Dual-parameter optical sensor with cascaded ring resonators for simultaneous refractive index and temperature sensing

Abstract

The optical sensors with the capabilities of eliminating external interference (EEI) and high sensitivity (S) are attractive properties in the next-generation photonic integration application. A cascaded period structure grating (PSG) ring resonator (PSGRR) with the properties of EEI and high S is proposed, in which two ring resonators are multiplexed serially and coupled to the PSG bus waveguide. In the structure, the light is optimally coupled into the two ring resonators by adjusting the width and the silicon duty cycle of the PSG pillar. By three-dimensional finite-difference time-domain (3D-FDTD) calculation, combined with the radiation and absorption loss, an optimal mode volume overlap factor of about 0.37 is achieved when the width and the silicon duty cycle of the PSG pillar are 600 nm and 0.65, respectively. The simulation result shows that the refractive index (RI) and temperature (T) sensitivities of the Ring_1 resonator covered by SU-8 are 0 and −67.3 pm/K, respectively. Simultaneously, the RI and T sensitivities of the Ring_2 resonator covered by analyte are 361.4 nm/RIU and 18.3 pm/K, respectively. Moreover, the maximum deviation values are about 0.149% and 0.230% with the change of T and RI for the Ring_1 and Ring_2 resonators, respectively. As a result, in the process of sensing without temperature controller, the Ring_1 resonator is considered as a temperature sensor, and also as a reference ring to resist the interference of T when the Ring_2 is used to detect the change of the RI. Therefore, the results indicate that the proposed structure is a promising dual-parameter and anti-interference sensor with high sensitivity and small detection deviation.

Keywords

• Period structure grating
• Ring resonator
• Optical sensors