Measurement of cavity loss and threshold gain in a vertical-cavity surface-emitting laser using an external mirror

Abstract

The threshold gain and the cavity loss are important parameters for the optimum design of vertical-cavity surface-emitting lasers(VCSELs). The internal loss is commonly determined from the dependence of the external slope efficiency on cavity length[1]. This method inevitably assumes that internal loss is same for each devices. Here we try to determine the cavity loss by varying the amount of light fed back to the VCSEL using an external mirror. The schematic diagram of the experimental setup is shown in Fig. 1. The tested VCSEL consists of super lattice structure surrounded by AlAs/Al0.3Ga0.7As distributed Bragg reflectors. Current is constricted by proton implantation outside a 15- μm diameter circle. A 15- μp m opening in the p-metalization acts as an output aperture. In the continuous wave operation, the threshold current of VCSEL undergoes a periodic change depending on the external cavity length. We found the position of the minimum threshold current by using a piezo-electric translator to the external mirror. Then, we measured the threshold current for different values of feedback.