2D Photonic Crystal Slabs
The controlled inclusion of defects in photonic crystal structures is highly interesting for application and industry, because it offers the possibility of designing high-Q cavities and waveguides on scales of the wavelength. From the experimental point of view this is still an unsolved problem for the case of three-dimensional crystals. But luckily, many of the interesting properties are still feasible in two-dimensional system. In the past many suggestions have been made for the use of 2D-crystal for applications in optical electronics. The problem is, that most of this suggestions base on idealized 2D models with an infinitely extended third dimension. But life is never ideal, let alone two-dimensional. The idea is now to make the structures finite and use total internal reflection to guide the light in the direction perpendicular to the 2D crystal plane.
In our group we analyze the optical properties of such 2D-slab systems in close cooperation with experimental and industrial partners, especially with respect to the effects due to finite height. Currently, we study propagation with very small group velocities in IOSOI (Insulator-on-Silicon-on-Insulator) sandwiches, patterned with a hexagonal hole lattice and various types of defects. In figures 1-3, for example, you can see waveguide-modes of a missing row of holes. This activity is part of the HiPhocs-Project funded by the BMBF and in close collaboration with the Max-Planck-Institut für Mikrostrukturphysik in Halle.
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All calculations are performed using programs based on FDTD-algorithms. Because this algorithm can solve very general scattering problems, we are also able to address the problem of integrating photonic crystal devices in conventional optical circuits. The following pictures show results of a diploma thesis, that dealt with the coupling of a conventional ridge waveguide to a line defect in a square arrangement of finite dielectric cylinders. Fig. 4 shows the geometrical setup, fig. 5-8 the energy density parallel to the 2D crystal plane and fig 9-12 perdendicular to it.
Fig. 4
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