Near-Field Characterization of Optical Micro/Nanofibres

Near-field scanning optical microscopy is used to investigate the waveguiding properties of optical micro/nanofibres (MNFs) by means of detecting optical power carried by evanescent waves. Taper drawn silica and tellurite MNFs, supported on low-index substrates, are used to guide a 532-nm-wavelength light beam for the test. Modification of the single-mode condition of the MNF in the presence of a substrate is observed. Spatial modulation of the longitudinal field intensity (with a 195-nm period) near the output end of a 760-nm-diameter silica MNF is well resolved. Energy exchange through evanescent coupling between two parallel MNFs is also investigated.