TIP OPTICS FOR ILLUMINATION NSOM - EXTENDED-ZONE APPROACH

We examine the coupling of light from a metal-coated fiber through a t apered conic section to a sub-wavelength aperture at the taper's apex. Using geometric optics and introducing a repeated-zone scheme, we dev elop expressions for throughput and gain of this linear taper. The exp ressions allow for consideration of arbitrary angular distribution of light at the large end of the taper, and thus permit analysis in terms of distributions which represent light in propagating modes of a fibe r. Solutions for throughput and gain of a taper pulled from a fiber ar e presented. Extension to geometric optics analysis of non-linear tape rs is outlined.