Ultra-compact efficient mode converter with metamaterial structures

Mode converters play a key role in the mode division multiplexing, which is an emerging technology to enlarge the information transmission capacity. The footprint and the performance of the mode converters are essential for the compact and energy-efficient integrated photonics. We numerically and experimentally demonstrate an on-chip multimode-interferometer-based mode converter, between the one-order mode and the fundamental mode, using metamaterial structures for phase shift and crosstalk suppression, and significantly reduce the footprint. The fabricated device has a high conversion efficiency of 79% and a broad 3 dB bandwidth of >50 nm, with an ultra-small footprint of only 2.4 x 8.9 mu m2.