Abstract
We present experimental results for combined mode-multiplexed and wavelength multiplexed transmission over conventional graded-index multimode fibers. We use mode-selective photonic lanterns as mode couplers to precisely excite a subset of the modes of the multimode fiber and additionally to compensate for the differential group delay between the excited modes. Spatial mode filters are added to suppress undesired higher order modes. We transmit 30-Gbaud QPSK signals over 60 WDM channels, 3 spatial modes, and 2 polarizations, reaching a distance of 310 km based on a 44.3 km long span. We also report about transmission experiments over 6 spatial modes for a 17-km single-span experiment. The results indicate that multimode fibers support scalable mode-division multiplexing approaches, where modes can be added over time if desired. Also the results indicate that mode-multiplexed transmission distance over 300 km are possible in conventional multimode fibers.
Highlights
Optical communication networks in the era of large data centers will require link capacities with 2 to 3 orders of magnitude in excess of the capacity of single mode fibers (SMFs) [1]
A transmitted signal that is coupled into multiple modes will suffer from modal dispersion as each mode travels with a different group velocity and multiple time delayed copies of the signal will appear at the end of the multimode fiber (MMF)
The experiments show a single wavelength channel capacity of 300 Gbit/s, an aggregate wavelength-division multiplexed (WDM) capacity of 18 Tb/s and a spectral efficiency of 9 bit/s/Hz for a transmission distance of 310 km, which results in a spectral-efficiency-distance product of 2790 bit/s/Hz km which is the largest demonstrated over MMFs to date
Summary
Optical communication networks in the era of large data centers will require link capacities with 2 to 3 orders of magnitude in excess of the capacity of single mode fibers (SMFs) [1]. The goal of this work is to investigate mode-division multiplexed transmission in conventional multimode fibers by using high performance photonic lanterns to selectively excite the mode groups of conventional MMFs. MDM in MMFs was first proposed by Faq et al [13] in 1982 for very short fiber lengths. It should be noted that modern multimode fibers have been specially designed to reduce the loss of the highest order mode group intended for transmission, and reduce the differential mode attenuation, and may present distinct advantages for transmission capacity and distance [23] Those advantages may be strongly manifested in practical deployments with frequent splices over long distances. Such designs configure the modes not intended to transmit data to have effective indices near the cladding index so as to be leaky, and they configure the index spacing between the desired mode having the lowest effective index and the leaky mode with the highest effective index to be sufficiently large so as to limit coupling between them
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