The current precision of radial-velocity spectrographs is limited by the wavelength calibration and used calibration sources. New types of calibration sources are needed to enable better wavelength calibration. The goal of my thesis work was to test several Fabry-Perots, which are systems that produce a spectrum of nearly-equidistant emission lines over a very large wavelength range. As such, and provided that the lines remain stable in wavelength over time, this source can be used as a wavelength reference. During the the second part of my thesis work, I investigated furthermore possible developments of our Fabry-Perot system as an alternative to current calibration sources. The declared objective was to improve the wavelength calibration accuracy of the HARPS spectrograph by combining the absolute spectral reference provided by the emission lines of a thorium-argon hollow-cathode lamp (HCL) with the spectrally rich and precise information delivered by the Fabry-Perot-based calibration source.