Vertical microgoblet resonator with high sensitivity fabricated by direct laser writing on a Si substrate

We propose a high-Q microgoblet resonator with improved refractive index (RI) sensitivity compared to conventional microdisk resonator. Through simulations with a finite element method (FEM), electric field distributions of a fundamental whispering-gallery mode (WGM) show that the spatial position of the WGM can be drawn from the rim of the microdisk into the vertical wall of the microgoblet resonator under proper structural modifications. The RI sensitivity could be greatly improved due to the enhancement of light-matter interaction, which is caused by the fact that the vertical microgoblet resonator exposes the double sides of its wall to the sensing medium, while for traditional microdisks, the confined electric field is only sensible from one side. The simulation results indicate that the optimized microgoblet resonator can be more sensitive than the microdisk with the same thickness. The designed microgoblet resonator is experimentally demonstrated by utilizing a direct laser writing method on a Si substrate, with Q factor on the level of 10⁵. Preliminary optical sensing experiments show that the RI sensitivity of the vertical microgoblet resonator is ∼24% higher than that of the microdisk with the same thickness. The studies provide a novel methodology towards designing and fabricating microcavities with enhanced optical sensibility, with potential applications in environmental, biomedical, and biochemical sensing or monitoring.