Ultra-compact Fiber-to-chip Metasurface-based Edge Coupler

We propose an ultra-compact metasurface-based fiber-to-chip edge coupler with coupling length of 23.5 mu m for aluminum nitride (AlN) photonics. The coupling loss is similar to 1.54 dB/facet through a commercially cleaved fiber with an 8 mu m mode diameter working at 2 mu m. We compare the coupling efficiency performance of scandium-doped AlN (AlScN) edge couplers with different concentrations of scandium, and the simulation results show the proposed edge coupler with a higher concentration of scandium achieves lower coupling loss for transverse electric (TE) mode. The fabrication process is simple and compatible with the standard foundry process.