Research Of All-optical Logic Gates Based On Kerr Nonlinear Effect

With the approach of the social informatization and the improved requirements of communication, it has presented higher requirements for the bandwidth and capacity in the communication networks. In the current opaque optical networks, the development of electronic exchange and information procession network has approached its limitation. In order to solve the problem of electronic bottleneck, in future's all-optical network, the electronic exchange will be replaced by all optical switching. The all optical switching is the fundamental device in the all optical networks, and it has many applications in the information technology. One of the most important applications is to be used as a logic gate. All-optical logic gates are the key components of the all optical computer and all optical communication transmission system, and they can realize all kinds of logic operation. Because of Kerr effect, the nonlinear directional couplers can realize the switching and can constitute the all optical logic gates, in recent years, they have attracted considerable attention. Meanwhile, in order to reduce the bias power of optical switching, the all optical flip-flop based on the bistability of microring resonator has gradually become a research hotspot. So in this paper, all optical logic gates based on nonlinear couplers and all optical flip-flop based on the bistability of microring resonator are studied. The main research works and results are as follows:Firstly, the structure of nonlinear optical coupler is introduced, and by using the coupled-mode theory, we have analyzed its switching characteristic and all optical logic gate operation. We also have introduced the operating principle of microring resonator, and based on the coupling principle of coupler, we do some analyses on single-coupler and double-couplers microring resonator, respectively. By simulating the relation curve of transmissivity and phase, we have discussed the switching characteristic, respectively.Secondly, for future research on nonlinear coupler, a pump with high power is coupled into the nonlinear optical coupler by wavelength division multiplex (WDM), due to the Kerr effect, the input of pump light produces the cross-phase modulation. Next, by using the coupled-mode theory, we have discussed the all optical logic gates when the initial phase of the input signal light are the same and different, respectively. The results show that:when the initial phases are the same, we can change the pump power to realize the switching, and after selecting an appropriate value for the pump power, we can realize different logic gates by different combinations of input signals. When the initial phases are different, we can change the dephasing to realize the switching, and after selecting an appropriate value for the dephasing, we can realize different logic gates by different combinations of input signals, too. So, we can conclude that by changing the pump power or altering the initial phase of signals, a variety of logic functions can be realized.Lastly, the paper has introduced the all optical flip-flop based on the double couplers microring resonator. Due to the Kerr effect and optical bistability, we analyzed the switching characteristic of microring resonator. According to the coupled mode theory, and considering the influence of the detuning on bistability, the analytical and numerical methods are used to compute the bistability in the nonlinear microring. The results obtained by the two methods are in agreement. Next, we compute the bistability when considering and ignoring the nonlinear and linear loss, respectively. In order to compensate the nonlinear and linear loss, Er is doped into the microring, and the bias signal power is reduced. For realizing the purpose of flip-flop, the set and reset pulses whose time durations are greater than the field build up time of the microring are added to the bias signal. Furthermore, by changing the time intervals between the set and reset pulses, we can obtain the required bit streams.