Design and modeling of grating-assisted devices for microwave and optical applications

Abstract

Grating structures have found applications in microwave, millimeter wave, and optical devices and systems. While analytical methods can handle infinite, periodic gratings well, numerical methods usually are needed for general finite and/or aperiodic gratings. We have carried out numerical investigations of a number of grating structures with the finite-difference time-domain approach (FDTD). This approach is selected because of its ability to model complex structures and materials. Some of the many grating applications we investigated include gratings that can be used in waveguide environments as output couplers to transfer guided wave energy into radiation fields which propagate into predefined directions, as mode converters to convert energy between various modes in the same waveguide, or as directional couplers to transfer energy between different waveguides. Optical switching is also shown to be achievable and an efficient WDM demultiplexer is proposed and analyzed. The performance of grating assisted couplers in the presence of dispersive materials is also characterized. We have shown that the FDTD simulator is very effective in modeling complicated grating structures. Novel device features and operating behaviors have been revealed through its use. These results and observations provide insight and guidelines for the future design of various other grating assisted devices.