While the demand for specially designed laser systems for high-bandwidth coherent optical (satellite) communication with wavelength division multiplexing (WDM) is increasing, there are also efforts to reduce the power consumption of the corresponding systems. In the context of ESA’s HydRON project (high throughput optical network), a prototype model of a highly efficient laser amplifier system (HELA) operating in the 1 µm wavelength range has been developed up to a technology readiness level of 4. The HELA system is designed to increase the power level of a 10 channel seed source ranging from 1 to 10 mW per channel to a total optical output power of 100 W. Here, the WDM approach combined with a single-mode, high average output power signal shall enable the realization of optical interconnections with up to Terabit per second data rates over large distances between satellites and with their corresponding ground stations. After defining an initial optical design based on a two-stage fiber amplifier architecture, a preliminary concept was first verified through the realization of a laboratory testbed system. In a second step, several design improvements were introduced, leading to the development and fabrication of a compact one-box prototype. In this pitch, we will highlight the design and key specifications of this HELA breadboard system. Its final design is based on a modular opto-mechanical concept, dividing its functional units into discrete sub-assemblies within the system. This approach allowed for an optimized assembly of the HELA breadboard system and its incorporation into a compact housing with outer dimensions of 400 x 400 x 90 mm3. The HELA system efficiently amplifies the 10-channel seed source with signal wavelengths of approx. 1060-1069 nm from the mW-level to an output power of 100 W in total. The employed Yb3+-based fiber technology, including fiber components specially designed and manufactured at Laser Zentrum Hannover e.V., as well as the utilization of efficient wavelength-stabilized 976 nm pump diodes, enabled a total wall-plug efficiency of the HELA system of > 28\% (assuming typical efficiencies of laser drivers and control electronics in a future space-qualified prototype). The system provides an optimum performance in terms of a flat gain characteristic ( 5\% peak-to-peak variations between the channels), polarization extinction ratio (PER > 21 dB) and output beam quality (M² = 1.03). Furthermore, the output power stability of the system has been verified in several 24-hour-tests at different output power levels. Here, the peak-to-peak variations of the total power did not exceed a value of 0.3\% (HELA goal: 1\%) at the nominal optical output power of 100 W. In summary, the HELA design demonstrates the potential of efficient laser systems for satellite communication at 1µm.