We report a simple spin-coating technique for the production of monolayer nonclose-packed colloidal crystals. Dispersions of submicron silica spheres in triacrylate monomers are spincoated and polymerized to form two-dimensional colloidal crystal-polymer nanocomposites. By removing the polymer matrix, wafer-scale nonclose-packed colloidal crystals with high crystalline quality can be made. The technique is compatible with standard microfabrication and allows for the production of microstructures for potential devices. Normal-incidence reflectivity spectra in the visible and near-infrared regions show sharp peaks due to Bragg diffraction from the colloidal monolayers. The peak position matches with the theoretical prediction using scalar wave approximation.

The superprism phenomenon is the extremely large angular dispersion experienced by a light beam when entering a photonic crystal. This arises from the anisotropy of the photonic band structure. Strong anisotropy can be present even in systems without a complete photonic band gap. Here, we describe a theoretical investigation of the superprism effect in three-dimensional macroporous polymer photonic crystals formed from colloidal crystal templates. From the complete photonic band structure, an equal-energy surface ͑dispersion surface͒ is obtained. The propagation direction inside the photonic crystal is determined by the gradient of this surface. Using this formalism, we explore the extreme sensitivity of the propagation direction to various input parameters, including the input angle, the light frequency, and the composition of the photonic lattice. Such effects can be exploited for sensing and filtering applications.

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We measure the normal-incidence transmission coefficient of photonic crystal slabs with hexagonal arrays of air holes in silicon. The transmission spectra exhibit sharp resonant features with Fano line shapes. They are produced due to the coupling of the leaky photonic crystal modes, called guided resonances, to the continuum of free-space modes. We investigate the effects of several types of structural disorder on the spectra of these resonances. Our results indicate that guided resonances are very tolerant to disorder in the hole diameter and to interface roughness, but very sensitive to disorder in the lattice periodicity.

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.