Optical antennas as nano-probes in photonic crystals and dielectric waveguide structures

The performance of dipole and bowtie nanoantennas coupled to a photonic crystal waveguide is analyzed by numerical simulations as a function of the antenna length. The antennas showed two resonances spectrally far apart from each other: one of them corresponds to the main antenna resonance and the other one to the allowed modes in the bandgap of the photonic crystal substrate. It is worth noting that the dipole shows a substrate resonance close to the lower edge of the bandgap and the bowtie shows a substrate resonance at the upper end of the bandgap. The results also show a nonlinear scaling between the resonant wavelength and the length of the antennas, this could be attributed to the coupling of the antenna resonance and the absorption resonance of the substrate material.