Ultra-compact, high-Q silicon microdisk reflectors

We demonstrate wavelength-selective reflectors based on silicon microdisk resonators integrated with compact Y-branch splitters, using a CMOS-photonics technology. A high quality factor (Q) of ~ 88,000 was measured in the reflection spectrum for a 2.5-μm-radius device with a small footprint of 6 × 17 μm(2) and a wide free-spectral range (FSR) of over 41 nm. As the radius is reduced to 1.5 μm, corresponding to a device footprint of 4 × 15 μm(2), the spectrum shows an ultra-wide FSR of over 71 nm with the compromise of having a reduced Q of ~ 4000. The coupling between a microdisk and a waveguide is numerically investigated. We further propose a multichannel sensing system using cascaded microdisk reflectors.