Spatial filtering by axisymmetric photonic crystals

Abstract

Photonic crystals due to their angular bandgaps and quasi-bandgaps can provide spatial (angular) filtering of light. Two-dimensional photonic crystals (photonic structures modulated along the longitudinal and along one transverse dimension) can provide spatial filtering in one one-dimensional, decreasing the beam divergence in one quadrature. Three-dimensional crystals can provide two-dimensional filtering, with the shape of the filtering window corresponding to the symmetry of photonic crystal (e.g. forming a quadratic, or hexagonal shape beams). For many applications axisymmetric spatial filtering is required, in order to obtain diffraction limited axisymmetric Gaussian beams. For that purpose we developed and fabricated axisymmetric photonic crystal-like structures (periodic in longitudinal direction, but aperiodic in transverse direction). We overview the axisymmetric filtering: physical principles, simulations, fabrication, and experimental measurements.