We demonstrate experimentally and numerically that in fiber tips as they are used in NSOMs azimuthally polarized electrical fields (|E$_{ \text{ azi}}$|$^2$/|E$_{ \text{ tot}}$|$^2$ $\approx$ 55% $\pm $ 5% for 1.4\mu m tip aperture diameter and \lambda$_0$ = 1550nm), respectively subwavelength confined (FWHM $\approx$ 450nm $\approx$ \lambda$_0$/3.5) magnetic fields, are generated for a certain tip aperture diameter (d = 1.4\mu m). We attribute the generation of this field distribution in metal-coated fiber tips to symmetry breaking in the bend and subsequent plasmonic mode filtering in the truncated conical taper.
Categories: physics.optics