Direct imaging of the leaky modes in a 2-D photonic crystal slab

In this paper, the resonances in a photonic crystal slab by imaging the near-field of the propagating modes is studied. This technique allows a separation of the direct and resonant contributions in the reflection and gives an unambiguous measure of the propagation length of the modes. The photonic crystals in our study consist of a square array of 300x300 holes with radius r ap270 nm and lattice constant a = 940 nm, fabricated in a 150 nm thick free standing AlGaAs membrane. To obtain an optical image of the near field in reflection, we illuminate the array with a strongly focused (NA=0.5) laser beam at a wavelength of 762 nm and image the reflected light onto a CCD camera.