|M.Sc Student||Segal Hagay|
|Subject||Light Transmission through 2D Structured Subwavelength Hole|
|Department||Department of Electrical Engineering||Supervisors||Professor Emeritus Gad Bahir|
|Professor Meir Orenstein|
|Full Thesis text|
A metal screen perforated by subwavelength holes can lead to a wide variety of optical phenomena such as enhancement and depression of light transmission at certain wavelengths. These observations have generated significant interest due to potential applications in near-field microscopy, photolithography, detectors and flat panel displays.
A fundamental limitation in light manipulation in these nanostructures is the extremely low transmission of these arrays of subwavelength holes. In this research, arrays of holes with novel shapes and different sample structures are analyzed in order to improve the transmission efficiency of the arrays. Polarization dependent array is an additional part of this research as well.
The typical sample consists of a glass substrate coated by a 200nm gold layer. A typical two-dimensional array consists of 23x23 holes with a constant period of 425nm.
This research focused on measuring zero-order transmission spectra through 2D arrays of holes with wavelengths from 400nm to 1000nm. The main challenge of the experimental set-up was obtaining a highly collimated white light (±2°) at a very narrow beam.
Arrays of four different hole shapes were fabricated: circular holes, square holes, circular coaxial holes and square coaxial holes. We show, to the best of our knowledge, the first systematic analysis of experimental coaxial holes based on numerical simulations of single holes as well as arrays of holes. Arrays of coaxial holes exhibit larger transmission efficiencies than arrays of circular and square holes of the same aperture area. These phenomena are probably due to the differences in cut-off wavelengths of each aperture.
A symmetrical dielectric-metal-dielectric sample was studied. In order to evaluate the hole filling influence on the transmission spectra, two different coating techniques on the air-metal interface of a typical sample were applied: index matching fluid coating and SiO2 deposition on perforated metal screen.
A supplemental transmission spectra efficiency of approximately 30% demonstrates by exchanging the unheated index matching fluid covering a hole array with heated index matching fluid. Record transmission efficiency of 52% for experimental finite arrays was achieved by covering a perforated gold screen of 100nm thick with SiO2.
We demonstrate, to the best of our knowledge, the first fabrication of an array of bow-tie holes and its evaluation for polarization dependencies. It demonstrated a polarization dependent filter behavior. To confirm the experimental results, simulations of geometrical parameter scans were presented which demonstrated various spectral tuning opportunities applicable on this unique structure.