Broadband Graded Index 3dB Adiabatic Coupler for Photonic Integrated Circuits

In this study, we present a novel graded index (GI) 3dB adiabatic directional coupler utilizing polymer material. Our design prioritizes both fabrication flexibility and superior performance. Through extensive numerical simulations and optimization using the R SoftCAD BPM, we demonstrate the broadband operation of our coupler across a wide spectral range. At the critical wavelength of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{1.55}\ \boldsymbol{\mu} \mathbf{m}$</tex>, we observe low insertion loss of 0.10 dB for both transverse electric (TE) and transverse magnetic (TM) modes, bending loss of 0.0017 dB, coupling loss of 0.02 dB for both TE and TM modes, and crosstalk levels of -31.10 dB and -30.16 dB for TM and TE modes, respectively. This device holds significant promise for high-speed optical interconnects in data centers, telecommunications networks, and integrated photonic systems.