On-chip fundamental mode attenuators for loss-equalization in MDM system

The development of mode-division multiplexing (MDM) technology expands the capacity of on-chip optical communication systems to an unprecedented level. Since the high mode-dependent gain or loss of transmission system complicates signal recovery at the receiver, we propose and fabricate two on-chip fundamental mode attenuators for loss-equalization in MDM network. The devices are based on asymmetric Y-junctions and Mach-Zehnder interferometers. By properly driving the electrode heater, a large attenuation of 12.8 dB can be achieved for E₁₁ mode, while maintaining minimal loss (<0.4 dB) for E₂₁ mode. And a 14.6 dB mode-dependent loss equalization range with less than 1.7 dB loss is also achieved for three-mode operation. The proposed devices open a new way to obtain large attenuation for E₁₁ mode, which holds great promise for advancing high performance on-chip MDM systems.