Optical MIMO signal processing for direct-detection mode-division multiplexing

Karthik Choutagunta, Sercan Ö. Arik, Mehrad Moradshahi, Joseph M. Kahn

Abstract: Adaptive optical multi-input multi-output (MIMO) signal processing is employed to compensate for intermodal coupling in short-reach direct-detection mode-division multiplexing systems. Complexity is minimized by cascading two stages of fundamentally lossless devices. All modes are first separated by a fixed demultiplexer, such as a mode-selective photonic lantern or multi-plane converter. Coupling within different mode groups is then compensated independently using adaptive 2×2 or 4×4 MIMO processing in Mach-Zehnder arrays. Adapting these MIMO arrays requires a non-standard algorithm. Convex optimization-based phase retrieval converges very rapidly, but requires high-speed analog-digital conversion (ADC). Self-configuration does not require ADC, but converges more slowly.