Spatial accumulation of phase difference in spoof plasmon based Mach-Zehnder Interferometer

An active beam steering structure comprising the spoof surface plasmon polariton (SSPP) waveguide is presented. The proposed structure consists of two stages: the two arms structure as a Mach-Zehnder interferometer (MZI), and free space propagation stage. The SSPP waveguide includes periodic grooves, which are filled with a thin layer of doped semiconductor like GaAs. By applying electric voltage at the electrodes on top of the waveguide, the depletion layer thickness and the effective refractive index of the dielectric inside the grooves can be changed. The effective refractive index of the dielectric inside the groove is derived analytically and the phase change of the propagation wave along the single sided SSPP waveguide is calculated as a function of input voltage. The relation between the input signal and the angle of maximum radiation of output beam is investigated and the linearity is improved. We have shown that the MZI beam steering section has the capability to bend the electromagnetic beam about 42 degrees. At the end, we presented an application of the proposed beam steering device as a spatially accumulated phase difference structure that can be utilized in devices such as digital-to-analog converter (DAC).