On-chip multi-band mode-division multiplexed optical interconnect using ultra-broadband inverse-designed digital metamaterials

Optical interconnects based on photonic integrated circuits (PICs) are emerging as a pivotal technology to address the relentless surge in data traffic driven by compute-intensive applications. Combining mode-division multiplexing (MDM) with wavelength-division multiplexing (WDM) offers a compelling approach to significantly enhance the shoreline density of optical interconnects. However, existing on-chip MDM systems encounter considerable challenges in simultaneously achieving a large optical bandwidth, multi-band operation, and ultra-compactness, thereby limiting scalability as conventional telecom band resources become increasingly constrained. Here we introduce, to our knowledge, the first inverse-designed multi-band mode multiplexer (MUX) utilizing a digital metamaterial structure to support the first three-order TE modes. The proposed device features an ultra-compact footprint of 6 μm ×4.8 μm and exhibits an exceptionally flat spectral response, with numerical simulations confirming spectral variations of less than 0.94 dB across the 1500–2100 nm range. Experimental results further validate its performance, demonstrating insertion losses below 4.3 dB and 4.0 dB, and crosstalk below −11.6 dB and −11.3 dB , within the 1525–1585 nm and 1940–2040 nm bands, respectively. Additionally, system-level optical interconnect experiments using a multi-band MDM circuit successfully achieve single-wavelength transmission rates of 3-modes×180 Gb /s at the 1.55 μm band and record-setting 3-modes×114 Gb /s in the 2 μm band. This work highlights the transformative potential of employing multi-band MDM technology to enhance bandwidth density and scalability, providing a robust foundation for next-generation high-capacity on-chip optical interconnects.