Integrated fiber components enable compact and robust laser systems but are usually not available with specialty fibers. However, specialty fibers allow power scaling of fiber lasers and amplifiers with all advantages of these fiber designs. In this context, chirally-coupled-core fibers show promising properties for optical fiber components. In this paper, we present the development of a highly-integrated signal and pump combiner in chirally-core-fibers using a side-pumping technology. Combining up to four fiber-coupled pump diodes, a pump-light limited power handling of 600 W can be achieved with an efficiency of 78%. The combiner was tested in a side-pumped single-frequency allfiber amplifier but can also be implemented in almost any fiber laser or amplifier.Index Terms-Specialty fiber, chirally-coupled-core fiber, signal and pump combiner. I. INTRODUCTIONA variety of applications such as light detection and ranging (LIDAR), atom cooling or gravitational wave detectors require high optical output power at a narrowband laser linewidth [1], [2], [3]. The demand for compact, reliable and efficient monolithic high power laser systems has been increased in recent years [4], [5]. The efforts of all-fiber solutions expedite the development of integrated optical fiberbased components for almost all laser applications. Especially, in the next generation of gravitational wave detectors singlefrequency and high-power laser sources have to fulfill special requirements with an excellent beam quality in a compact and reliable system [3], [6]. It has been shown that fiber amplifiers and especially all-fiber systems with integrated signal and pump combiners can be a suitable option to overcome current limitations [7]. The ultimate limitation of single-frequency fiber amplifiers is the nonlinear effect of stimulated Brillouin scattering (SBS). In general, to reduce the impact of such nonlinearities, the mode area of the fiber core is enlarged and special fiber types like photonic crystal fibers (PCF), photonic bandgap fibers

Specialty fibers such as chirally-coupled-core fibers show a high potential for further power scaling of singlefrequency fiber amplifiers. For the first time, we demonstrate a spliceless all-fiber amplifier, where all optical components are directly integrated in a single Yb 3+ -doped 3C ® -fiber. Such a spliceless laser design enables a compact and robust architecture using specialty fibers, while maintaining excellent beam properties. At an output power of 336 W operating at 1064 nm, a fundamental mode content of 90.4% at a polarization extinction ratio above 13 dB was measured without any impact of transverse mode instabilities or other parasitic effects. This work emphasizes the field of applications of 3C ® -fibers in high-power laser systems.

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