Abstract
We present polarization-dependent optical transmission properties of a W1 photonic crystal (PhC) waveguide realized in the completely symmetric insulator-on-silicon-on-insulator (IOSOI) material system. For an IOSOI W1 PhC waveguide we found a polarization crosstalk of -15 dB between TE- and TM-polarization. Furthermore, we found a transmitted signal in a spectral range where the calculated bandstructure predicts a bandgap and could verify this by FDTD simulations. This facts have to be taken carefully into account when designing PhC circuits.