Surface effects and reflection refractometry of optical fibres

Refractive index profiles of several types of silica-based low-loss optical fibres have been measured by the surface reflection technique. When polished samples are used inaccurate data are obtained. For germanium- and phosphorus-doped samples good results are obtained using samples prepared by fracturing the end of the fibre. For borosilicate fibres rapid changes due to atmospheric exposure result in inaccurate data.