The superprism effect allows wide-angle deflection of the light beam in a photonic crystal (PC) by a slight change of the wavelength or the incident angle. In this paper, we discuss such light deflection outside the PC, which is expected when the output end of the PC is tilted against the input end. The analysis of the dispersion surfaces indicates a deflection angle of +/-50degrees in a two-dimensional PC composed of triangular lattice airholes by changing the incident angle by +/-2degrees or the wavelength by +/-2%. Light deflections inside and outside the PC are numerically demonstrated by the finite difference time-domain method. It displays not only the main output beam but also many diffracted waves, which satisfy the wavevector conservation condition. These waves are sufficiently suppressed and an almost collimated output beam is realized by a flat interface.
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