| dc.description.abstract | In recent years, surface plasmon polariton (SPP) has been widely investigated and applied to various fields such as biomedicine sensors, high-density data storage and access, super-resoultion microscopy, and high-efficiency solar cell etc. On the other hand, optical integrated circuits have regained more attentions due to the capability of metallic waveguide structures to overcome diffraction limit. As a consequence, there is a significiant growth on experiments and theories devoted to the research of SPP. In this thesis, finite-difference time-domain method (FDTD) was utilized for the simulation of the interaction between electromagnetic waves and structured materials. The linear and nonlinear propagation characteristics of proposed plasmonic waveguide structures were investigated, and the feasibility of using plasmonic waveguide devices to optical communications is assessed.
In the aspect of linear propagation, coupled rib plasmonic waveguides (CRPW), coupled plasmonic waveguides array (CPWA), and hetero-plasmonic waveguides (HPW) were proposed for wave-guding, polarization beam splitting, and wavelength-division multiplexer, respectively. The proposed CRPW was predicted to have a propagation length of 169μm at wavelength of 1550nm, knocking down presnt world record. In addition, bent waveguide and dual channel directional coupler basing on the same structure were investigated, aiming at assessing the feasibility of subwavelength optical integrated circuits. The results reveal that the CRPW can be utilized to construt subwavelength optical devices. Secondly, CPWA was proposed as a polarization beam splitter (PBS) that can separate TE and TM mode in spatially distinct output ports. After optimization of structural and material parameters, the obtainable insertion loss, extinction ratio, and the operational bandwidth are 1dB, 20dB, and 450nm, respectively. It is realizable on a chip size as small as 100nm×2000nm. Finally, a HPW was proposed as an angular wavelength-division multiplexer. The resolving power is estimated to be 2.1°/nm, which is higher by 200 times than a conventional prism and comparable to those made of photonic crystals. This device is potentially applicable to near field antenna.
In the aspect of nonlinear propagation, coupled nonlinear plasmonic waveguides array (CNPWA) was proposed as optical limiters constructed by metal array embedded in nonlinear materials. According to optical Kerr effect (OKE) and two-photon absorption (TPA), the optical limiters can be classified by Au/Kerr/Au waveguides array and Au/GaAs/Au waveguides array. The nonlinear absorption of Au/Kerr/Au waveguides array is due to the variation of plasmonic dispersion, which using strong fields to enhance the propagation constant of plasmonic, and then to increase the absorption of plasmonic. The nonlinear absorptions of Au/GaAs/Au waveguides array, which utilizes high transmittance and surface enhanced energy effect to enhance the absorption of nonlinear material, include TPA and TPA induced free carrier absorption (FCA). The linear transmittance is higher than 85.18﹪, and the effective modal area is a half of the introduced waveguide, which result in a upgraded optical intensity, and the optical limiting threshold is shrunk down to 42.69GW/cm2. Moreover, the area of Au/GaAs/Au waveguides array is 300nm×500nm, which is advantage for the realization of highly dense optical integrated circuits. On the other hand, the TPA induced free carrier is disadvantage for a highly speeding demand of logic gate due to the slower response time. According to the assessments of this investigation, while optical pulsewidth is 10fs, and even the intensity is 89GW/cm2, the variation of transmission caused by TPA induced FCA is only ~ 1﹪.
Devices based on plasmonic waveguides can be further shrink down to ~ 0.1 to 1 times of the operating wavelength, which thereby satisfying the demand of highly dense optical integrated circuits. Practically, however, the plasmonic waveguides may not be able to replace all dielectric waveguides completely as the fundamental components in OICs due to the intrinsic ohmic loss of metallic materials. Nevertheless, we have shown that plasmonic waveguides could substitute some functional devices, such as subwavelength waveguide, polarization beam splitter, angular dispersive device, and optical limiter. | en_US |