Frequency and intensity modulation characteristics of GaAs lasers in an external cavity

Frequency and intensity modulation characteristics were measured for external cavity GaAs diode lasers as a function of modulation frequency. The data, displayed as a chirp-to-power ratio (CPR), showed at low modulation frequencies a flat response and a 0 degrees or 180 degrees relative phase, depending on laser structure. A model incorporating a carrier-density-dependent imaginary part of the differential gain (Henry alpha factor) is developed to explain the data. The model yields simple scaling of the CPR with injection current and photon lifetime. The agreement between the model and data including scaling is excellent. These results provide strong evidence for transverse spatial hole burning in these lasers.<
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