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The submicron size doughnut shape focal spot, which is traditionally measured by scattering off a nanoparticle or a fluorescent bead, is measured for the first time by a near-field scanning optical microscopy (NSOM) fiber probe. Measurement results agree very well with calculations. This method offers superior repeatability, better control and is less time-consuming than the traditional method as the probes are mechanically protected by their insertion into fiber optic ferrules, which also greatly facilitates the alignment of the tip to the focal spot.

A new type of micro-lensed optical fiber through stacking appropriate high-refractive microspheres at designed locations with respect to the cleaved end of an optical fiber is numerically and experimentally demonstrated. This new type of micro-lensed optical fiber can be precisely constructed with low cost and high speed. Deep micrometer-scale and submicrometer-scale far-field light spots can be achieved when the optical fibers are multimode and single mode, respectively. By placing an appropriate teardrop dielectric nanoscale scatterer at the far-field spot of this new type of micro-lensed optical fiber, a deep-nanometer near-field spot can also be generated with high intensity and minimum joule heating, which is valuable in high-speed, high-resolution, and high-power nanoscale detection compared with traditional near-field optical fibers containing a significant portion of metallic material.

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