Optical Characteristics Of Nanoscale Waveguide And Its Application In Near Field Lithography

Surface plasmonic polaritons is the surface electromagnetic mode formed by the free electron coupling between the electromagnetic wave and the metal surface. In general, it can be divided into localized surface plasmons and propagative surface plasmons. This paper focuses on the exploration of localized surface plasmons and propagative surface plasmons. Numerical simulations and experimental studies on the nanoscale ridge apertures in near-field photolithography and plasmonic waveguide transmission characteristics have been done. Our research shows the excellent performance of nanoscale ridge apertures in low cost and high resolution near field lithography which extends the application of surface plasmonic polaritons in the micro nano optical field.We obtain some achievements as follows:1. The thesis studies the spectral resonance in nanoscale bowtie aperture. Results demonstrate that the bowtie aperture has hybrid resonance characteristics: F-P resonance and plasmonic resonance. The F-P resonance is dominated by the film thickness while the plasmonic resonance is sensitive to the gap distance. Both resonances are closely related to the outline dimension of the aperture. These results reveal the internal mechanism of the resonance effects and provide effective tuning methods to optimize bowtie apertures. The experimental data is in good agreement with numerical results. Understanding these effects provides significant insight to design the geometry of bowtie aperture for many applications benefiting from high optical resolution and near-field enhancement.2. Imaging contrast and field intensity for nanolithography using C-shaped aperture and regular shape apertures are studied by numerical simulations and experiments. The results demonstrate the advantages of the C aperture in achieving nanoscale resolution with both high transmission intensity and high imaging contrast. The imaging contrast for achieving 50 nm and 100 nm resolution is also investigated. The depth of focus for exposing 50nm features by different shape apertures are also calculated based on the minimum imaging contrast required for exposing the photoresist. Furthermore, we simulate different ridge sizes and film materials to optimize the C aperture design for nanolithography. The simulation results indicate that the C aperture has better lithography performance when the ridge is smaller and the aluminum film is chosen.3. We use back-side milling method to fabricate bowtie aperture with ultra small gap which is 10.12nm in the thesis and 21 nm lithography resolution of a single dot and 18 nm lithography resolution of a line have been achieved in static lithography and scanning lithography experiments. The experimental results are very impressive. Image contrast of nanoscale bowtie apertures with different geometric parameters is numerically studied. These results show that the high image contrast is obtained in the near field region and decreases quickly with the increasing distance. It is worth noting that smaller gap size achieves higher image contrast and deeper depth of focus. Our results demonstrate the great potential of the nanoscale bowtie aperture in high precision near-field scanning lithography.4. A novel long range hybrid tube-wedge plasmonic(LRHTWP) waveguide consisting of a high index dielectric nanotube embedding on a metallic wedge surrounded by low index medium is proposed. A comprehensive numerical study is conducted and the corresponding results reveal that the proposed waveguide has low propagation loss and extreme light confinement. In addition, further evaluations in detailed fabrication errors such as inaccuracies of the wedge tip curvature radius and horizontal misalignment between the nanotube and the metal wedge have been investigated. The obtained results show that the proposed structure is fairly tolerant to these geometric fabrication errors. This novel configuration of LRHTWP waveguide has great application prospects in numerous functional nanophotonic components including various passive devices and active components such as plamon nanolasers and plasmonic resonators.5. We improve the fabrication process of metal wedge waveguide structure. Compared with the previous methods, the new process has high processing precision and success rate. Through numerical simulation analysis of the transmission characteristics of different wedge angle wedge plasma waveguide, we find that the wedge plasmonic polaritons transmit on the side surface of wedge and a multi peak distribution valve, When the wedge angle gets larger, the optimal excitation wavelength is larger with higher coupling efficiency and less the transmission loss. In order to improve the excitation efficiency of the plasmonic waveguide, we have proposed to add the excitation end in the waveguide, and the excitation structure of the grating and the triangle are designed and compared. Finally, we discuss the influence of structural defects on the transmission characteristics of the tapered waveguide. The results show that the transmission modes on both sides of the wedge are independent of each other, and the defect structure will lead to the asymmetric distribution of wedge plasmonic polaritons mode.