Elaborately-designed asymmetrical curved active waveguides are introduced to improve the gain properties of semiconductor optical amplifiers (SOAs) by internal distributed optical-feedback suppression. An analytical model of the double-energy-level system is utilized in the simulation and designed by the finite difference time domain (FDTD) method. Under a 280 mA driving current, the optimized curved SOAwith the simple device structure without isolators performs a more than 18 dB fiber-to-fiber gain, 980 mW spontaneous emission power, and 13 dBm saturation power.