Researchers from the University of Southampton and from Mesophotonics Ltd., both in Southampton, UK, have reported the fabrication of a photonic crystal superprism that operates at visible wavelengths. They described the optical element in the July 19 issue of Applied Physics Letters.The researchers created the structure by inscribing 160-nm-diameter air holes into silicon nitride waveguides on N-type silicon using electron-beam lithography and dry etching. The photonic crystal took the form of a 186 × 500-µm rectangular array of 600 rows of holes.To characterize the performance of the superprism, they employed broadband spectral and angular spectroscopy at wavelengths across the visible spectrum and into the near-infrared. Angular dispersion exceeded 1°/nm near the principal photonic bandgaps, which is more than 100 times greater than for a conventional prism of the same refractive index and 10 times greater than for an equivalent diffraction grating.