Subwavelength Grating Polarization Device Design

With the rapid progress in microfabrication technology in recent years, it is of practical significance to design and consider subwavelength optical elements. The subwavelength optical elements with features smaller than the wavelength of the incident illumination do not give rise to diffraction other than the zeroth orders in the substrate and incident medium. Furthermore, they are thin, compact and suitable for the integrated optical systems. A direct result of the progress in nanofabrication techniques is the increasing demand for accurate models of the optical behavior of these novel structures. Numerical simulations provide a framework for quick low-cost feasibility studies and allow for design optimization before devices are fabricated. In this dissertation, a reflective polarizer based on a double-layer subwavelength metal-dielectric grating structure has been designed for the first time. The rigorous coupled-wave analysis technique for describing the diffraction of electromagnetic waves by periodic grating structures is reviewed. Numerical simulations show that at normal incidence, it is difficult to achieve high polarization extinction ratio which is reflected by the single-layer subwavelength metal or dielectric grating.A reflective polarizer based on a double-layer subwavelength metal-dielectric grating structure is presented here. Numerical simulations show that at normal incidence, this polarizer reflects light polarized perpendicular to the grating lines (transverse magnetic polarization), but strongly absorbs parallel-polarized light (transverse electric polarization). The polarization extinction ratio is very high. This polarizer is an attractive candidate because it is in a compact format, and the fabrication can be made compatible with the existing semiconductor technology. We investigate the effect of fabrication errors on the performance of the novel polarizer. The results of our simulations indicate that the polarizer is sensitive to overetching fabrication errors. However, it is relatively immune to the effect of fabrication errors in the duty cycle and underetching. Consequently, we should avoid the overetching fabrication errors in the process of fabrication.