Fluorescence enhancement by a two-dimensional dielectric annular Bragg resonant cavity

We show that photons can be efficiently extracted from fluorescent molecules, utilizing the strongly enhanced local field of a two-dimensional dielectric annular Bragg resonant cavity. Due to the diffraction and constructive interference together with the annular focusing, the periodic ring structure converts the normal incident light into planar guided modes and forms a hot spot at the center of the structure. Theoretically, the field can be enhanced more than 40 times, which leads to the averaged 20-fold enhancement of the fluorescence signal observed in experiments. Compared with fluorescence enhancement by plasmonic structures, this dielectric approach does not suffer from pronounced quenching that often occurs near metallic structures. These results not only can be applied as ultrasensitive sensors for various biological systems, but also have broad potential applications, such as optical trapping and fluorescent microscopy.