Gain-dependent linewidth enhancement factor in the quantum dot structures

Abstract

We measured the linewidth enhancement factor (alpha factor) of InAs quantum dot (QD) laser diodes (LDs) with two different QD structures. One is a normal QD LD with the same energy bandgap for each active QD layer, while the other is chirped with different energy bandgaps. The differential gain of the chirped InAs QD LDs is found to be about five times smaller than that of normal InAs QD LDs, whereas no overall wavelength shift with injection currents is observed in both QD LDs. The a factor is approximately five times higher in the chirped InAs QD LDs than in the normal InAs QD LDs. This relatively large a factor in the chirped InAs QD LDs is attributed to the asymmetrical, wide inhomogeneous gain profile.