Proc. SPIE. 5635, Nanophotonics, Nanostructure, and Nanometrology
KEYWORDS: Gold, Optical imaging, Light sources, Finite-difference time-domain method, Super resolution, Numerical simulations, Near field scanning optical microscopy, Near field, Optical storage, Near field optics
In this paper the near-field distributions of bow-tie apertures in visible range are characterized by the method of 3D finite-difference time-domain (FDTD). The numerical simulation results reveal theoretically the relation of field enhancement effect of bow-tie aperture and its several parameters including tip angle, aperture size and film thickness. For the bow-tie aperture with a certain tip angle, the metallic film's thickness can be firstly determined at its resonant peak, and then the aperture size can be determined at a tradeoff between the field enhancement and the field distribution. The calculation results of the transformed bow-tie apertures indicate that the transformation at tip angle will bring an obvious change to light field distribution. The bow-tie aperture can be directly used as an exit aperture of a very small aperture laser (VSAL) or as an unattached shield, to produce a sub-wavelength light source with high transmission. It is possible to be used in near field super-resolution imaging, high-density optical data storage, nano-photolithograhy and so on.
We summarize some design tips and design procedures of nanoapertures with strong field enhancement, based on the theoretical calculations and analyses of near-field distributions of unconventional C apertures and bow-tie apertures by a finite-difference time-domain method. A novel L-shaped aperture is proposed and further validates the proposed design rule. As a result, a 15×15-nm full width half maximum spot forms in the light exit plane of the L aperture. Its intensity maximum enhancement reaches a factor of about 568 and the power throughput is bigger than unity. The mechanisms of electromagnetic field enhancement are preliminarily analyzed. This unconventional nanoaperture is likely to be directly used as an exit aperture of very small aperture lasers, or as an unattached shield, to produce a subwavelength light source with high transmission.
Based on theory and method of the near-field optics, optical resolution of near-field scanning optical microscopy (NSOM) is beyond the classical optical diffraction limit and down to tens of nanometer or even less. In this paper, a collection mode NSOM is built to detect and analyze local near-field distribution. The output optical field of a standard 1μm×1μm scale 2D grating has been detected. This NSOM system can also be used to study local near-field distribution of the focused spot of solid immerging lens (SIL) and the result can be directly used to evaluate SIL and compared with the calculation of its theoretical model and as a result, to improve the theoretical model.
Nanometric light source is one ofthe most important elements in near-field optical system. In this paper the nearfield distribution of nano-aperture lasers (NAL) with square and asymmetrical C aperture are characterized by the method of 3D finite-difference time-domain (FDTD). The simulation results theoretically reveal that the output power peak from the asymmetrical NAL is three or four orders of magnitude higher than that from the normal square or round aperture with the comparable light spot size in the near-field region and power throughput is more than unity. The maximum ofthe field enhancement occurs at the C aperture size corresponding to one third ofwavelength. The effects of configuration, aperture dimension, electric field component, polarization and separation in local near field close to the aperture have been investigated theoretically and numerically. The mechanism of electromagnetic field enhancement is also discussed. The asymmetrical NAL with higher throughput may expand the range of applications possible in near-field optics.