Optical fibre based transmission systems are an essential part of telecommunication networks. One of the most important issues when designing and building transmission systems is the cost of the network infrastructure, since the end users require delivery of high quality services at low cost. Utilization of the optical fibre 1310 nm wavelength domain has key advantages: absence of chromatic dispersion compensation, use of low cost semiconductor components like semiconductor optical amplifiers (SOAs), and by utilizing transmission parallel to the 1550 nm wavelength domain, better utilization of the legacy fibre resources is achieved. This book is devoted to applications of 1310 nm SOAs in modern fibre optic telecommunication systems. Three types of applications are studied: high speed 1310 nm DWDM transmission over short and metro distances, e.g. 4x40 Gbit/s, all optical 1310-to-1550 nm wavelength conversion as well as switching of the 1550 nm data signals by the 1310 nm SOA. The book is intended for advanced level students, professional communication engineers and academics involved in the research and design of cost effective optical fibre communication systems.