APPLICATION SPECIFIC NANOANTENNAS AND NANOPHOTONIC DEVICES

Abstract

Recently, nanoantennas have become one of the most fascinating technologies in the field of optics and photonics. Nanoantennas have been found capable of producing strong enhanced and highly localized light fields. Existing research on them has shown their considerable applications in diverse fields such as the near-field optical microscopy, spectroscopy, chemical, bio-sensing, and optical devices. Thus the useful results prompt us to implement a more systematic and further exploration on nanoantennas of some specific configurations of interest. Nanoantennas are known for converting electromagnetic energy into confined field. Electric field enhancement and radiation efficiency are the important parameters for measurement of harvesting efficiency of nanoantenna. In this thesis, different structures of nanoantennas have been designed to enhance and confine the electric field, when it interacts with electromagnetic radiation in the optical region. A petal shaped nanoantenna has been designed and studied for radiation efficiency and harvesting efficiency. Various geometrical parameters, such as the length, the width, the height and the gap of the nanoantenna have been varied to find their effect on the radiation efficiency and the harvesting efficiency. Additionally, the significance of the material of the nanoantenna has also been studied by choosing four different types of materials, and their corresponding radiation efficiency, harvesting efficiency and electric field enhancement have been reported. Other than this, flower shaped nanoantenna, arrow shaped nanoantenna, tapered cone shaped nanoantenna have been designed for the same application. Further, novel designs of nanoantennas for the enhancement of magnetic field in the near infrared region have been modelled. The designed nanoantennas have been thoroughly analysed by varying various geometrical parameters to find their effect on magnetic field enhancement. Also, different materials have been considered for the nanoantenna, to investigate the significance of the choice of the material effect on magnetic field enhancement. The proposed structures can prove to be a good alternative for the enhancement of magnetic field as compared to the various paramagnetic and ferromagnetic materials, having weak magnetic properties in the optical regime. Plasmonics is widely used for converting electromagnetic radiation into energy and confining electromagnetic radiation below the diffraction limit. However, the ultra narrowband and high electromagnetic field cannot be obtained simultaneously because of resistive loss and radiation damping in the metals. In this thesis, a metallic ultra-narrow band perfect absorber VI has been proposed consisting of an array of four squares on a silver layer. The structure shows more than 99% absorption and full width at half maxima less than 2 nm at resonance wavelength. The absorption mechanism has been revealed by calculating electric and magnetic field profiles. The dependence of the structure on the geometrical parameters has been studied and the structure has thus been optimized at 692 nm i.e. in the visible range of frequency. The proposed structure is then investigated for sensing application. The structure shows high sensitivity of 680 nm/RIU in the visible range of wavelength and a high figure of merit of 348.72. In previous years optical trapping of nanoparticles such as magnetic nanoparticles, proteins, λ-DNA, gold nanoparticles, polystyrene and silica beads catches researcher’s attention. Plasmonic nanoantenna due to its ability to enhance electric field in subwavelength region are widely used for optical trapping. For ideal trapping high trapping stiffness is required along with using a low intensity power Laser, so that there will low heat generation and no damage occurred to delicate nanoparticles. In this thesis, an attempt to design a nanoantenna which can trap nanoparticle of order tens of nanometre with high trapping stiffness using low power Laser has been done so that nanoparticle can easily be trapped without getting damaged.