Yb^3+-ring-doped fiber for high-energy pulse amplification

We report what is to our knowledge the first demonstration of pulse amplification in a cw-pumped fiber in which the doped gain medium has a ring shape surrounding a single-mode core. For a given pump power, ring doping reduces the gain and hence the power lost to amplified spontaneous emission. Thereby, a significantly larger amount of energy can be stored in the amplifier. Using an Yb³⁺-doped fiber pumped by 540 mW of power at 1000 nm, we measured $69 \mathit{\mu }\mathrm{J}$ of extracted pulse energy at 1047 nm, the highest value reported to date from a single-mode Yb³⁺-doped fiber. We predict that a fiber cladding pumped by a diode bar can produce pulse energies in excess of 1 mJ.