Measurement of laser parameters of a vertical-cavity surface-emitting laser using an external mirror

The threshold gain and the cavity loss are important parameters for the optimum design of vertical-cavity surface-emitting lasers (VCSEL). Here we try to determine the cavity loss by varying the amount of light fed back to the VCSEL using an external mirror. The tested VCSEL consists of a superlattice active region surrounded by AlAs/Al/sub 0.3/Ga/sub 0.7/As distributed Bragg reflectors. The nonlinear gain effect is introduced in estimating the internal parameters of VCSELs. Since most VCSELs operate at a carrier density much higher than the transparency level, the nonlinear gain effect should be nonnegligible and be considered. Therefore, this method is appropriate even for a large threshold-gain (like the VCSEL) and/or a large amount of the feedback light (more than a few percents).