Transmission and reflection characteristics of metal-coated optical fiber tip pairs.

The optical transmission and reflection in between two metalized optical fiber tips is studied in the optical near-field and far-field domains. In addition to aluminum-coated tips for near-field scanning optical microscopy (NSOM), specifically developed gold-coated fiber tips cut by focused ion beam are investigated. Transverse transmission maps of subwavelength width clearly indicate optical near-field coupling between the tips for short tip distances and become essentially Gaussian-shaped for larger distances in the far-field regime. Moreover, concentric reflection fringes observed for NSOM-type tips illustrate the influence of the receiving fiber tip on the emission pattern of the source tip.