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Toward high peak power ultrashort pulses using normal dispersion thulium fiber in all-fiber amplifier and compressor

In fiber lasers, operating in normal dispersion regime benefits high peak power operation thanks to no pulse breakup as in anomalous dispersion. However, the spectral range of Thulium (Tm) emission lies in anomalous dispersion regime for conventional optical fibers. Hence, a customized W-type step-index Normal Dispersion Thulium Fiber (NDTF) is designed to have strong waveguide dispersion at the Tm emission band. The dispersion of NDTF is -28.97 ps/nm.km at 1.9 μm wavelength. An all-fiber seed source based on a ring oscillator was built with the NDTF as the active fiber and produce mode-locked soliton pulses near 2 μm. Subsequently, the pulses are amplified through the NDTF in an all-fiber amplifier stage. The NDTF amplifier produced pulses of ~593 nJ pulse energy in a ~4.4 ps FWHM pulse width. The amplified pulse is then compressed to ~1.91 ps giving a peak power of ~310 kW in an all-fiber compressor consisting of SMF28 fiber. This represents a potential to generate high peak powers in ultrashort pulses at 2 μm wavelength in all-fiber configuration.