A Compact and Efficient 2D Grating Coupler for Polarization-Insensitive Fiber-to-Chip I/O

We experimentally demonstrate a compact and efficient 2D grating coupler fabricated with optical lithography. A fiber-to-chip efficiency of −2.9 dB with a footprint of $55 \times 37 \mu \text{m}^{2}$ including spot size converters can be achieved.