Photonic integrated circuits are chips in which different components are integrated that work with light (or photons). This is in contrast to the traditional electronic circuits that work with electrons. Photonic integrated circuits offer a distinct advantage in some applications compared to electronics, but their wide adoption is hampered by the fact that some functions are hard to realize in the photonic domain. One particular function that is hard to realize on silicon based photonic circuits is the modulation of the phase of light. At Ghent University, a unique technology has been developed to integrate thin films of PZT (lead zirconate titanate) on photonic chips. Recently, high speed phase modulation was demonstrated. But this is only the first step and still a lot of research is necessary to understand the properties of the PZT based phase modulators and to improve their properties. In my PhD I plan to improve the efficiency of the phase modulators drastically, thereby reducing the necessary footprint of a single phase modulator. This will allow to demonstrate as much phase modulators as possible on a certain area. By also investigating and demonstrating the optical nonlinearity of the PZT, I think I can demonstrate new types of photonic circuits that make full use of the PZT technology. The circuits that I plan to demonstrate could be used in the detection of objects around self-driving cars or as holographic displays in virtualy reality devices.