Development of Polygonal Toroidal Micro Optical Resonators

Tanabe Lab. has realized a polygonal silicatroid micro optical resonator that strongly confines light. The structure was fabricated by a combination of isotropic etching, anisotropic etching, and laser reflow, and is now in the process of measurement.

Conventional silicatroid resonators have very high performance, but their circular shape makes it difficult to control the coupling efficiency with tapered fibers. The newly developed octagonal silicatroid resonator allows longer coupling lengths, which results in stable coupling efficiency, and its smooth corners maintain high performance. Stable coupling is an important factor for practical applications such as optical frequency comb and particle detection using silicatroid resonators.

In this study, (1) anisotropic etchant KOH (potassium hydroxide) was used as a silicon sacrificial layer etchant, and the structure was fabricated by combining it with isotropic etching (Figure 1). Furthermore, it was found that the bonding efficiency can be controlled by using the edge and corner portions separately (Figure 2).

Part of this research was sponsored by the Strategic Information and Communications R&D Promotion Program (SCOPE). This research was also supported by Toray Science and Technology Research Grant and Keio University Next Generation Research Project Promotion Program.