Transmitted radiation through a subwavelength-sized tapered optical fiber tip

The far-field angular intensity dependence of the λ = 633 nm radiation transmitted through a 60 nm circular aperture located at the apex of an aluminum-coated tapered optical fiber tip is mapped as a function of the angle θ spanning the tip axis and the detector direction. Measurements are performed for polarized radiation with its electric field oriented (a) in the scan plane or (b) perpendicular to it. The existing predictions for a subwavelength-sized circular aperture in a thin perfectly conducting planar screen fails massively to describe the far-field measurements results. The photon intensity of the evanescent wave near the tip is measured by approaching the photosensitive region of a cleaved p-n GaAs photodetector in the near field of the tip aperture.