Integrable nanophotodiode devices have attracted much research interest in recent years because of their potential applications in all-optical computing and optical communication systems. We propose a new optical diode design scheme. We use genetic algorithms (GAs) to design an optical diode, which has a device footprint of only 2.5×2.5µm2. These devices designed by GA have the ability to achieve high-efficiency unidirectional transmission. Simulations show the forward transmission efficiency can reach higher than 65% for a Gaussian beam between the wavelengths of 1400 and 1600 nm, and the peak transmission efficiency reaches 75%. The transmission contrast at the design wavelength between 1500 and 1600 nm is higher than 90%, which meets the requirements of high unidirectionality, wide operational bandwidth, and small scale. The devices have more advantages for optical diodes compared with structures designed by photonic crystals and gratings. The application of this scheme provides a new idea for the design and research of all-optical diodes in the field of optical communication.