Abstract

Phase modulators are key building blocks for Photonic Integrated Circuits (PICs). Si modulators based on plasma dispersion suffer from spurious amplitude modulation and high insertion losses. Pockels effect has been explored for more efficient phase modulators. However, Si doesn’t exhibit Pockels effect due to its centrosymmetric structure. Co-integration of thin-film electro-optic materials possessing a strong linear electro-optic coefficient on Si has therefore been proposed as an ideal alternative for more efficient phase modulators. Strongly electro-optic thin films of ferro-electric Lead Zirconate Titanate (PZT) grown on Si waveguides allow for Hybrid PZT/Si phase modulators. We present here a TE/TM electro-optic modulator with bias-free operation, bandwidths beyond 10Ghz, and negligible spurious amplitude modulation. The modulator is a phase shifter which comprises of straight Si waveguides and thin films of PZT spin-coated on the waveguides. The phase shifters were experimentally characterized by beating the modulated signal with an external acousto-optic modulator and evaluating the ratio between both signals. This experiment enables fast and easy characterization of phase modulators as proof of concept