Performance Analysis And Optimization Design Of All-optical Logic Gates Based On Photonic Crystals

All-optical logic gates have a broad prospect of application in all-optical signal processing, photonic computing and all-optical networks. As a new kind of artificial electromagnetic material with photonic gap bands, photonic crystals possess many good characteristics, such as compact size, convenient to be integrated, restraining spontaneous radiation noise and so on. The size of photonic crystals-based devices can be reduced to the scale of optical wavelength, and the devices have low power consumption and are convenient to be integrated. Therefore, it is significant to research on the design and application of integrated circuits based on photonic crystals. This thesis studied design and performance optimization of all-optical logic gates based on photonic crystals, and the main work are as follows.Firstly, design and performance optimization of photonic crystals-based all-optical logic gates used for intensity modulation optical signals are researched. Through introducing Kerr nonlinear material at the bend of waveguide in the ideal two-dimensional photonic crystals with square lattice, a kind of all-optical AND logic gate used for intensity modulation optical signals is realized based on the principle of light-by-light. Power thresholds of different working frequencies are analyzed using simulation software, and the threshold of the all-optical AND logic gate is determined, then performance results of the logic gate in the whole C-Band (1530～1565nm) bandwidth are calculated. The output power contrast ratio between Logic1and Logic0of the all-optical AND logic gate in the whole C-Band is not less than20dB. Then, in the further exploration, the cascade structure of two all-optical AND logic gates is designed, and threshold of the device is determined by simulation. The calculated performance results of the cascade structure are also good, which proves the feasibility of multiple AND logic gates to be cascade. But the simulation results also show that the cascade of all-optical logic gates brings rise of threshold, decrease of effective working bandwidth and logic-level contrast ratio. Therefore, the actual cascade number can’t be too many.Then, design and performance optimization of photonic crystals-based all-optical logic gates used for BPSK optical signals are researched. Based on the principle of3dB coupler, a two-dimensional photonic crystal slab is adopted to design a kind of multimode interference (MMI)-based photonic crystal all-optical XOR/XNOR logic gate which is new and very compact. A3π/2phase shift is introduced between two input ports in the photonic crystal device through designing two waveguides with different length for the two input ports, which makes the logic gates can be directly used for logic operation of BPSK signals. Two all-optical XOR/XNOR logic gates are designed, one has no waveguide bends and the other has. The numerical results of simulations show that, the Logic1to Logic0logic-level contrast ratio is more than21dB for XOR operation and17dB for XNOR operation in the C-Band (1530～1565nm). On the basis of the XOR/XNOR logic gate with waveguide bends, OR and NAND logic gates are realized by two parallel XOR/XNOR logic gate structures. The contrast ratio for OR and NAND logic operations is not less than13dB in the whole C-Band.