Interference Measurement Of Waveguide Preform Refractive Index Distribution - Destructive Method With Plane Wave Of Interference

Abstract

Exploitation parameters of a waveguide mostly depend on the distribution of the refractive index in it. Therefore, control over the distribution of the refractive index in the waveguide preforms out of which the waveguides are drawn is necessary in waveguide production and in working out a proper technology of preform production. Interference methods prevail in refractive index distribution measurements because of their great measurement accuracy. Observation of the preform along its axis provides us with information about the actual refractive index distribution in this preform. In order to obtain this information: it is necessary to cut a slice out of the preform and to place it in the measurement setup so that the light beam goes along the symmetry axis of the preform, slice. Owing to the fact that the refractive index does not change along the run of the beam parallel to the preform axis, this method makes it possible to determine the actual refractive index distribution. The method of three interferograms is a destructive method and it makes it possible to measure the refractive index distribution with an accuracy of 1x10-6 for a slice of 1mm thickness as well as the sample thickness distribution. Although the method presented here is simpler, it constitutes a model method for nondestructive methods. This method makes it possible to make measurements of varying accuracy whether we take into account the distribution of the thickness of the examined slice based on other measurements, or whether the slice wedge alone is considered, or whether the slice thickness is assumed as constant.