Micro-/nano-fiber structures based on wet-etching for efficient mode coupling between optical waveguides

Abstract

For the commercialization and application of the integrated photonics, an efficient optical coupling method between the optical fiber systems and the photonic integrated circuits (PICs) is important. The essential conditions for implementing such a fiber-to-PIC interface system are to overcome the differences in effective refractive indices of ~60% and the modal field cross-sectional area of ~1,000 times between the optical fibers and the PICs. To overcome the intrinsic limitations, this dissertation proposes an adiabatic coupling method based on evanescent-field on an adiabatic optical fiber taper (AOFT), which is an essential building block for an efficient fiber-to-chip coupling, and an oil-free chemical wet-etching fabrication method for the reproducible AOFTs and the verification of the adiabaticity are mainly discussed. In addition, by understanding the adiabatic properties and applying it to an optical fiber-based ring resonator with an inch-scale diameter, the performance of the ultra-high-Q factor and low repetition rate fiber ring resonator is enhanced, and a microstructure for improving the performance of the fiber-based Fabry-Pérot interferometer is also introduced. As described above, the characteristics of new concepts micro-/nano-scale optical fiber structures based on the chemical wet-etching are discussed, and the analysis and their operation principles are thoroughly investigated from an optical perspective.