A Design Guideline for Mode (DE) Multiplexer Based on Integrated Tapered Asymmetric Directional Coupler

A tapered asymmetric directional coupler is considered as a promising structure for high tolerance and efficient on-chip mode (de)multiplexers. However, the optimum geometry parameters selection still remains empirical without specific numerical guidance. Here, an in-depth analysis has been carried out based on coupling mode theory. A theoretical model is built aiming to combine the consideration of device efficiency, mode crosstalk and fabrication tolerance. According to that, mode (de)multiplexers (TE
$_0$
-TE
$_1$
, TE
$_0$
-TE
$_2$
, TM
$_0$
-TM
$_1$
, TM
$_0$
-TM
$_2$
) with broad operation wavelength (C + L band) and low mode crosstalk (minimum −30 dB) are fabricated. The proposed theoretical model can serve as a guideline for the design and optimization of the tapered ADC based mode (de)multiplexers.