Study On All-optical Logic Gates In Periodically Poled Lithium Niobate

With the advent of the information era, various telecommunicationservices are explosively growing, which results in that the traffic of Internet isincreasing with the speed exceeding the “Moore’s Law”. As a consequence,the crisis which is the so called “electronic bottleneck” emerges. In order toavoid limitations from “electronic bottleneck” for high speed optical networkin the future, it’s necessary to implement all-optical signal processing. As keydevices in all-optical signal processing, all-optical logic gates attract more andmore attention in recent years. The all-optical logic gates have extensiveapplications in optical packet switching, optical wavelength conversion,optical computing and optical signal regeneration. Periodically poled lithiumniobate (PPLN), with properties of ultra-fast response, no excess noise, andcomplete transparency, etc. is becoming hot in research on high speedall-optical logic devices.In this dissertation, by using second-harmonic generation (SHG),sum-frequency generation (SFG), difference-frequency generation (DFG) andtheir cascading based on quasi phase matching (QPM) technology, which is obtained in magnesium oxide (MgO) doped peridocially poled lithium niobate(MgO:PPLN) waveguides, we theoretically investigate the all-optical logicgates based on intensity. In addition, by exploiting electro-optic Pockels effectand taking advantage of polarization beam splitter (PBS), polarization-basedall-optical logic gates were realized in our experiment, which is indicating thepotential application for complex logic functions and optical computing. Thedetailed research contents are as follows:1. In MgO:PPLN crystal, we analyze and discuss the second-ordernonlinearity in detail, including SHG, SFG, DFG, cascaded second-harmonicgeneration and difference-frequency generation (cSHG/DFG), and cascadedsum-frequency generation and difference-frequency generation (cSFG/DFG).By employing type I QPM cSHG/DFG and cSFG/DFG in one MgO:PPLN,and type0QPM SFG in another MgO:PPLN, we simulate and discusssimultaneous all-optical logic AND, NOR and XNOR gates With40Gbit/sRZ input signal.2. By using of PBS and employing electro-optic Pockels effect, an approachto process binary all-optical logic signal which is encoded in polarization isproposed and validated. In our experiment, we defined that optical signal withvertical and horizontal polarization state as logic0and logic1respectively.As the function of PBS, there are two different channels for optical signal with a given polarization state to travel, one directly connect with the analyzer,while the other one is designed to pass through MgO:PPLN. When the properelectric field applied along the transverse of MgO:PPLN, the polarizationstate of the input optical signal could be rotated by90°; otherwise, it will keepits original polarization state. Besides, if we choose external applied electricfield as another signal, it can realize AND and OR functions by given therepresentation of logic0and logic1. In our approach, as optical signal isencoded in polarization, the intensity could not be a barrier for cascadinggates and may realize much more complex logic functions.