Photonic Crystal Acts as Visible-Wavelength Superprism

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.