Feasibility of Plasmonic Circuits in Nanophotonics

Abstract

The configuration of plasmonic circuits comprising SiO2-load waveguides and their characteristics within the nanophotonic range are presented and compared with electronic and lightwave circuits in 1300 and 1550 nm wavelength bands. In the nanophotonic range of less than 1 m, plasmonic signals propagate in narrow waveguides with cross-sections less than a few hundred square nanometers, while lightwaves exhibit only slight propagation in high-refractive-index (i.e., Si) waveguides owing to the transmission loss increase via the cut-off wavelength of the waveguide. Additionally, the plasmonic signal transmission loss is lower than that of electric signals for transmission lengths less than a few hundred micrometers. During signal transmission, a narrow spectral width of the plasmonic signals is needed to suppress any signal shape deformation induced by the frequency dependence of the collective oscillation of electrons in plasmonic signals. In the nanophotonic range, the degree of integration for plasmonic circuits is not governed by the transmission loss but by the leak distance of the plasmonic signal optical field from the side-walls of the waveguides and components. Employing a metal/insulator/metal structure in plasmonic circuits is a valid way to heighten the integration density, and its effectiveness is numerically and experimentally confirmed in a plasmonic multiplexer less than 1 m in length. On the basis of these results, the feasibility of plasmonic circuits is discussed and it can be said that plasmonic circuits including waveguides and components are promising photonic techniques for signal transmission in the nanophotonic range.INDEX TERMS Integrated circuit, Integrated optics, Integrated optoelectronics, Nanophotonics, Optical interconnection, Plasmonics, Surface plasmon polariton, Wavelength division multiplexing. I. INTRODUCTIONPhotonics has historically been used to support daily life of our society, and the techniques in the field are indispensable for constructing and maintaining societal infrastructure. These techniques require key photonic components whose scale and power consumption requirements are being reduced as technology advances. Recently, optical interconnects have begun to be used in silicon integrated circuits (ICs) to enhance the information processing speed and catch up with the explosive increase in information demand. The lightwave circuits of interconnects typically comprise silicon waveguides that possess a relatively high refractive index. In the range of less than sub-wavelength optics, however, photonic crystals and high-refractive-index waveguides using lightwaves as signals are physically difficult to apply to circuits [1].At such small scales, surface plasmon polariton (SPP) waveguides are effective for constructing nanophotonic circuits. Various kinds of plasmonic waveguides have been developed and reported, such as index waveguides [2]-[5], grooved waveguides [6], [7], hybrid waveguides [8]-[10], and metal/insulator/metal (MIM) structured waveguides [11]-[16]. These v...