UC Santa Barbara

This study reports ultralow drive voltage Mach-Zehnder modulators in highly confined substrate removed GaAs/AlGaAs optical guides with buried doped QW electrodes. Separation between the doped QW electrodes, which is the electrode gap, is only 0.15 μm. Such a small electrode gap results in very high electric fields overlapping very well with the optical mode. A careful analysis of the physical effects contributing to index change is presented and techniques to use these index changes efficiently are described. Fabrication details are given. Results of careful characterization of phase and Mach-Zehnder intensity modulators are presented. Variation of propagation loss and extinction ratio with applied voltage are investigated. Intensity modulators with 7-mm-long electrodes have 0.3 Vπ under push-pull operation with 15 dB extinction ratio. This corresponds to a 0.21 V·cm modulation efficiency in bulk compound semiconductors. © 2013 IEEE.