Analysis of optical integration between Si3N4 waveguide and a Ge-based optical modulator using a lateral amorphous GeSi taper at the telecommunication wavelength of 1.55 µm

Abstract

We report on the theoretical investigation of using an amorphous Ge[subscript 0.83]Si[subscript 0.17] lateral taper to enable a low-loss small-footprint optical coupling between a Si[subscript 3]N[subscript 4] waveguide and a low-voltage Ge-based Franz-Keldysh optical modulator on a bulk Si substrate using 3D Finite-Difference Time-Domain (3D-FDTD) simulation at the optical wavelength of 1550 nm. Despite a large refractive index and optical mode size mismatch between Si[subscript 3]N[subscript 4] and the Ge-based modulator, the coupling structure rendered a good coupling performance within fabrication tolerance of advanced complementary metal-oxide semiconductor (CMOS) processes. For integrated optical modulator performance, the Si[subscript 3]N[subscript 4]-waveguide-integrated Ge-based on Si optical modulators could simultaneously provide workable values of extinction ratio (ER) and insertion loss (IL) for optical interconnect applications with a compact footprint. Keywords: germanium; silicon nitride; optical interconnect; Franz–Keldysh effect