Multi-wavelegth Pump-probe Numerical Analysis of Tunneling Injection Quantum Dot Semiconductor Optical Amplifier Operating at Telecommunication Wavelegnth

The modulation bandwidth of all semiconductor lasers is limited by the gain nonlinearity, which is strongly affected by hot carrier injection. An attractive way to diminish the hot carrier effect is to employ a tunneling injection structure, which feeds cold carriers from an injection well (IW) reservoir directly to the lasing state.

A detailed study of the carrier dynamics is best done in an optical amplifier since it is a single pass device and therefore the responses are not masked by resonances from end facets. We employ a comprehensive finite difference time domain model to simulate the carrier dynamics in a 1.55 μm TI QD amplifier. The model treats the active medium of the amplifier as a cascade of effective two-level systems and solves simultaneously Maxwell and Schrödinger equations in the density matrix formalism considering also the QD gain inhomogeneity and non-resonant effects. It is unique in that it calculates the response to a pulsed perturbation at any wavelength across the gain spectrum and at every point in space behind the pulse. The spectral and spatial profiles of the refractive index are also obtained so that space can be transformed to a time and hence the recovery (behind the pulse) of the carrier population and the inversion can be easily obtained.

We investigated numerically carrier dynamics in TI QD SOA across its gain spectrum by simulating a broad band pump probe experiment. Fast carrier replenishment in the QDs within the spectral range of tunneling injection, is demonstrated. The effect of different perturbation wavelengths was analyzed.