Abstract
The charge carrier dynamics of improved InP-based InAs/AlGaInAs quantum dot (QD) semiconductor optical amplifiers are examined employing the multi-wavelength ultrafast pump-probe measurement technique. The transient transmission response of the continuous wave probe shows interesting dynamical processes during the initial 2-3 ps after the pump pulse, when carriers originating from two photon absorption contribute the least to the recovery. The effects of optical excitations and electrical bias levels on the recovery dynamics of the gain in energetically different QDs are quantified and discussed. The experimental observations are validated qualitatively using a comprehensive finite-difference time-domain model by recording the time evolution of the charge carriers in the QDs ensemble following the pulse.
Highlights
Ultra-fast charge carrier dynamics across the spectrum of an optical gain media based on InAs/AlGaInAs/InP quantum dots
The superior device characteristics are related to the carrier and gain dynamics that are complex due to the effect of high energy unconfined carriers, which are coupled to the confined carriers in the quantum dots (QDs),[13] and due to the gain inhomogeneity of the self-assembled QDs.[14]
Gain and index dynamics were obtained in single wavelength coherent pump-probe experiments[17] while multi wavelength experiments, which use a continuous wave (CW) probe signal,[18,19] yielded energy dependent gain saturation and recovery rates[18] as well as the phenomenon of instantaneous gain[20] under high electrical and optical excitations. These multiwavelength investigations of InP-based QD amplifiers revealed the important role played by two photon absorption (TPA).[18,19,20]
Summary
Ultra-fast charge carrier dynamics across the spectrum of an optical gain media based on InAs/AlGaInAs/InP quantum dots. During the first 2 ps of the transients following the pump pulse, we observe interesting dynamical processes indicated by a clearly observed plateau in the transmission, preceding its recovery to higher values by carrier capture into the QDs. Its origin is pursued and clarified by measuring the bias, wavelength, and excitation intensity dependencies of the transient transmission, as follows.
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