Design and analysis of silicon ring resonator for bio-sensing application

In this work, a ring resonator is designed with two rings for the sensing application. The waveguide is designed with 400nm wide and 180nm high. Both the rings are designed with 3.1μm radius each. The straight waveguide couples with the ring at 1550nm wavelength. The mode profiles and the spectrum of resonances are observed at mid-infrared wavelength, 1550nm. The measurements of the mode profile, refractive index and spectral properties of the design facilitate to monitor and modify the optical properties of the ring resonator structure. The phase shift in the resonance is observed, which can be implemented in the design of the sensor based ring resonator. In sensing applications the small size of ring resonator plays an important role, the interaction length of ring resonator with few tens of centimeters or even longer gives better sensing performance. Ring resonator offers enhanced light intensity near its surface with the enhancement being proportional to the Q-factor, which is due to the circulating nature of the resonant light. The coupling between the straight waveguide and the ring at 1550nm wavelength and is simulated using Lumerical FDTD. In optical sensors, a thin layer is attached to one of the ring surface, to observe the phase shift in the resonance. Since the refractive index of the thin layer on top of the ring structure is different from the surrounding medium which is typically water based, a change of index happens at the surface of the sensor which is measured for detecting the presence of additional layer in the cover medium. Hence the ring resonator structure can be implemented for bio-sensing application.