Comparative Study of Mode Control in Vertical-Cavity Surface-Emitting Lasers With Photonic Crystal and Micropillar Etching

The dependence of spectral, power versus current and small-signal modulation characteristics versus the etch depth in two types of surface-etched vertical-cavity surface-emitting lasers (VCSELs) are experimentally and theoretically investigated. One type has a photonic crystal (PC) fabricated in the top distributed Bragg reflector (DBR), whereas the second type has a micropillar (MP) created by removing the DBR surrounding it. The aim of both fabrication designs is to improve the single-mode high-power output. Theoretical and experimental results are found to be in qualitative agreement. It is shown that mode-selective optical losses, introduced by the etched holes of the PC in the DBR, control the optical modes of the PC-VCSEL. Single-fundamental-mode radiation is observed for deeply etched PC- and MP-VCSELs. In contrast, improved modulation characteristics are found for shallowly etched devices. Higher-order single-mode generation with improved modulation characteristics is demonstrated for PC-VCSELs with an etch depth of 1.54 μm. PC-VCSELs demonstrate higher slope efficiency, lower threshold current, and series resistance compared with MP-VCSELs of the same etching depth.