A robust and tunable add-drop filter using whispering gallery mode microtoroid resonator

We fabricated and theoretically investigated an add-drop filter (ADF) using an on-chip whispering gallery mode (WGM) microtoroid resonator with ultrahigh-quality factor (Q) side coupled to two taper fibers, forming the bus and drop waveguides. The new device design incorporates silica side walls close to the microresonators which not only enable placing the coupling fibers on the same plane with respect to the microtoroid resonator but also provides mechanical stability, leading to an ADF with high drop efficiency and improved robustness to environmental perturbations. We show that this new device can be thermally tuned to drop desired wavelengths from the bus without significantly affecting the drop efficiency, which is around 57%.