Analysis of signal excited-state absorption for improving extended L-band erbium-doped fibers

The precise characterization of signal excited-state absorption (ESA) in erbium-doped fibers (EDFs) is achieved through an ON/OFF pumping scheme, using a supercontinuum source in conjunction with a bandpass tunable filter to generate the input signal. Normalizing the ESA profile, by the value of the ESA peak, allows sample comparisons independent of their erbium concentration. This method directly assesses the impact of ESA on the net gain within the 1600-1730 nm range, providing a significant means to study how to expand the gain bandwidth toward longer wavelengths. As an illustrative application, we investigate the effect of chemical elements, such as Er, Al, and Ba, and their concentrations on ESA. We then optimize the Al content to enhance erbium solubility without inadvertently inducing detrimental ESA effects. This advancement in the ESA characterization presents substantial advantages for the pursuit of efficient extended L-band erbium-doped fiber amplifiers (EDFAs).