Imaging local index variations in an optical waveguide using a tapping-mode near-field scanning optical microscope

A method has been developed for imaging directly the local index of refraction of optical waveguides using near-field techniques. Imaging local index of refraction variations with two different optical structures, one a well-understood BK-7 glass prism and the other a side-polished optical fiber waveguide has been clearly demonstrated. With an achievable increase in signal to noise, one can obtain high contrast mapping of variations in the refractive index on both optical waveguide structures and on optical materials in total internal reflection with near-field spatial soliton.