Low Loss Fiber-to-Waveguide Converter With a 3-D Functional Taper for Silicon Photonics

We demonstrate a low-loss and broad-bandwidth fiber-to-waveguide converter with a 3-D functional SiO
₂
taper for silicon photonics. The converter is composed of a cantilevered SiO
₂
waveguide and Si nano-tapers. In order to reduce the loss from the cleaved fiber, a 3-D functional SiO
₂
taper is designed to compress the size of optical mode field. Using cleaved optical fibers with a mode field diameter of 10.5 μm at 1550 nm, we characterized the optical performances of the converter. With an index-matching liquid, the lowest coupling loss of TE mode is 1.5 dB/facet and the lowest coupling loss of TM mode is 2.1 dB/facet. For both TE and TM modes, the 1-dB bandwidth is more than 100 nm, and the alignment tolerances for 1-dB excess loss are, respectively, ±2.5 and ±2 μm in horizontal and vertical directions.