A kind of tapered segmented cladding fiber (T-SCF) with large mode area (LMA) is proposed, and the mode and amplification characteristics of T-SCFs with concave, linear, and convex tapered structures are investigated based on finite-element method (FEM) and few-mode steady-state rate equation. Simulation results indicate that the concave tapered structure can introduce high loss for high-order modes (HOMs) that is advantageous to achieve single-mode operation, whereas the convex tapered structure provides large effective mode area that can help to mitigate nonlinear effects. Meanwhile, the small-to-large amplification scheme shows further advantages on stripping off HOMs, and the large-to-small amplification scheme decreases the heat load density induced by the high-power pump. Moreover, single-mode propagation performance, effective mode area, and heat load density of the T-SCF are superior to those of tapered step index fiber (T-SIF). These theoretical model and numerical results can provide instructive suggestions for designing high-power fiber lasers and amplifiers.

A scheme of triangular-shaped pulses with full duty cycle generation is proposed and analyzed. Benefiting from the feature of orthogonal polarization, two approximate sinusoidal signals on different polarization states can be combined without inducing coherent interference. By tuning the time mismatching between the two signals, an approximately triangular-shaped profile can be obtained in the optical intensity. It is found that the modulation index β is no longer a fixed one, but it can be aligned within a proper range of 0.92 to 1.57. To evaluate the proposal, impacts of radio frequency voltage fluctuation, bias voltage drift, and time mismatching are discussed. Within the defined fitting error (η≤3%), the tolerable range of the modulation index, time mismatching, and voltage have been found, which insures a simple operation in practice.