Optical encoders are widely used circuits that are used in digital circuits. One of the most critical features of an optical encoder is the power values in two logic states, low and high. The difference between these two values is expressed with the Contrast Ratio (CR) parameter. In this research, an optical encoder with four inputs and two outputs based on a two-dimensional photonic crystal has been designed and simulated. The results show that the proposed structure has low power in low mode and high intensity in high mode. This difference in two logical modes has caused the proposed encoder to have CR = 19.8dB, which is improved compared to previous works. Also, the proposed structure has a very small size, equal to 96.88 µm2. This encoder can be used in optical integrated circuits with low error according to the obtained values.