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Digital-to-analog converters (DACs) for high-speed optical communication systems based on CMOS technology have bandwidths lower than nowadays electro-optic components. A promising concept to circumvent this bottleneck is the frequency-interleaved DAC (FI-DAC) concept. In this paper, experimental results for the application of a 180 GS/s FI-DAC with 40 GHz analog bandwidth based on two DACs in a high-speed optical link are discussed and compared with simulation results. Thereby, phase and power mismatches, spectral overlap, clipping and the required DAC resolution are investigated. Signal-to-noise ratio (SNR) estimations based on a discrete multi-tone (DMT) signal show the influence of the individual analog components on the signal quality.