Abstract

The present work proposes a new, to the best of our knowledge, approach of hetero-cladding for silicon photonic waveguides and outlines its contribution towards realization of a compact directional coupler. The proposed hetero-cladding, comprising ferroelectric ${{\rm BaTiO}_3}$ and ${{\rm SiO}_2}$, helps control the distribution of modes and evanescent modes in the structure. The results, using a straight waveguide configuration of the coupler, show very small and nearly identical coupling lengths for both TE and TM modes (7.18 µm for TE, 7.12 µm for TM) with reduced device cross section (${\sim}{3.1}\;{\unicode{x00B5}{\rm m}}$). Considering the bending arms at the ports in an optical design of the coupler, the coupling length is seen to be further reduced (5.2 µm). This promises a huge reduction in the footprint of both conventional and programmable photonic integrated circuits. This concept could also be utilized to design compact, low loss, and energy-efficient waveguides based other optical devices.

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