title: Generation of wavelength-tunable soliton molecules in a 2-μm ultrafast all-fiber laser based on nonlinear polarization evolution.
abstract: We report on the experimental observation of stable single solitons and soliton molecules in a 2-μm thulium-holmium-doped fiber laser mode-locked through the nonlinear polarization evolution technique within an anomalously dispersive cavity. Single 0.65 nJ solitons feature a 7.3 nm spectral FWHM and 540 fs temporal duration, yielding a time-bandwidth product close to the Fourier-transform limitation. Under the same pumping power of 740 mW, stable out-of-phase twin-soliton molecules, featuring a temporal separation of 2.5 ps between the two ∼700  fs pulses, are generated in a deterministic way, while the central wavelength of the soliton molecules can be tuned from 1920 to 1940 nm. Finally, we present strong experimental evidence of vibrating soliton molecules.
authors.forename: Pan
authors.initials: P
authors.lastname: Wang
authors.forename: Chengying
authors.initials: C
authors.lastname: Bao
authors.forename: Bo
authors.initials: B
authors.lastname: Fu
authors.forename: Xiaosheng
authors.initials: X
authors.lastname: Xiao
authors.forename: Philippe
authors.initials: P
authors.lastname: Grelu
authors.forename: Changxi
authors.initials: C
authors.lastname: Yang