Beam combining of fiber lasers has attracted much interest as a practical means to power scale fiber laser/amplifiers
beyond the limitations of a single mode output from an individual fiber [1]. Almost all of the high power demonstrations
to date that deliver good beam quality after the combing process (coherent and spectral) require some linewidth control
for efficient combining, typically less than 10GHz [2,3,4]. Previously we demonstrated single mode, Yb-doped LMA
fiber amplifiers operated with around 7GHz linewidth at 1kW output power [5]. In this paper, the latest generations of
these amplifiers, based on the latest developments in LMA Yb-doped fiber technology demonstrate the capability to
operate with linewidths around 3GHz at the 1kW power level. We present the latest data on optical properties of these
new Yb-doped amplifiers and the SBS threshold as a function of input seed laser linewidth and discuss the technologies
being developed to operate at higher power levels and narrower linewidths.
We report on a new class of novel optical fiber structures, designed for use in harsh environments typical of Oil and Gas Applications. Specifically, we focus on fiber designs that alleviate the effects of hydrogen ingression and its associated darkening of optical fibers in harsh environments. We demonstrate theoretically, how a carbon coated optical fiber structure consisting of an array of randomly or systematically placed voids running along the length of the fiber, can lead to significantly reduced hydrogen ingression effects. The array of voids can be of arbitrarily varying shapes and sizes, along the length of the fiber. We derive an equation describing the increase in the fiber lifetime as a function of the average cross-sectional fraction of voids in the fiber. Fiber darkening effects are predicted to decrease by factors of as much as x10, for moderately low fraction of voids in the fiber cross-section. Theoretical predictions are confirmed experimentally by performing ingression tests in a hydrogen test chamber with on-line monitoring capability, simulating down-hole temperatures and pressures. Additional geometric factors, such as fiber diameter, that may also be optimized to further improve the hydrogen ingression resistance of fibers are discussed; in this vein a new larger form-factor fiber, different from the standard 125um fiber is proposed. Finally, the lifetime predictions greater than 5-10 years obtained for such void-filled optical fibers in typical down-hole conditions make them extremely attractive candidates for use in Oil and Gas applications such as well monitoring and logging.
Optical fibers with improved hermeticity, strength and chemical resistance are presented. Specifically, we provide data demonstrating the resistance of carbon coated optical fibers to hydrogen (high partial pressures and temperatures) and acidic environments. As well we provide data and analysis indicating that carbon coated fibers with increased n-values provide long lifetimes under stressed conditions.
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