Fibre and Waveguide Refractive Index Measurements with AFM Resolution

The use of preferential etching and atomic force microscopy to measure the refractive index profiles of optical fibres and silica waveguides is discussed. The validity of the technique itself is investigated. Several types of fibres including an elliptical core fibre have been profiled and the results compared to the preform refractive index profiles. Similarly, planar waveguides made by Plasma Enhanced Chemical Vapour Deposition (PECVD) have been measured and the results correlated with the fabrication process. The lateral resolution of this technique is of order a few nanometers.