METHOD OF AND APPARATUS FOR THE MEASUREMENT OF THE REFRACTIVE-INDEX PROFILE IN MONOMODE OPTICAL FIBRES

摘要

ABSTRACTThe present invention provides a method which is of theguided near field type so as to exploit fibre propagationcharacteristics, and requires no complex processing of a measuredvalue. In this method, an image of the fibre output end isradially scanned, and for each value of a distance r from theimage axis, two image-intensity measurements are effected, thefirst after optically filtering the beam emerging from the fibreso as to modulate the beam according to a factor p4 (with p =a ? sin .THETA., .THETA. being the angular beam coordinate, and a the dis-tance of the generic filter point from the fibre output end),the second meansurement being effected by directly collectingthe beam leaving the fibre end, the refractive index value atthat point being derived from the ratio between the first andthe second measurement.