Role of carrier reservoirs on the slow phase recovery of quantum dot semiconductor optical amplifiers

Abstract

The gain and phase recovery dynamics of quantum-dot ͑QD͒ semiconductor optical amplifiers are calculated, including all the optical transitions involved in successive carrier recovery processes. The carrier recovery dynamics of inhomogeneously broadened QDs is simulated by solving 1088 coupled rate equations. The respective contributions of QD states and quantum-well carrier reservoirs to the gain and phase changes are identified both temporally and spectrally. We show that the slow phase recovery component of the QD ground state is induced by the slow carrier dynamics of the carrier reservoir due to a slowly varying line shape function of the refractive index change.

Ultrafast characterization of the electron injection from CdSe quantum dots and dye N719 co-sensitizers into TiO2 using sulfide based ionic liquid for enhanced long term stability

“…1(b 48,49 It has been reported that the electron injection rate from the singlet excited state of N719 to metal oxide electrodes is one order of magnitude faster than that from the triplet state. 38,46 Another explanation could be that both the two injection processes mostly correspond to electron injection processes from the triplet excited state due to some inhomogeneities in the TiO 2 nanoparticle surfaces, resulting in different electronic couplings between N719 and the TiO 2 . Considering the ultrafast intersystem crossing time of 100 fs from the singlet excited state to the triplet excited state in N719, the electron injection from the singlet excited state would be unfavorable if the injection time was longer than 100 fs and its component would be small.…”

“…According to the Drude theory, 38,41 we can consider that only free photoexcited electrons and holes are responsible for the population grating signals. 35,39,40 For bulk CdSe, the effective masses of electrons and holes are 0.13m 0 and 0.44m 0 (m 0 is the electron rest mass), respectively, 42 so both the photoexcited electron and hole carrier densities in the CdSe QDs contribute to the signal.…”

“…Fig electrode is negligible and the TG signals can be considered to result from the optical absorption of the CdSe QDs and the dye. 27,35 The TG signal of the semiconductor QDs on the fast time scale used in this study (less than 1 ns) is proportional to the change in the refractive index ∆ ( ) of the sample due to photoexcitation, which can be approximately determined by 35,[38][39][40][41] …”

Sub-Nanosecond Phase Recovery in Quantum-Dot Semiconductor Optical Amplifiers

“…On the other hand, the phase response of the QD-SOA under the OP and EOP schemes is much better than that under the EP scheme. The slow phase recovery in an electrically pumped QD-SOA is attributed to a signicant contribution of the carrier reservoir in the index changes [14]. Since under the OP and EOP schemes the US and the QW state have a negligible eect on the index changes, a superior phase response appears under the OP and EOP schemes.…”

“…Both theoretical and experimental studies have proven the unique capabilities of these devices. Ultrafast gain recovery [14], low noise gure of 3.5 dB [5], high saturated output power [57], pattern-eect free XGM--based wavelength conversion up to 160 Gbits/s [8], and capability of operation at Tbits/s speeds in presence of a control signal [9] are among these capabilities.…”