Photonic Molecule-Based Refractive Index Sensor Using Coupled Fabry-Perot Resonators

When two resonators are brought into proximity, their optical fields interact, splitting the original resonance into two distinct frequencies corresponding to the symmetric and antisymmetric supermodes. Such coupled resonators, often referred to as photonic molecules, bear a strong analogy to the electronic states in diatomic molecules, making them a versatile platform for exploring light-matter interactions [1, 2]. We report on a photonic molecule-based refractive index sensor formed by side-coupling two Fabry-Perot (FP) resonators shown in Fig. 1(a). The refractive index of an analyte covering the device affects the coupling strength between the resonators. Therefore, it enables both resonance shifts and changes in resonance splitting, providing a robust and multi-parameter sensing mechanism, enhancing sensitivity and reliability.