Highly coherent long cavity GaAs/AlGaAs single quantum-well lasers

Measurements of the spectral properties of ridge waveguide graded index separate-confinement heterostructure single-quantum-well GaAs/AlGaAs lasers are discussed. Long cavity lasers (800 mu m) exhibit remarkably pure single-longitudinal mode spectra under continuous operation in spite of the short cavity mode spacing. At an output power of 5 mW, the sidemode suppression exceeds 24 dB and the linewidth is 1.5 MHz. The linewidth-power product is 6.4 MHz-mW. Measurements of the linewidth power product as a function of cavity length L gives an L/sup -2/ dependence in agreement with theory for lasers with small internal loss. The results are used to deduce the linewidth enhancement factor alpha at the gain peak wavelength ant its dependence on the excitation level. A decrease in alpha was observed for lasers operating at the second quantized state due to a recovery of the differential gain.<
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