Mach-Zehnder modulators and optical switches on III-V semiconductors

Key components of interferometric structures, i.e., phase modulators and beamsplitters, as well as a Mach-Zehnder modulator are investigated. Inverted rib waveguide phase modulators have been fabricated using vapor phase epitaxy (GaAs and InP homostructures) or a combination of vapor phase epitaxy and metal-organic vapor phase epitaxy (GaAlAs/GaAs double heterostructure). Two different beamsplitters, the three-guide coupler and the etched semitransparent mirror, have been studied both experimentally and theoretically. Experimental results have been obtained by fabricating semitransparent mirrors with the reactive ion etching. Using the three guide coupler, a GaAs homostructure Mach-Zehnder modulator has been realized. The required switching voltage is -14 V for 6-mm-long electrode and a crosstalk of 18 dB has been measured. The use of the semitransparent mirror for Mach-Zehnder interferometers is also discussed. In order to minimize the diffraction losses, the use of higher order waveguides, rather than single-mode waveguide looks promising.<
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