Terahertz Sideband Generation Based on a Schottky Varactor Diode Array

This work focuses on the design and fabrication of a quasi-optical 1.6THz sideband generator. To create the sideband generator, an array of planar gallium arsenide Schottky diodes are used as varactor mixers. The array is modulated by a 50 GHz lower frequency pump signal to create the desired sideband at 1.55THz. The goal is to create a sub-millimeter sideband generator with conversation losses less than -30 dB, and an output power generation greater than 50 μW at the first lower sideband. This approach varies from other sub-millimeter designs in three key aspects. The most noticeable difference is the use of a quasi-optical coupling of signals. A quasi-optical design eliminates the need for a waveguide and uses a high-resistivity silicon lens to focus the RF power on the sideband generator. Another variation from typical submillimeter sideband generators is the use of an array. The array allows for more power handling capability when compared to a single diode device and creates advantageous boundary conditions which are exploited in the design. The last major variation is the addition of a tuning element in parallel with the diode itself. The tuning element is used to create a parallel resonance circuit within the array design, helps alleviate the effects of parasitics surrounding the anode contact, and eases the fabrication tolerances of the diode design. The added parallel tuning element, in addition with a series tuning element, common to most planar millimeter and submillimeter diode designs, allow the diode to modulate between an open and short circuit. The added phase shift created by the resonance circuits is intended to increase the conversion efficiency of the proposed sideband generator. In addition to increasing the efficiency, the added tuning element simplifies the fabrication process, circuit modeling, and reduces parasitic effects associated with the device geometry.