Abstract
Abstract 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.
Highlights
Over recent decades, fiber lasers and amplifiers have attracted great interest owing to their advantages of high slope efficiency, high beam quality, superior thermal management property, and compactness[1]
The laser characteristics of the tapered segmented cladding fiber (T-segmented cladding fiber (SCF)) under a large-to-small amplification scheme are analyzed by substituting the mode parameters calculated in the first part into Equations (4)–(7), and are compared with that of the tapered step index fiber (T-step index fiber (SIF)) under a large-to-small amplification scheme
We preliminarily optimize the fiber parameters to ensure that the loss of LP01 of T-SCF is lower than 0.1 dB/m[33] and to ensure saturation amplification for LP01 mode
Summary
Fiber lasers and amplifiers have attracted great interest owing to their advantages of high slope efficiency, high beam quality, superior thermal management property, and compactness[1]. Large-core SCF can simultaneously support LMA and single-mode operation, which is attractive for high-power fiber lasers and amplifiers. In addition to these longitudinal uniform LMA fibers, a novel promising tapered fiber design has been developed in recent years. Single-mode operation is easier to achieve for TSCF under small-to-large amplification scheme, whereas heat load density of T-SCF under large-to-small amplification scheme is much lower than that under small-to-large amplification scheme These results suggest that the tapered structure and amplification scheme have an effect on the mode characteristics and laser performance, which provides theoretical foundations for developing compact high-power fiber lasers and amplifiers
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