Complete suppression of filamentation and superior beam quality in quantum-dot lasers

Comparative near-field and beam-quality ${\mathrm{(M}}^2)$ measurements on narrow stripe quantum-dot (QD) and quantum-well (QW) lasers of identical structure, both emitting at 1100 nm, are presented. Intrinsic suppression of filamentation in the QD lasers is observed. QD lasers emitting at 1300 nm again show no filamentation. For a 6-μm-stripe, QW laser, $M^2$ increases from 2.6 to 6.1 with output power increasing from 5 to 60 mW and with increasing stripe width (20 mW, $\text{3→10\hspace{0.17em}μ}\mathrm{m},$ $M^2\text{=2.6→4.7).}$ In the QD lasers, filamentation is suppressed up to 8 μm (1100 nm) and 9 μm (1300 nm) stripe width and no dependence on output power is observed.