Adjustable coupling-coefficient waveguide Bragg grating with doubly periodic structures

Waveguide Bragg gratings serve as essential components in both passive and active photonic integrated circuits. It is essential to achieve a desired coupling coefficient; however, the available methodologies are currently constrained. Here, we show that the doubly periodic sidewall waveguide Bragg gratings, consisting of the <i>m</i>th-order Bragg grating on one side of the waveguide and the <i>2m</i>th-order Bragg grating on the other, can significantly adjust the coupling coefficient. We also comprehensively study the grating strength control by varying the offset between the corrugations in sidewalls. Finally, we experimentally demonstrate AlN doubly periodic waveguide Bragg gratings with the <i>1st</i>-order grating on one side and the <i>2nd</i>-order grating on the other. The measured results are in very good agreement with simulations.