An on-chip tunable add-drop filter using a microtoroid resonator

We present an add-drop filter (ADF) with a drop efficiency of 57% and quality factor of 4.5 × 10⁶ composed of an on-chip whispering gallery mode (WGM) ultra-high quality factor (Q) microtoroid resonator side coupled to two taper fibers. Different than the exisiting microtoroid based ADF designs, we fabricated reflowed silica side walls along the microtoroid resonators to support the fiber-taper waveguides, not only making the alignment process easier but also providing mechanical stability. As an additional benefit, we observe that the drop-wavelength can be tuned without compromising drop efficiency.