Highly Sensitive Refractive Index Sensor Based on Vernier Effect in Coupled Micro-Ring Resonators

In this paper, we propose and theoretically design a highly sensitive refractive index (RI) sensor based on Vernier effect in three coupled micro-ring resonators (CMRR) with identical geometries. When the whispering gallery mode phases of different microresonators match with each other, transmittance of the CMRR increases and the envelope peak wavelength shift of the modulated spectrum could be exploited for wavelength-interrogated RI sensing based on Vernier effect. Further simulation results indicate that RI sensing could be achieved within a wide RI range of 1.33 to 1.43 by adjusting RI of the liquid kept inside the control cavity, and limitless sensitivity could be achieved for some specific RI ranges which are mainly determined by geometric parameters of the resonators and the order of selected envelope peak for sensing, making the sensor available for different sensing requirements. The proposed CMRR provides a compact, flexible and low-cost solution for biochemical sensing applications. And moreover, the proposed RI sensing range extension method as well as limitless sensitivity mechanism pave a new way toward the development of dynamic RI sensing and tunable optoelectronic devices.