We describe a global method for the generation of an amplitude modulated optical wave in the range of telecommunication frequencies. This method is based on the optical heterodyning of two DFB lasers. With the assumption of longitudinal multimode lasers, we study the influence of the laser ray width on the spectral purity of the signal generated by the photodiode. We describe the experimental set-up which permits to obtain a tunability of the source up to 275 GHz. We present the results obtained in reception by beat of two identical lasers in a large bandwidth photodiode. A study of the power and frequency stability of the generated signal in the quadratic receiver is carried out for several hours. An experimental fusion set-up by CO2 laser has been developed in our laboratory to ensure the realisation of fibre optical components. Studying these components behaviour under fast optical wave variation is a new approach which brings some useful information regarding component bandwidth. This property enables the validation of components for high rate transmissions. The lasers beating set-up is successfully used to test tapered fibres. The optical component is placed at the coupler output. Tapered fibre bandwidth is measured by an optical wave modulation frequency sweeping in the 0-40 GHz range.
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