Large mode area fibers have become indispensable in addressing the power requirements of laser sources in gravitational wave detectors. Besides high power capabilities, the system must provide an excellent beam quality and polarization. In this Letter, we present the characterization of a monolithic high-power fiber amplifier at 1064 nm, built using an ytterbium-doped chirally coupled-core fiber, which achieves an output power of 100 W in a linearly polarized {\$} {\rm TEM}_00 {\$}TEM00 mode in an all-fiber setup.