Boosting photoconductive large-area THz emitter via optical light confinement behind a highly refractive sapphire-fiber lens

We report on a sapphire-fiber-based lens that can be used to enhance the emitted THz power of a large-area photo-conductive antenna (PCA). Using numerical simulations, we demonstrate that the lens provides a spatial redistribution of the photocarriers density in the PCA's gap. By optimizing the diameter of the sapphire-fiber, one could reach efficient confinement of the photocarriers in the vicinity of the PCA electrodes with a 10-mu m gap size for a 220-mu m-thick sapphire-fiber. This allows enhancing the coupling of the incident electromagnetic waves at the interface between the sapphire fiber and the semiconductor with the antenna terminals by similar to 40 times for a single PCA element, as well as boosting the total efficiency of the large-area PCA-emitter up to similar to 7-10 times. To validate our approach, we propose a step-by-step process that can be used for the precise and controllable placement of the sapphire-fiber on the surface of a single PCA. (C) 2022 Optica Publishing Group