High-power frequency comb in the range of 2-2.15 μm based on a holmium fiber amplifier seeded by wavelength-shifted Raman solitons from an erbium-fiber laser
Coluccelli, N.; Cassinerio, M.; Gambetta, A.; Laporta, P.; Galzerano, G.
Optics Letters 39(6): 1661-1664
ISSN/ISBN: 1539-4794 PMID: 24690863 DOI: 10.1364/ol.39.001661
We demonstrate a room-temperature high-power frequency comb source covering the spectral region from 2 to 2.15 μm. The source is based on a femtosecond erbium-fiber laser operating at 1.55 μm with a repetition rate of 250 MHz, wavelength-shifted up to 2.06 μm by the solitonic Raman effect, seeding a large-mode-area holmium (Ho) fiber amplifier pumped by a thulium (Tm) fiber laser emitting at 1.94 μm. The frequency comb has an integrated power of 2 W, with overall power fluctuations as low as 0.3%. The beatnote between the comb and a high-spectral-purity, single-frequency Tm-Ho laser has a linewidth of 32 kHz over 1 ms observation time, with a signal-to-noise ratio in excess of 30 dB.