Two mode optical fibers with low and flattened differential modal delay suitable for WDM-MIMO combined system

We propose two mode optical fibers (TMFs) with minimally low differential modal delay (DMD) slope which are suitable for wavelength division multiplexing and multiple input multiple output (MIMO) combined transmission system. We designed and fabricated three different kinds of TMF, nearly zero-DMD (zTMF), positive-DMD (pTMF) and negative-DMD (nTMF) with a graded index core and a depressed inner cladding. We confirmed that the fabricated zTMF has DMD of below 15 ps/km in the C band and the fabricated pTMF and nTMF have the same degree of effective areas. We also confirmed that a DMD compensation line with a length of 100 km composed of pTMF and nTMF can successfully achieve the best properties of low DMD in the C + L band and low mode conversion.