Subwavelength focusing of light by a tapered microtube
We propose a mechanism for subwavelength focusing at optical frequencies based on the use of a tapered microtube fabricated from a glass capillary tube. Using coherent illumination at 671nm and a near-field scanning optical microscope probe which was mounted on a 3-axis piezo nanopositioning stage, a sequence of 2-D intensity profiles were obtained. Our experimental results reveal the smallest focal spot with a near diffraction-limited full width at half-maximum of ~435nm(0.65λ)at a distance of ~1.47μm (2.2λ) from the output endface of microtube. The experimental results are in excellent agreement with our numerical simulation.
physics.optics↗