Efficient coupling between an integrated photonic waveguide and an optical fiber.

Because on-chip integration of light sources cannot be realized effectively now, integrated nanophotonic chips must couple external light to the integrated photonic waveguide with high efficiency. Realizing high efficiency coupling requires a low-loss coupling structure. In this paper, the factors allowing high efficiency coupling to be realized are analyzed theoretically and the coupling between a lensed fiber and a tapered silicon nitride (Si3N4) waveguide is realized experimentally. Because the coupling efficiency of this structure is not ideal in the experiment, a scheme of direct alignment between the lensed fiber and a cantilever waveguide is proposed. Although the scheme offers a very high coupling efficiency in theory, because of the warpage of the waveguide they cannot be directly aligned experimentally. Finally, this paper advances a scheme for the tapered fiber to be directly overlapped onto the Si3N4/SiO2 cantilever. It is found that the coupler maintains an ideal coupling efficiency for wavelength from 1530 nm to 1600 nm, laying a foundation for the integration of nano-photonic devices and optical fibers.