Beyond traditional bandwidth tunability in grating-assisted couplers: enhanced design techniques and theoretical limitations

Grating-Assisted Contra Directional Couplers (GACDCs) are versatile photonic devices used to implement adddrop responses with unlimited free-spectral range, steep roll-off and low ripple: due to these properties, GACDC are suitable integrated solutions for Wavelength Division Multiplexing (WDM) systems and many other applications transparent optical spectral processing. Different design techniques can be deployed to optimize their static response, with thermal control being used to dynamically adjust the drop bandwidth, allowing for further implementation flexibility. A new design technique that involves altering the periodicity of the gratings (pitch chirping) can enhance the dynamic control, leading to much wider bandwidth tunability without changing the required control scheme. In this work, we investigate the limits of such technique, highlighting the advantages through simulation of both the optical response as well as the thermal control.