The combining of double-clad (DC) doped fibers and semiconductor pump laser diodes has allowed the development of high power optical sources in CW or pulsed regimes. Compared to bulk medium, the main limitations for achieving high peak powers inside optical fibers are due to small mode field size and large propagation length. Nonlinear effects such as the optical Kerr effect, Stimulated Raman Scattering (SRS) or Stimulated Brillouin Scattering (SBS) can be observed in high power amplifiers as short as a few meters of doped fiber length. A description of the different non-linear dynamics for optical pulse amplification in dependence with temporal pulse duration (ps, ns and µs regimes) will be presented. Theoretical modelling has also investigated to confirm the observed signal distortions in the case of a ∼6 µm core doped fiber amplifier. The power increase requires the design of new doped fibers with a large core to enhance simultaneously stored energy and nonlinear effects threshold. The peak power threshold in dependence with temporal pulse duration (ps, ns and µs regimes) will be given in relation with core diameters of double-clad fibers.

We describe an all-fiber ytterbium-doped laser followed by a double-stage ytterbium-doped double-clad fiber amplifier of 10-W output power for helium pumping. Different cavity designs are investigated with the goal of achieving high-power multimode emission at 1083 nm, wavelength tunability over the helium absorption bands, and linewidth envelope control over the range 1-3 GHz. We point out the domains with unstable output power and discuss their origin.

We report a high power, single frequency, linearly polarized master oscillator power amplifier emitting 110 ns, 1 kW peak power pulses at 2050 nm. A 20% slope efficiency and a beam quality of M2=1.21 are achieved with three-stage double-clad Tm(3+)-doped fiber architecture. Various pump schemes are compared leading to the conclusion that 793 nm pump wavelength is the most efficient for amplification at 2050 nm. Based on numerical simulations, the Brillouin gain coefficient around 2 μm in Tm(3+) highly doped silica fiber is estimated to 1.2×10(-11) m/W. Output peak power is limited by stimulated Brillouin scattering to 535 W without mitigation and to 1 kW with application of a strain distribution along the doped fiber.

Large amounts of hyperpolarized 3 He gas with high nuclear polarization rates are required for use in neutron spin filters or nuclear magnetic resonance imaging of human lung. Very high efficiency can be obtained by metastability exchange optical pumping using multimode lasers to excite the 2 3 S-2 3 P transition at 1083 nm. Broadband Ytterbium-doped tunable fiber lasers have been designed for that particular application. Different options for the architecture of the fiber oscillator are presented and compared. Emphasis is given to a linear cavity configuration that includes a high reflectivity fiber mirror and a low reflectivity tunable fiber Bragg grating. Optical measurements are performed to finely characterize the spectral behavior of the lasers. Atomic response is also quantitatively probed to assess the optimal design of the oscillator for optical pumping. Multimode operation matching the 2 GHz Doppler-broadened helium resonance line and tunability over more than 200 GHz are demonstrated. Boosting the output of this fiber laser with a Yb-doped fiber power amplifier, allfiber devices are built to provide robust, high power turn-key sources at 1083 nm for improved production of laser polarized 3 He. 42.55.Wd; 32.80.Bx PACS

Increase in transmission symbol-rate as well as order of quadrature amplitude modulation (QAM) is identified as the most economical way to reduce cost per transmitted bit. In particular, next generation transponders aim at supporting datarates up to 1 Tb/s employing superchannels due to electrical components' bandwidth limitations. Furthermore, the introduction of a flexible-grid architecture can maximize throughput by minimizing spectral gaps in available optical spectrum. Keeping in view these design options, we conducted several high capacity experiments with tier1 operator Orange using their field deployed standard single mode fiber (SSMF, G.652), having a total length of 762 km, connecting the cities Lyon and Marseille in France. In particular we employed four subcarriers per Tb/s superchannel, each modulated by PM-16QAM, PM-32QAM and PM-64QAM with per carrier symbol-rates of 41.2 GBd, 33 GBd and 34 GBd, respectively. The subcarrier spacing was 50 GHz for the PM-16QAM case and 37.5 GHz for both the PM-32QAM and PM-64QAM cases allowing in total 24×1.0 Tb/s, 32×1.0 Tb/s and 32×1.2 Tb/s superchannels over C-band and resulting in potential C-band capacities of 24.0 Tb/s, 32.0 Tb/s and 38.4 Tb/s, respectively. After field transmission the maximum available OSNR0.1nm margin compared to the required OSNR0.1nm at forward error correction (FEC) threshold was 8.2 dB, 5.4 dB and 4.2 dB for PM-16QAM, PM-32QAM and PM-64QAM, respectively. The transmission reach for PM-16QAM and PM-32QAM modulated superchannels was extended to ∼1571 km and ∼1065 km using erbium doped fiber amplified SSMF spans of ∼101 km length.