FOCES is a highly stabilized high-resolution optical Échelle spectrograph operated with the 2m telescope at the Wendelstein Observatory. After an extensive temperature- and pressure-stabilization upgrade, reaching the m/s-level, we now focus on the wavelength calibration process. Due to our latest improvements, we are able to perform simultaneous wavelength calibration using our new 4-_ber-slit assembly. This allows us to couple the spectrum of a star and light from a ThAr/UNe hollow cathode lamp or our frequency comb_ at the same time into the spectrograph. We present the design, production process and performance of this new multi-fiber assembly and also evaluate the stability as a test for the upcoming high precision radial velocity measurements in search of exoplanets.