We demonstrate monolithically integrated n-GaAs/p-Si depletion-type optical phase shifters fabricated on a 300 mm wafer-scale Si photonics platform. We measured the phase shifter performance using Mach–Zehnder modulators with the GaAs/Si optical phase shifters in both arms. A modulation efficiency of VπL as low as 0.3 V·cm has been achieved, which is much lower compared to a carrier-depletion type Si optical phase shifter with pn junction. While propagation loss is relatively high at ∼6.5dB/mm, the modulator length can be reduced by the factor of ∼4.2 for the same optical modulation amplitude of a Si reference Mach–Zehnder modulator, owing to the high modulation efficiency of the shifters.

We present an accurate, easy-to-use large-signal SPICE circuit model for depletion-type silicon ring modulators (Si RMs). Our model includes both the electrical and optical characteristics of the Si RM and consists of circuit elements whose values change depending on modulation voltages. The accuracy of our model is confirmed by comparing the SPICE simulation results of 25 Gb/s non-return-to-zero (NRZ) modulation with the measurement. The model is used for performance optimization of monolithically integrated Si photonic NRZ and pulse-amplitude-modulation 4 transmitters in the standard SPICE circuit design environment.