Coupling of a whispering gallery mode to a silicon chip with photonic crystal

TL;DR

This paper demonstrates highly efficient coupling between a silica whispering gallery mode microresonator and a silicon chip using a photonic crystal waveguide, achieving near-critical coupling with high quality factors.

Contribution

The study introduces a novel coupling method using a silicon photonic crystal waveguide that achieves 99.5% efficiency and enables critical coupling with high-Q whispering gallery modes.

Findings

Achieved 99.5% coupling efficiency between whispering gallery mode and silicon chip.

Realized critical coupling with a Q factor close to 10^7.

Showed the effectiveness of photonic crystal waveguides in coupling applications.

Abstract

We demonstrate the efficient coupling (99.5%) of a silica whispering gallery mode microresonator directly with a silicon chip by using a silicon photonic crystal waveguide as a coupler. The efficient coupling is attributed to the small effective refractive index difference between the two devices. The large group index of the photonic crystal waveguide mode also contributes to the efficient coupling. A coupling Q of 2.68*10^6 is obtained, which allows us to achieve the critical coupling of a silica whispering gallery mode with an intrinsic Q of close to 10^7 with a Si chip.