An investigation of the bending effects in single mode optical fibres

Light losses caused by bending effects in singlemode optical fibres are a major problem when inadvertently introduced during the fibre cabling or installation process. Such optical losses originate from two major mechanisms; namely, the macrobending and microbending effects. The approaches used for the modelling of bending effects in optical fibres are mainly based on either analytical solutions or the beam propagation method (BPM). However, the analytical solutions are generally piecewise and fragmented in that a separate analytical solution is needed for each particular loss mechanism. Similarly, the modelling of bend-induced losses using the BPM approach has been hampered in the past by restrictions imposed by the employed BPM algorithms (e.g. Fast Fourier Transform BPM). Modern BPM algorithms (e.g Finite Difference BPM)) arising from developments in integrated optics are generally more efficient and very flexible. The Finite Difference BPM (FD-BPM technique has been applied in this investigation to model the optical loss behaviour of some macrobending and microbending effects in singlemode fibres. Both pure bend losses and transition losses are explored within the modelling of macrobending effects whereas microbending is investigated for the case of an optical fibre subjected to a series of cons taut curvature bends (some times referred to as the pseudo-microbending). Moreover, spectral behaviour of the losses is considered for both loss mechanisms. The predictions of both pure bend losses and transitions losses are made with a good overall accuracy in comparison with the predictions from previous analytical solutions and FFT-BPM studies. The resonant attenuation peak structure which is a characteristic of periodic microbending is also predicted by utilising the FD-BPM technique. The results are Found to exhibit good agreement with the available experimental observations. Similarly, spectral attenuation predictions produced by the simulations are also compared with both analytical and practical results. It is also noted that whilst the FD-BPM technique is very effective and flexible for application to a wide range of optical fibre propagation problems, it produces consistent and accurate predictions which are comparative to those obtainable with the other modelling approaches.