Ultrahigh quality factor cavity based on double dielectric nanocylinder metasurfaces

An optical cavity with a high quality factor (Q-factor) is essential for a wide range of applications, including lasers, single-photon sources, optical filters, and sensors. A high Q-factor cavity can enhance the interaction between light and materials, thereby improving the performance of optical devices. The Fabry–Pérot (FP) cavity is a typical optical device capable of achieving a high Q-factor; however, it often relies on distributed Bragg reflectors, which increase the size of the optical device. In recent years, Mie scattering-based metasurfaces with high reflectivity have been studied as alternatives to distributed Bragg reflectors. We propose a scattering-based FP cavity consisting of two metasurface layers. In our structure, a FP cavity with high reflectivity is formed by back-forward scattering from a single dielectric cylinder array. Our findings show that the structure exhibits a Q-factor of 4.36 × 10¹⁰ when the period and gap size are 658.8 nm and 740 nm, respectively. This high Q-factor is maintained even with misalignment between the two layers. Additionally, we confirmed that a high Q-factor of 2.6 × 10⁶ appears in the low-index substrate structure, with the Q-factor increasing with the number of double cylinders in the finite structure. We also observed a strong directionality in the z-axis direction when examining the far field. We designed the dielectric FP cavity with a subwavelength thickness, is expected to significantly contribute to enhancing the Q-factors of various types of optical cavities.