Polarization control of surface plasmon polaritons and its application to polarimeter

Abstract

Surface plasmon polaritons (SPPs) are electromagnetic waves propagating along the metal-dielectric interface. Plasmonics has been rigorously studied over the last decade, since SPPs are considered as one of the most promising candidates to accomplish highly integrated photonic circuits with their unique ability to squeeze light under the diffraction limit. Among various efforts to develop plasmonic elements in both passive and active ways, it is still a crucial issue how to generate SPPs with high coupling efficiency. Recently, nano-antennas with asymmetric structures have been showing that they could give directivity to generation of SPPs, so that the coupling efficiency could be more enhanced. In addition to directional excitation of SPPs, control of the direction attracts research interests in terms of plasmonic routers and multiplexed plasmonic elements. The polarization states of incident light is an adequate component to be a control signal, making use of polarization-selective nature of both SPPs and anisotropic scatterers. However, controllability of previous studies is bounded by binary operation in general with respect to the helicity or the orientation angle of the incident light. This dissertation investigates polarization control of SPPs and their application to a compact polarimeter. The controllability of SPPs is extended based on periodic nano-aperture arrays and polarized light, and their applications are suggested. First, the issue of interferometric-controlled optical devices is discussed. Interaction between light and optical devices can be tuned in all-optical manner with high modulation depth by controlling interference of coherent light. When two parallel arrays of aperture pairs are illuminated by linearly polarized light, interference of counter-propagating SPPs excited by the arrays can be controlled by the orientation angle of the incident light. Translation of optical path length can be replaced by the orientation angle rotation of the incident field. This makes experimental setup of the interferometry be significantly simplified. The second application deals with a compact polarimeter, an optical analyzer that detects the state of polarization (SOP). In order to measure the full-Stokes parameters, polarizers with different measuring SOPs are required. Polarization-selective excitation of SPPs can play a role of a polarizer since the selective excitation implies that SPPs are extinguished at a certain polarization. Hybrid aperture pair array and X-shaped aperture array are proposed to launch SPPs to a single direction when illuminated by the target elliptical SOP. Then, the aperture arrays are applied to the polarimeter, which are equivalent to four different elliptical polarizers. Polarization states can be measured at a single shot detection within a tiny system. I expect that this dissertation can help to develop more compact optical systems based on polarization-sensitive optical elements. Furthermore, I hope that this work inspires research on optical angular momentum interaction mediated by nano-structures surface waves.