SCH dependence of the linewidth enhancement factor in high-speed 1.55-mu mmultiple quantum well laser diodes

As the optical confinement factor (Gamma) of a laser diode is maximized at the thickness of SCHGamma max (Separate-Confinement Heterostructure for max imum Gamma), the linewidth enhancement factor (alpha) is also expected to b e improved for a thickness near SCHGamma max. Although the improvement in a lpha with decreasing SCH thickness for thicker SCH (> SCHGamma max) is well -known, to the best of our knowledge, it has not been measured for thin SCR (< SCHGamma max). We report the measured alpha curves of three distributed feedback laser diodes with different SCH thicknesses of 500, 750, and 1000 Angstrom, which are all smaller than SCHGamma max (similar to 1500 Angstro m for the 1.24-mu m p-InGaAsP layer given here). Additionally, the optical field profiles for various SCH thicknesses were calculated to estimate the corresponding optical confinement factors for comparison with the variation of the measured alpha. It is shown that cu is improved as the SCH thicknes s increases for thin SCH (< SCHGamma max).