Soliton pulses in an erbium-doped fiber ring laser and its use in supercontinuum generation
孤子光脉冲的产生及其应用研究

We present a source of soliton pulses in an erbium-doped fiber ring laser. The passive mode-locking is achieved by using the nonlinear polarization rotation technique. The system generates 352 fs pulses with repetition rate of 12.5 MHz and the 3dB spectrum width of about 7.8 nm at the central wavelength of 1563.3 nm. A low-cost erbium-doped fiber amplifier is employed to boost the peak power of the pulses. Single-mode supercontinuum is obtained by passing the amplified pulses through a photonic crystal fiber with the length of 101 nm. Further more, we show the evolution process of the supercontinuum with different optical pump power. It is shown that, with the low-intensity femtosecond pulses, the spectrum broadening is caused by the fission of the higher-order solitons. With the increase of the pump power, the threshold of stimulated Raman scattering (SRS) is achieved, and the energy transfer through SRS spreads toward the long wavelength and the short wavelength sides. On further increasing the pump power, the coupling between SRS and parametric four-wave mixing will result in the appearance of waves with new wavelengths, and the spectrum will become broader and more smooth.