Inverse-designed, normal incidence grating couplers for multi-core fiber I/O

We experimentally demonstrate normal incidence grating couplers designed using topology optimization to couple into multi-core fiber. The insertion loss of polarizing and polarization demultiplexing gratings was 5.5 dB and 7.7 dB, which is within 0.8 dB of the performance obtained using a conventional fiber array.