I. Introduction
With the rapid development of optical communication technology, high-performance vertical-cavity surface-emitting lasers (VCSELs) have become key devices for the high-speed and high-density optical interconnects. The structure of a VCSEL is mainly composed of an active region, an oxide aperture, a top reflector, and a bottom reflector [1]–[3]. VCSELs have many advantages such as low threshold current, low power consumption, small beam divergence angle, circular symmetrical spot, dynamic single longitudinal mode, easy two-dimensional integration, and on-wafer testing. At present, VCSELs have been widely used in optical interconnects, sensing, light detection and ranging (LiDAR), and so on [4]–[6].