We propose and theoretically analyze three-level cladding-pumped fiber lasers in which the laser-active dopant is placed in a ring around a single-mode core. A ring-doped laser can work efficiently at wavelengths with strong small-signal absorption. This is otherwise difficult in a cladding-pumped fiber. Moreover, ring doping makes the laser less sensitive to quenching of the laser-active dopant and to excited-state absorption of the lasing field. In simulations of a Yb(3+) -doped fiber laser, ring doping increased the slope efficiency to 62%, up from 13% for a conventional core-doped fiber.

By pumping with a cw diode-pumped Nd:YAG laser operating at 946nm laser operation of a new Yb-doped phosphate glass with 440mW cw output power and a slope efficiency of 48% with respect to the absorbed pump power was achieved at room temperature.

We report what we believe to be the first results on short-pulse generation in Yb(3+) :silica fiber. By applying the stretched pulse technique in a unidirectional, polarization-switch Yb(3+) fiber laser incorporating a prism-based dispersive delay line, we obtain self-start mode locking and 100-pJ pulses that can be compressed to give clean chirp-free <100-fs pulses. We believe such sources to have great potential for use not only in all-solid-state, high-power femtosecond pulse systems based on Yb(3+) :silica glass but also as seeds for conventional Nd(3+) :glass amplifier chains.

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A beam-shaped 20-W diode bar has longitudinally pumped a Nd:YAG laser in a ring configuration. Unidirectional single-frequency operation is enforced by a Faraday rotator. Intracavity frequency doubling with a KTP crystal has produced 3 W of stable single-frequency TEM00 output at 532 nm.