Progress in Er-doped fibers for extended L-band operation of amplifiers

Erbium (Er)-doped fiber amplifiers (EDFAs) have revolutionized optical fiber communication, facilitating long-distance, large-capacity, and high-reliability data transmission. The explosive growth in transmission capacity, particularly in dense-wavelength-division-multiplexed (DWDM) communication systems, necessitates the development of efficient EDFAs beyond the C-band (1530–1565 nm) and traditional L-band (1565–1610 nm). However, the expansion of bandwidth is limited by signal-induced excited-state absorption (ESA) effects in EDFs, highlighting the importance of optimizing fiber core compositions with appropriate co-dopants and concentrations in designing extended L-band EDFs. High-performance EDFAs in the extended L-band require improvements in gain, bandwidth, noise figure, and efficiency. This paper reviews the spectroscopic properties of EDFs in alumino-silicate, phospho-silicate, and ternary AlPO₄–SiO₂ glass hosts, with a particular focus on ESA effects. We review the current state of the art of extended L-band EDFAs in single-stage amplification, emphasizing silica-based glass hosts with tailored material compositions of the fiber core. Various novel co-dopants are discussed, like ytterbium (Yb), cerium (Ce), and yttrium (Y). We also explore the optimization on the pump wavelengths and amplification schemes, including single-pass and double-pass configurations. In addition, this review addresses both the temperature and radiation effects of L-band EDFAs, demonstrating the potential of radiation-resistant EDFAs for advancing aerospace-based optical communications.