A dispersion-varying tapered planar waveguide is designed to generate supercontinuum efficiently in the mid-infrared region. The rib waveguide of lead-silicate glass on silica is 1.8 cm long, consisting of a segment with longitudinally increasing etch depth. The mechanism involves nonlinear soliton dynamics. The dispersion profile is shifted along the propagation distance, leading to continuous modification of the phase-matching condition for dispersive wave (DW) emission and enhancement of energy transfer efficiency between solitons and DWs. With low input pulse energy of 45 pJ, simulation demonstrates the generation of both broadband and flat near-octave spectrum spanning 1.3-2.5 μm at the -20  dB level.

A mode-locked erbium-doped fiber ring laser that is easy to set up is proposed and experimentally demonstrated to generate a high-repetition-rate optical pulse train with an ultrashort pulse width. The laser combines a rational harmonic mode-locking technique and charcoal nanoparticles as saturable absorbers. Compared to a solely active mode-locking scheme, the scheme with charcoal nanoparticles can remove the supermodes and narrow the pulse width by a factor of 0.57 at a repetition rate of 20 GHz. Numerical simulation of the laser performance is also provided, which shows good agreement with the experimental results.

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We propose and demonstrate a hybrid mode-locked erbium-doped fiber ring laser by combining the rational harmonic mode-locking technique and passive mode locking based on nonlinear polarization rotation in a highly nonlinear photonic crystal fiber. By carefully adjusting the modulation frequency and the polarization controllers in the cavity, a 30 GHz pulse train with improved stability and narrower pulse width is generated. The pulse width at 30 GHz using rational harmonic mode locking alone is 5.8 ps. This hybrid scheme narrows the pulse width to 1.9 ps at the repetition rate of 30 GHz. Numerical simulations are carried out that show good agreement with the experimental results.