Intracavity Phase Interferometry (IPI) makes use of the frequency comb of a mode-locked laser to perform precise phase measurements. IPI achieves extremely high measurement quality in a simple tabletop setup for a wide array of applications. This text summarizes work on intracavity interferometers and introduces two new IPI setups using optical parametric oscillators (OPO). It describes the design and numerical simulation of OPOs and their application as intracavity interferometers. In particular the option of an intracavity pumped OPO is investigated in theory and experiment. Finally some ground work towards future intracavity interferometers is included. This includes the potential use of semiconductor lasers to pump an OPO.