Large mode area saddle-shaped core Yb-doped fiber enabled monolithic high-power, high-efficiency, near-diffraction-limited MOPA laser

Abstract

A specially-designed active optical fiber with a constant cladding size and a saddle-shaped profile core is proposed and demonstrated, which called saddle-shaped core (SSC) Yb-doped fiber. The SSC fiber is manufactured through a conventional modified chemical vapor deposition (MCVD) process followed by post-processing of the fiber preforms. The fabricated SSC fiber possesses a large-core region (core/cladding diameter of ∼30/600 μm) at both fiber ends and a small-core region (core/cladding diameter of ∼20.8/600 μm) in the middle length. The output laser characteristics of this SSC fiber are proved through a monolithic high-power continuous-wave MOPA configuration, on the conditions of the co-pumping and counter-pumping manners. It shows that the output lasing powers of co-pumping and counter-pumping regimes are scaled up to ~1.8 kW and ~1.5 kW associated with ~83.3% and ~86.6% slope efficiency, respectively. Before the transverse mode instability (TMI) threshold, a good beam profile quality is measured to M 2 ~1.4, and no evidence of stimulated Raman scattering (SRS) is observed. As far as we know, this is the first demonstration of saddleshaped fiber for kilowatt-level near-single-mode continuous-wave fiber lasers. By further optimizing the fiber design, a higher lasing power connected with near-diffraction-limited beam quality can be achieved in the future.

Optimization and Demonstration of Direct LD Pumped High-Power Fiber Lasers to Balance SRS and TMI Effects

“…In the aspect of fiber coiling, we found the abnormal phenomenon of increasing the TMI threshold by increasing the fiber coiling diameter [10,72]. In addition, we propose varying core diameter active fiber represented by tapered fiber, spindle-shaped fiber, and saddle-shaped fiber, which can balance SRS and TMI in the fiber and break through the power limit of conventional fiber [73][74][75][76][77][78][79][80][81]. In this work, we will focus on the optimization and demonstration of the technologies that balance the suppression of both SRS and TMI, including common methods such as fiber coiling, pump configurations, and novel methods including pump wavelength optimization and various core active fiber.…”