Transverse mode instability

In this paper, an all-fiberized and narrow-linewidth 5 kW power-level fiber amplifier is presented. The laser is achieved based on the master oscillator power amplification (MOPA) configuration, in which the phase-modulated single-frequency laser is applied as the seed laser and bidirectional pumping configuration is applied in the power amplifier. The stimulated Brillouin scattering (SBS), stimulated Raman scattering (SRS), and transverse mode instability (TMI) effects are all effectively suppressed in the experiment. Consequently, the output power is scaled up to 4.92 kW with a slope efficiency of as high as ~ 80%. The 3 dB spectral width is about 0.59 nm, and the beam quality is measured to be M 2 ~ 1.22 at maximum output power. Furthermore, we have also conducted detail spectral analysis on the spectral width of the signal laser, which reveals that the spectral wing broadening phenomenon could lead to the obvious decrease of the spectral purity at certain output power. Overall, this work could provide a well reference for obtaining and optimizing high-power narrow-linewidth fiber lasers.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

All-fiberized and narrow-linewidth 5 kW power-level fiber amplifier based on a bidirectional pumping configuration

Liu

et al. 2021

“…where N 1 /N 2 and N Yb are the lower/upper state population and Yb 3+ ion concentration, respectively; P + p/s,i and P − p/s,i represent the forward and backward pump/ith modal power; σ ap /σ ep and σ as /σ es are the absorption/emission crosssections at the pump and signal wavelengths; α p (z) and α s,i (z) are the pump loss and ith mode loss that can be calculated according to Equation (3), and the units for those losses are dB/m; the pump and ith mode power fill factor are denoted by Γ p (z) and Γ s,i (z); and A dope (z) is the effective ion-doped area that is mainly dependent on Equation (1). The rare-earth-doped core can act as a heat source under a high-power pump [32] , and thus the longitudinally varying core radius of T-SCF results in longitudinally varying heat load density that is…”

Section: Theory and Modelmentioning

confidence: 99%

Amplification characteristics in active tapered segmented cladding fiber with large mode area

Xie

Ning

Jiao

et al. 2021

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.

“…Email: fanwh@opt.ac.cn (W. Fan); ypzhang@xjtu.edu.cn (Y. Zhang) evolution on the output power of fiber lasers in the past two decades [4] . However, the evolution is suffering from a sudden halt owing to mode degradation phenomena [5,6] .…”

Section: Introductionmentioning

confidence: 99%

Effective suppression of mode distortion induced by stimulated Raman scattering in high-power fiber amplifiers

Gao

Fan

et al. 2021

Mode distortion induced by stimulated Raman scattering (SRS) has become a new obstacle for the further development of high-power fiber lasers with high beam quality. Here, an approach for effective suppression of the SRS-induced mode distortion in high-power fiber amplifiers has been demonstrated experimentally by adjusting the seed power (output power of seed source) and forward feedback coefficient of the rear port in the seed source. It is shown that the threshold power of the SRS-induced mode distortion can be increased significantly by reducing the seed power or the forward feedback coefficient. Moreover, it has also been found that the threshold power is extremely sensitive to the forward feedback power value from the rear port. The influence of the seed power on the threshold power can be attributed to the fact that the seed power plays an important role in the effective length of the gain fiber in the amplifier. The influence of the forward feedback coefficient on the threshold power can be attributed to the enhanced SRS configuration because the end surface of the rear port together with the fiber in the amplifier constitutes a half-opening cavity. This suppression approach will be very helpful to further develop the high-power fiber amplifiers with high beam quality.