End-fire injection of light into high-Q silicon microdisks

High-quality (Q)-factor silicon microdisks are promising platforms for revolutionizing bio-sensing, medical diagnoses, and frequency combs. Nevertheless, their practical applications are hindered by the regular waveguide–resonator coupling configuration, which relies on sophisticated and high-cost nanofabrication. Here, we demonstrate a simple, cost-effective, and counterintuitive mechanism to couple light into a high-Q silicon microdisk. In contrast to the evanescent coupling, the incident light is injected into silicon microdisks through the waveguides directly connected to them. The end-fire injection coefficients and Q factors of waveguide-connected microdisks are around 57% and 2×10^5–7×10^5, comparable to conventional microdisks. Importantly, the end-fire injection configuration is quite robust to fabrication deviations and can be simply realized without using electron-beam lithography. Meanwhile, their applications in monitoring nanoparticles and tiny ambient changes have also been explored. This research will route a new way to on-chip biosensors and integrated photonic circuits.