A filtered-transform scanning microscopic method for refractive-index profiling of optical waveguides and surface profiling

A new filtered-transform scanning microscopic method that determines nondestructively the parameters that describes the index or surface profiles of optical waveguides is described. The profiling method makes use of the principle of obtaining amplitude and phase information from the intensity pattern of the reflected (or transmitted) beam from an object sample under focused coherent illumination by introducing a spatial filter in the Fourier plane of a microscopic imaging system. The profiling procedure is composed of two steps. In the first step a test pattern is scanned in the reflection mode as a calibration procedure. The test pattern will usually be taken from a steplike phase sample (e.g. metal strips) in which the thickness and widths of the steps have been independently determined. In the second step the test sample is scanned, and the parameters for the profile are determined