Suspended optical fiber-to-waveguide mode size converter for Silicon photonics

Abstract

In this paper, an efficient and novel optical fiber-to-waveguide mode size converter for Si Photonics devices with sub-micron waveguides is developed on the SOI platform. This optical converter is composed of a suspended SiO₂ waveguide and overlapped Si nano-tapers located in the center of suspended SiO₂ waveguide. Laterally connected SiO₂ beams provide structural support for the suspended SiO₂ waveguide. The optical input signal from the optical fiber is launched into the suspended SiO₂ waveguide, and then coupled into the Si nano-taper. The measured coupling loss using a lensed fiber with 5 µm spot diameter is 1.7 ~2.0 dB/facet for TE mode and 2.0 ~2.4 dB/facet for TM mode in the wavelength range of 1520 ~1600 nm. When a cleaved fiber with 9.2µm spot diameter is used, the coupling losses for both TE and TM modes are less than 4.0 dB/facet at 1550 nm. For the case of lensed fiber, the alignment tolerances for both TE and TM modes are about ± 1.7 µm for 1 dB excess loss in both X and Y axes. The alignment tolerances for both modes of TE and TM are relaxed, exceeding ± 2.5 µm for 1 dB excess loss in both X and Y axes when a cleaved fiber is used.