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

Theory and simulations demonstrate that photoactive layers placed in vertical-cavity surface-emitting laser (VCSEL) cavities eliminate the power modulation during laser switch-on. As is well known, this power modulation is caused by the increasing rate of carrier depletion that occurs with increasing photon flux ∂(dN/dt)/∂P<0, inducing cavity relaxation oscillations. The presence of photoactive layers with appropriately chosen parameters reverses the sign: ∂(dN/dt)/∂P>0, which means a decreasing depletion rate with increasing laser power. The relaxation frequency then becomes pure imaginary, and the laser cavity behaves as an overdamped oscillator that asymptotes to the final steady state without power modulation or spiking. A flat frequency response over order(s)-of-magnitude higher bandwidth is predicted under direct VCSEL modulation.