InGaAsP/InP double-heterostructure lasers: Simple expressions for wave confinement, beamwidth, and threshold current over wide ranges in wavelength (1.1-1.65 µm)

For InGaAsP/InP devices emitting in the wavelength range of m, we present novel and accurate analytical approximations of the crucial parameters in laser design: the radiation confinement factor ; the effective refractive index Neff; and the transverse beamwidth . It is found that is independent of wavelength or step-index difference and becomes independent of wavelength as the active layer thicknesses decreases below 0.15 μm. An explicit analytical expression is derived for the threshold current density Jth. The new linear gain-current relationship (cm^-1) = 28.5 is deduced from a critical assessment of recent experimental data. A theoretical framework is provided to explain experimental observations such as: the Jthversus curve is independent of wavelength, the threshold has a negligible variation over the m active-layer thickness range, and the normalized threshold current density ( , for m) varies strongly (3-5 kA/cm²/μm) with cavity length.