Tailored UV Emission by Nonlinear IR Excitation from ZnO Photonic Crystal Nanocavities

For many applications in photonics, e.g., free-space telecommunication, efficient UV sources are needed. However, optical excitation of such sources requires photons of even higher energies, which are difficult to integrate into photonic circuits. Here, we present photonic crystal devices based on zinc oxide (ZnO) that allow excitation using highly abundant sources in the near-infrared (NIR). These devices offer control of generating tailored photonic modes in the UV range via higher order nonlinear processes by combining the wide electronic band gap and pronounced nonlinear effects in ZnO with the adjustable properties of photonic crystal (PhC) membranes. Two different techniques for fabricating such ZnO-based PhC membranes are discussed, including the presentation of a novel bottom-up approach. Furthermore, dispersive theoretical simulations are introduced to determine the size and position of the photonic band gap, leading to an optimized cavity with only one dominant mode. This is followed by an evaluation of dominant loss channels, comparing cavities for both fabrication techniques, where we implemented a semianalytical model to determine scattering losses at imperfections of the PhCs. Additionally, energetic fine-tuning of such a mode as well as for other photonic modes that are formed by different cavity types is demonstrated. Ultimately, we validate that both linear one-photon and nonlinear three-photon excitation is possible with the presented devices, which renders them potential candidates for efficient UV light emitters that are powered by IR or NIR light sources.