SPIE Photonics West: LASE
Current research focuses on very-large-mode-area fibers (core diameters of 34 μm and above) and all-fiber laser systems to deliver high output power with linear polarization, low noise properties, narrow-band linewidth and high fundamental mode content. All-fiber systems have the advantage of low-maintenance and alignment-free operation. Because power scaling in fiber-based amplifiers is limited by non-linear effects like stimulated Brillouin scattering, very-large-mode-area fibers such as specialty fiber designs like the chirally coupled core (CCC) fiber are investigated. This fiber type offers a signal core of 34 μm or larger while also providing a near single-mode output beam quality. It thereby enables further power scaling in systems that are limited by such nonlinear effects. However, efficient components such as signal-pump-combiners (SPC) with this fiber type need to be developed. The SPC couples the required pump light of multiple high power laser diodes into the gain fiber of the laser system. We report on the development of a SPC with an integrated 34=250 μm feed-through CCCfiber with a pump-to-signal fiber coupling efficiency of 90\% and three input pump fibers with a signal-to-pump isolation of 30 dB. The device is tested with an input power of up to 380 W. In addition, different experiments for monolithic implementation of the CCC-fiber type into systems that rely on standard polarization-maintaining (PM) fibers are conducted. We show the polarization maintaining behavior (polarization extinction ratio (PER) < 19 dB over several hours) of the fiber by imprinting externally induced birefringence on the fiber. Experiments with all-fiber setups using the CCC-fiber and a step-index PM-fiber show a PER of < 15 dB with reduced long-term stability.