Optical parametric oscillators (OPOs), which rely on an optical parametric amplification in a cavity, can extend the available optical frequency range of common lasersources. In a doubly resonant OPO (DROPO) two optical frequencies resonate in thecavity and with their ability to phase-lock to the pump, tailored multi-color electricfields can be generated. For example, such fields can be used for high harmonic generation or to generate THz radiation with MHz repetition rate.This thesis focuses on the design, characterization and stabilization of a high powerfemtosecond doubly resonant optical parametric oscillator (DROPO) that emits in the2 µm wavelength range. The system is pumped by a femtosecond Kerr-lens modelocked Yb:YAG thin-disk laser, with a central wavelength around 1 µm, tens of wattsof output power and a repetition rate in the MHz range. Due to the phase dependentamplification condition of the nonlinear process, a complex spectral behaviour arises,when the cavity length is detuned. It is strongly influenced by the dispersion in thecavity. The detuning behaviour is experimentally examined in this work and numericalmodels for its explanation are derived. DROPOs show characteristic on/off switchingresonances when the cavity length is detuned. A new way to extend the number ofdetuning resonances in the degenerated regime is found and experimentally proven.In order to stabilize these systems on one of these resonances dither based schemesare often employed. These schemes induce additional noise in the oscillator which candisturb the experiment. In this work, a dither free approach is chosen which takesadvantage of an asymmetry between a spectrally filtered sum frequency signal and theDROPO’s signal, when the cavity is detuned. Thus, it allows to use a proportionalintegral servo controller to stabilize the DROPO resonances for longer time scales. Inaddition to stability over time, some experiments also require high peak power. Passiveenhancement cavities are well known for their ability to confine pulses and generatehigh peak powers to drive nonlinear processes. Before this work it was unknown ifDROPOs can also achieve this enhancement. This thesis answers this question andshows that by choosing the right cavity parameters a strong enhancement is possible.The experimental results are underlined with a semianalytical model which elaboratesthat the theoretical limits of the maximum enhancement are similar to the passiveenhancement cavity ones.To summarize, in this thesis a DROPO in the 2 µm wavelength range is presented,which will be used for the generation of single cycle THz pulses in the future.