1 Department of Photonics Engineering, Technical University of Denmark2 Plasmonics and Metamaterials, Department of Photonics Engineering, Technical University of Denmark3 Nanophotonics, Department of Photonics Engineering, Technical University of Denmark
This thesis describes the development, design and fabrication of the nanocoupler that is a device coupling light from conventional optical fiber to the nanosize plasmonic slot waveguide. This device can decrease the coupling region to several micrometers providing compact interface between an optical fiber and future optical integrated circuit. Multiple nanocoupler possibilities are analyzed. Two realizations are investigated: negative index metamaterial and plasmonic nanoantenna based. The cubic symmetric negative index metamaterial Split cube in Cage and Split cube in Carcass designs for the telecom frequencies are proposed. It is shown that despite the exceptional bulkness (effective properties do not depend on the number of layers) and cubic symmetry the abovementioned designs exhibit strong spatial dispersion in the frequency range of interest. That prevents treating them as an isotropic negative index material. The wave propagation retrieval method for metamaterials with linear and circular eigenpolarizations and the field averaging of the restored Bloch mode method are proposed for metamaterials effective properties characterization. The methods are based on observation of the wave propagation in the metamaterial slab. The methods are unambiguous, simple, can be applied to lossy and lossless metamaterials with negative and positive refractive index, permittivity and permeability. The technology of silver nanometallization of complex 3D dielectric structures is developed. The metallization is based on silver reduction from the silver-ammonia complex with formaldehyde. Continuous and smooth silver layer can be deposited starting from 30 nm. The technology can be used for the complex photonic structures fabrication for the infrared frequencies. The coupling effects between metamaterials monolayers are investigated. It is shown that some metamaterials can be treated as homogeneous in the resonant frequency region, but some cannot at any value of the metamaterials period. The quantitative homogenization condition is formulated. Five types of the nanoantenna based couplers are developed: dipole antennas outside symmetric and asymmetric waveguide, antennas gratings, antennas inside waveguide and battle axe nanocoupler. It is shown that the usage of the side and top reflectors generally increases the power captured by the nanocoupler from the incident wave. The optimized geometrical parameters of the nanoantenna couplers are found out. The best performance is shown by the battle axe nanocoupler that has an antenna figure of merit equal to 1.8 μm2 for five antenna periods. That is 90 times larger than antenna figure of merit for the waveguide without nanocoupler (0.02 μm2). The antenna nanocoupler fabrication technology is optimized. Plasmonic antennas nanocouplers are fabricated. Coupling to the plasmonic slot waveguide is experimentally demonstrated.