Sch Dependence Of Linewidth Enhancement Factor For High Speed 1.55 Mu M Multiple Quantum Well Laser Diodes

The linewidth enhancement factor is the crucial design parameter with others, such as gain and refractive index changes for semiconductor laser diodes (LD). The changes of characteristics are measured according to the variation of the thickness of SCH (Separate Confinement Heterostructure, 1.24 mu m p-InGaAsP). The gain spectra were obtained from the spontaneous emission for three LD's. The threshold current; I-th were about 15mA. The optical field profiles for various SCH thickness was calculated from the effective index and transfer matrix method and the corresponding optical confinement Factors are compared with the variation of measured alpha. It is meaningful to find the SCH thickness, SCHGamma max, of maximum confinement Gamma for given LD structure. Although the improvement of the linewidth enhancement factor (alpha) in thicker SCH (>SCHGamma max) has been known, it has not been measured for thin SCH (< SCHGamma max). Here, we compare the measured linewidth enhancement factors of three DFB-LD's with different SCH thickness of 500, 750, and 1000 Angstrom, which are all smaller than the SCHGamma max for given structure. It iis shown that alpha would be improved as SCH thickness increases up to 1500 Angstrom (similar to SCHGamma max) for given structure if other design parameters permit.