A 3-18 GHz Microwave Signal Generator Based On Optical Phase Locked Semiconductor DFB Lasers

Recently, there has been great interest in optical phase locked loops (OPLLs) with semiconductor lasers for optical generation of microwave signals with high spectral purity [l]-[4). The 11se of semiconductor lasers as opposed to solid state lasers, such as the Kd:YAG, is attractive due to their compactness and potential for monolithic opto-electronic integration. A major drawback of semiconductor lasers is, however, phase noise which must be reduced significantly for most practical applications. For this purpose. a wideband OPLL can he very efficient if properly designed [2]. We present the experimental results of a 3 to 18 GHz microwave signal generator based on a heterodyne OPLL with offset phase locked 1.5 µm DFB lasers without external cavities or electrical feedback for linewidth narrowing.