Experimental verification of cross talk reduction in photonic crystal waveguide crossings

We have experimentally demonstrated a very low cross talk in photonic crystal waveguide crossings of any kind. For cross talk reduction, we added a resonant cavity to the waveguide intersection designed to operate in microwave frequencies. The two-dimensional waveguide crossing structure was sandwiched between two parallel metal plates to eliminate radiation loss in the vertical direction. Transmission measurements revealed that when designed properly the cross talk reduction was as large as -30 dB at resonance, which is qualitatively consistent with simulation results. From the experimental results, the detailed resonant mode shape at the waveguide intersection was found to play a key role in relaying the input signal in the forward direction and therefore reducing cross talk.