Optical Amplifiers for Terabit Capacity Lightwave Systems

Publisher Summary This chapter discusses the fundamentals of erbium-doped fiber amplifiers (EDFAs) and design considerations followed by system and network issues related to EDFAs. EDFAs consist of erbium (Er)-doped fiber having a silica glass host core doped with active Er ions as the gain medium. The gain medium in the amplifier is a specially fabricated optical fiber with its core doped with Er. It is found that for small input signal power, the gain is constant and starts to decrease as the input power is increased further. In the saturation region, the output power is approximately proportional to the pump power. The spontaneous emission arises when light emitted by spontaneous decay of excited erbium ions is coupled to the optical fiber waveguide. The spontaneous emission is amplified by the gain in the medium and therefore increases with the gain. The amplifier design has to optimize the noise performance of the amplifier, while maintaining high output power and maintaining low cost and high reliability. It is found that even with the intermodal distortion and crosstalk in semiconductor optical amplifier, accurate detection can be made with suitable adjustment of detection threshold level, and the effect of gain fluctuations becomes smaller as the number of channels increases.