Electron and hole dynamics of InAs∕GaAs quantum dot semiconductor optical amplifiers

Self Cite

The gain and phase dynamics of InAs/ GaAs quantum dot amplifiers are studied using single and two-color heterodyne pump probe spectroscopy. The relaxation of the wetting layer carrier density is shown to have a strong effect on the phase dynamics of both ground and excited state transients, while having a much weaker effect on the gain dynamics. In addition, the dynamical alpha factor may also display a constant value after an initial transient. Such behavior is strongly encouraging for reduced pattern effect operation in high speed optical networks. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2823589͔The physics of quantum dot ͑QD͒ photonic devices has been a subject of great interest since the development of self-assembly growth techniques. One of the principle motivating factors for the study of QD lasers was the possibility of substantially reducing the phase-amplitude coupling ͑␣ factor͒ of semiconductor lasers from values in the region of 3-5 for quantum well devices. 1 Among the expected benefits of such a reduction were low modulation chirp, reduced filamentation in high power devices, and reduced sensitivity to optical feedback. 1 To date, QD lasers have displayed a wide range of ␣ factors, the value displaying a strong dependence on the measurement conditions. 2,3 Recent analysis has shown that the low ground state ͑GS͒ gain saturation of QD devices coupled with a large amount of nonresonant carriers in the QD's excited states ͑ES͒ and barrier states can result in large values above threshold 4 and as a consequence, directly phase modulated devices have been demonstrated. 5 In addition, it has been proposed that the unique carrier dynamics of QD semiconductor optical amplifiers ͑SOAs͒ would lead to a reduction of patterning effects compared to conventional devices, for both linear and nonlinear applications. 6,7 As the understanding of relevant carrier relaxation processes in QD structures improves, additional device functionalities will be realized.Heterodyne pump probe spectroscopy has been established as an ideal tool to directly record the ultrafast gain and refractive index dynamics of SOA devices. Previous studies of the gain and phase dynamics of QD SOAs have been performed by Borri et al., who investigated the effects of carrier heating and spectral hole burning in InAs/ InGaAs QDs, 8 while related techniques have been used to measure the ␣ factor in various conditions. 9 Previously on InAs/ GaAs QDs, we demonstrated the importance of Augermediated carrier capture using a single color pump probe technique 10 and illustrated the effects of ultrafast hole relaxation on the gain recovery 11 using a two-color technique. In this letter, we report on two-color phase measurements of the same structure, and note the presence of a strong phase recovery component at the same time scale as the wetting layer carrier recovery. In addition, we combine these phase measurements with two-color gain measurements to calculate an ␣ factor for the device as a function of pump probe delay. The experimental...

“…The experimental arrangement is similar to that reported in Ref. 11. Calibrated phase changes are obtained using a scheme similar to Ref.…”

mentioning

confidence: 82%

mentioning

confidence: 99%

Phase dynamics of InAs∕GaAs quantum dot semiconductor optical amplifiers

O'Driscoll¹,

Piwoński²,

Houlihan³

et al. 2007

Self Cite

“…Its active region included six stacks of InAs/ GaAs QDs in a dots-in-a-well structure, grown by Zia, Inc. (see Ref. 15 for details of material). In forward bias, inhomogeneously broadened transitions (due to QD size dispersion) are apparent at 1320 nm (GS) and 1250 nm (ES).…”

mentioning

confidence: 99%

Mixed state effects in waveguide electro-absorbers based on quantum dots

Piwoński

Pulka

Huyet

et al. 2011

Self Cite

Multi-pulse heterodyne pump-probe measurements are used to investigate the reverse bias dynamics of InAs/GaAs quantum dots in a waveguide structure. Using a femtosecond pulse, we simultaneously populate high energy ground states and low energy excited states and measure the resulting gain and phase dynamics over the bandwidth of the pulse. We identify a similar to 5 ps timescale in the phase dynamics which can be associated with low energy ground states outside the pulse bandwidth and may provide an explanation for the deterioration of monolithic mode locked laser performance at high reverse voltages. (C) 2011 American Institute of Physics. (doi:10.1063/1.3653287

“…This corresponds to a mode-locked laser with a 10 GHz repetition rate with an absorber recovery time of 13 ps and a gain recovery time of 100 ps as extracted from pump-probe spectroscopy measurements. 7,8 We took ␥ = 30, which corresponds to a 17 nm gain bandwidth. For q 0 = 3.5, the modelocking threshold occurs at g 0,th = 0.11 and a periodic pulse train is emitted ͓Fig.…”

mentioning

confidence: 99%

Stabilization of a passively mode-locked laser by continuous wave optical injection

Rebrova

Habruseva

Huyet

et al. 2010

We investigate numerically and experimentally the properties of a passively mode locked quantum dot semiconductor laser under the influence of cw optical injection. We demonstrate that the waveform instability at high pumping for these devices can be overcome when one mode of the device is locked to the injected master laser and additionally show spectral narrowing and tunability. Experimental and numerical analyses demonstrate that the stable locking boundaries are similar to these obtained for optical injection in CW lasers. (C) 2010 American Institute of Physics. (doi:10.1063/1.3483231