In order to generate an amplitude modulated optical wave up to 275 GHz, we present an heterodyne technique using two 1.55 μm DFB lasers controlled in temperature by PC. Experimental set-up is described. Theoretical and experimental studies of the lasers spectrum are presented. Beating signal is observed in a 60 GHz bandwidth photodiode, frequency and power stability study is reported. Our final aim is the bandwidth measurement of photoreceivers and optical passive components for optical communications.
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.
We describe a method for generating an amplitude modulated optical wave in the range of telecommunication frequencies. The principle is based on optical heterodying of two free DFB lasers. Frequency modulation of the optical wave resulting from beat is equal to the difference of the two laser wave frequencies. Control in temperature of laser sources ensure their wavelength stability. We theoretically study and also simulate the influence of the spectral width of the laser rays on spectral purity of the generated signal in a quadratic receiver. We then 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 60 Ghz bandwidth photodiode. The signal generated in quadratic receiver is in terms of spectral width (FWHM) of about 37 MHz for a power level of - 35 dBm. Study of power and frequency stability of the generated signal in photodiode is carried out. This work permits to test large bandwidth photodiodes, it would also allow to characterize in bandwidth passive optical components.