Thermo-optical tuning of cascaded double micro-ring resonators for dynamic range enhancement

We report on a silicon-photonic cascaded microring sensor with thermo-optic tuning for extension of detection range. Cascaded microring resonators have been used to realize refractive index sensors with high sensitivity in the intensity detection mode. In this configuration, one ring is used to probe analyte while the other ring (called filter) is used for spectrum overlap measurement. A significant drawback of this configuration is decreased range of detection. We overcome this problem by thermo-optically tuning the spectrum the filter ring to track the position of maximum overlap, as the spectrum of the probing ring undergoes shift. Using this peak tracking method, we have experimentally demonstrated range enhancement by a factor of 7.8, compared to the intensity detection scheme. This method can use a broadband source for operation, and has a potential for development of low cost, point of care biomedical applications.