Most previous studies of two-dimensional (2D) photonic crystals have focused almost exclusively on the propagation of light within the array plane. In the present work, we have studied experimentally the propagation along directions that lie both inside and outside the array plane. These results provide information relevant to all applications envisioned for such 2D photonic crystals, including optical waveguiding and the inhibition of spontaneous emission, because in all practical situations the propagating light is not strictly confined to the array plane. This work was possible because of the availability of relatively large nanochannel-glass-based photonic crystals, with volumes greater than several cubic millimeters and submicrometer periodicities. Our initial experiments have examined the propagation of light through relatively low index-contrast photonic crystals, consisting of triangular arrays of glass cylinders within a matrix composed of a different glass. By sandwiching these photonic crystals between suitable glass prisms, we have gained access to precisely defined out-of-plane propagation directions.
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