Excitation of sound waves upon propagation of laser pulses in optical fibres

A revised, more comprehensive model of excitation and propagation of acoustic vibrations, electrostrictively induced in optical fibres by laser pulses, is presented. An analytic expression for the acoustic response function of the refractive index in a standard single-mode fibre is derived. Response functions are found for a standard fibre as well as for a single-mode double-clad fibre, which offers much promise for fibreoptic communication lines and where the effective area of mode-field cross section is increased with respect to a standard fibre. It is shown that the intensity of excited sound waves in double-clad fibres is usually several times higher than that in standard fibres. This intensity is determined mainly by the shape of the radial distribution of the electromagnetic field in the pulse, which is different for the fibres considered in this paper.