Planar magneto-photonic and gradient-photonic structures : crystals and metamaterials.

In the field of photonics, two new types of material structures, photonic crystals and metamaterials, are presently of great interest. Both are studied in the present work, which focus on planar magnetic materials in the former and planar gradient metamaterials in the latter. These planar periodic structures are easy to handle and integrate into optical systems. The applications are promising field for future optical telecommunication systems and give rise to new optical, microwave and radio technologies. The photonic crystal part emphasizes the utilization of magnetic material based photonic crystals due to its remarkable magneto-optical characteristics. Bandgaps tuning by magnetic field in bismuth-gadolinium-substituted lutetium iron garnet (Bi0.8 Gd0.2 Lu2.0 Fe5 O12) based one- dimensional photonic crystals are investigated and demonstrated in this work. Magnetic optical switches are fabricated and tested. Waveguide formulation for band structure in magneto photonic crystals is developed. We also for the first time demonstrate and test two- dimensional magneto photonic crystals optical. We observe multi-stopbands in two- dimensional photonic waveguide system and study the origin of multi-stopbands. The second part focus on studying photonic metamaterials and planar gradient photonic metamaterial design. We systematically study the effects of varying the geometry of the fishnet unit cell on the refractive index in optical frequency. It is the first time to design and demonstrate the planar gradient structure in the high optical frequency. Optical beam bending using planar gradient photonic metamaterials is observed. The technologies needed for the fabrication of the planar gradient photonic metamaterials are investigated. Beam steering devices, shifter, gradient optical lenses and etc. can be derived from this design.

Negative index metamaterials and metaspacers for optical frequencies

Metamaterials are artificial materials that exhibit properties, such as negative index of refraction, that are not possible through natural materials. Due to many potential applications of negative index metamaterials, significant progress in the field has been observed in the last decade. However, achieving negative index at visible frequencies is a challenging task. Generally, fishnet metamaterials are considered as a possible route to achieve negative index in the visible spectrum. However, so far no metamaterial has been demonstrated to exhibit simultaneously negative permittivity and permeability (double-negative) beyond the red region of the visible spectrum. This study is mainly focused on achieving higher operating frequency for low-loss, double-negative metamaterials. Two double-negative metamaterials have been proposed to operate at highest reported frequencies. The first proposed metamaterial is based on the interaction of surface plasmon polaritons of a thin metal film with localized surface plasmons of a metallic array placed close to the thin film. It is demonstrated that the metamaterial can easily be scaled to operate at any frequency in the visible spectrum as well as possibly to the ultraviolet spectrum. Furthermore, the underlying physical phenomena and possible future extensions of the metamaterial are also investigated. The second proposed metamaterial is a modification to the so-called fishnet metamaterial. It has been demonstrated that this ‘modified fishnet’ exhibits two double-negative bands in the visible spectrum with highest operating frequency in the green region with considerably high figure of merit. In contrast to most of the fishnet metamaterials proposed in the past, behavior of this modified fishnet is independent of polarization of the incident field. In addition to the two negative index metamaterials proposed in this study, the use of metamaterial as a spacer, named as metaspacer, is also investigated. In contrast to naturally available dielectric spacers used in microfabrication, metaspacers can be realized with any (positive or negative) permittivity and permeability. As an example, the use of a negative index metaspacer in place of the dielectric layer in a fishnet metamaterial is investigated. It is shown that fishnet based on negative index metaspacer gives many improved optical properties over the conventional fishnet such as wider negative index band, higher figure of merit, higher optical transmission and stronger magnetic response. In addition to the improved properties, following interesting features were observed in the metaspacer based fishnet metamaterial. At the resonance frequency, the shape of the permeability curve was ‘inverted’ as compared to that for conventional fishnet metamaterial. Furthermore, dependence of the resonance frequency on the fishnet geometry was also reversed. Moreover, simultaneously negative group and phase velocities were observed in the low-loss region of the metaspacer based fishnet metamaterial. Due to interesting features observed using metaspacer, this study will open a new horizon for the metamaterial research.