1.6-THz frequency upconverter with integrated GaAs diode circuit

Abstract

THz frequency sources have a variety of applications ranging from molecular spectroscopy, atmospheric remote sensing, scaled radar range systems, sensing and monitoring of chemical and biological molecules to wireless communications. However, there is a lack of frequency tunable sources at these wavelengths. A frequency upconverter can be used to generate frequency tunable sidebands as a tunable high frequency source from a fixed source, such as Far Infrared (FIR) Laser. The development of 1.6 THz frequency upconverters with integrated diode circuit are described in this paper. The integration of the diode with the embedding circuit enhances mechanical robustness and makes the circuits easy to handle compared with a whisker-contacted diode structure. A nonlinear analysis is used to determine the optimum varactor diode parameters. Through the optimization, the circuit quartz substrate thickness is chosen to be 10 um and the anode diameter is determined to be 1 um. With the non-ohmic cathode contact technique and air bridge process (eliminating the surface channel etch process), the 1.6 THz integrated circuits were fabricated in University of Virginia with high yield. Furthermore, the conversion loss is measured and presented. The test setup consists of an FIR Laser, beam splitter, polarizer, parabolic mirror, silicon etalon and other optical components. The average conversion loss was measured to be approximatly 25 dB over 8 GHz microwave pump. Equivalent circuit models and simulations are presented to corroborate these results.