Ultra‐Compact and Efficient Integrated Multichannel Mode Multiplexer in Silicon for Few‐Mode Fibers.

Space‐division multiplexing (SDM) is one of the key enabling technologies to increase the capacity of fiber communication systems. However, implementing SDM‐based systems using multimode fiber has been challenging with the need for compact, low‐cost, and scalable mode de/multiplexer (DE/MUX). Here a novel integrated mode MUX for few‐mode fibers (FMFs) is presented which can launch up to eight spatial and polarization channels. The new design is composed of a 2D multimode grating coupler (MMGC), highly compact spot size converters (SSCs), and adiabatic directional couplers (ADCs). Eight data lanes in FMFs can be selectively launched with integrated optical phase shifters. Experimental results reveal efficient chip‐to‐fiber coupling with peak efficiencies of −3.8, −5.5, −3.6, and −4.1 dB for LP01, LP11a, LP11b, and LP21b modes, respectively. Thanks to the use of an integrated subwavelength Mikaelian lens for mode‐independent field size conversion with loss ≤−0.25 dB, the total footprint of the MMGC and SSCs is only 35×35 µm2. The proposed design shows great potential for densely integrated photonic circuits in future SDM applications. [ABSTRACT FROM AUTHOR]