Research On All-optical Logic Gate Based On QD-SOA

With the development of the information,the all-optical networks have attracted considerable attention due to the demand of high band width.All-optical networks provide further advantages.In these networks,the information is kept permanently in the optical domain during the whole transmission.As digital communication needs tremendous operation speed,electronic systems are incapable of processing large amounts of data at high speed.It is called “electronic-bottlenecks”.All-optical networks can prevent “electronic-bottlenecks” in intermediate nodes,caused by a detour of the transmitted information over the electrical domain.Also,all-optical packet switching networks have the advantages of flexible,high speed,reconfigurable and high utilization ratio of network resources.QD-SOAs have been attracting considerable attention for their excellent nonlinear characteristics.Such as,ultrafast gain recovery,low threshold current,low temperature sensitivity,low chirp and small linewidth enhancement factor.In addition,these characteristics can significantly improve the performance of all-optical devices based on QD-SOA.Based on XPM effect and XGM effect of QD-SOA,refining segmentation method is used in modeling the static and dynamic process.The Newton iteration method by the four order Runge-Kutta format is used to solve the transition rate equation and light propagation equations.The function of the all-optical wavelength conversion and all-optical logic gate is simulated.The main contents are summarized as follows:1.The all-optical wavelength conversion is achieved based on the XPM effect.In order to obtain the high extinction ratio of the converted optical signal,a method is analyzed in detail.We also study the BER(bit error rate)of the all-optical wavelength converter based on XGM effect in this paper.The results indicate that:(1)In the all-optical wavelength converter based on the XPM effect,when the power of the two probe lights keep balance,a high extinction ratio is obtained.(2)In the all-optical wavelength converter based on XGM effect,for the input pump power,in a certain range(-20 dBm to-10dBm),the BER of output signal is relatively small(1410-).A smaller BER is obtained with larger maximum mode gain and larger length of active region.On the base of achieving the wavelength conversion,by optimizing key parameter,a high accuracy of the output can be obtained.2.The logic function of the QD-SOA-MZI structure based all-optical logic AND gate is simulated.The product of power and contrast ratio is used as a parameter to measure the performance of the all-optical logic gate,by which we can quickly get the optimal workingpoint of the gate.Meanwhile,the influence of the key parameters such as the time delay of the MZI structure and the input optical power on the characteristic parameters are discussed.It has been shown that the optimal delay time is 15 ps,and the optimal input power is 15 dBm,for these parameters the optimal performance of the all-optical logic AND gate can be achieved.3.The logic function of the MZI structure based all-optical logic XOR gate is simulated.In order to optimize the performance of this logic gate and improve the quality of output signal.Q factor is studied in this paper from three aspects: the inherent parameters of QD-SOA,the parameters of the input light and the delay of the probe light.The results demonstrate that,with the increase of the input signal power,Q factor increases up to the maxima which appears at 10 dBm of the input signal power and then begin to decrease.The Q factor decreases with the increase of the maximum mode gain,linewidth enhancement factor,electron relaxation time from the wetting layer to excited state and the input light pulse width.Q facter also increases with the increase of the injection current.As for the delay,it can be taken to be half of the period of input signal.With properly chosen parameters,Q factor reaching 12.4181 dB is obtained.The performance of the scheme is optimized.4.The logic function of cascaded single-port-coupled QD-SOAs based all-optical logic AND gate is simulated.Single-port QD-SOA is used as the front-level of this cascade structure.The output characteristics of the front level can be improved,and the delay interferometer is useless in this system.Cascaded single-port-coupled QD-SOAs structure can be more simple and practicable.In order to improve the quality of the output signal,pattern effect is used as the standard.By increasing the power difference between input signal A and B,the width of active region,output magnification of front-level and the injection current of the first QD-SOA,the pattern effect can be decreased.With properly chosen parameters,pettern effect reaching 0.0145 dB is obtained.The performance of the scheme is optimized.