Synchronization of Quantum Dot Lasers with an Optoelectronic Feedback Circuit BASIM ABDULLATTIF GHALIB, 1 GHAIDAA ABDUL HAFEDH, 2 and AMIN H. AL-KHURSAN 3,4 1.—Laser Physics Department, Science College for Women, Babylon University, Hilla, Iraq. 2.—Physics Department, Science College, Babylon University, Hilla, Iraq. 3.—Nassiriya Nano- technology Research Laboratory (NNRL), Science College, Thi-Qar University, Al-Muntazah, Nassiriya, Iraq. 4.—e-mail: ameen_2all@yahoo.com Synchronization of quantum dot semiconductor lasers with optoelectronic feedback has been modeled by use of rate equations; the model includes wetting layer, ground state (GS), and excited state. It is shown that good synchronization is achieved when the transmitter and receiver lasers are similar. Synchronization is best for a long delay time between the lasers. It is shown that the properties of the carriers in the GS are important to synchronization. Key words: Synchronization, quantum dot, receiver, transmitter, ground state INTRODUCTION Chaos synchronization (CS) should occur between two nonlinear systems is not self-evident and is a real surprise, because we cannot expect the same output even for the same two chaotic systems if the two systems are isolated from each other. 1 After proposal of a method of CS, it has been demonstrated for a variety of nonlinear systems, including lasers. We prepared two almost similar nonlinear systems with the same properties. A fraction of the output from one of the chaotic sys- tems (chaotic transmitter) was sent to the other system (chaotic receiver). The receiver (R) output then synchronizes with the transmitter (T) signal under appropriate conditions. 2,3 Figure 1 shows a schematic diagram of semiconductor lasers (SL) with mutual optoelectronic coupling. Synchronization phenomena occur widely in physics, chemistry, biology, the social sciences, and many other fields, and have attracted much atten- tion in recent years. In particular, synchronization of chaotic oscillations in coupled nonlinear lasers has become a topic of much interest since the first prediction of CS between two lasers. 2–6 In general, rich nonlinear dynamics, including chaos, are easily generated for SL under one or more external per- turbations, for example current modulation, optical injection, optical feedback, and optoelectronic feed- back (OPF), 7–10 and SL have proved excellent can- didates for investigation of the synchronization properties of coupled nonlinear systems. OPF cir- cuits are used to improve the stability and linewidth of SL. Experimental and theoretical studies of the CS of mutually coupled SL with OPF have been reported. 11 This phenomenon has many potential applications in high-speed secret communications, because of such unique properties as large dimen- sions and broad bandwidth. Use of quantum dot (QD) nanostructures in the active region of SL has resulted in substantially different behavior. 12 Synchronization of QD lasers with optical feedback has been studied very recently and improved correlation between fields has been achieved. 13 In the work discussed in this paper we studied CS in QD nanostructure lasers with OPF. RATE EQUATIONS MODEL FOR CS IN QD SL WITH OPF Here, we considered the self-organized InAs/ InGaAs/GaAs QD material 14 which consists of GaAs as barrier, InGaAs as wetting layer (WL), and InAs (Received December 12, 2013; accepted December 12, 2014; published online January 8, 2015) Journal of ELECTRONIC MATERIALS, Vol. 44, No. 3, 2015 DOI: 10.1007/s11664-014-3594-3 Ó 2014 The Minerals, Metals & Materials Society 953