Multifunctional beam steering via switchable negative refraction, self-collimation, and zero refraction effects in conventional and annular photonic crystals

Negative refraction (NR), self-collimation (SC), and zero refraction (ZR) effects of photonic crystals play an important role in beam steering. In this work, we report a multifunctional beam steering concept in photonic crystals, i.e., integrating two or three of the NR, SC, and ZR effects together at the same frequency. We find the square-lattice dielectric ring photonic crystal is an ideal candidate to realize the switchable function of ZR-SC while the square-lattice dielectric ring photonic crystal is more suitable for realizing the ZR-SC, ZR-NR, and ZR-SC-NR functions. The photonic band theory and an equivalent waveguide model are employed to explain these switchable functions in conventional and annular photonic crystals.