Study On Dynamic Characteristics Of Single - Ended Quantum Dot Semiconductor Optical Amplifier

All-optical communication is the main development direction of the optical fiber communication technology, it can solve the O/E/O conversion bottleneck problem, at the same time can improve the optical fiber bandwidth utilization effectively. All-optical signal processing is the foundation of all-optical communication showing advantages, and signal processing depends on different optical devices especially the SOA, moreover various functional devices based on SOA is the key to achieve signal processing in all-optical domain. SOA can be divided into traditional Bulk-SOA, QW-SOA, quantum wire SOA and quantum dot semiconductor amplifier(QD-SOA). In all kinds of SOA, the QD-SOA performance is superior, such as higher gain, lower temperature sensitivity, lower linewidth enhancement factor, smaller threshold current characteristics and so on, and its state density is discrete delta function. However, the extinction ratio(ER) will degrade easily when the traditional double end QD-SOA is applied in all-optical communication network. Different from the dual port QD-SOA, the single port QD-SOA is coated with a reflective film at the back end facet, it can eliminate the ER degradation through the round-trip gain. This paper focuses on the single port QD-SOA application in the all-optical information processing, the main contents are as follows:1. Firstly, we discuss optical fiber communication development history in detail, and the basic composition units(source, the transmission medium and optical device) in the communication system are also described. We also analyze the reason of all-optical network solving O/E/O conversion bottleneck problem. Secondly, the conventional methods in achieving all-optical wavelength conversion and logic gate are introduced. Finally, we elaborate the purpose and significance in studying the single port QD-SOA.2. On the basis of traditional SOA and dual port QD-SOA operating mechanism and structure, we introduce the single port QD-SOA structure features and achieving optical double amplification principle in detail, besides the active region state density, quantum dot material preparation and practical application value are also described.3. According to the optical field propagation equation in QD-SOA, segmentating active region method and the Newton method for solving nonlinear three energy levels carrier transition equations, the static theoretical model for studying single port QD-SOA is established. Through the static model, we analyze the active region static gain and carrier distribution between the three energy levels.Refining segment active region, and applying the fixed step four order Runge-Kutta method for solving the nonlinear transition rate equations, the dynamic simulation model for studying single port QD-SOA is finally established.4. The single port QD-SOA wavelength converter scheme based on cross gain modulation(XGM) is set up, and we mainly study the wavelength converted optical gain, chirp and ER characteristics according to the dynamic theoretical model. The relationships between these three characteristics and the input optical power, active region length, maximum modal gain, the linewidth enhancement factor, the carrier transition time on the energy levels, the wavelength conversion interval are researched. Especially, we compare the single port QD-SOA wavelength converted optical extinction ratio with the dual port wavelength converter extinction ratio, and the single port structure converter shows a better extinction ratio performance. As for the single port QD-SOA all-optical logic NOR gate based on XGM, we conclude that changing input optical pulse sequence combination will have no effect on logic NOR function through theoretical simulation, and we also confirm by reducing optical pulse width can eliminate the pattern effect when signal transmitted at ultra high speed.