Linewidth and Mode Structure of Proton-Implanted Vertical Cavity Laser Diodes

We have performed linewidth measurements on low threshold planar gain-guided vertical cavity laser diodes. Mode structure and linewidth are determined as a function of driving current for various laser structures. The linewidth shows a linear increase with inverse modal output power at a characteristic slope of about 6 MHz-mW. A mode competition effect can be made responsible for the increase of the fundamental mode linewidth at the onset of higher order transverse mode oscillation. The experimentally determined mode patterns and corresponding wavelength discriminations are in quantitive agreement with theoretical calculations.