(a), SEM image of the device. (b-d), Zoom-in SEM images bounded by the rectangles are marked with yellow lines in a, numbered by 1, 2 and 3, respectively. (f, g), Simulated and experimental transmittance spectra for the output ports over the wavelength range of 1500–1600 nm and 1530–1580 nm, respectively. Credit: Xiaoqian Shu, Qi Zhong, Kai Hong, Oubo You, Jian Wang, Guangwei Hu, Andrea Alù, Shuang Zhang, Demetrios N. Christodoulides & Lin Chen.