Broadband Mode Multiplexer Formed With Non-Planar Tapered Directional Couplers

We propose a broadband mode multiplexer based on the structure of cascaded planar and non-planar tapered directional couplers (DCs), which are designed for processing vertically symmetric and anti-symmetric modes. The DCs are tapered to widen the operating bandwidth, reduce the polarization dependence, and improve the fabrication tolerance. As an example, we design and fabricate a five-mode (de)multiplexer with polymer material to combine or separate the
$E_{11}$
,
$E_{12}$
,
$E_{21}$
,
$E_{31}$
, and
$E_{22}$
modes. Our typical fabricated device has a length of 2.1 cm and shows the mode coupling efficiency of almost larger than 94.5% for each DC over the
$C+L$
band with weak polarization dependence. The proposed structure is scalable and can be implemented with different material platforms.