Quantum-dot semiconductor optical amplifiers for high-bit-rate signal processing up to 160 Gb s^-1and a new scheme of 3R regenerators

Abstract

This paper presents a theory and simulation of quantum-dot semiconductor optical amplifiers (SOAs) for high-bit-rate optical signal processing. The theory includes spatial isolation of quantum dots, carrier relaxation and excitation among the discrete energy states and the wetting layer, grouping of dots by their optical resonant frequency under the inhomogeneous broadening, and the homogeneous broadening of the single-dot gain, which are all essential to the amplifier performance. We show that high-speed gain saturation occurs due to spectral hole burning under the optical pulse trains up to at least 160 Gb s-1 with negligible pattern effect, and that the self-assembled InGaAs/GaAs quantum-dot SOAs have about two to three orders faster response speed than bulk InGaAsP SOAs, with one order larger gain saturation for the 160 Gb s-1 signals. We also show that switching functions can be realized by the cross gain modulation between the two wavelength channels when the channel separation is within the homogeneous broadening. These results indicate great potential of quantum-dot SOAs for all-optical high-speed switches. As one of their possible applications, we propose a new signal-processing scheme of a `quantum-dot 3R regenerator'.

Pattern Effect Mitigation Technique Using Optical Filters for Semiconductor-Optical-Amplifier Based Wavelength Conversion

“…The most practical approach to overcome pattern effects is to decrease the SOA recovery time by proper design , optimum operation conditions (Girardin et al, 1998), an additional assisting light (Manning et al, 1994), and choice of new fast materials (Sugawara et al, 2002). Other approaches to mitigate the pattern effects are cascading several SOAs (Bischoff et al, 2004;Manning et al, 2006) or by using SOAs in a differential interferometer arrangement.…”

“…Throughout this work, rather than decreasing the SOA recovery time by proper material design or choice of new fast materials (Sugawara et al, 2002), the main attention will be paid to mitigate pattern effect by optimum operation conditions and careful configuration design.…”

New Approach to Ultra-Fast All-Optical Signal Processing Based on Quantum Dot Devices

“…GS and ES in QDs are characterized by homogeneous and inhomogeneous broadening Bányai (2005). The homogeneous broadening caused by the scattering of the optically generated electrons and holes with imperfections, impurities, phonons, or through the radiative electronhole pair recombination Bányai (2005) is about 15meV at room temperature Sugawara (2002). The inhomogeneous broadening in the optical transition energy is due to the QDs variations in size, shape, and local strain Bányai (2005), Sugawara (2004), Ustinov (2003).…”

“…System of equations (6)- (8) with the average pump and signal photon densities (14) and phases (15) constitutes a complete set of equations describing XGM and XPM in QD SOA related by the LEF α as it is seen from equations (11), (12) and (15). In order to investigate the possibility of XGM in QD SOAs due to the connections between different QDs through WL at detunings between a signal and a pumping larger than the homogeneous broadening we modified equations (6)- (8) dividing QDs into groups similarly to Sugawara (2002), Sugawara (2004), Sakamoto (2000). We consider a limiting case of the groups 1 and 2 with a detuning substantially larger than the homogeneous broadening, in order to investigate the possibility that they are related only due to the carrier relaxation from WL to ES Ben-Ezra (2007).…”

Optimising uniformity of InAs/(InGaAs)/GaAs quantum dots grown by metal organic vapor phase epitaxy

“…Over the past 15 years there has been intense research on quantum dots (QDs) and the associated growth conditions [1], [2], [3] and [4], due to their potential for improved optoelectronic components, such as lasers [5], [6] and [7], semiconductor optical amplifiers [8] and quantum dot infrared photodetectors (QDIP) [9] and [10]. Important advantages of QD lasers are reduced threshold currents and higher temperature stability, while the main advantages of QDIPs, when compared to quantum well infrared photodetectors (QWIPs), are reduced dark current and the possibility to detect radiation at normal incidence.…”