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. Fiber lasers and amplifiers are widely used in the field of laser marking, material processing, and many other industrial applications. Although the power of single-mode fiber laser system has already reached a high level of 10 kW, scientific and industrial applications seek much higher laser power and light beam quality. However, nonlinear effects induced by high laser power limit further scaling of the output power. For example, single-frequency or narrow-linewidth fiber lasers' power scaling is limited by stimulated Brillouin scattering (SBS), and power scaling for ultrashort pulsed fiber laser systems is limited by stimulated Raman scattering (SRS). Therefore, suppressing nonlinear effects is particularly critical for further scaling of the output power from high-power fiber lasers and amplifiers[5,6]. The most direct and effective approach to increase the threshold of nonlinear effects is to increase the effective mode area (Aeff), and the simplest and most obvious way of increasing Aeff is to increase the core diameter (D) and decrease numerical aperture (NA). Fibers that achieve large mode area (LMA) by increasing the core diameter and decreasing NA are widely applied in high-power fiber laser system. Such LMA fibers can effectively mitigate nonlinear effects, but there are two emerging problems in practical applications. One is that they support high-order modes (HOMs) owing to the larger core diameter and lower NA, which results in transverse mode instability (TMI) at high average power levels; the other is that such fibers become highly sensitive to bending, which results in high bending loss and severe mode area compression. Therefore, it is important for LMA fibers to suppress nonlinear effects and ensure transverse mode stability simultaneously.
Set citation alerts for the article
Please enter your email address