Polarization dynamics of birefringent index-guided Vertical-Cavity Surface-Emitting Lasers

We study the polarization behavior of birefringent multi--transverse
mode index--guided Vertical--Cavity Surface--Emitting Lasers (VCSELs)
during CW and modulation operation. The model we use incorporates the
linewidth enhancement factor, different carriers populations associated with
different magnetic sublevels of the conduction and heavy hole valence
bands in quantum well media, spin-flip relaxation processes and cavity
anisotropies. The effect of carrier diffusion and spatial hole
burning on the polarization behavior within the fundamental mode
regime is also considered. We find that spin-flip dynamics and the
linewidth enhancement factor are crucial for the selection of the polarization
state corresponding to a given injection current. We also analyze the
direct-current polarization modulation response for both the small and
large signal modulation regimes. In both cases the current is
modulated around the polarization switching (PS) current, but in the
large signal modulation regime the current goes from below threshold
to above the PS current. A frequency doubled polarized output is
obtained under large signal modulation for modulation frequencies
smaller than 10 MHz. At greater frequencies (around 100 MHz)
transient mode polarization partition noise becomes important. At the
greatest considered frequency (1 GHz) no PS is observed. Finally the
effect of multiple transverse mode operation is addressed by
considering the two lowest order modes: LP₀₁ and LP₁₁.

paper.ps