Ring-doped cladding-pumped single-mode three-level fiber laser.

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.

Enhanced Q switching in double-clad fiber lasers.

A novel cladding pumped Nd(3+) fiber laser operating in an enhanced Q-switched regime with a stable repetition rate is described. By exploiting fiber nonlinearities in the laser cavity, we demonstrated a peak power of 3.7 kW enhanced by an order of magnitude greater than that of conventional Q-switched fiber devices. Pulse durations as short as 2 ns have been achieved.

Environmentally stable picosecond ytterbium fiber laser with a broad tuning range.

We demonstrate a widely tunable passively mode-locked fiber laser operating at a fundamental frequency of 80 MHz with an output power of 90 mW. The laser is capable of generating 5-ps pulses in the region 1010-1064 nm. A strong mode-locking mechanism promoted by frequency-shifted feedback allows us to operate in simultaneous Q-switched and mode-locked regimes and to obtain peak power in excess of 1.2 kW.

Efficient single-frequency fiber lasers with novel photosensitive Er/Yb optical fibers.

Boron- and germanium-doped highly photosensitive cladding is used in a novel design to achieve photosensitive Er/Yb-doped fibers, permitting short, strong gratings (length approximately 1 cm, reflectivity >99%) to be written without hydrogenation. The high absorption at 980 nm in Er/Yb fibers permits efficient pump absorption over a short device length, which is ideal for achieving highly efficient single-frequency fiber lasers. Both single-frequency Bragg-grating reflector and distributed-feedback lasers with slope efficiencies of 25% with respect to launched pump power have been realized in such fibers.

Cladding-pumped passively mode-locked fiber laser generating femtosecond and picosecond pulses.

Passively mode-locked fiber lasers cladding pumped by broad-area diode-laser arrays are described. With a dispersion-compenstated erbium-ytterbium fiber oscillator, 200-fs pulses with pulse energies up to 100 pJ are generated at a wavelength of 1560 nm. In a highly dispersive cavity, pulse widths of 3 ps with pulse energies up to 1 nJ are obtained. A saturable absorber is used for pulse startup, whereas nonlinear polarization evolution is exploited for steady-state pulse shaping. An environmentally stable design is ensured by use of a compensation scheme for linear polarization drifts in the cavity.

Cladding-pumped passive harmonically mode-locked fiber laser.

A passive harmonically mode-locked fiber laser cladding pumped by a broad-area diode-laser array is described. Harmonic mode locking is obtained in a frequency range from 33.3 to 128.6 MHz, where the higher frequency limit is imposed because of insufficient available pump power. The maximum pulse jitter in one cavity roundtrip time is between 300 and 50 ps in the whole frequency range, and the sidebands in the frequency domain are suppressed by as much as 50 dB. 600-fs bandwidth-limited pulses with pulse energies of as much as 20 pJ are obtained, giving rise to an average output power as great as 2.5 mW.