High Frequency Modulation Characteristics of GaAs-Based Semiconductor Coupled-Waveguide Optical Modulators

The coupled waveguide optical modulator/switch (the electrically switched optical directional coupler) is one of the most important components in guided-wave and integrated optics, and several device structures for GaAs-based or InP-based semiconductors have been devised[1-11]. All of them are based on the electrooptic effect in the depletion region of the reverse-biased pn junction or Schottky contact. Among them, a double-heterostructure (DH) device with pn junction in strip-loaded channel waveguide configuration as shown in Fig.1 is expected to have the lowest modulating voltage and modulating power per bandwidth P/∆f because of the most efficient overlap of the modulating electric field with the optical field [4,12]. Similar but homostructure devices were fabricaed by Carenco and others [13,14]. Recently GaAs-Al0.04Ga0.96As DH devices with nearly full switching characteristics have been fabricated for the first time [10].