Determination Of Bending Losses From Spot-Size Measurements In Single-Mode Fibres

Abstract

ABSTRACT The determination of the sensitivity of a single-mode optical fibre to microbending and macrobending is of great importance. Two kinds of spot-size rule such a sensitivity: wn, the r.m.s. width of the near-field, and WQQ, the inverse of the transverse propagation constant in the cladding. While measurement techniques for wn are already known, this paper proposes an original method for w^ measurements and concentrates on more plausible algorithms for macrobending and microbending loss determination from those measurements. 1 - INTRODUCTION In this work the sensitivity of single-mode fibres to both macro- and microbending is discussed with the purpose of giving a more synthetic experimental characterization of their bending loss performances, a feature of great importance in view of their use in optical telecommunication systems.From the study of the physics involved, it comes out that an important role in the prediction of both macro- and microbending losses is played by the spot-size w^ , related to the fundamental mode propagation constant [1].This fact suggests that w^, besides the well known near-field r.m.s. spot-size wn, can be used for the description of the bending properties of the fibre. While measurement techniques for wn exist and are well consolidated, none has been devised until now for the experimental determination of w^. To overcome such a weakness, we propose an original method for the measurement of w^, capable to provide very promising experi­ mental results. In this way all the important features of a single-mode fibre, such as splice loss, micro- bending loss, macrobending loss, can be characterized by means of very few directly measurable parameters.To check the validity of the proposed approach, the obtained values of w^ have been used for a theoretical prediction of microbending loss.A comparison of the predicted values with the ones measured in laboratory leads to the conclusion that taking into account the w^ influence a more reliable evaluation of the losses is possible.