  In this work, we demonstrate an integrated 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 an exposed microdisk resonator coupled to an external clad
microring resonator fabricated on silicon-on-insulator (SOI) platform. We
report a RI sensitivity of 23 nm/RIU, achieving a limit of detection (LOD) of
1.6 x 10-3 refractive index units (RIU) with improved stability in a compact
footprint of 40 x 40 {\mu}m2, representing a good solution for real-life
applications in which measurement conditions are not easily controllable.
