Fast, surface plasmon-polariton-based optical phase modulator

摘要

There exists a growing need for fast spatial optical phase modulators in various applications including laser communication for both terrestrial and ground-to-space communications, ultrafast laser pulse shaping as well as in medical imaging. The two principal phase spatial light modulator technologies currently available namely, liquid crystal and digital micro-mirror are limited to frame rates of a few kHz. A need therefore exists for faster MHz-range spatial phase modulating devices. Existing solid state electro-optical modulators such as based on LiNbO_3 crystal, although capable of GHz rate modulation rates, cannot be used for 2-D spatial light modulation. This is due to their relatively small electro-optical coefficient which requires the use of a relatively thick layer and its associated large, (100's of Volt) modulating signal, thereby barring their practical use as spatial light or phase modulators. Surface plasmon polariton resonances which can be excited at the metal-dielectric interfaces have been shown to significantly affect both the amplitude and the phase of the traversing optical beam. In this work we present a preliminary study of metallic nano-particles embedded in a solid state electro-optical modulator (EOM), as potential spatial phase modulating device. Here, the spatial refractive index modulation of the EOM, allows, the modulation of either amplitude of phase modulation, with the added advantage of potentially ultra-fast frame rates. The results of computer simulations, based on finite difference time domain (FDTD) method, with various nano-particle geometries are reported, describing the achievable phase modulation along with the associated absorption losses.