Research On All - Optical Logic Gate Based On QD - SOA - XGM

The unique advantages of optical fiber transmission technology promote the rapid development of optical fiber communication. All-optical network can make full use of the bandwidth capacity and improve the transmission rate of the optical fiber. All optical wavelength converters and logic gates have become integral parts of the next generation all-optical networks. The quantum dot semiconductor optical amplifiers have been widely used in all optical signal processing due to outstanding nonlinear characteristics.The rate equations and light field transfer equations based on the three-dimensional confinement theory model of the QD-SOA and XGM are solved by using the segment method, Newton method and forth-order Runge-Kutta method. The static and dynamic characteristics of QD-SOA are theoretically simulated. The characteristics of all optical wavelength conversion based on QD-SOA-XGM are studied, the gain recovery time and conversion efficiency are discussed. Besides, all-optical logic AND gate based on the QD-SOA cascade structure and logic NAND gate based on the QD-SOA parallel structure have been studied, and the performance of logic gates have been analyzed in detail. The main contents are summarized as follows:1. The research background, applications, achievements and different implementation scheme of all-optical wavelength converters and logic gates are clarified.2. Based on the QD-SOA rate equations and light field transfer equations, the sectional model is established, Newton method and forth-order Runge-Kutta method are introduced, the static and dynamic characteristics of QD-SOA are simulated, and the simulation results are discussed.3. The optical wavelength converter is achieved based on the XGM of QD-SOA. The gain recovery time and conversion efficiency of optical wavelength converter are analyzed in detail. The gain recovery time for the QD-SOA is shorter than that for the Bulk-SOA, and moreover, the recovery process can be accelerated by increasing the injection current and by reducing the electron relaxation time from the WL to the ES, the maximum mode gain, the width of active region, the electron transition time from the ES to the GS. The conversion efficiency can be improved by increasing the probe power, the length and width of active region, the maximum mode gain and by decreasing the pump power, the pulse width, the absorption coefficient of the material.4. A scheme for all-optical AND gate based on the QD-SOA cascade structure is investigated. The working process of all-optical logic AND gate is simulated. The output effect can be improved by increasing the pump peak power and the injection current of the first level, the maximum mode gain, the length of active region, by decreasing the width of active region, the absorption coefficient of the material.5. A scheme for all-optical NAND gate based on the QD-SOA parallel structure is investigated. The theoretical result for all-optical NAND gate at 50 Gb/s is obtained. The contrast ratio and pattern effect are used as the index to measure the performance of the logic gate. The simulation results show that the performance of the NAND gate can be improved by increasing the difference of peak power, the injection current,the maximum mode gain, the absorption coefficient of the material and by decreasing the width of active region.