RESUMO
In the past few years, although annealing effects have been widely used to restore the power features of fiber amplifiers, their noise feature has not yet been sufficiently investigated. Thanks to the recovery of partial color centers (especially the ${{\rm Yb}^{2 + }}$Yb2+ center) through photobleaching, the absorption of seed signal light due to the presence of color centers is weakened, and the sensitized path of the irradiated erbium-ytterbium co-doped fiber amplifier (EYDFA) is partially restored, which helps to suppress amplified spontaneous emission as well as increases the gain of the EYDFA. The thermal annealing process is performed by the first amplification stage of the EYDFA, and the increase in the optical signal-to-noise ratio of the signal light indicates that our proposed scheme could be also exploited to further improve the output performance of the EYDFA. This work is anticipated to open up new prospects for future optical communications systems based on pre-amplification technology.
RESUMO
The classical thermodynamic criterion for phase transition predicts whether the phase transition will occur according to whether the nth derivative of the state parameter is discontinuous, and the continuity verification of multi-order derivatives increases the difficulty and complexity of judgment for phase transition to a certain extent. Based on the reverse shifts of the DOS curves near the Fermi level, we propose a new criterion for solid-state phase transition named Conch Criterion, which has been verified in the TMD system. The new criterion can observe the occurrence of phase transition from another perspective besides the thermodynamic properties while mutually confirming the thermodynamic criterion.
