Low-dimensional photonic crystals for integrated optics

Photonic crystals (PCs), or photonic bandgap (PBG) materials, are periodic dielectric structures that forbid the propagation of electromagnetic waves in certain frequency ranges. Although a full PBG is only possible in three-dimensional (3D) PCs most of all the intriguing phenomena characteristic for wavelength-scale periodic structures can already be observed and utilized in 2D PCs (periodicity in one plane) and even in 1D ones (well known Bragg reflector). Since fabrication of 3D PCs is still a challenge a lot of research effort is devoted to PCs of lower dimensions. Defect waveguides in 2D PCs capable of light confinement and lossless guidance through sharp bends, open new routes for compact integrated circuits. Unique dispersion properties of PCs can be utilized for realizing efficient light sources, dispersion compensators, or very narrow band optical filters. In the first part of this talk I will give a short introduction explaining basic properties of photonic crystals and some possible applications. In the second part I will review the research on 1D and 2D photonic crystals at the Royal Institute of Technology (KTH). KTH research on 2D PCs, formed as air holes etched through InP based slab waveguides, started in 2000 as a part of the European consortium on Photonic Crystal Integrated Circuits (PCIC) dedicated to integrated optics applications for the 1.5 μm telecommunication window. KTH has been focused on PC based optical filters, and has been active in both the fabrication, modelling, and optical characterization. In other KTH projects we have also dealt with optical filtering in ID PCs made as alternating layers of Si and SiO₂, and have recently started fabrication of 2D PCs in Si on SiO₂ substrate (silicon-on-insulator). Selected design examples as well as two recently realized filter demonstrators will be presented.