2026 Islam THz Optoelectronic Mixer

We report the design, modeling, and on-wafer characterization of a photoconductive heterodyne mixer implemented as a true terahertz monolithic integrated circuit (TMIC). Unlike previous photoconductive heterodyne demonstrations based on antenna coupling or direct probe measurements without controlled RF/IF embedding, the proposed circuit is characterized using the figures of merit normally expected from an RF integrated mixer, including input return loss, broadband impedance matching, RF/IF port isolation, and quantitatively optimized conversion loss. We design a fully coplanar mixer combining a microcavity photoconductor with a broadband matching network (Ti shunt resistor), an RF DC-block (series MIM capacitor) and an RF/IF decoupling element (shunt MIM capacitor), and we develop a parametric circuit-level model that captures both the time-varying photoconductance and the measured CPW embedding. The passive part of the model is validated up to 500 GHz by VNA measurements of the unilluminated (R off ∼1 MΩ) full TMIC, showing good agreement with the circuit simulation using the same off-state device. This anchors the predictive value of the simulation under operating conditions: simulated with the lowest on-state resistance measured at the maximum applied optical pump power (R on ∼110 Ω),|S 11|remains below−10dB up to 215 GHz and below−6.5up to 500 GHz, which, although not optimal, constitutes an acceptable matching level at these frequencies. Measured and simulated conversion losses agree within±1 dB.