Out-of-plane scattering in photonic crystal slabs

Photonic crystal slabs combine a slab waveguide with an in-plane photonic c rystal. Light is then confined in-plane by the photonic crystal and out-of- plane by the slab waveguide. The etched structures will cause light to scat ter out of the waveguide plane, We studied the out-of-plane scattering loss es using a two-dimensional approximation of this three-dimensional structur e, with etched slots instead of holes, Our simulation techniques include mo de expansion with perfectly matched layer absorbing boundary conditions. We show that the losses increase with higher index contrast, but that with ve ry high-index contrasts light can be coupled into lossless Bloch modes.