Silicon-on-insulator (SOI) evanescent field whispering gallery mode (WGM) ring (disk) sensors are promising components for biological sensing applications. We study the optimum design parameters that result in the highest sensitivity (S) and figure of merit (FOM) simultaneously, for single and dual coupled SOI WGM ring (disk) based sensors. These devices are respectively consisting of one and two silicon ring (disk) resonator coupled to a straight waveguide. Periodic behavior of coupling parameters in biological solutions, are modelled by analytical conformal transformation method and coupled mode theory. These methods are verified by experimental results. We demonstrate optimum design parameters at twelve different configurations of single SOI ring (disk) based sensors. Based on the results, the calculated quality factor of second TE WGM resonance at these resonators in water solutions is Qt ≥ 25000. This gives S and FOM parameters to be 193 (134) nm/RIU and 3112 (2161) /RIU, for single ring (disk) resonator sensor. We also obtain an ultra-improved intrinsic limit of detection (ILOD=7.32 × 10−8 RIU) biosensor based on two coupled ring resonators. The ILOD value, shows that our structure performs two and three orders of magnitude better than respectively two and three SOI cascade ring resonators based sensors, reported lately.
