ABSTRACT
Optical polarization anisotropy on the surface of subwavelength air-dielectric structures was studied by polarization-modulation near-field optical microscopy. A large degree of polarization anisotropy was measured in the higher topographic region of transparent gratings. In two-dimensional air-hole arrays, the largerpolarization anisotropy occurs in the dielectric regions. Both dielectric and air regions have a 90 degrees difference in the directions of maximum transmission. From calculations with the finite-difference time-domain method, we verified that diffracted light from the mesoscale topographic edges contributes to polarization anisotropy and directional differences.
ABSTRACT
Subwavelength focusing in mesoscale structures was measured in the near field. Specifically, we found that plane waves form focused beams in higher topographic regions when they propagate through mesoscale transparent air-dielectric structures. By finite-difference time-domain simulations we verified that light diffracted off topographic edges and its convergence at higher topographic regions are the mechanisms for focus. This subwavelength focusing effect provides a simple way for mass production of mesoscale periodic structures. We made subwavelength gratings and hole arrays to demonstrate their feasibility.
ABSTRACT
The propagation and the distribution of the optical near field in nanometallic slits are measured by a near-field scanning optical microscope. The optical near field for the p-polarized wave is confined to the middle of the slit. In contrast, the near field for the s-polarized wave is located at the edges. Asimulation by the finite-difference time-domain method verifies that the near-field distribution for the s-polarized wave is due to the propagation of the surface plasmon wave (SPW) at the air-metal surface. The existence of the SPW also accounts for the extraordinary transmittance of s-polarized light, which is one order of magnitude larger than that of p-polarized light.
