טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentPazi Yuval
SubjectLocal Field Enhancement Using Rosette and Fractal
Nano- Antennas
DepartmentDepartment of Electrical Engineering
Supervisor Professor Meir Orenstein
Full Thesis textFull thesis text - English Version


Abstract

In the field of localized plasmonics it has been long understood that different structures made from different materials, create changes in the electromagnetic field enhancement spectrum. These nanometric sized structures are commonly referred to as "optical antennas" as they transform energy from near-field to far-field and vice versa, all in the optical regime. Although many types of antennas have been researched throughout history, both in the more common RF regime, and in the more newly developed optical regime, no optimal solution has been found for cases where large enhancement area, polarization independence, and flat spectral responses in two or more wavelengths, are desired. In recent years, many optical antennas have been designed in order to achieve these goals, however most of the resulted antennas were either lacking in spectral uniformity, or in polarization independence.

We investigate theoretically and experimentally different types of optical antennas, including fractal-shaped antennas, and a unique optical antenna, named the Rosette antenna, which shows promising characteristics in terms of both polarization and spectrum tunability. We have conducted a thorough simulative analysis of the parameters of the antennas leading to optimization of the parameters of the antennas given current fabrication capabilities. An enhancement of two orders of magnitude of the electric field intensity was achieved.  In addition, alterations in the structure of the rosette antenna were made in order to tune the spectral response of the antenna to achieve the goals set by this research including addition of resonances whilst maintaining the polarization independence of the antenna. After the simulation process, some of the rosette antennas were fabricated using electron beam lithography, and finally scattering experiments were conducted in order to experimentally verify consistency with the simulation results.

A 25?30% enhancement in the reflection coefficient of the rosette antenna was experimentally demonstrated at the expected resonance wavelength of the antenna. In addition, the expected polarization dependence of the antennas was successfully demonstrated for both the polarization dependent and independent antennas.

We expect this new type of antenna and its derivatives to have a great impact on devices currently enhanced by optical antennas, which were until now only limited to very small enhancement areas, or only utilizing part of the polarization space. As fabrication abilities advance, enabling greater enhancements, the Rosette antenna has an appreciable advantages for polarization independent applications with one or more working wavelengths.