Tapered Fiber Amplifier with High Gain and Output Power¹

J. Kerttula^a, *, V. Filippov^a, Y. Chamorovskii^b, V. Ustimchik^b,
K. Golant^b, and O. G. Okhotnikov^a

^a Optoelectronics Research Centre, Tampere University of Technology,
P.O. Box 692, 33101 Tampere, Finland

^b Institute of Radio and Electronics of the Russian Academy of Sciences,
Mokhovaya 11, bld. 7, Moscow, 125009 Russia

*e-mail: juho.kerttula@tut.fi

Received February 7, 2012; published online October 1, 2012

Abstract—We present a high-power ytterbium fiber amplifier based on active tapered double-clad fiber
(TDCF) and capable of high single-pass gain. The T-DCF power amplifier seeded with a 320 mW narrowband
signal generates up to 110 W of average output power corresponding to more than 25 dB gain. The amplifier
exhibits near-diffraction-limited beam quality (M² = 1.06) at the highest output power, which was limited by
the available pump power. With a broadband seed source, the amplifier produced a gain of nearly 40 dB
obtained for low-signal limit of the seed. The high output power combined with high gain is achieved owing to
amplified spontaneous emission (ASE) filtering and increased stimulated Brillouin scattering (SBS) threshold
inherent to the axially non-uniform geometry. The amplifier operates efficiently with a wide range of input seed
powers thus providing the basis for one-stage tapered amplifier which combines the functions of preamplifier
and power amplifier and can be a competitive alternative to multi-stage design.

DOI: 10.1134/S1054660X12110059

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