Transmission lines on periodic bandgap metamaterials: from microwaves to optics applications

The paper presents a transmission line (TL) approach developed in the field of metamaterials for planar devices and circuits. Materials under consideration are dielectric substrates, containing or not nanoscaled ferromagnetic inclusions, that can be arranged in a periodic way with specific impedances and phase velocities. They form photonic or periodic bandgap (PBG) substrates, on which planar guiding structures are deposited. These PBG substrates show some similarities with integrated Bragg reflector topologies previously investigated in the optical range. Using the TL concept, defect modes in PBG planar devices are studied. A theoretical explanation of defect mode operation, which is validated by measurement on a dielectric PBG structure, is proposed. It is then transposed to a magnetic PBG structure based on arrays of nanoscaled ferromagnetic nanowires. The effect on its frequency response of varying the defect length is discussed, in order to design planar sensors and filters. Extension of the magnetic PBG structure for applications in the optical range is finally proposed.