High-power multijunction VCSELs for LiDAR and related sensing applications

Increasing the number of active regions is an effective approach for scaling optical output power in vertical cavity surface emitting lasers (VCSELs). This, in addition to high power conversion efficiency, miniaturized packaging, addressability, fast pulse rise time, and minimal spectral shift with temperature, make multijunction VCSELs an attractive alternative to conventional edge-emitting lasers (EELs) for variety of automotive, industrial, and consumer markets. Especially, LiDAR applications using Time of Flight (ToF) mapping methods require power efficient VCSELs with high throughput and fast rise times for achieving high spatial resolution and longer detectable ranges. However, with greater available optical gain in multijunction VCSELs, comes a more complex cavity structure which includes multiple active regions, tunnel junctions, and optical confinement layers. These can interconnectedly affect the optical, spectral, and electrical characteristics of these devices. For example, wider far-field beam divergence angle for multijunction VCSELs than those of the single-junction structure has been observed, which could be due to structural design parameters, in addition to device processing variability. This can severely reduce the usable output power from these devices, which is typically defined to be enclosed within certain angular limits. In this paper, we will demonstrate the recent advances in the development of high power multijunction VCSELs with up to eight active junctions, lasing in the wavelength range of 850-940nm. Both continuous-wave and short pulse characteristics of these devices measured at room temperature and wider temperature range show their reliable performance and demonstrate their suitability for integration in variety of LiDAR and other high-power sensing applications.