Recent Advances in Mode-Division Multiplexed Transmission using Few-Mode Fibers

We review recent advances in few-mode fiber transmission. DSP complexity and mode-dependent gain (MDG) control are two key implementation issues. While DSP may be reduced by managing differential modal group dispersion (DMGD) and by using frequency-domain equalization, complexity still grows super-linearly with number of modes. MDG arises in inline amplifiers and can be controlled to a certain degree by optimizing the doping profile. The use of mode scrambling may ultimately be the most effective way of combatting both problems by enabling DMGD and MDG to grow only as the square root of distance. FMF are most likely to be deployed in data-centers that can benefit from high spatial information density. Elliptical-core FMFs is an attractive solution that behaves physically like parallel single-mode fibers.