Dahv Kliner

Gamma-Radiation-Induced Photodarkening in Unpumped Optical Fibers Doped With Rare-Earth Constituents

Fibers doped with rare-earth constituents such as Er3+ and Yb3+ are exceedingly important to designers of fiber-optical systems due to their ability to amplify signals in the near infra-red, low-absorption regions of conventional silicate fibers. Extending the range of operating conditions for these systems to include adverse radiation environments requires a detailed study of the behavior of the fiber when subjected to relevant radiation fluxes of various cumulative doses and dose rates. Of particular interest in many applications is the effect of gamma radiation, which is known to degrade optical signal transmittance by creating absorption centers in the material. A study of radiation-induced photodarkening effect in unpumped Er3+, Yb3+, and Er3+/Yb3+ co-doped fibers under Co60 gamma-irradiation is the focus of this paper. Specifically, the temporal evolution of the fiber transmittance in the near infra-red region from ~1.0 μm-1.6 μm was investigated, subjected to a multitude of exposure conditions spanning different dose-rates and total accumulated doses. The Er3+/Yb3+ co-doped fiber was found to be the most radiation resistant, while the Er3+ doped fiber was found to be the most radiation sensitive in this wavelength region. Dose rate and compositional dependencies were also observed in all fibers.

1.2-kW single-mode fiber laser based on 100-W high-brightness pump diodes

We have demonstrated a monolithic (fully fused), 1.2-kW, Yb-doped fiber laser with near-single-mode beam quality. This laser employs a new generation of high-brightness, fiber-coupled pump sources based on spatially multiplexed single emitters, with each pump providing 100 W at 915 nm within 0.15 NA from a standard 105/125 μm fiber. The fiber laser is end pumped through the high-reflector FBG using a 19:1 fused-fiber pump combiner, eliminating the need for pump/signal combiners. The output wavelength is 1080 nm, with a linewidth of < 0.5 nm FWHM. A peak power of 1.5 kW was reached in modulated operation (1-ms pulse duration) with M2 < 1.2.

4-kW fiber laser for metal cutting and welding

We have developed a commercial 4-kW fiber laser consisting of seven, 600-W modules whose outputs are combined with a fused-fiber combiner. The system architecture has several practical advantages, including pumping with reliable single-emitter diodes, monolithic fused-fiber construction (no free-space beams), and end pumping using a 91:1 pump combiner (eliminating the need for complex pump/signal combiners). Typical results at 4-kW output power are a beamparameter product of 2.6 mm-mrad, 8-hr power stability of < 0.5% rms, central wavelength of 1080 nm, and linewidth of 1.2 nm FWHM. These lasers have been incorporated into Amada machines used for cutting metal sheet and plate and have been used to cut aluminum, mild steel, stainless steel, brass, titanium, and copper with a thickness up to 19 mm. A world-record cutting speed of 62 m/min has been demonstrated for 1-mm aluminum sheet metal.

kW fiber lasers

We describe a monolithic (fully fused), 1.2-kW, Yb-doped fiber laser with single-mode beam quality. This laser employs a new generation of 100-W, high-brightness, fiber-coupled pump sources based on spatially multiplexed single emitters and a simple, end-pumped design for high efficiency, reliability, and environmental stability.

Embedded-mirror side pumping of double-clad fiber lasers and amplifiers

Embedded-mirror side pumping enables fabrication of compact, efficient fiber sources using a variety of pump sources. It is the only method capable of employing the output of an unformatted diode bar. We discuss recent progress.

Special Section Guest Editorial: Fiber Lasers

This PDF file contains the editorial “Special Section Guest Editorial: Fiber Lasers” for OE Vol. 50 Issue 11