On-chip integrated mid-infrared GaAs/AlGaAs Mach-Zehnder interferometer

We report the design, fabrication, and first functional verification of mid-infrared (MIR; 3-12 μm) Mach-Zehnder interferometers (MZIs). The developed MIR-MZIs are entirely chip-integrated solid-state devices based on GaAs/AlGaAs technology waveguide fabricated via conventional optical lithography and reactive ion etching (RIE). Thus, fabricated MIR-MZIs were combined with a broadly tunable quantum cascade laser (tQCL) providing a wavelength coverage of 5.78-6.35 μm. MIR-MZIs have been designed with a waveguide width of 5 μm to ensure single mode behavior, avoiding optically undefined interference patterns. Several structures with different opening angles of the Y-junction were fabricated and tested for maximizing IR radiation throughput. This study demonstrates the feasibility of the very first chip-integrated mid-infrared Mach-Zehnder structures via interference patterns produced by minute amounts of water deposited at different positions of the MIR-MZI structure.