Determining of Refractive Index Profile of Optical Fibers from Measured Intensity in Near-Field Zone

摘要

Procedure is considered of determining of refractive index profile of optical fibers from measured radiation intensity in near-field zone. Setup for realization of the near-field zone method contains optical system, CCD photosensor , A to D converter, and control computer. Measured values are averaged from results of 10 measurements, are normalized and smoothed out to exclude high-frequency noise. Then the intensity is used in wave equation for calculation of refractive index profile. Methods are studied of elimination of perturbing factor influence on near-field zone intensity; the methods include smoothing out of measured spatial intensity with the use of least square technique based on the orthogonal Laguerre functions and on the use of the Butterworth low-pass filter.