Font Size: a A A

Investigation Of The Properties Of The Optical Antennas

Posted on:2009-10-16Degree:DoctorType:Dissertation
Country:ChinaCandidate:J YangFull Text:PDF
Abstract/Summary:PDF Full Text Request
In the radio wave regimes antennas are widely used to convert electromagnetic radiation into localized energy and vice versa. In the optical wavelength range, the efficient interconversion of propagating light and localized, enhanced fields is also a key issue for the integrated optics and nanophotonics. Optical antennas can efficiently convert the propagating light to the localized field and have been commonly used in the near-field signal detection and near-field enhancement. In this thesis, we propose a V-shaped optical resonant antenna, which has a high field enhancement. Then we analyse the resonant mode in the L-shaped optical antennas. Finally we propose a new method to fabricate high quality optical probe.In order to obtain a high field enhancement, we propose a V-shaped optical resonant antenna, in which both dipolar and quadrupolar modes can be effectively excited. Its electric field enhancing properties is analyzed by using finite-difference time-domain (FDTD) technique. The influence of the open angle on the field enhancement is investigated. Compared with full-wave dipole antennas, the V-shaped antenna exhibits stronger electric field enhancement due to the higher radiation directivity and the smaller curvature radius of the two antenna arms. Moreover, its structure is more asymmetric and the quadrupolar mode can be excited effectively. Quadrupolar antennas have bigger antenna size than that of the dipolar antennas and thus the fabrication process is easier.We study the local surface plasmon mode of L-shaped nanoparticles and its dependence on the incident polarization. It is found that only odd or even order LSP mode can be excited when the polarization of the incident light is perpendicular or parallel the symmetric axis of the L-shaped nanoparticles with equal arms because of symmetry matching. This can reasonably explain the high-energy and low-energy bands of the experimental extinction spectra for two orthogonal incident polarizations. For an L-shaped nanoparticle with unequal arms, all modes can be excited. The field enhancement properties of the L-shaped nanoparticle also strongly depend on the polarization.We propose an improved tube etching method to fabricate SNOM probes by pre-treating the fiber before etching. We first reduce the diameter of one end of the fiber to a range from 7μm to 20μm by etching it in HF solution and form a tapered end. Then we coat the tapered part of the fiber with a thick layer of polymethylmethacrylate (PMMA) and etch it again. The purpose of the pre-treating process is to form a smaller convection volume compared to the tube etching method. Using our method, the apex diameter can easily be less than 50 nm and the tip cone angle can reach as high as nearly 90°.
Keywords/Search Tags:Optical antenna, Surface plasmon resonance, V-shaped antenna, L-shaped antenna, Near-field fiber probe
PDF Full Text Request
Related items