Experimental study of pulse dispersion in multimode optical fibre waveguides

Abstract

An experimental study of temporal broadening of light pulses in multimode optical fibre waveguides has been carried out. A mode-locked He-Ne laser and a mode-locked ruby laser were used as the sources to produce the pulses of light and, in addition, with the aid of an optical shutter, an optical sampling 'oscilloscope' with picosecond time resolution, was constructed to enable a high resolution of the output pulse. Many solid and liquid-cored fibres, all having sharp core-cladding boundaries, were investigated for the effect upon pulse broadening (dispersion) of launching beam semi-angle, launching angle of incidence, wavelength of the launched probe pulse, peak pulse power of the probe pulse, length of the fibre, launched spot-size at the fibre input end face etc. Pulse dispersion was strongly dependent on the input beam semi-angle and further, for large angles, the output pulse was asymmetrical with the trailing part sustaining the major dispersion. A ray propagation model gave good agreement with the experimental results. It was further found that under similar launching angle, dispersion was essentially independent of the wavelength. A narrow input angle can be converted to a wider angle soon after launch and thereafter the dispersion is a linear function of length. This has also been found in long lengths of liquid-cored fibres. Non-linear effects can occur in optical fibres if the peak power in the launched pulse is high. Therefore it is shown which parameters are important and must be cited when quoting the dispersion of a particular fibre, and how the propagation characteristics of optical fibres can be elucidated with reasonable confidence by performing relatively simple measurements, hence providing the necessary and important feedback for the production of fibres having even greater transmission capacities.

More information

Identifiers

Catalogue record

Export record