A near-field light probe with an optical slot-waveguide structure

In this study, we present a new design for an optical near-field probe with a slot-waveguide structure and evaluate it using a finite-difference time-domain simulation. Our model, with a 50-nm slot core, enables illumination around the tip of the probe using a small optical spot 50-250 nm wide with 20%-30% transmission efficiency. Based on the high-index-contrast structure in a slot waveguide, a nanosized optical spot is easily generated, which is impossible with a normal slab waveguide. Similar properties of optical spot and transmission efficiency are obtained for different geometric configurations of flat-faced and tapered dielectric slot waveguides in illumination mode. The transmission efficiency of our models is the same or higher than that in conventional metallic tapered optical probes. When operating in illumination and collection modes, a near-field light reflected at 50-200-nm-wide measured objects is clearly observed, and a spatial resolution of ~50 nm is obtained. These findings suggest the potential for slot-waveguide structures to expand the versatility of nanosized optical probes.