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  • Open Daily: 10am - 10pm
    Alley-side Pickup: 10am - 7pm

    3038 Hennepin Ave Minneapolis, MN
    612-822-4611

Open Daily: 10am - 10pm | Alley-side Pickup: 10am - 7pm
3038 Hennepin Ave Minneapolis, MN
612-822-4611
Power Scaling of Ytterbium(3+)-Doped Phosphate Fiber Lasers and Amplifiers.

Power Scaling of Ytterbium(3+)-Doped Phosphate Fiber Lasers and Amplifiers.

Lee, Yin-Wen

Paperback

Biology

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ISBN10: 1243581328
ISBN13: 9781243581327
Publisher: Proquest Umi Dissertation Pub
Pages: 112
Weight: 0.47
Height: 0.23 Width: 7.44 Depth: 9.69
Language: English
The initial motivation for this work was to build a high-power single-frequency, single-mode, linearly polarized fiber MOPA for gravitational-wave detection. Although spectacular progress has been made over the past few years in the development of single-frequency Yb3+-doped silica fiber laser sources, their maximum output powers are still limited by the onset of stimulated Brillouin scattering. To further scale the output power of single-frequency silica fiber laser sources with step-index single-mode fibers, increasing the ion concentration in the gain fiber is required. Unfortunately, excessive amounts of rare-earth ions in silica fibers cause concentration quenching, photodarkening, and crystallization. To this end, phosphate glass is a good alternative because of the high solubility of rare-earth oxides in this host. For example, the solubility of Yb2O3 in phosphate glass is at least 26 wt.%, i.e., 10 times higher than in silica. Such a high ion concentration significantly reduces the required fiber length and enables the use of a short step-index single-mode fiber without suffering from SBS up to very high output powers. To investigate the feasibility of extracting high powers from this gain medium, we measured several key material properties of the Yb3+-doped phosphate fibers, including the SBS gain coefficient, photodarkening resistance, and fiber background loss. Our experimental results showed that, compared to silica fibers, phosphate fibers exhibit a 50% weaker SBS gain coefficient and allow a 6-times-higher Yb3+ concentration without the onset of photodarkening. We measured the scattering and absorption loss of the phosphate fiber by using an integrating sphere and a fiber calorimeter, respectively. The results showed that 77% of the fiber background loss originates from impurity absorption, and the rest from scattering. It indicates that absorption loss must be reduced to improve the efficiency of the fiber laser. The studies of these material properties allow us to precisely evaluate the potential for power scaling of phosphate fiber lasers and amplifiers. As a proof of principle, we experimentally demonstrate truly single-mode fiber lasers and amplifiers with record output powers of several tens of watts. These laser sources include a 57-W multiple-frequency 1.06-mum fiber laser with a slope efficiency of 52.7%, and a 16-W single-frequency fiber MOPA. This is the first report of a watt-level CW Yb3+-doped phosphate fiber amplifier. We showed through numerical simulations that the exceptional characteristics of phosphate fibers can be extended to a ∼700-W single-frequency fiber amplifier from a step-index single-mode fiber. The peak thermal load of this 700-W phosphate fiber MOPA was calculated to be ∼800 W/m, which can be handled by suitable cooling. In summary, all results presented in this dissertation confirm that Yb3+-doped phosphate fibers constitute a promising gain element for power-scaling truly single-mode single-frequency fiber laser amplifiers.

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