Spatial filtering by chirped photonic crystals

Abstract

We show, theoretically and experimentally, that chirped photonic crystals (where the longitudinal modulation period varies along the propagation direction) can provide a substantial spatial (angular) filtering of light beams. The chirped photonic crystals, in gapless configuration, were recorded in a bulk of glass, where the refraction index has been periodically modulated using tightly focused femtosecond laser pulses. The spatial filtering performance has been studied in detail, and the filtering efficiencies up to approximately 50$%$ have been experimentally demonstrated.