Fabrication of photonic crystals for the visible spectrum by holographic lithography

The term 'photonics' describes a technology whereby data transmission and p rocessing occurs largely or entirely by means of photons. photonic crystals are microstructured materials in which the dielectric constant is periodic ally modulated on a length scale comparable to the desired wavelength of op eration. Multiple interference between waves scattered fr om each unit cell of the structure may open a 'photonic bandgap'-a range of frequencies, ana logous to the electronic bandgap of a semiconductor, within which no propag ating electromagnetic modes exist(1-3). Numerous device principles that exp loit this property have been identified(4-8). Considerable progress has now been made in constructing two-dimensional structures using conventional li thography(3), but the fabrication of three-dimensional photonic crystal str uctures for the visible spectrum remains a considerable challenge. Here we describe a technique-three-dimensional holographic lithography-that is well suited to the production of three-dimensional structures with sub-micromet re periodicity. With this technique we have made microperiodic polymeric st ructures, and we have used these as templates to create complementary struc tures with higher refractive-index contrast.