Fourier space imaging of light localization at a photonic band-edge located below the light cone

We observe light localization in a two-dimensional geometry, induced by residual disorder at a photonic band edge located below the light cone. The combination of a spectrally selective illumination and a grating assisted k-space imaging technique allows us to image the equifrequency surfaces associated with such a photonic band, with high accuracy and without aberrations. Thanks to this approach, the impact of the nonideal nature of real planar photonic crystals on the propagation properties of the Bloch wave at the band edge is decorrelated from the contribution of the intrinsic out-of-plane losses. As a by-product, our result demonstrates an immersion free effective numerical aperture as high as 3.5 in k space.