title: Polarization-independent self-collimation based on pill-void photonic crystals with square symmetry.
abstract: We investigate discrepancy and similarity in dispersion relations between transverse-electric (TE) and transverse-magnetic (TM) polarizations in rectangular, square and triangular two-dimensional photonic crystals. It is found that the square lattice is the most appropriate candidate to realize polarization-independent, i.e. absolute self-collimation (ASC) in the first photonic band since it possesses not only a relatively broad angular range for self-collimation but also a small difference in dispersion relations between TE and TM modes. By tailoring the shape of air voids in the square-lattice-based structure, the electric-field vector can be rotated to reduce the discrepancy between TE and TM modes whereby the frequency bandwidth of ASC can be enlarged to approximately 4.8%. The ASC phenomenon is demonstrated by numerical experiments based on a finite-difference time-domain (FDTD) technique with negligible propagation losses.
authors.affiliation: Laboratory of Photonic Information Technology, School for Information and Optoelectronic Science and Engineering, South China Normal University, Guangzhou 510006, PR China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Xu
authors.forename: Xiao-Jun
authors.initials: XJ
authors.lastname: Chen
authors.forename: Sheng
authors.initials: S
authors.lastname: Lan
authors.forename: Qiao-Feng
authors.initials: QF
authors.lastname: Dai
authors.forename: Qi
authors.initials: Q
authors.lastname: Guo
authors.forename: Li-Jun
authors.initials: LJ
authors.lastname: Wu