All dielectric compact broadband silicon waveguide mode converters

Abstract

Compact mode order converters (MOCs) operating at the mid-infrared regime are reported using silicon-on-calcium fluoride platform. The suggested designs convert the fundamental transverse electric (TE) mode to first and second order TE modes with total device lengths of only 5.89 μm and 5 μm, respectively, at λ = 3.14 µm. The full vectorial 3D finite-deference time-domain is utilized to analyze the TE₀ → TE₁ and TE₀→TE₂ MOCs. The proposed designs depend on using dielectric material of Si₃N₄ inside the Si core region to improve and facilitate the mode conversion process. The conversion efficiencies (inter-modal crosstalks [CTs]) are equal to 93.4% (− 19.2 dB), and 90% (− 17 dB) for TE₀: TE₁ and TE₀:TE₂ MOCs, respectively. Moreover, the reported designs have a wide wavelength range of 300 nm, where the conversion-efficiency (CE) and maximum CT are > 86% and <  − 14.3 dB, respectively. Further, the fabrication tolerance of the suggested structures is handled to guarantee the presented mode converter’s fabrication viability. The reported designs can also be extended to other wavelength bands. In this regard, our device’s numerical results at λ = 1.55 µm are reported and compared to other conventional MOCs. The conversion efficiencies (inter-modal crosstalks [CTs]) are equal to 90% (− 19 dB), and 88% (− 19.7 dB) for TE₀: TE₁ and TE₀: TE₂ MOCs, respectively, at λ = 1.55 µm.