Multi-dimensional reconfigurable optical add/drop multiplexer for WDM-MDM systems

In the rapidly evolving fields of optical networks, the demands for increased flexibility and capacity are ever-growing, especially in the context of ultra-large data centers. To meet these demands, we propose and demonstrate a versatile multi-channel reconfigurable optical add/drop multiplexer (ROADM) that utilizes a crossbar optical switching network. The proposed ROADM is compatible with both wavelength-division multiplexing (WDM) and mode-division multiplexing (MDM) systems. Unlike traditional ROADM devices for WDM-MDM systems, our innovation allows for simultaneous reconfiguration of both mode and wavelength dimensions through a single add/drop port. The insertion loss of the optical links, including mode coupling loss and crossing loss, is less than 7.0 dB, while the crosstalk for the fabricated device remains below -13.4 dB. Additionally, each individual add/drop port of the device can concurrently download multiple data signals in a bus waveform, paving the way for potential applications in future ultra-high-capacity data centers.