Silicate-based erbium-doped fiber extended to L-band and its amplification performance

Abstract

With the continuous development of mobile internet, cloud computing, Internet of things, and 5G, the annual growth rate of the existing communication transmission capacity is far from meeting the growing demand. The gain bandwidth of L-band erbium-doped fiber amplification (EDFA) has become the main factor for limiting the bandwidth extension. Owing to its negative effect on the gain and noise figure after 1580 nm, the excited state absorption (ESA) is regarded as a key factor that directly limits the L-band expansion of EDFA. If the ESA coefficient has the same value as the stimulated emission coefficient, the net gain coefficient becomes zero. At the same time, signal amplification cannot be obtained no matter how the pump power and fiber length are adjusted. Improvements from the perspective of erbium-doped fibers, such as changing the host glass and doping components, are extremely beneficial to L-band extension based on simple amplifier configurations. In the present study, an erbium-doped fiber extended to the L-band is fabricated by the modified chemical vapor deposition technology. The saturation curve of the fiber is measured, and then the rate of clustering is obtained. In addition, the absorption coefficient and emission coefficient of the fiber are tested by the truncation method, then the effect of ESA is studied. We demonstrate that modulating the ratio of P to Al in the fiber core has a significant inhibitory effect on the ESA of Er<sup>3+</sup>. To better characterize the amplification performance of the fiber, a single-stage and a multi-stage amplifier system are built respectively. At an input signal injection with a power value of –9 dBm, the fiber exhibits a gain of 10.5 dB with a maximum noise figure of 5.9 dB at 1625.3 nm, based on a single-stage amplifier system under a 980 nm forward-pumping excitation. It indicates that the amplification performance of the fiber in the long-wavelength has improved, which is consistent with the conclusion of the suppression effect on the ESA. By optimizing the fiber length for the first, second and third stage to 19 m, 26 m and 10 m, respectively, a gain of 23.4 dB is obtained at the longest wavelength. The maximum noise figure is 6.3 dB, and the saturation output power is 24.8 dBm. In the meantime, the pump conversion efficiency arrives at 13%. This is the first report on the L-band extended silicate-based erbium-doped fiber that can achieve long-wavelength gain extension to 1625.3 nm.