Elimination of cavity relaxation oscillation in vertical-cavity surface-emitting lasers with photoactive feedback

Theory and simulations demonstrate that photoactive layers placed in vertic al-cavity surface-emitting laser (VCSEL) cavities eliminate the power modul ation during laser switch-on. As is well known, this power modulation is ca used by the increasing rate of carrier depletion that occurs with increasin g photon Aux partial derivative(dN/dt)/partial derivative P < 0, inducing c avity relaxation oscillations. The presence of photoactive layers with appr opriately chosen parameters reverses the sign: partial derivative(dN/dt)/pa rtial derivative P > 0, which means a decreasing depletion rate with increa sing laser power. The relaxation frequency then becomes pure imaginary, and the laser cavity behaves as an overdamped oscillator that asymptotes to th e final steady state without power modulation or spiking. A flat frequency response over order(s)-of-magnitude higher bandwidth is predicted under dir ect VCSEL modulation. (C) 2000 Optical Society of America.