Study of an integrated-optical slow light ring-resonator for sensing applications

Integrated-optical (IO) micro-ring, -disk, and -sphere resonators have been long considered as a good candidate to enhance optical sensor performance. To the best of our knowledge, none of previous reported works has explicitly attributed such (expected) enhancement to slow-light phenomenon, i.e. a phenomenon where the group velocity of light is much lower than the light velocity in vacuum (c); a phenomenon which obviously can be expected also for a properly-designed ring-resonator circuiT. Consequently, none of those works has explicitly made use of this phenomenon for optimizing the sensor performance. Hence, so far, the reported detection limit of ring-resonator based sensor (best reported value around 1E-7 RIU) is in general poorer than IO Mach-Zehnder interferometer (MZI) sensor (best reported value around 1E-8 RIU). In this work, we present a theoretically study on slow-light in ring-resonator circuits and discuss quantitatively its role in enhancing the sensor performance. The model is based on the transfer matrix method and the complex transmission coefficient approach, by assuming a homogeneous refractometric IO sensor with MZI read-out scheme. The modeling results show that using realistic structure parameters and a typical read-out capability, a refractive index detection limit of one order better than the present state of the art IO MZI sensing structure can be expected by the inclusion of such a slow-light structure. The realization of such device is under progress at the moment of the preparation of this abstract. The device will be based on $Si_3N_4$ IO technologies with a serrodyne phase readout scheme employing a ZnO electro-optical modulator. The latest results of the realization and experimental progress will be reported in the conference as well.