Design, nano-fabrication and analysis of near-infrared 2D photonic crystal air-bridge structures

Selective wet etching is a technique that allows fabrication of freely suspended thin slabs in epitaxial heterostructures. This technique, together with high-aspect ratio dry etching, is used to create two-dimensional (2D) photonic crystals for near-infrared wavelengths in thin suspended AlGaAs membranes. The active photonic crystal areas contain hexagonal arrays of cylindrical holes completely perforating the membrane. For an appropriate selection of the slab thickness and the lattice parameter, dispersion relations for the guided modes are explicitly computed by solving the Maxwell equations in a geometry containing a 2D photonic crystal defined in the core layer of a dielectric waveguide structure. Measurements of the spectral transmittance in air-bridge samples show a narrow 30-dB-deep stop band for TM polarized incident light. The spectral position of the stop band shows a good agreement with theoretical band structure calculations when also the ‘quasi-guided’ resonant modes outside the light cone are taken into account.