Bloch mode excitation in two-dimensional photonic crystals imaged by Fourier optics

Coupling into the Bloch modes of a two-dimensional photonic crystal (PhC) field is investigated by Fourier optics. The PhC was designed to operate in the second band above the air-light line, close to the autocollimation regime for TE polarization. The sample was fabricated in an InP-based heterostructure and an access ridge waveguide provides in-plane excitation of the PhC. The spatial Fourier transform of the field maps obtained from finite-difference time-domain simulations and those calculated by plane-wave expansion are compared to the experimentally obtained equifrequency surfaces (EFS). The shape of the imaged EFS and its variation with the excitation wavelength is shown to be consistent with the theoretical simulations. Finally, the results indicate that if combined with different excitation geometries, Fourier optics can be a powerful technique to assess photonic crystal devices and to design efficient structures.