InGaAs/InGaAsP quantum well distributed feedback laser

The authors describe a deep 900-Å 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 μm. The SCH wafer was grown by atmospheric organometallic vapor-phase epitaxy (OMVPE) and consisted of three InGaAs quantum wells of 80 Å each separated by a 200-Å InGaAsP barrier. On both sides of the quantum-well stack there was ≈1000 Å of 0.95-eV InGaAsP acting as a waveguide. Semi-insulating InP provided the 1.5-μm 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 ≈40 Å 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