the market, the challenge remains to make three-dimensional systems — especially on a large scale.

Now, Jiaqi Chen and co-workers1 at the University of Texas at Austin in the USA have made three-dimensional photonic crystals from polymeric materials using holographic lithography. With a specially designed prism, a He–Cd laser was split into four beams that overlap to generate a three-dimensional interference pattern that can be used to pattern a photoresist. Depending upon the nature of the photoresists, the regions exposed to the laser light are either made soluble or insoluble — and the soluble portions are washed away with solvent to produce a periodic structure.

By tuning the wavelength of the laser and using different photoresists, photonic crystals with lattice spacings of 610 nm and 820 nm were produced. These materials can operate in the 1460–1565 nm window and can be used to guide the infrared radiation that is commonly used in optical communications.