Wavelength-tunable picosecond laser source based on filtering and amplifying broadband dissipative soliton pulse

A method for obtaining picosecond pulse sources with continuously tunable central wavelengths is demonstrated numerically and experimentally. A dissipative soliton (DS) mode-locked erbium-doped fiber (EDF) laser based on the nonlinear polarization rotation provides the seed pulse with a flat-top spectral profile and a 55 nm spectral bandwidth. Then it is filtered by a wavelength-tunable super-Gaussian bandpass filter and amplified by two segments of EDFs with different doping concentrations. The output DS pulse from the EDF laser can be compressed from 5.532 ps to 0.291 ps by using a single-mode fiber (SMF-28e), while the pulse energy is about 1.6 nJ. Furthermore, the about 4 ps and 6.84 nJ pulses with continuously tunable central wavelengths ranging from 1535 to 1580 nm can be obtained by amplifying the spectrally filtered pulses. The tunable picosecond pulse source based on the extra-cavity filtering method is very useful for many practical applications because of its flexible wavelength control.

Intracavity incoherent supercontinuum dynamics and rogue waves in a broadband dissipative soliton laser

Understanding dynamical complexity is one of the most important challenges in science. Significant progress has recently been made in optics through the study of dissipative soliton laser systems, where dynamics are governed by a complex balance between nonlinearity, dispersion, and energy exchange. A particularly complex regime of such systems is associated with noise-like pulse multiscale instabilities, where sub-picosecond pulses with random characteristics evolve chaotically underneath a much longer envelope. However, although observed for decades in experiments, the physics of this regime remains poorly understood, especially for highly-nonlinear cavities generating broadband spectra. Here, we address this question directly with a combined numerical and experimental study that reveals the physical origin of instability as nonlinear soliton dynamics and supercontinuum turbulence. Real-time characterisation reveals intracavity extreme events satisfying statistical rogue wave criteria, and both real-time and time-averaged measurements are in quantitative agreement with modelling.

3 W average-power high-order mode pulse in dissipative soliton resonance mode-locked fiber laser

Recently high-order modes (HOMs) lasers have been extensively investigated due to their potential applications in mode-division multiplexing. In this paper, we present two schemes of generating HOMs from the mode-locked fiber lasers (MLFLs) in the dissipative soliton resonance (DSR) regime. Watt-level HOM outputs are implemented through intra-cavity mode conversion. 3 W average-power HOMs with an efficiency slope of 25% can be obtained based on an MLFL in the DSR regime, which is achieved by incorporating a long-period fiber grating (LPFG) and a dual-resonant acoustically induced fiber grating (AIFG), respectively. Their different spectrum responses enable flexible mode conversion in the MLFLs. Both fiber mode converters are exploited to show their robust capability of efficient mode manipulation. The MLFL with an LPFG inserted in the cavity can achieve wide-bandwidth intra-cavity optical vortex beams (OVBs) near the dispersion turning around point because of the pulses of the fundamental mode and high-order vortex eigenmodes oscillating in the cavity with the same group velocity to form spatiotemporal mode locking. The MLFL based on a dual-resonant AIFG can perform the function of fast switching (∼0.3 ms) in LP01, LP11a, and LP11b modes with a high modal purity of 96%. These different modes with high-energy pulses can be flexibly switched with programmable radio frequency modulation. Furthermore, a quarter-wave plate and a polarizer are employed at the output of fiber laser to realize the controllability of the mode field, which is possible to generate a controllable mode field of OVBs based on the first-order Poincaré sphere. This control method can be integrated with the MLFLs to extend the flexibility of high-power HOMs generation.