  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(0.65{\lambda})at a distance of ~1.47{\mu}m
(2.2{\lambda}) from the output endface of microtube. The experimental results
are in excellent agreement with our numerical simulation.
