Axial Separation Detection for Liquid Refractive Index Based on Dual-Cylinder-Cone Microresonators

We proposed an axial separation sensing method for detecting the aqueous environment using a dual-cylinder-cone microresonator (DCCMR). Benefiting from the novel structure of the microresonator, the axial separation method can completely avoid the interference of the detection environment on the coupling region. We demonstrated mode field characteristics and liquid refractive index (RI) sensing based on the DCCMR theoretically and experimentally. Proof of concept measurements performed on the coupled microresonator revealed a good RI sensitivity (RIS) of 376 pm/RIU. By optimizing the mode volume, the sensitivity increased to 453.7 pm/RIU. The unique spatial separation between the coupling region and the sensing region enhances the service life of the testing system, ensuring stable detection while preventing mode attenuation. The results show that the flexibility and versatility of the DCCMR in sensing are remarkable, and this novel microresonator based on probe-type detection is a promising candidate for microcavity array and biochemical sensing.