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We demonstrate an integrated photonic platform comprising a refractive index (RI) sensor based on Photonic Molecule (PM) that effectively mitigates the influence of environmental perturbations using a differential measurement scheme while providing high quality-factor (Q) resonances. The RI sensor consists of a partially unclad microdisk resonator coupled to an external clad microring resonator fabricated on silicon-on-insulator (SOI) platform. We report a RI sensitivity of 24 nm/RIU, achieving a limit of detection (LOD) of 1.7 × 10-3 refractive index units (RIU) with improved stability for an operation range of 0.15 RIU in a compact footprint of 40 × 40 μm2, representing an important solution for real-life applications in which measurement conditions are not easily controllable.

We propose a compact Si3N4 Photonic Molecule for robust and differential measurements in sensing applications. The simulations show that a refractive index sensitivity of 131.3 nm/RIU with high thermal stability can be achieved.