Chip-scale hollow photonic coupler cum mode transformer based on 2-D taper

Abstract

Efficient coupling between conventional optical fibers and deeply subwavelength nanophotonic waveguides remains a major challenge in integrated photonics due to the large mismatch between the micron-scale optical mode of fibers and the nanoscale confined modes of compact waveguides. This thesis presents a Complementary Metal-Oxide-Semiconductor (CMOS)-compatible silicon-based hollow two-dimensional (2-D) taper coupler cum mode transformer for efficient adiabatic conversion of weakly confined photonic modes into strongly confined plasmonic-like modes. The proposed structure employs simultaneous lateral and vertical tapering of a silicon–air hollow geometry, enabling gradual mode compression and enhanced field localization near the silicon–air interface. The device is numerically analyzed using Ansys Lumerical MODE, Finite-Difference Time-Domain (FDTD), and Eigenmode Expansion (EME) simulations at the telecommunication wavelength of 1550 nm.