Advancing terahertz photomixers through the integration of photoconductive antennas with optical waveguides

Continuous wave (cw) terahertz (THz) radiation has a wide array of applications, ranging from sensing to next-generation wireless communication links. Industrial applications frequently require THz systems that are broadband, highly efficient, and compact. Photomixer-based solutions hold promise in meeting these demands, offering extremely broadband operation and the potential for miniaturization through photonic integration. However, current photoconductive antenna (PCA) receivers used in these systems are top-illuminated, which strongly limits their efficiency and renders them incompatible with photonic integration. To overcome these limitations, we developed optical waveguide-integrated photoconductive antennas (win-PCAs) for cw-THz detection. These antennas not only facilitate integration into photonic integrated chips (PICs) but also allow us to explore new device geometries to optimize the PCA’s responsivity. By optimizing the absorber geometry of the win-PCAs, we achieve a 22-fold increase in photoresponse, a 500-fold improvement in THz responsivity, and a 4.7-fold reduction in noise-equivalent power compared to state-of-the-art top-illuminated PCAs. In a coherent cw-THz spectrometer, these improvements enable measurements with a peak dynamic range of 123 dB for 300 ms averaging, which is 11 dB higher than what is achievable with comparable top-illuminated receivers. The presented win-PCAs represent a significant step toward fully integrated, high-performing photonic cw-THz systems for both spectroscopy and high-capacity wireless links.