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.

Generation of nanosecond pulses with 55-mJ energy and 4.8-MW peak power are demonstrated in a multistage fiber amplifier system, which is seeded with 10-nm broadband pulses from a superluminescence diode. The pulses are at low repetition of 10 Hz and with width of 10 ns. High energy and high peak power for nanosecond pulses are obtained simultaneously from fiber amplifier. In particular, the peak power is at least two times the previous peak power for nanosecond pulses.

Traditional feature matching methods of optical and synthetic aperture radar (SAR) used gradient are sensitive to non-linear radiation distortions (NRD) and the rotation between two images. To address this problem, this study presents a novel approach to solving the rigid body rotation problem by a two-step process. The first step proposes a deep learning neural network named RotNET to predict the rotation relationship between two images. The second step uses a local feature descriptor based on the Gaussian pyramid named Gaussian pyramid features of oriented gradients (GPOG) to match two images. The RotNET uses a neural network to analyze the gradient histogram of the two images to derive the rotation relationship between optical and SAR images. Subsequently, GPOG is depicted a keypoint by using the histogram of Gaussian pyramid to make one-cell block structure which is simpler and more stable than HOG structure-based descriptors. Finally, this paper designs experiments to prove that the gradient histogram of the optical and SAR images can reflect the rotation relationship and the RotNET can correctly predict them. The similarity map test and the image registration results obtained on experiments show that GPOG descriptor is robust to SAR speckle noise and NRD.

Nanosecond (~10 ns) laser pulses with high peak power of 8 MW and high energy of 100 mJ are reported, which are generated by a cascaded pulsed Yb-doped fiber amplifier system working at a repetition frequency of 10 Hz. The peak power that is higher than the self-focusing threshold for Gaussian beams is achieved for the first time in the fiber lasers. To analyze the self-focusing threshold for multimode lasers in fibers, a novel mode decomposition based on the beam quality measurements is introduced. Based on the mode decomposition and nonlinear laser propagation simulations, the threshold of self-focusing for our case is estimated.

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.

Stimulated Raman scattering (SRS) is an important limiting factor for achieving high peak power intensity in fiber amplifier systems. It was proposed to use partially coherent light to increase the SRS threshold significantly. In this paper, the SRS threshold of partially coherent light in silica fibers is investigated by both experiments and theoretical analysis, which show that the SRS threshold is independent on light coherency when the bandwidth of the light is much narrower than 30 nm.