High-Efficiency Focusing Double-Etched SiN Grating Coupler for Trapped Ion Qubit Manipulation

A high efficiency and low crosstalk SiN grating coupler was demonstrated for trapped ion qubit manipulation. By optimizing a chirped double-etch grating with inverse design, a diffraction efficiency of 98.0 % was achieved for 729 nm. Additionally, an ellipse-shaped beam resulted in a low crosstalk of -36 dB assuming 7.07 µm neighboring ion spacing.