Optimal design and experimental demonstration of a silicon-based ultra-compact mode splitter

To improve the flexibility of the mode division multiplexing (MDM) system, we propose and experimentally demonstrate a mode splitter by using the inverse design method. The proposed mode splitter has an ultra-compact footprint of 5 × 3 µm 2 , and the functional region occupies a footprint of only 5 × 1 µm 2 . The optimized mode splitter can separate the TE 0 and TE 1 modes without changing the mode order. When transmitting the TE 0 mode, the measured insertion loss and crosstalk are 2.14 dB and −13.34 dB, respectively, at the operating wavelength of 1550 nm. The 3-dB bandwidth is >66 nm, and the crosstalk is lower than −12.37 dB over the C + L band. When transmitting the TE 1 mode, the insertion loss and crosstalk are 3.04 dB and −16 dB, respectively, at 1550 nm. The 3-dB bandwidth is >57 nm, and the crosstalk is below −12.89 dB over the whole C + L band.