A pulsating soliton exists in various passively mode-locked fiber lasers. Versatile categories of pulsating solitons have been investigated in a steady regime. However, the formation dynamics of pulsating solitons have not been fully revealed. Herein, we experimentally captured both single pulsating soliton and two pulsating soliton formation processes in an all-normal-dispersion laser. With the help of the time-stretch dispersion Fourier transform technique, the real-time temporal and spectral evolutions of pulsating solitons, during the buildup process, were investigated. It is found that pulsation directly derives from the background noise. In addition, both types of pulsations experience several characteristic stages, including an unstable Q -switch, spectral shaping, broadening, oscillating, and narrowing, which might be induced by the transient non-balance between the gain and loss of the cavity. We anticipate that the work in this Letter can improve the understanding of pulsating behaviors and bring new insights into the dynamic phenomenon of nonlinear optical systems.

An all-polarization maintaining mode-locked Yb-doped fiber integrated laser with a nonlinear amplifying loop Mirror (NALM) under the operation regime of dissipative soliton resonance (DSR) has been demonstrated. The mode-locked laser can generate DSR pulses at 1.04 μm at the repetition rate of 2.59MHz. The output DSR pulses can be tuned in pulse width from hundreds of picoseconds to a few nanoseconds by adjusting the pump power. By changing the pump power of the main loop and the NALM, the maximum output average power of 51.4 mW and the corresponding pulse energy about 20 nJ are achieved, respectively. Pulse breaking of the DSR pulses was observed apart from the typical pulse broadening at a fixed pulse peak power due to the peak power clamping effect, while solely increasing the main loop pump power. In addition, the characteristics of the DSR pulses such as pulse width, pulse energy, output power and optical spectrum with the changing of main loop pump power and NALM pump power are also discussed respectively.

In this paper a single-channel chirped pulse amplification laser system based on Yb-doped photonic crystal fiber was constructed, which achieved a pulse energy output of 1 mJ with a beam quality close to the diffraction limit. Pulsed synchronous pumping was used to suppress amplified spontaneous emission at a repetition rate of 1 kHz. The de-chirped pulse width of 231 fs was achieved by precise systematic dispersion control, and the corresponding peak power reached 3.85 GW.

We propose a numerical model to simulate amplification in a pulsed synchronously pumped chirped pulse amplifier (CPA) operating at a low repetition rate. The generalized nonlinear Schrödinger equation and dynamic rate equations are employed to facilitate an accurate treatment of time-space-dependent-gain, wavelength-dependent saturation energy, nonlinearity, and dispersion. Because of an accurate instantaneous gain term, the model can adequately explain pulse distortion and spectral redshift during amplification. The bidirectional amplified spontaneous emission, final output energy, and evolution of temporal and spectral intensities are also investigated through simulations. In addition, a pulsed synchronously pumped CPA fiber system is estbalished to validate the model. The experimental results for the wave shape, spectrum and energy show excellent agreement with those of simulations.

Speckle is an important phenomenon in various applications. It can be quantified by speckle contrast. However, at present the influence of the phase relations among the various wavelengths on speckle contrast is rarely analyzed theoretically. Herein, a thorough method for numerically simulating the speckle pattern is presented to considering the impact of relative phase relations among wavelengths on speckle contrast. This method contains spectral shape, width, and phase relations. In addition, a superluminescent pulse amplifier (SPA) with 6.5-nm bandwidth and a mode-locked laser (MLL) with 21-nm bandwidth are established to conduct the verification experiment. The experimental results show that the SPA light attains lower speckle contrast even with a narrower bandwidth than MLL light. It is manifested that relative phase relations among wavelengths has significant effect on speckle contrast, and chaotic phase relations could be more advantageous for reducing speckle than just a broad spectrum. The simulation results agree well with experimental results. Therefore, this method could provide a reliable approach to describe the characteristics of speckle pattern caused by broadband light carrying phase information. Considering the speckle contrast is positively proportional to optical coherence, this method could also be used to analyze the coherence of partially coherent light.