All-optical Logic Processing Technologies Based On Highly-Nonlinear Devices

High-speed all-optical logic gates are key elements in all-optical switching networks, which can realize header recognition, clock recovery, signal regeneration, all-optical packet self-routing, optical signal coding, buffering, etc. Once these technologies become commercially mature, current optical network would benefit from these technologies significantly, like what transistor and integrated circuit (IC) did to the information society in 1900s.All-optical logic gates cover XOR, AND/NAND, OR/NOR, NOT, and other complex logic gates, like half-adder, full-adder, etc. Many approaches have been proposed to achieve various all-optical logic functions including simple logic gates and complex logic gates, based on the nonlinear effects in semiconductor material, in optical fibers or in waveguides. However, it is more attractive to realize multi-functional logic gates by using the same architecture or few alterations because of the flexible logic operations and potential applications in massive photonic integration.Therefore, this dissertation mainly focuses on the technologies of highly-nonlinear-materials-based all-optical logic gates realization, including all-optical AND, OR/NOR, XOR and NOT, etc. The main research efforts are summarized as follow. A theoretical model considering length effect and polarization effect in a SOA has been built to study the polarization-dependent gain, polarization-dependent phase and polarization-dependent chirp. Experimental characteristics based on a simple pump-probe setup have been carried out to investigate the influence of polarization dependent gain (PDG) on the nonlinear polarization rotation (NPR) response in SOAs. The results show that PDG enhances the NPR effect in SOAs. Additionally, the influences of input probe power, input probe polarization and input pump polarization in the NPR. response in SOAs are also measured experimentally. The results indicate that the PDG, input optical power, wavelength and polarization affect NPR effect significantly.The performance of an all-optical switch based on NPR and sideband filtering in a SOA has been theoretically studied to help the following all-optical multi-logic gate scheme, which is based on NPR and sideband filtering in a SOA. Specifically, the influences of pump pulsewidth, the bandwidth and center wavelength setting of the bandpass filter have been investigated.Based on the above experimental and theoretical results, a novel multi-logic gate based on NPR and sideband-filtering in a single SOA has been proposed. Digital logic operations including AND, XOR, OR, and NOT are realized at 10 Gb/s numerically, with Q factor of 15.95,8.35, 20.84,12.89 respectively. Then, A·B and A·B gates, which can be combined together to realize XOR, are realized simultaneously in a same experimental setup at 2.5 Gb/s, indicating the feasibility in experimental realization of XOR gate. Further experiment on the influences of pattern length and operation speed on the logic gates have been investigated, indicating that by exploiting a SOA with faster gain recovery time, this scheme can work at higher speed.Cross phase modulation (XPM) in a HNLF is proposed to realize all-optical multi-logic gate. Digital logic operations including XOR, AND, and OR of two input data signals are demonstrated using a single device. We obtain error free operation at 10 Gb/s and the receiver sensitivity for a BER of 10-9 is below-15.0 dBm. Power penalties for XOR, AND, and OR logic operations are 5.9 dB,-1.0 dB and 2.9 dB, respectively.Further analyses of the feasible application of the scheme in the whole C-band have been carried out numerically, concluding the influences of wavelength choosing of signals and wavelength separation between two signals on the performance of the scheme. Moreover, the influence of the length of HNLF on the performance has been studied either.1. we use only one nonlinearity (i.e., XPM), which makes the experiment easy to control,2. we use only two input data signals, thereby avoiding the need for additional sources such as a continuous wave (CW) or a clock signal, and3. the experiment is configurable, which means all three logic gates (XOR, AND, and OR) are realized by only adjusting two bandpass filters, i.e., there is no need to change input variables/parameters such as power, wavelength, or polarization.A novel scheme for pulse generation with a self-cascaded EAM is presented and experimentally demonstrated at 10 GHz. In the case of optimal tuning of time delay in the fiber loop, the improvement of 50% on pulsewidth with improved extinction ratio is obtained and the narrowest pulse generated with this method is about 11 ps.The self-cascaded EAM has also been applied in a 300km 8×10Gb/s OTDM transmission system as a demultiplexer. With the more than 50% decreased switching window, an error free demultiplexing is obtained with a sensitivity of-19dBm, a power penalty of 1.4dB is achieved compared with the back-to-back case.