Microtube's Tapers Affect its Subwavelength Focusing Effect

A tapered microtube fabricated from a glass capillary tube can achieve subwavelength focusing at optical frequencies. This focusing effect is influenced by many factures. The role of taper ratios is invested in this paper with theoretical analysis and numerical simulation. It revealed that when the taper ratio is larger, the focusing spot has higher intensity and smaller FWHM.