Multifilament-core fibers for high energy pulse amplification at 1.5 microm with excellent beam quality.

We report on what we believe to be the first demonstration of an erbium-ytterbium-doped multifilament-core (MFC) fiber for single-mode amplification of narrow linewidth high peak power pulses. A master-oscillator-power-fiber-amplifier laser source has been demonstrated using a 37-filament MFC fiber in the last amplification stage. Pulses with 750 microJ (940 W peak power) and laser linewidth<1 MHz have beam generated with M2 approximately 1.3. This value is close to the theoretical value M2 approximately 1.5.

Highly polarization-dependent periodic coupling in mechanically induced long period grating over air-silica fibers.

A very flexible and versatile tunable mechanical grating platform is introduced, with which highly polarization-dependent mode coupling is observed for three types of air-silica microstructured fibers: hollow core fiber, hexagonal-boundary holey fiber (HHF), and circular-boundary holey fiber. The resonances of gratings showed highly polarization-dependent broadband coupling compared with conventional single-mode fibers due to their unique beat-length dispersions between the core and the cladding modes, which could find applications in wideband polarization-dependent loss compensation. We further present significance of the spatial symmetry of HHF in distinct mode coupling for different rotation angles around the fiber axis.

Defect and lattice structure for air-silica index-guiding holey fibers.

We propose new design parameters for index-guiding holey fiber that can provide flexibility in defect and lattice design and adiabatic mode transformation capability. The new defect consists of a central air hole and a germanosilicate ring surrounding it, which results in a large-area annulus mode profile, low splice losses to standard fiber, 0.7 dB at 1.55 microm, and chromatic dispersion with a low slope, 0.002 ps/km nm2.

Multiport N x N multimode air-clad holey fiber coupler for high-power combiner and splitter.

We report 2 x 2 and 4 x 4 multimode air-clad holey fiber couplers fabricated by a novel fusion and tapering technique. The devices showed excellent port-to-port coupling uniformity over a wide spectral range of 800-1650 nm. The 4 x 4 coupler showed a low insertion loss of 9.9 dB and excess loss of 3.9 dB at 1310 nm. Because of its unique air cladding and the high numerical aperture of the holey fiber structure, the device showed strong potential in high-power applications.

Passive Q-switching by Tm3+co-doping of a Yb3+-fiber laser.

Q-switching of a wavelength tunable Yb3+-doped double-clad fiber laser by a Tm3+-codoping in the gain fiber is demonstrated. This system showed up to 2.4 W output power, up to 140 kHz repetition rate, a maximum pulse energy of 21.8 microJ and a minimum pulse duration of 1.1 micros. Using a grating pair in Littrow-Littman configuration the emission wavelength was tunable between 1055 nm and 1090 nm. The output radiation showed a maximum spectral linewidth of 4 GHz.

High-power cw neodymium-doped fiber laser operating at 9.2 W with high beam quality.

We report on a 9.2-W cw, two-times diffraction-limited, neodymium-doped fiber laser operating in the 1.06-microm region. For a silica-based double-clad fiber, slope efficiencies of more than 25% are observed for pumping by a diode-laser system operating near 810 nm.