Gap Plasmon Phase Modulator (IMAGE) Rutgers University Caption Surface plasmons are propagating electronic oscillations localized to metal-insulator (e.g. gold-air) interfaces. Gap plasmons (GPs) arise when two such interfaces are separated by a narrow gap across the insulator layer, transversely confining the electromagnetic energy in an MIM (metal-insulator-metal) waveguide. In this illustration, a free-space excitation laser (vertical light on the right) couples to GPs (alternating red/blue light) in a gold/air/gold nanofabricated waveguide. A grating is used to match the laser light momentum with to a GP. The GP propagates through the waveguide under free-floating micro-beams in the top gold layer (color coded to show depth). When the beams are electrically actuated towards the bottom gold layer, the effective refractive index of the waveguide increases under the beams, phase-retarding the GP. Credit Brian Dennis, Rutgers University Usage Restrictions Permission is granted to reproduce the image in connection with news coverage of this story. All other rights are reserved. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.