Beam quality study for single-mode oxide-confined and photonic crystal VCSELs

A high-quality single mode beam is desirable for the efficient use of lasers as light sources for optical data communications and interconnects. This work shows a parametric study of the beam quality of vertical-cavity surface-emitting lasers (VCSELs). Using a novel vertical setup we calculated the beam quality factor, M2, from beam radius measurements across the operating range of on-wafer devices. The device operating range is determined from the light-current-voltage measurement. We measured spectral content across the operating range to determine the number of operating modes, with single mode devices being of primary interest, and calculate the root-mean-square line widths and side-mode suppression-ratio to further quantify the beam quality. We characterized the beam quality of VCSEL devices emitting 850 nm with oxide-confined apertures of the 2.5 and 5 mu m and photonic crystal confinement with varying hole etch depths and b/a ratios. Device characterization and beam quality data for each of the studied devices is presented and discussed.