Signal Manipulation Based On Four-Wave Mixing Effects In Plasmonic Subwavelength Waveguides

Surface plasmons (SPs) are electromagnetic waves that exist at the interface between metal and insulator. Traditional optical components are generally bulky due to the diffraction limits. A prominent way to overcome such limits and improve integration density on single chips is to utilize the phenomenon of the surface plasmons. Because of the localized electric-field enhancement, the SPs waves can generate stronger nonlinear effects in subwavelength devices and find broad applications in spectrum manipulation, transmission enhancement, all-optical signal processing, and so on.In this paper, we investigate the nonlinear signal manipulation in plasmonic subwavelength waveguides theoretically and numerically.First of all, the basic principle of SPs and finite-difference-time-domain (FDTD) method are introduced, followed by the analysis of the features of negative permittivity materials (silver, gold, and so on).Then, by calculating the Maxwell’s equations, the characteristics (i.e. propagation mode, effective index, cutoff wavelength, and transmission spectrum) of the MIM-waveguides are investigated.Finally, FWM effects in MIM waveguides and the relationship between FWM efficiency and phase mismatch are theoretically analyzed. For a MIM waveguide with the core thickness of50nm, TM polarized lights could be transmitted, while the TE polarized ones are prevented. According to this phenomenon, NOT, NOR and NAND quasi logic functions are proposed. For a MIM waveguide with the core thickness of300nm, both TM and TE polarized lights could be transmitted. However, perpendicularly polarized incident lights could not lead to the FWM process due to the birefringence-associated phase mismatch. According to this phenomenon, NAND quasi logic function is proposed. These all-optical logic gates can overcome diffraction limits, which might have potential for the design of ultra-miniature and highly integrated all-optic circuits.