Characteristics of Cross-Gain (XG) Wavelength Conversion in Quantum Dot Semiconductor Optical Amplifiers (original) (raw)

Small-Signal Cross-Gain Modulation of Quantum-Dot Semiconductor Optical Amplifiers

IEEE Photonics Technology Letters, 2006

The small-signal cross-gain modulation (XGM) characteristics of a p-doped quantum-dot (QD) semiconductor optical amplifier (SOA) are measured and compared with a theoretical model. The measured small-signal XGM responses show an average 3-dB bandwidth of 3.5 GHz and have no significant dependence on the pump-probe detuning wavelength. This indicates that the main XGM mechanism of the p-doped QD SOA is the total carrier density change rather than spectral hole burning. The measured small-signal conversion efficiency is compared with a theoretical model, which is derived from rate equations for QD SOAs. Based on our theoretical results, we find that the reduced intersubband (from the QD excited to ground state) carrier relaxation time due to p-type doping will decrease the small-signal 3-dB XGM bandwidth of QD SOAs.

Nonlinear properties of quantum dot semiconductor optical amplifiers at 1.3 \mm

Chinese Optics Letters, 2008

The dynamics of nonlinear processes in quantum dot (QD) semiconductor optical amplifiers (SOAs) are investigated. Using small-signal measurements, the suitabilities of cross-gain and cross-phase modulation as well as four wave mixing (FWM) for wavelength conversion are examined. The cross-gain modulation is found to be suitable for wavelength conversion up to a frequency of 40 GHz.

Cross gain modulation in quantum dot semiconductor optical amplifiers under the influence of the Probe

University of Thi-Qar Journal of Science, 2023

The Pulse effect on the cross-gain modulation (XGM) in the quantum dot (QD) semiconductor optical amplifiers (SOAs) is investigated using the combining of the SOA power with the QD rate equations system. The QDs structure includes three regions: ground state (GS), excited state (ES) and wetting layer (WL). Thus, a set of rate equations for pump and probe signals is introduced for both steady-state and small-signal power values, which are solved numerically. The pulse shape was included in the analysis, for pump and probe signals. The theoretical results showed a good agreement with the experimental results. It was found that decreasing pulse width of pump/probe ratio is efficient to increase XGM efficiency and bandwidth.

Numerical Analysis of Gain Saturation, Noise Figure, and Carrier Distribution for Quantum-Dot Semiconductor-Optical Amplifiers

IEEE Journal of Quantum Electronics, 2008

The gain saturation behaviors and noise figure are numerically analyzed for quantum-dot semiconductor optical amplifiers (QD-SOAs). The carrier and photon distributions in the longitudinal direction as well as the photon energy dependent facet reflectivity are accounted in the rate equations, which are solved with output amplified spontaneous emission spectrum as iterative variables. The longitudinal distributions of the occupation probabilities and spectral-hole burning are presented for electrons in the excited and ground states of quantum dots. The saturation output power 19.7 dBm and device gain 20.6 dB are obtained for a QD-SOA with the cavity length of 6 mm at the bias current of 500 mA. The influences of the electron intradot relaxation time and the QD capture time on the gain spectrum are simulated with the relaxation time of 1, 30, and 60 ps and capture time of 1, 5, and 10 ps. The noise figure as low as 3.5 dB is expected due to the strong polarization sensitive spontaneous emission. The characteristics of gain saturation and noise figure versus input signal power for QD-SOAs are similar to that of semiconductor linear optical amplifiers with gain clamping by vertical laser fields.

High-Speed Small-Signal Cross-Gain Modulation in Quantum-Dot Semiconductor Optical Amplifiers at 1.3 mu\mumum

IEEE Journal of Selected Topics in Quantum Electronics, 2009

Wavelength conversion using cross-gain modulation (XGM) in quantum-dot (QD) semiconductor optical amplifiers (SOAs) is investigated. Small-signal measurements reveal that the XGM bandwidth as well as the conversion efficiency strongly depends on the bias current. Thus, it is possible to tune the XGM by increasing the current from a low efficiency with a 10-GHz bandwidth to a very efficient one with bandwidths well exceeding 40 GHz. Two different saturation mechanisms are responsible for this pronounced influence of the bias current: 1) total carrier depletion that leads to a slow broadband cross-gain saturation and 2) spectral hole burning that causes spectrally narrow-band high-speed XGM. With increasing current, the saturation by depleting the carrier reservoir, which feeds the QDs, is minimized, and therefore, spectral hole burning becomes more dominant. Large-signal wavelength conversion experiments using 50 ps pulses indicate that efficient high-speed XGM is feasible for pump and probe signal detuning up to 10 nm. With increasing detuning, larger pulse broadening and a decreasing efficiency are observed, consistent with the small-signal results. The results on the QD SOAs are compared to conventional quantum-well devices.

Integral gain in quantum dot semiconductor optical amplifiers

Superlattices and Microstructures, 2013

In this paper, a new formula of integral gain in quantum dot (QD) semiconductor optical amplifiers (SOAs) depending on the QD states has been derived instead of conventional bulk relation. This formula will pave the way to develop all information in regard to SOA devices. Wetting layer (WL), excited state (ES), and ground state (GS) of SOAs have been employed to study the effects of important parameters in such these devices. Good results were obtained, since the effective capture time in QD is controlled. In addition, a suitable effective capture time must give a high integrated gain that required for all-optical applications. For the bulk model, the capture time to GS is not formulated well in previous studies therefore, it underestimates QD model.

Theoretical and Experimental Study of High-Speed Small-Signal Cross-Gain Modulation of Quantum-Dot Semiconductor Optical Amplifiers

IEEE Journal of Quantum Electronics, 2009

We numerically and experimentally investigate the high-speed small-signal cross-gain modulation (XGM) characteristics of a quantum-dot (QD) semiconductor optical amplifier (SOA). From a p-doped QD SOA operating at 1.3 m, high-speed small-signal XGM responses up to 40 GHz are measured from low to high injection currents and improve at high injection currents. In the numerical model, we set up about six hundred coupled rate equations, where the carrier dynamics of QD electron and hole states are considered separately and the enhanced hole occupation due to p-type doping is included. The high-speed small-signal XGM spectra are calculated at various modulation frequencies and pump-probe detunings. We identify how the two separate XGM mechanisms of total carrier density depletion (TCDD) at low injection current and spectral hole burning (SHB) at high injection current affect the high-speed small-signal XGM behavior. From the measured and calculated results, we show that high-speed small-signal XGM responses of QD SOAs can be improved by injecting more carriers to the QD excited states, which enhances high-speed XGM induced by SHB rather than by TCDD.