Theoretical analysis of extremely small linewidth enhancement factor and enhanced differential gain in modulation-doped strained quantum-well lasers

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Abstract
The possibilities of extreme reduction in the linewidth enhancement factor α and of chirpless operation are theoretically investigated in InGaAs/InGaAsP quantum‐well lasers. First, the condition for lasing operation at the peak of the differential gain spectrum is derived. Lasing characteristics are then calculated taking into account the effects of strain on the valence subband structure. It is shown that by appropriate application of detuning and p‐type modulation doping to a compressive‐strained quantum well, it is possible to reduce the α factor to virtually zero while keeping the laser operating in the region of positive gain.