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Monolithic dual wavelength DFB lasers for narrow linewidth heterodyne beat-note generation

We have developed a dual wavelength DFB laser for the generation of a widely tunable microwave signal. In order to obtain a narrow linewidth of the generated signal, we have focused the development of the source on the reduction of the linewidth of each generated wavelengths. The best results were obtained with a device using 2500 µm long DFB sections that generated linewidths narrower than 300 kHz. Beating the two wavelengths from this chip on a photodetector resulted in a beat note having a linewidth of 600 kHz. This microwave signal could be tuned from 3 to 20 GHz with a linewidth kept below 1 MHz.