Terahertz InGaAs-based Schottky diode receivers for atmospheric research

Kurzfassung

Far-infrared spectroscopic measurements of physical and chemical processes in the Earth’s atmosphere, especially in the unexplored mesosphere-lower-thermosphere (MLT) region, are crucial for climate and weather modelling. Detection of gas and molecular species, such as the hydroxyl radical (OH) and atomic oxygen (OI), at 3.5 and 4.7 THz, respectively, in the MLT region is key to achieving this goal. There is a need for compact terahertz receivers with sufficient sensitivity that operate without active cryocooling for long lifetime missions such as Keystone. Schottky diode-based mixers were the workhorses behind several space missions, including MIRO, MLS, ARCTIC, ISMAR, and JUICE. They are an ideal candidate for ambient-temperature operation, fast response, and wide IF bandwidth. However, above 3 THz, several challenges in the fabrication of integrated circuits, machining of THz mixer blocks, and inefficient power coupling to the diode have to be addressed. In this talk, we will present the ongoing characterization of InGaAs-based single-ended Schottky diode mixers. The local oscillator signal generated by the quantum-cascade laser and the radio-frequency signal are coupled to the mixer using a Mylar beam splitter. The InGaAs mixer has a pyramidal horn integrated into a rectangular waveguide WM-57. We will present the characterization results of mixers with two different Indium concentrations: In0.22Ga0.78As and In0.53Ga0.47As.