Low-cost, monolithic and integrated whispering gallery mode ring resonator for sensing applications

In this paper, a monolithic fabrication process for implementing a sensor device consisting of a ring resonator and dielectric image-waveguide on Silicon-on-Insulator (SOI) is presented for sensing applications. The device is implemented on high resistive silicon with the resistivity greater than 1000 Ω-cm to minimize the dielectric loss. The set of ring resonator and dielectric waveguide are optimized to excite the whispering gallery mode (WGM) of the ring resonator. The proposed fabrication process has less than 0.25 microns tolerance which enables one to implement the sensor very close to its critical coupling mode without any need for post-fabrication tuning. Since the device is in near critical coupling mode, it can be used for very high sensitivity sensing applications. The measurement results at V-band for sensing different liquid samples are presented to demonstrate the capabilities of the sensor and the proposed fabrication process.