Edge spontaneous emission from 850 nm vertical-cavity surface emitting lasers

The edge emission from 850 nm vertical-cavity surface emitting lasers has a much larger linewidth and a larger redshift coefficient than the surface emission. These differences explain why the threshold current increased asymmetrically when temperature deviated from the temperature associated with the lowest threshold current. The gradient of the edge intensity–current (L–I) curve declined when current exceeded the threshold value. This decline indicates the competition between stimulated emission and other mechanisms for recombining carriers. Thus, the optimal lasing power can be derived from the edge L–I curve, and the deviation from the measured value is the sum of unwanted optical loss.

► Threshold current of 850 nm VCSELs increases asymmetrically with temperature.
► The edge spontaneous emission and the surface lasing emission are compared.
► Reason for the asymmetrical increase of threshold current is presented.
► Gradient of the edge L–I curve declines when current exceeds threshold.
► The edge spontaneous emission is valuable for investigating the VCSEL.