We present a generalized picture of out-of-plane diffraction in a two-dimensional photonic crystal using the concept of photonic bands and employing a three-dimensional, equal-frequency-surface analysis. We show that the discrete spots of diffraction pattern in a weakly modulated photonic crystal, including those of conventional diffraction gratings, become continuous when the dielectric modulation becomes finite. Furthermore, in a finite-modulated photonic crystal, the diffraction can take place even in the region prohibited by Bragg’s law: there are available states for the incident light, which are evanescent in the case of a diffraction grating (weakly modulated photonic crystal).
© 2008 Optical Society of America
Diffraction and Gratings
Original Manuscript: September 18, 2007
Revised Manuscript: March 2, 2008
Manuscript Accepted: March 7, 2008
Published: April 21, 2008
G. Alagappan, X. W. Sun, and M. B. Yu, "Out-of-plane diffraction of a two-dimenisonal photonic crystal with finite dielectric modulation," J. Opt. Soc. Am. A 25, 1098-1103 (2008)