Membrane InGaAsP Mach-Zehnder Modulator Integrated with Optical Amplifier on Si Platform

A high-efficiency Mach-Zehnder modulator (MZM) using InGaAsP phase shifters and a semiconductor optical amplifier (SOA) using multiple-quantum-well (MQW) are integrated on Si-waveguide circuits. Membrane structure is easy to optically couple to the widely-used 220-nm-thick Si waveguides, because both layers have comparable effective refractive indices. To integrate different bandgap III-V compound semiconductors; InGaAsP-based MQW for SOA and InGaAsP bulk for MZM, we employ epitaxial regrowth on thin-InP layer that is directly bonded on a silicon-on-insulator (SOI) wafer. Their thicknesses are smaller than the critical thickness (∼430 nm) for epitaxial growth of the InP-based layers bonded on the SOI wafer. This fabrication procedure is beneficial for the wafer-level integration of InP-based devices with different bandgaps on Si-photonic circuits. Furthermore, membrane lateral p-n and p-i-n diode structures improve the modulation efficiency of the MZM and reduce the power consumption of the SOA due to the high optical confinement factor and small active area. The integrated 300-μm-long SOA and MZM with 500-μm-long phase shifters show a fiber-to-fiber lossless operation with the SOA current of only 24 mA at room temperature. The modulation efficiency of the compact MZM is high enough for eye opening with non-return-to-zero (NRZ) signals from 28 to 40 Gbit/s. By using the SOA to amplify the signals modulated by the MZM, the fiber output power of −3.4 dBm was obtained without any significant pattern effect.