Photonic Crystal Spatial Filters Fabricated by Physical Vapour Deposition

Summary form only given. The idea of the angular, or equivalently - spatial, filtering by photonic crystals (PhCs) is based on a selective diffraction of the light propagating through the double-periodic photonic structure. The angular components of the incident light at a resonance with the transverse and longitudinal periodicities of the structure diffract efficiently and are removed from the zero-diffraction order of the transmitted beam. On the other hand, the propagation of the angular components that are out of the resonances is unaffected. Therefore, the angular/spatial filtering can be obtained by a suitable geometry of the PhCs. This idea already proven itself as a useful alternative to conventional spatial filtering techniques, and is being implemented in several applications, for instance for intracavity angular filtering in microlasers [1]. Previously, the spatial filtering has been shown in so called Laue configuration of PhCs, where the longitudinal period is substantially larger than the wavelength. Here we present the first experimental demonstration of the angular filtering in the Bragg (subwavelength) configuration, where the longitudinal period is approximately the half of the wavelength. The spatially filtering photonic structure is fabricated by physical vapour deposition technique, specifically - glancing angle deposition (GLAD) method, which allows to vary the refractive index of individual layers easily and with high precision [2]. Preferred geometries are selected in accordance to finite difference time domain (FDTD) calculations. The main result, as described below, is still far from a "clean" angular filtering, however it already shows the signatures of the phenomenon, see Fig. 1.