The all-optical encoder (AOE) based on photonic crystals (Ph.Cs.) is one of the most important devices in computing systems. The essential related parameters are the delay time, the switching speed and the contrast ratio (CR). Moreover, the design simplicity, the compact size and the multi-wavelength operation have come as a fabrication and functional relevant attributes. Throughout the upcoming lines, an introduction for the important assessment factors and definitions will be presented. Finite difference time domain (FDTD) and plane wave expansion (PWE) methods were used for analyzing all structures. An intensive overview of the photonic crystals (AOE) was achieved for the recently published (4x2) and (8x3) types. The corresponding functional parameters for each design were explored, and comparison tables were organized. Finally, numerical methods were discussed with the accompanying commercial software packages; then a future view for the higher-performance operation was attained.