Design of all-optical logic gates avoiding external phase shifters in a two-dimensional photonic crystal based on multi-mode interference for BPSK signals

In this paper several new structures of all-optical logic gate in a two-dimensional photonic crystal (PC) based on multi-mode interference (MMI) are proposed and designed. 3π/2 phase shift is introduced between two input ports in the photonic crystal devices through different lengths of the waveguide of two input ports, which makes the logic gates to be directly used for logic operations of binary-phase-shift-keyed (BPSK) signals. XOR, XNOR, OR and NAND logic gates are realized. In order to simulate the performance of the proposed logic gates, the plane wave expansion method (PWEM) and finite difference time domain (FDTD) method are employed. Numerical results reveal that the contrast ratio between Logic 1 and Logic 0 logic-levels is more than 21 dB for XOR, 17 dB for XNOR, and 13 dB for OR and NAND logic operations in the whole C-Band (1530-1565 nm). This kind of structure does not adopt nonlinear optical properties, and hence, the power consumption of the device is very low and the size of the device is very small. Therefore, the proposed logic gate has the potential to constitute photonic integrated components that will be used in all-optical signal processing, photonic computing and all-optical networks.