Reentrant Delocalization Transitions in One-Dimensional Photonic Quasicrystals

The one-dimensional Aubry-Andre model describes tight binding systems with a quasiperiodic modulation of on-site potentials. The model predicts a localization of eigenstates that is generic for waves after reaching a threshold modulation strength, which has been previously studied in acoustic and photonic systems. We fabricate a one-dimensional photonic quasicrystal at varying modulation strengths using plasma enhanced chemical vapor deposition (PECVD), where alternating layers of Si and SiO2 are deposited at thicknesses similar to the Aubry-Andre model. The sample is then characterized by a super continuum laser, and we observe a strong suppression of the transmission of light, correlated with a sharp localization of electromagnetic eigenstates, at a threshold modulation strength. We also observe a novel second "reentrant" transition upon further increasing modulation strength where transmission of light becomes unsuppressed and the eigenstates enter a delocalized phase; We explain these effects qualitatively through a dimerized tight binding system with long-range couplings.