Internal Spatial Modes and Local Propagation Properties in Optical Waveguides Measured Using Near-Field Scanning Pptical Microscopy

Near-field scanning optical microscopy has been used to measure the internal spatial modes and local properties controlling optical wave propagation in glass/silica buried waveguides. The period of the observed standing modes provides a direct measure of the effective index, which combined with the measured transverse modal shape and decay constants, determines the values of all spatial components of the wave vector.Typically, small fluctuations in the material properties of structures can prevent proper operation as well as accurate diagnostic device modeling. The NSOM local probe measurements provide a means of detailed characterization, and defects in processing and their affects on performance are readily identified. We have also developed a technique that can obtain information about the locations of remote dielectric interfaces based upon the rate of change in the phase of the standing wave as a function of wavelength. Finally, experimental results addressing the issue of perturbation of the NSOM probe on the measurement of the local field shows a weak but measurable perturbation, and the dependence on aperture and material parameters will be discussed.