In this paper, a spectral model by incorporating SRS effect is proposed and established, which is feasible for analyzing the SRS effect both in high-power fiber oscillator and master oscillator power amplifier (MOPA) system. The theoretical results show that the SRS effect is tightly related to the bandwidths of the fiber Bragg gratings (FBGs) and it can be efficiently suppressed by optimizing the bandwidth of the FBGs. Besides, the established theoretical model is also feasible for analyzing the influence of seed power on the SRS effect. The theoretical predictions agree well with the previous experimental results.

In this paper the stimulated Raman scattering (SRS) effect in high-power fiber amplifiers seeded by the narrow-band filtered superfluorescent source (SFS) is firstly analyzed both theoretically and experimentally. Spectral models for the formation of the SFS and the spectral evolution in high-power fiber amplifiers seeded by filtered SFS are proposed. It is found that the SRS effect in high-power fiber amplifiers depends on the spectral width of the filtered SFS seed. The theoretical predictions are in qualitative agreements with the experimental results.

A new approach for the complete modal decomposition of the optical fields emerging from the multimode fiber is presented in this paper. Based on the stochastic parallel gradient descent algorithm, mode coefficients for all the bound modes in the multimode fiber can be exactly calculated by utilizing one intensity profile of the beam. Numerical simulation validates the feasibility, and the reconstructed error is below 0.1%. In the case of six modes within the fiber, the running time is about 2 s.

No abstract

We report the direct generation of 0.4 μJ, 7 kW ultrabroadband picosecond noise-like pulses from an Yb-doped all-fiber oscillator based on dual nonlinear optical loop mirrors (NOLMs). Under the highest pump power, the average power of the main output port reached 1.4 W, and the 3 dB spectral bandwidths reached 76 nm and 165 nm from the two output ports, respectively. The design of dual-NOLMs shows both exceptional compactness in construction and distinct flexibility on the engineering of the mode-locking behaviors. To the best of our knowledge, this is the first demonstration of a watt-level dual-NOLM-based fiber laser. Based on this laser, the pulse energy and peak power of picosecond noise-like pulse from an all-fiber oscillator have been elevated by an order of magnitude.