Research on Dielectric-Loaded Surface Plasmon Polariton Waveguides

Abstract

Surface plasmon polaritons (SPPs) are electromagnetic waves which propagate along metal-dielectric interfaces. SPPs can overcome the diffraction limit, and they have received a lot of interest due to strong confinement of energy. Therefore, a variety of nanoplasmonic waveguides based on SPPs have been investigated. Dielectric-loaded surface plasmon polariton (DLSPP) waveguides are a representative example of nanoplasmonic waveguides. In this thesis, improvement of two characteristics of a DLSPP waveguide is studied, and realization of DLSPP waveguides is investigated. First, the efficiency of coupling between a DLSPP waveguide and a photonic waveguide is improved. For this purpose, the use of a dielectric with a higher refractive index than the previously used dielectric in [Opt. Express 18, 5314 (2010)] is proposed. The loss of the coupling between the photonic and DLSPP waveguides based on a dielectric of refractive index 1.57 is reduced to 2.3 dB, and the coupling is achieved through a 3-µm-long coupling region. The coupling loss is further reduced by modifying the DLSPP waveguide into a double-dielectric-loaded surface plasmon polariton (D2LSPP) waveguide. The D2LSPP waveguide can be coupled to the photonic waveguide with a coupling loss of 1.1 dB through a 4-µm-long coupling region. Moreover, almost only the fundamental transverse-magnetic mode of the D2LSPP waveguide is excited after the short coupling region. The coupling loss is about a third of that in the reference, and the coupling region length is about one order of magnitude smaller than that in the reference. Second, bends of DLSPP waveguides are improved. For this purpose, 60º fan-shaped bends of DLSPP waveguides are proposed. By reducing a bending angle from 90 to 60 and introducing a fan-shaped structure, the bending radius of the 60º fan-shaped bend is reduced to 2 µm, and its bending loss is just 0.76 dB. Finally, a fabrication process of DLSPP waveguide based on the commercially available photoresist SU8 is developed. The process consists of optical lithography, a lift-off step, e-beam lithography, etc. The characteristics of the fabricated DLSPP waveguides are discussed. Based on the DLSPP or D2LSPP waveguides and the 60º fan-shaped bends, which are investigated in this work, a highly-integrated planar lightwave circuit with a relatively low loss may be developed.