Near Field Control of Optical Wavefronts

Photonics is the study of interaction between light and matter, of using various forms of structured and unstructured matter to shape and control the propagation of light. Plasmonics, using near field interactions of metal-dielectric interfaces to control the propagation of optical wavefronts, is a rich area of study with applications in fields such as biosensing, thin film metrology, high-speed ultra-compact integrated modulators, and metamaterials, to name a few. In this work, plasmonics is used to develop devices that enhance both non-linear optical phenomenon and linear electro-optic processes. Non-linear optical phenomenon, such as raman scattering from biological media and two-photon absorption in silicon where enhanced via light concentrating plasmonic media, such as millimeter-scale high-density nanoantenna arrays and and roughened noble metal thin-films, were used to realize ultra-fast optical auto-correlators on a silicon-chip photo-detector and to implement compositional analysis of DNA base pairs via surface enhanced raman spectroscopy. Likewise, the knowledge gained from these efforts in manipulating light in the near-field evanescent regime to enhance non-linear optical phenomena inspired a novel approach of space-variant modulation of free-space optical wavefronts based on surface plasmon resonance enhancement of the linear electro optic or pockel's effect. Current state of the art spatial light modulators are limited to kHz speeds. To realize higher operating speeds, advances in high speed free-space electro-optic transduction are necessary. In this work, electrically driven control of free-space optical fields at a wavelength of 1550 nm at GHz modulation speeds is demonstrated using a programmable plasmonic phase modulator based on near field interactions between surface plasmons and materials with a high linear electro-optic (Pockel’s) response. High χ(2) dielectric thin films are used as an active modulation layer in a surface plasmon resonance configuration to realize programmable space-variant control of optical wavefronts at GHz speeds. The programmable plasmonic phase modulator demonstrated here represents a proof of principle demonstration of a path towards GHz speed spatial light modulation