The Research Of All-optical Logic Gates Based On Two-dimensional Photonic Crystal

All-optical logic gates as one of the most important elements in ultrafast information processing devices and all-optical computing systems have attracted extensive attention. Recently, a number of schemes have been proposed to realize all-optical logic gates such as using dielectric(or metallic) waveguides, semiconductor optical amplifier, nonlinear effects in optical fibers and so on. However, these schemes usually have intrinsic limitations, such as NLF logic gates have the problems of big size, complex structure and high power consumption. The SOA logic gates usually suffer from their spontaneous emission noise. As to the progress of photonic crystal research and technology, various photonic devices based on photonic crystals have been not just a dream. Using the characteristics of photonic crystal to realize all optical logic gates has been reported. So far, all-optical logic gates based on photonic crystals can be realized by means of the self-collimation effect, the third-order nonlinear optical effect, the multi-mode interference effect or the resonance of cavity, whereas most of them often suffer from complex design or high power consumption. In contrast, linear interference effect-based all-optical logic gates by making waveguides in the photonic crystals possess superior characteristics, such as simple structures and low power consumption. Nevertheless, because it can’t control phase difference of the input signal beams change continuously, such design schemes usually tend to be difficulty in precise control of the phase difference for all input signals and obtaining a variety of logical functions with high intensity contrast ratio between output logic states “0” and “1”.This paper presents ultra compact all-optical AND, XOR, and NOT logic gates based on the light beam interference effect in the two-dimensional triangular-lattice photonic crystals. The proposed devices have the advantages of high contrast ratio, small size, simple structure and low power consumption. The main research contents and achievements were as follows:1. In order to design excellent all-optical logic gate structures based on the two-dimensional photonic crystals. The band gap and dispersion relation are studied by the plane wave expansion method. Using two-dimensional triangle-latticed photonic crystals of dielectric cylindrical Si rods embedded in SiO2 slab. By properly adjusting the length of the input waveguide in the Y-branch waveguide to achieve the goal of changing light path difference for input beams, so the structures of logic gates are achieved.2. In order to reduce the power consumption of the all optical logic gates as much as possible, we select linear interference effect not nonlinear photonic crystals to design the logic gates. The working principle of logic gates is analyzes. In order to get a better interference effect and achieve high contrast ratio, a large number of experiments are tried.3. The proposed logic gates are simulation and numerical analysis by FDTD method, the transmission and contrast ratio. Moreover, the thresholds for logic “1” and “0” states are defined through the numerical analysis. The field distribution is achieved by simulating the transmission process of the light waves in photonic crystal, which proves the logical function of the logic gates.4. In order to improve the performance of the proposed logic gates, two scattering rods are introduced at the Y-branch connection point close to the head of the output waveguide. The influences on the performance of the logic gates by the size of scattering rods are calculated and analyzed. By precisely controlling the phase differences and properly choosing the size of scattering rods, higher contrast ratios and the optimal performance are achieved. The contrast ratio of the proposed devices reaches 5.4dB for the AND gate, 33 dB for the XOR and NOT gates, respectively.5. The response time and transmission speed are the most important parameters for an all-optical logic gate. We calculated and found that the proposed logic gates can operate at a bit rate of 1.47Tbits/s for AND gate and 0.78Tbits/s for XOR and NOT gates.