Graded-index thin-film stack for cladding and coupling

Kim Peng Lim; Doris Keh Ting Ng; Jing Pu; Yeow Teck Toh; Tjiptoharsono Febiana; Krishnamurthy Vivek; Qian Wang

doi:10.1364/AO.55.006752

Graded-index thin-film stack for cladding and coupling

Appl Opt. 2016 Aug 20;55(24):6752-6. doi: 10.1364/AO.55.006752.

Authors

Kim Peng Lim, Doris Keh Ting Ng, Jing Pu, Yeow Teck Toh, Tjiptoharsono Febiana, Krishnamurthy Vivek, Qian Wang

PMID: 27556999
DOI: 10.1364/AO.55.006752

Abstract

A graded-index multilayer thin-film stack is optimized to act as a cladding layer on top of a silicon (Si) nanowaveguide and also a collimator for chip coupling where the waveguide ends. The numerical example shows an optimized graded-index profile from 2.35 to 1.45 provides an optical coupling to the standard single-mode fiber with efficiency close to 90% while retaining tight light confinement for the Si nanowaveguide. The corresponding material realization of a graded-index profile with a Si-rich nitride SiN_x/SiON/SiO₂ system is explored using inductively coupled plasma chemical vapor deposition, and a SiN_x cladded Si waveguide is demonstrated.