Detailed investigation of anomalous modal behavior in fabricated bottom-emitting intra-cavity contacted 960 nm range vertical cavity surface emitting lasers (VCSELs) have been performed. At low currents the broad-aperture VCSELs show multi-mode operation at 945 nm via whispering gallery-like modes. Subsequent increase of pump current results in rapid increase of fundamental mode intensity and switching to a pure single transverse mode lasing regime at 960 nm with the higher slope efficiency. As a result record single transverse mode output power of 15 mW with a side-mode-suppressionratio (SMSR) above 30 dB was achieved. The observed phenomena cannot be explained by oxide-index guiding or changes in current pumping. 2D heat transport simulations show a strong temperature gradient inside the microcavity due to an effective lateral heat-sinking. This creates an effective waveguide and results in lower optical losses for the fundamental mode. At fixed pump current in pulsed regime (pulse width < 400 ns) high-order modes dominate, however the subsequent increase of pulse width leads to a rapid rise of optical power for the fundamental mode and SMSR increasing. Thus the self-heating phenomena play a crucial role in observed VCSEL unusual modal behavior.

Date Published: 7 February 2012
PDF: 7 pages
Proc. SPIE 8276, Vertical-Cavity Surface-Emitting Lasers XVI, 82760W (7 February 2012); doi: 10.1117/12.907346

Published in SPIE Proceedings Vol. 8276:
Vertical-Cavity Surface-Emitting Lasers XVI
Chun Lei; Kent D. Choquette, Editor(s)