Circular core polarization-maintaining optical fibers withelliptical stress-induced cladding

The reproducible technology for producing high-birefringence fibers with stress-induced elliptical cladding and circular core is described. The authors have obtained fibers that have a birefringence of about (1-3) 10^-4, a mode coupling parameter of about (2-7) 10 ^-5 m^-1, and loss of less than 0.5 dB/km at 1.6 μm. The authors have found effects restricting the capability of test fibers to maintain the state of linear polarization     

Eigenstates of polarization of elliptical single-mode fibers

The degree of polarization of radiation in an elliptical polarization-maintaining fiber and the polarization states of eigenpolarization modes of such fibers have been experimentally investigated in a wide spectral range. It has been shown that the elliptical fibers are uniform, homogeneously twisted fibers with elliptically polarized eigenpolarization modes. The ellipticity of the eigenpolarization mode is independent of fiber length and increases with wavelength, while the azimuth of the eigenpolarization mode is spectrally independent     

Amplification of femtosecond pulses in Er/sup 3+/-doped single-mode optical fibres

Femtosecond pulse amplification in Er/sup 3+/-doped single-mode optical fibres has been experimentally investigated. The effect of amplified pulse compression from 80 to 55 fs has been observed. The amplified pulse energy was evaluated as 5 nJ. Maximum gain for the amplified signal was 26 dB.<>     

1 Watt Er/Yb singlemode superfluorescent optical fibre source

A singlemode superfluorescent Er/Yb optical fibre source is described, capable of generating >1 W of output power. The spectral bandwidth of the source can be varied between 0.5 and 4 nm by filtering     

Heading off emergencies in large electric grids

Until recently, power systems in the United States could be counted on to operate reliably. For more than half a century, generating and transmission reserves were ample enough to absorb constant increases in the consumption of electricity. But in recent years, that growth has combined with two other trends-larger than ever bulk transfers of electricity over ever wider areas-to subject power systems to operating conditions unanticipated during their original design. Here, the authors describe how the blackouts that swept power systems in the Western USA in 1996 could have been prevented by the use of a centralized automatic response system.     

Fracture Behavior of Single-Crystal Alloys Under Thermocyclic Loading

Strength of Materials - Experimental study results for thermal fatigue fracture of sand-glass specimens from a ZhS32 single-crystal alloy with different crystallographic orientations are presented...     

Compact high-power tunable three-level operation of double cladding Nd-doped fiber laser

We present a compact high-power continuous-wave tunable neodymium-doped double cladding fiber laser operating on three-level /sup 4/F/sub 3/2/-I/sub 9/2/ transition with a maximum output power up to 810 mW. At 926.7 nm, it has a maximum slope efficiency of 49.3% against absorbed 808-nm pump. By compressing the fiber Bragg grating, 15-nm tuning range is achieved.     

Characteristics of Q-switched cladding-pumped ytterbium-doped fiberlasers with different high-energy fiber designs

We theoretically and experimentally analyze Q-switched cladding pumped ytterbium-doped fiber lasers designed for high pulse energies. We compare the extractable energy from two high-energy fiber designs: (1) single- or few-moded low-NA large mode area (LMA) fibers and (2) large-core multimode fibers, which may incorporate a fiber taper for brightness enhancement. Our results show that the pulse energy is proportional to the effective core area and, therefore, LMA fibers and multimode fibers of comparable core size give comparable results. However, the energy storage in multimode fibers is mostly limited by strong losses due to amplified spontaneous emission (ASE) or even spurious lasing between pulses. The ASE power increases with the number of modes in a fiber. Furthermore, spurious feedback is more difficult to suppress with a higher NA, and Rayleigh back-scattering increases with higher NA, too. These effects are smaller in low-NA LMA fibers, allowing for somewhat higher energy storage. For the LMA fibers, we found that facet damage was a more severe restriction than ASE losses or spurious lasing. With a modified laser cavity, we could avoid facet damage in the LMA fiber, and reached output pulse energies as high as 2.3 mJ, limited by ASE. Theoretical estimates suggest that output pulse energies around 10 mJ are feasible with a larger core fiber, while maintaining a good beam quality     

Experimental study of single-mode W-type optical fibre

The development and experimental study of a single-mode W-type optical fibre is described. It was found that this type of optical fibre has considerably lower bending and micro-bending losses compared with usual single-mode single-cladding fibres.     

Compact high-energy Q-switched cladding-pumped fiber laser with atuning range over 40 nm

We describe a compact Q-switched diode pumped double-clad ytterbium-doped fiber laser. The fiber laser was bidirectionally pumped by two laser diodes (2 W of output power each) via two side-injecting pump-couplers. We used a large multimode core of 15 μm diameter to increase the laser gain volume and thus to achieve higher pulse energy. Experimentally this laser produced pulses with energy up to 170 μJ with a peak power of 2 kW (at a low repetition rate of 500 Hz) and was tunable from 1060 to 1100 nm