Date of Graduation

5-2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Electrical Engineering

Advisor/Mentor

Simon S. Ang

Committee Member

Roy C. McCann

Second Committee Member

Zhong Chen

Third Committee Member

Surendra P. Singh

Keywords

Diffraction grating, Guided mode resonance, Near IR polarizer

Abstract

The objective of this research is to design a larger submicron linear polarizer in the near-infrared wavelength range with a wide bandwidth which can be fabricated using the conventional thin-film microfabrication technology to reduce cost. For this purpose, a gold (Au) wire-grid transmission-type transverse-magnetic (TM) polarizer and a silicon (Si) wire-grid reflection-type TM polarizer, were designed using the guided-mode-resonance filter. The Au wire-grid TM polarizer of 700nm grating width and 1200nm grating period has 95% transmittance at 2400nm, more than 1000nm resonance peak bandwidth, and an extinction ratio (ER) of around 300 with a moderated level of sidebands. The 700nm grating width and 1200nm grating period satisfied the microfabrication requirements and achieved the low-cost objective of this research. The ER increases with increasing the wire grid thickness but in this case, its resonance peak moves to longer wavelengths. A cavity resonance existed for the first time between two adjacent wire grids when the grid thickness is greater than 800nm. The Si wire-grid polarizer of 500nm grating width and 1400nm grating period has two high transmission bands, one at 1500nm-1950nm with a 40% transmittance and the other at 2100nm to 3500nm with an above 95% transmittance. However, this Si wire-grid polarizer has a low extinction ratio and very noisy sidebands. Optimizations of these polarizers were performed by changing their periods, wire grid widths, and thicknesses using the COMSOL wave optics simulation tool. The benefit of using this tool is that besides zero-order diffraction, 80 to 120 higher-order diffractions can be included to simulate submicron polarizers to yield more realistic simulation results.

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