Effect of internal optical loss on the modulation bandwidth of a quantum dot laser

We show that the internal optical loss, which increases with free-carrier density in the waveguide region, considerably reduces the modulation bandwidth omega(-3 dB) of a quantum dot laser. At a certain optimum value j(0)(opt) of the dc component of the injection current density, the maximum bandwidth omega(max)(-3dB) is attained and the modulation response function becomes as flat as possible. With internal loss cross-section sigma(int) increasing and approaching its maximum tolerable value, omega(max)(-3dB) decreases and becomes zero. As with j(0)(opt), there also exists the optimum cavity length, at which omega(-3 dB) is highest; the larger is sigma(int), the longer is the optimum cavity. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3697683]