Slanted-pore photonic band-gap materials

We present a detailed analysis of three-dimensional photonic band-gap materials consisting of lattices of slanted pores with n=2, 3, and 4 pores per unit cell. These slanted pores emanate from one or two masks consisting of a two-dimensional square or triangular lattice of holes placed on the top surface of the crystal. We also consider the case in which the top surface is "polished" at an angle after the first set of slanted pores is generated from the first mask. A second set of slanted pores is then generated from a second mask placed on the new angled surface. Using these architectures, we demonstrate photonic band gaps of up to 25% of the gap center frequency when the crystal is made from materials with a dielectric constant ratio of 11.9:1 (silicon with air pores). The proposed structures are amenable to microfabrication using established techniques such as x-ray lithography or two-photon direct writing in a polymer template, followed by inversion and replication of the template with polycrystalline silicon. They can also be microfabricated by direct plasma etching in single crystal semiconductors. An alternative fabrication protocol consists of photoelectrochemical etching of deep pores in a single crystal semiconductor followed by focused ion beam or reactive ion etching of the second lattice of directed pores.