SECONDARY PULSATIONS DRIVEN BY SPATIAL HOLE-BURNING IN MODULATED VERTICAL-CAVITY SURFACE-EMITTING LASER-DIODES

It is shown that significant optical power is generated in secondary p ulsations after switch-off of vertical-cavity surface-emitting laser d iodes (VCSEL's) when the laser is modulated from an above-threshold st ate to a current that is at or below the threshold value. It is found from simulations that the optical power in the secondary pulsations ca n be as much as 25% of the power in the lasing state. The initial redu ction of optical output power subsequent to the switch-off permits a s patial redistribution of charge carriers that in turn permits a transi ent recovery of the modal gain above the threshold value, thus enablin g the secondary pulsations to occur. The phenomenon occurs as a result of the interplay between the transverse-mode structure and the gain m edium and, as such, cannot be predicted by spatially independent rate equation models. Implications of the phenomenon for practical applicat ions of VCSEL's with pseudorandom nonreturn-to-zero modulation formats are pointed out. (C) 1995 Optical Society of America