Polymer spot size converter on silicon photonics chip for enabling high coupling to single-mode fiber

Abstract

Silicon photonics (SiPh) technology has gained considerable attention as a result of the growing demand for high-bit-rate optical interconnections. Low coupling efficiencies, resulting from the difference in spot size between silicon photonic chips and single-mode fibers (SMFs), remains a challenging issue. To solve this problem, we fabricated a novel, to the best of our knowledge, polymer spot size expander (SSE) device on the end face of a silicon chip. The fabrication of SSEs using self-written waveguide technology and a dipping method using UV-curable resin was highly reproducible. The spot size of the original 3.83 µm of the SiPh chip was expanded to approximately 7.82 µm at a wavelength of 1.55 µm, and the maximum coupling efficiency achieved with the SMF was –0.88 dB. In addition, the –3 dB tolerance of the coupling efficiency along the vertical optical axis was ±4.4 µm.