A superprism is a photonic crystal

Photonic crystal

Photonic crystals are periodic optical nanostructures that are designed to affect the motion of photons in a similar way that periodicity of a semiconductor crystal affects the motion of electrons...

 in which an entering beam of light will lead to an extremely large angular dispersion

Dispersion (optics)

In optics, dispersion is the phenomenon in which the phase velocity of a wave depends on its frequency, or alternatively when the group velocity depends on the frequency.Media having such a property are termed dispersive media...

. The ability of the photonic crystal to send optical beams with different wavelengths to considerably different angles in space in superprisms has been used to demonstrate wavelength demultiplexing in these structures.