Abstract: The technology of this application relates to an erbium-doped fiber. The erbium-doped fiber can be used in the fields of amplifiers, optical communications, rare-earth-doped fiber preparation, and the like. A fiber core of the erbium-doped fiber includes a first layer and a second layer from inside to outside. The first layer includes a center of the fiber core. The second layer is an annulus, and an outer ring of the annulus is an outer ring of the fiber core. An average doping concentration of erbium ions of the first layer is higher than an average doping concentration of erbium ions of the second layer. An ASE can be reduced by reducing a doping concentration of erbium ions of the second layer, to further reduce a noise figure of the erbium-doped fiber and improve communications quality.

Abstract: A box underframe end structure of a railway vehicle includes an underframe boundary beam, an end beam, a front draft sill, and a coupler mounting seat, and further includes a rear end cross beam located on one side in a rear of the front draft sill, an end floor fixed between the end beam and the rear end cross beam, and a coupler cross beam fixed with the coupler mounting seat into a whole. A draft sill includes the front draft sill and a rear draft sill respectively arranged on a front side and a rear side of the coupler mounting seat. The coupler cross beam, the rear end cross beam, and the end floor are welded and fixed with the underframe boundary beam. The front draft sill, the rear draft sill, and the coupler cross beam are welded and fixed on a lower surface of the end floor.