In today’s hyper-connected world, the significance of high-speed large capacity optical fiber communication systems cannot be overstated. These systems have become the backbone of global communication networks, enabling the transmission of vast amounts of data over long distances with unprecedented speed and reliability. With the widespread adoption of technologies such as cloud computing, streaming services, and big data analytics, the demand for higher bandwidth and faster transmission speeds has surged. However, traditional optical fiber communication systems face challenges such as signal attenuation, dispersion, and noise, calling for innovative solutions to drive the development of next-generation high-speed large capacity optical fiber communication systems. This chapter introduces the background, key technologies, and challenges of high-speed large capacity optical transmission systems, providing an overview of related research and advancements, and laying the foundation for in-depth discussions in subsequent chapters.