Simultaneous measurement of the refractive index and the pressure based on perforated micro-ring resonator with two standing wave modes

Abstract

A perforated micro-ring resonator (PMRR) on the flexible SU-8 substrate is proposed and theoretically demonstrated for detecting the refractive index (RI) and the pressure simultaneously. Once a perforation defect is introduced, the symmetric and the asymmetric standing wave modes (SWMs) are formed during the mode splitting. The energy distributions of the two SWMs are quite different so that the sensitivities of two modes toward the variation of RI and pressure applied to the device show differences. Through the numerical simulations, we obtain an RI sensitivity of 76.03 nm / RIU and a high pressure sensitivity of 5.37 pm / kPa for the symmetric SWM, and an RI sensitivity of 68.82 nm / RIU and a high pressure sensitivity of 6.15 pm / kPa for the asymmetric SWM. By solving a second-order sensitivity inverse matrix, we can measure the changes in RI and pressure simultaneously, thereby eliminating the influence of the strain-optical coupling effect in the field of flexible biosensor. Therefore, the proposed structure provides an approach to achieve flexible biosensing application in the real world and has tremendous potentiality in achieving multi-sensing applications.