Dynamic Control of Distal Spatial Mode Pattern Output From Multimode Fiber Using Integrated Coherent Network

The mode field distribution at the distal end of a multimode fiber can vary randomly when environmental perturbations introduce changes in the relative phases of different eigenmodes and variations in coupling among modes. Random rotations of the high-order mode-field distribution at the distal end can produce large coupling losses at the multimode waveguide grating coupler (MWGC) in the fiber-chip interface. In this paper, we propose a solution to this problem by using a novel approach based on controlling the relative phases and amplitudes of different modes launched at the proximal end of the fiber. We implemented an integrated mesh of Mach Zehnder Interferometer at the transmitter to demonstrate control of the distal end mode field distribution to ensure low coupling losses in the receiver's MWGC. The MWGC on the silicon-on-insulator (SOI) platform had measured coupling efficiency of (−5.7 dB, −7.1 dB) for (LP01x, LP11ax) modes, without needing any manual adjustment to align the mode orientation with the MWGC. The coherent Mach-Zehnder Interferometer (MZI) network can be dynamically controlled to produce the desired mode pattern at the distal end of the FMF to enable low-loss coupling at the distal end. This enables the practical deployment of mode division multiplexing with MWGC without needing manual control of fiber orientation at the receiver. The proof-of-concept experiment demonstrates that the transmitter mode control is suitable for future deployment of mode division-multiplexing (MDM) data center interconnects.