High-Power Low-Divergence Single-Mode Multi-Junction Cascade VCSELs

Seven-junction cascade vertical-cavity surface-emitting lasers (VCSELs) with a long monolithic cavity have been demonstrated to improve single-mode output power up to 10.8 mW under continuous-wave (CW), room temperature operation. The several active regions in series connected via tunnel junctions are introduced to greatly increase the slope efficiency (SE) up to 4.4 W/A. To avoid significantly increasing the round-trip optical loss, the additionally extended cavity is sandwiched between the active region and n-type distributed Bragg reflectors (DBRs). The cavity spacer is capable of enhancing higher order modes diffraction losses and single-mode optical power. The increased large diffraction loss of higher order modes and the small effective refractive-index difference between the core and cladding regions result in a low-divergence angle of only 16°. Due to the simple fabrication process and the low cost, it is promising for the designed VCSELs to offer alternate solutions for applications requiring high single-mode performances of VCSELs.