Dependence of guided resonances on the structural parameters of terahertz photonic crystal slabs

Using terahertz spectroscopy, we measure the normal-incidence transmission coefficient of photonic crystals consisting of a periodic lattice of air holes in a silicon slab. Sharp resonant features are observed in the transmission spectra due to coupling of the leaky photonic crystal modes, called guided resonances, to the continuum of free-space modes. The resonances show considerable sensitivity to the structural parameters of the slab, including the slab thickness. By varying each crystal parameter systematically, we study the dependence of the resonances on the geometry of the photonic crystal slabs. Even small changes in a parameter such as the slab thickness, for example, can lead to dramatic changes in the optical spectrum. We also compare the transmission spectrum of a photonic crystal slab with a hexagonal lattice to that of a slab with a square lattice. In most cases, the experimental results match very well with numerical simulations based on the finite element method. (C) 2008 Optical Society of America.