Photonic Crystal: Slabs / Gas-Sensors
Abstract
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C. Jamois, R. Hillebrand, F. Müller and R.B. Wehrspohn
This project deals with planar photonic crystals (PPCs). PPCs are a quite new class of PCs that consists of two-dimensional PCs in thin slabs of high-index material. Under some conditions a total internal reflection happens at the interface between the slab and the lower-index materials lying above and below it. This is a way to obtain three-dimensional light confinement in two-dimensional PCs. Using an analogy with fiber optics the central slab is usually called core and the two external layers claddings.
We are working here with a hexagonal lattice of air pores in a silicon core and two silicon oxide claddings (Fig. 1). The optimum design of the bulk PC leads to a full band gap for even (TE-like) modes larger than 30% (Fig. 2). Our aim is to introduce linear defects into the lattice to build waveguides and to study their dispersion properties both theoretically and experimentally.
Fig. 1. PC slab in an IOSOI structure.
The band structure and field distribution computations of the super-cell models are done applying the MIT package (http://ab-initio.mit.edu/photons/index.html ). The eigenvalue problems are solved by a frequency-domain based procedure. Iterative eigensolvers calculate the eigenstates of Maxwell’s equations. The fully-vectorial algorithm allows to identify the frequency eigenstates as well as the electromagnetic field modes.
Fig. 2. Band structure of the bulk PPC with r/a = 0.366 and h/a = 0.4, even (TE-like) modes only.
The transmission through the waveguides is studied with a FDTD method. The thicknesses of the different layers are 200 nm for the silicon core and 1 µm for both oxide layers. The lattice constant a of the structures is 450 nm and the pores have a diameter 2r of 300 nm. They are defined by lithography and etched using a RIE and ICP process through a Cr mask.