High-performance microcavity optical sensor connected with a waveguide

In this letter, we have numerically demonstrated a high-performance microcavity sensor which is connected with a waveguide directly. With input light and output light transmitting in the same waveguide, we propose a robust direct coupling mechanism of the microcavity. For a circular microcavity with a diameter of 4 μm and effective refractive index of 3.3, our numerical results show that the coupled modes are excited and more than 10⁶ Q-factor is calculated from the transmission spectrum. Dramatically, the spectrum shows a Fano-shape resonance at specific wavelength. Using the Fano resonance, we detected a refractive index change on the order 10^-5 and a nanoparticle with radius 5 nm. What's more, the sensor is insensitive to waveguide width and refractive index.