Carrier capture delay and modulation bandwidth in an edge-emitting quantum dot laser

Abstract

We show that the carrier capture from the optical confinement layer into quantum dots (QDs) can strongly limit the modulation bandwidth ω−3 dB of a QD laser. As a function of the cross-section σn of carrier capture into a QD, ω−3 dB asymptotically approaches its highest value when σn→∞ (the case of instantaneous capture). With reducing σn, ω−3 dB decreases and becomes zero at a certain nonvanishing σnmin. The use of multiple-layers with QDs significantly improves the laser modulation response—ω−3 dB is considerably higher in a multilayer structure as compared to a single-layer structure at the same dc current.

Ultrafast direct modulation of a single-mode photonic crystal nanocavity light-emitting diode

“…To better understand the system, we employ a three-level rate equation model and experimentally measure various lifetime processes 14 . The coupled rate equations are as follows:…”

Effect of excited states on the ground-state modulation bandwidth in quantum dot lasers

“…The difference in x max À3 dB between a 5-and a singlelayer-structure becomes larger at noninstantaneous relaxation-it is considerable [9.4 vs. 1.9 GHz in (a), 11.2 vs. 2.4 GHz in (b), and 11.4 vs. 2.5 GHz in (c)] already at a short relaxation time s 21 ¼ 0.2 ps. The physical mechanism behind the enhancement of x max À3 dB in a multi-layer structure is similar to the case of single-level QDs 8 -with increasing N s (i.e., number of QD layers and/or surface density of QDs in a single-layer), the carrier exchange [either direct or excitedstate-mediated-see the second through fifth terms in the right-hand side of Eq. (1)] between the OCL and the lasing ground state in QDs becomes faster.…”

“…Several factors can affect the dynamic properties of QD lasers and limit the modulation bandwidth. Among such factors are the carrier capture delay from the higher-dimensionality reservoir regions (2D wetting layer [4][5][6][7] and bulk optical confinement layer (OCL) 8 ) into QDs, the internal optical loss, which increases with carrier density in the OCL, 9 and the gain compression (see, e.g., Ref. 10).…”

Harmonic mode-locking in quantum dot lasers with tunnel-coupled waveguides

“…Maximum direct modula tion frequency f max of quantum dot laser diode is deter mined theoretically by so called K factor: f max = (2π/K), which depends on photon lifetime and nonlinear gain saturation. In real quantum dot heterostructures due to rather long carrier capture time [2] and large gain compression factor [3] maximum modulation fre quency does not exceed 10 GHz.…”