Experimental investigation of variation of backscattered power level with numerical aperture in multimode optical fibres

Experiments have been performed to determine how the backscattered power level varies with numerical aperture. It is found that graded-index fibres are more sensitive to such variations than step-index fibres. By taking into account the dependence of the Rayleigh scattering coefficient on numerical aperture, the experimental results agree well with theory.     

Backscattering signatures from optical fibers with differential mode attenuation

The effect of differential mode attenuation (DMA) on backscattering signatures of multimode graded-index fibers is investigated experimentally and theoretically. Differential mode attenuation curves are determined for various commercial fibers and subsequently used to predict the backscattering response of the fibers. Theory and experiment indicate that only small variations in the local backscatter attenuation coefficient appear between various mode-filtered excitations of a given fiber.     

Mode dependence of splice loss in graded-index optical fibers

Various measurements of the mode dependence of loss in fusion splices are presented. Both laser diodes and light-emitting diodes are employed as sources and measurements are made using both the cutback method and the backscattering technique. Empirical relations, quantifying the form of the mode dependent loss function, are derived and discussed.     

Role of the fusion splice in the concatenation problem

Near-field measurements used to derive an empirical model of a fusion splice have indicated that fusion splices generate very little mode coupling between multimode graded-index fibers of identical parameters. Results of dispersion measurements confirm this. In particular it is found that the bandwidth of a concatenated link of identical fibers (respliced fibers from the same preform) is determined by longitudinal profile variations and not splice characteristics. Fusion splices between nonidentical fibers can generate a larger degree of mode coupling. This unequal parameter-induced mode coupling has a measurable effect on file dispersion properties of concatenated fiber links.     

Backscattering signatures from graded-index fibres with diameter variations

The effect of slow diameter changes on backscattering signatures is considered. Experimental measurements of back-scattered power from fibres with programmed core diameter variations are presented. A simple model is proposed to explain the experimental results.     

Backscatter attenuation measurements in graded index fibres

A comparison is made of the attenuation values obtained by the backscattering technique and the more conventional cut-back method, and the backscattering technique is shown to provide highly accurate and reliable results.     

Backscatter readout from serial microbending sensors

Backscattering measurements performed on test fibers perturbed by several serially placed microbending sensors reveal the surprising result that the loss induced in a given sensor is nearly independent of the losses induced in the other sensors. A simple theoretical model is constructed to predict the conditions under which this desirable phenomenon can occur.     

Loss mechanisms in single-mode fibers jacketed with a loose jelly-filled tube

A study has been made of temperature induced losses in single-mode fibers with a loose jelly-filled jacket. It has been found that at low temperatures where the fiber has to buckle to fit into the tube, the losses have the character of macrobend losses. At high temperatures where the fiber is pressed against the tube wall, the losses are of the microbending type.