Surface-Plasmon Waveguides as Transmission Lines for Optical Signal and Electrical Bias

Using metal plasmonic waveguides as transmission lines for optical signals and an electrical bias is shown to be feasible in Si-based devices with a separation gap formed between the waveguide and Au/Si Schottky-barrier diode (SBD). Optical signal transmission is confirmed by calculating the radiation pattern from the waveguide edge and measuring the photocurrent detected at the SBD. From a finite-difference time-domain simulation, the radiation pattern from the waveguide edge is represented as an interference fringe. The simulation result for the separation-length dependence of the detected photocurrent at the SBD corresponds well with experiment. Moreover, the intensity-modulated optical signal at 10 MHz is also observed across the 3-μm-length separation gap. The electrical bias separation is confirmed by applying a bias voltage between the waveguide and the Si substrate and generating a bias current through the waveguide. The detected photocurrent at the SBD barely increased with changing bias voltage and was clearly smaller than that under changes in optical intensity. In addition, electrical current produced no influence on the surface-plasmon signal on the waveguide.