InGaAs/InGaAsP quantum well distributed feedback laser

The authors describe a deep 900-AA first-order grating that was fabricated on the top InGaAsP waveguide layer of a three-quantum-well separate-confinement heterostructure (SCH) wafer to provide for distributed-feedback (DFB) operation at 1.515 mu m. The SCH wafer was grown by atmospheric organometallic vapor-phase epitaxy (OMVPE) and consisted of three InGaAs quantum wells of 80 AA each separated by a 200-AA InGaAsP barrier. On both sides of the quantum-well stack there was approximately=1000 AA of 0.95-eV InGaAsP acting as a waveguide. Semi-insulating InP provided the 1.5- mu m lateral electrical and optical confinement using a semi-insulating planar buried heterostructure configuration. Laser chips of 0.5- and 1-mm cavity lengths were mounted on copper studs and run continuously at room temperature, with current thresholds of 15 and 24 mA, respectively. There was a weak dependence of the current threshold and differential quantum efficiencies on cavity length, which confirms the low internal loss in quantum-well lasers. Below threshold, a stopband of approximately=40 AA was seen in the laser spectrum. Above threshold two DFB modes were usually seen on each side of the stop band, although in some cases a single mode was observed due to the suppression of the other mode. The linewidth was 5-MHz FWHM at 1-mW output power, which represents a marked improvement over previous results. Some improvement was also observed in the linewidth enhancement factor.<
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