Gapped Surface Plasmon Polariton Waveguide Device Based on a Liquid Crystal

We propose a gapped surface plasmon polariton waveguide (G-SPPW) device based on a liquid crystal (LC) at a wavelength of 1.55 μm. The G-SPPW device is composed of an input 2.0-μm-wide and 5.0-μm-long insulator-metal-insulator waveguide (IMI-W), an 8-μm-long gap, and an output 2.0-μm-wide and 25.0-μm-long IMI-W. The LC is used for the gap and the 5.15-μm-thick upper and lower dielectric layers. The input surface plasmon polaritons (SPPs) propagate and jump over the gap in the G-SPPW with a coupling loss of less than ~0.68 dB. The propagation and coupling losses of the 38-μm-long G-SPPW device are varied in the range of ~0.5268 dB to ~2.6716 dB and ~0.1446 dB to ~0.6784 dB, respectively, with LC tilt angles (θ1,2) = 0°~90° at a fixed 90° twist angle. The normalized transmission of the G-SPPW device is also varied in the range from -3.351 dB to -0.6714 dB with θ1,2 = 0°~90° at a fixed 90° twist angle. The output SPP characteristics of the G-SPPW device can be properly controlled by the orientation of the LC molecules. The proposed G-SPPW device shows potential for new active plasmonic device applications.