Inkjet-printed waveguide-coupled passive wedge-shaped microdisk resonator with refractive index tunability

Abstract

We incorporate a passive wedge-shaped organic microdisk supporting spatially separated whispering gallery modes into an SU-8 photonic integrated circuit (PIC) by using direct inkjet printing. This innovative method allows the mixing of multiple organic materials, enabling tunability of the refractive index of microdisks, thereby overcoming limitations of single-material resonators from conventional lithography. In this study, the microdisk resonator, with a refractive index matching that of SU-8 by mixing hyperbranched polymers, is mounted horizontally to an optical waveguide, achieving directional coupling between the microdisk and PIC at a wavelength of 1550 nm. Geometrical conditions for successful coupling were obtained by measuring the cross-sectional profile of the fabricated structure’s surface via atomic force microscopy, determining ways to adjust the coupling efficiency.