Topic 35.a: Design and fabrication of ultrahigh-Q LiNbO3 microdisk optical resonator

Problem Statement and Approach: Sensitive detection of electromagnetic (EM) fields at microwave frequencies underlies crucially many high-energy physics (HEP) experiments that rely on the measurement of weak couplings between ultralight dark matter and electromagnetism. These HEP experiments require the sensing of EM fields down to single photon level. Unfortunately, detection of single microwave photons remains significant challenge. Moreover, highly efficient transduction between microwave photons and optical photons is crucial for building a distributed quantum network that will be built upon a combination of vastly different quantum systems that operate based upon the quantum states of microwave and optical photons. One elegant approach to resolve this challenge is to convert microwave photons into the optical domain with high efficiency. We proposed to design and fabricate ultrahigh-Q optical microresonator on chip-scale thin-film lithium niobate platform that exhibit optimal electro-optic coupling for applications in ultra-sensitive transduction between microwave and optical photons. The proposed devices will utilize a novel on-chip integrated photonic platform that was recently developed by the team member. The proposed LN microresonator is expected to offer optical Q > 107 in the telecom band. Moreover, the on-chip platform enables full integration of the optical microresonator with electrical driving/detection structure that will maximize the coupling between microwave and optical modes, offering strong transduction between the two spectral regimes. In compared with conventional approaches, the proposed device is expected to offer unprecedented performance with more than 100× reduction of the device footprint and 100× increase of microwave-optical conversion efficiency. In particular, the chip-scale fully integrated approach enables wafer-scale mass production that will dramatically reduce the cost. Phase I Efforts: The focus of our Phase 1 project is to develop and prototype the high-Q LN microresonators that not only exhibit high optical Q, but is also well suited for highly efficient microwave-to-optic transduction. As such, the goals of the Phase 1 effort are two folds: 1) to identify, via numerical modeling and design, the device geometry that not only supports high optical Q >107, but also produce optimal electro-optic coupling; 2) to further optimize the fabrication process to improve the optical Q. Commercial Applications: The proposed project, if successful, will offer to the market the first commercially available cost-effective ultrahigh-Q LN microresonator devices that can be produced massively on the whole wafer scale. These devices will offer an immediate solution to the HEP experiments for ultrasensitive detection of microwave photons. Moreover, the commercial availability of the proposed device with high performance is of immense importance for the development and implementation of distributed quantum network that builds upon disparate quantum systems operating in vastly different spectral regimes from microwave to visible. This SBIR/STTR effort aims to directly fulfill this emerging market demand. On the other hand, the proposed devices are of great potential for broad classical applications in radar, biomedicine, infrared/THz imaging, etc., where sensitive detection of microwaves (and electric field in general) is extremely critical. The resonator devices developed in this SBIR/STTR program is expected to have a profound commercial impact on a broad market.