NANOTRANSDUCER · Modeling and Design of Thin Film Waveguides Terminated with Nano-optical Transducers

Modeling and Design of Thin Film Waveguides Terminated with Nano-optical Transducers

Project context and objectives There has been increasing interest in intense optical spots smaller than the diffraction limit for use in emerging nanotechnology applications. To address practical problems for utilisation in technological applications such as high-density data storage, the analysis and design of systems that address large body mass, high cost, and manufacturing difficulties are necessary. In this project, thin-film structures that offer advantages for overcoming these problems are analysed and designed. These structures can be mass-produced at a fraction of the cost of their three-dimensional (3D) counterparts using lithographic and thin-film deposition techniques known from modern integrated-circuit processing. Thin-film structures can make advanced optical devices more accessible to consumer electronics and research tools due to this reduced cost. In addition, thin films provide a small body mass compared to traditional lenses, which makes emerging data-storage applications more feasible. Project methodology In the first part of this project, the modelling and design of thin-film waveguide light-focusing devices are developed. Planar dielectric and metallic waveguides that have micro-optical elements such as planar solid-immersion lenses and planar solid-immersion mirrors are investigated. Using the developed model, the light localisation of planar waveguides with planar solid-immersion lenses and planar solid-immersion mirrors has been investigated for both linear and radial polarisation. A detailed formulation of the optical-field propagation in micro-optical elements is obtained. To model these structures, a ray-tracing-based algorithm is developed for the waveguide modes. The propagation of a waveguide mode through the micro-optical elements etched onto the waveguide are traced using reflection and transmission laws of optics, and the waveguide modes around the focal area are integrated. The formulation is similar to Richards and Wolf's vector-field equations. However, these equations were extended to waveguide modes. The formulation and code development is not only performed for the linearly polarised waves, but it is also performed for the donut mode analogous to the radial polarisation. A modelling tool is developed based on the results of the formulation. Using this modelling tool, various scenarios are investigated. Also in this project, thermal models are developed to address heating concerns for utilisation in high-technology applications. To calculate unknown thermal profiles, a three-dimensional finite-element method is used. The developed model is based on a time-dependent solution of the heat transfer equation. Therefore, the temporal evolution of the heating in near-field optical problems is obtained. Using the thermal model, various parameters regarding the radiative heat transfer in near-field optical problems are investigated. Thermal issues are particularly important for emerging nanotechnology applications, such as heat-assisted magnetic recording, which require localised radiative energy transfer that can be achieved using intense optical spots beyond the diffraction limit. When objects are separated by less than a sub-wavelength scale, the radiative energy transfer between the surfaces can be several orders higher than predicted by Planck's blackbody radiation. The drastic improvement of the radiative energy transfer has potential applications in emerging technologies including heat-assisted magnetic recording, thermo-photovoltaic energy devices, and optically-assisted nanomanufacturing. Despite these potential applications, there has been little attention paid to the heating problems for near-field optical problems in the literature. Recently, there has been increasing research on the radiative-energy exchange between objects separated by less than a sub-wavelength scale. Heating issues are an important concern for near-field optical problems since the near-field optical applications utilise high input power focused into a small region in space. In this part of the project, thermal models are developed to address heating concerns for near-field optical problems. Using this model, various parameters regarding the radiative heat transfer in near-field optical problems are investigated. Another contribution of this project is the development of novel transducers and their detailed investigation and comparison with existing transducers. In this project, a novel nanotransducer has been constructed using the fundamentals of equivalence principle and image theory. The novel perpendicular-oriented-ridge waveguide nanotransducer, which is designed in this project, can be defined using lithographic techniques on the same plane as the magnetic heads. Therefore, it can be more easily integrated into the manufacturing technology of the current hard-disk-drive heads as compared to its longitudinal counterpart. This novel nanotransducer designed in this part of the project is a potential candidate for emerging technology for consumer products, such as heat-system magnetic recording. Other novel nanotransducers are also developed and analysed in this project, and these modelling and design results regarding these novel transducers are published in SCI journals. Project results The results of this research have been published in high-impact factor journals including Applied Physics Letters, Optics Express, and Physical Review A. Throughout this project, 12 refereed journal papers have been published in refereed SCI-index journals. In addition, Kursat Sendur and his students presented the findings of the research project at international conferences and invited talks at various institutions. A total of 23 international conferences and invited talks have been given during the reintegration period. In addition, Dr Kursat Sendur recruited and trained four graduate students as a part of his research group. Three of these students, Umut Tok, Erdem Ogut, and Hasan Kurt, are PhD students, and Eren Unlu is an MS student. These students are now actively pursuing research in this area and contributing to the literature. Training these students with the help and knowledge created during the Marie Curie International Reintegration Grant has been an important contribution of this project for producing qualified researchers. The results of this project are very encouraging for emerging high-technology applications, particularly for data-storage systems. Planar optical elements that are investigated in this study are important for these emerging technological applications and they offer many advantages over their counterparts. They can be mass-produced at a fraction of the cost of their 3-D counterparts using lithographic and thin-film deposition techniques known from modern integrated-circuit processing. Thin-film structures can make advanced optical devices more accessible to consumer electronics and research tools due to the reduced cost. In addition, thin films provide a small body mass compared to traditional lenses, which makes emerging magneto-optical data storage applications more feasible. The results and designs have shown that the devices suggested in this project provide very promising results in terms of many metrics such as optical spot size, transmission efficiency, radiative energy transfer, and polarisation aspects at the nanoscale. The realisation of these devices that were designed in this project can address technological difficulties such as the major slowdown in the pace of areal density of hard disk drives. The practical devices that can be built based on these design tools will enable these advanced technologies, such as data storage, to reach the European Community, and will support information-technology-based economical growth throughout Europe. Advancements in these areas will contribute to European excellence through better computers and electronic consumer products.

Data: CORDIS, © European Union