Nearly degenerate four-wave mixing in Fabry–Perot semiconductor lasers

Nearly degenerate four-wave mixing in Fabry–Perot semiconductor lasers is studied for pump–probe detunings that range from a few hundred megahertz to as high as 20 GHz. It is observed that the conjugate reflectivity and probe amplification decrease with slopes of −60 and −20 dB per frequency decade, respectively, when the detuning exceeds the relaxation-oscillation frequency. A resonance enhancement of the four-wave mixing signal is observed at both the relaxation-oscillation frequency and twice the relaxation-oscillation frequency. Cascade four-wave mixing signals are observed under a very weak (−37-dBm) input probe beam. A quantitative fit to the nearly degenerate four-wave mixing data is obtained, permitting the extraction of basic semiconductor-laser parameters by use of this technique.