Abstract
To unlock the cost benefits of space division multiplexing transmission systems, higher spatial multiplicity is required. Here, we investigate a potential route to increasing the number of spatial mode channels within a single core few-mode fiber. Key for longer transmission distances and low computational complexity is the fabrication of fibers with low differential mode group delays. As such in this work, we combine wavelength and mode-division multiplexed transmission over a 4.45 km low-DMGD 6-LP-mode fiber by employing low-loss all-fiber 10-port photonic lanterns to couple light in and out of the fiber. Hence, a minimum DMGD of 0.2 ns (maximum 0.357 ns) is measured after 4.45 km. Instrumental to the multi-mode transmission system is the employed time-domain-SDM receiver, allowing 10 spatial mode channels (over both polarizations) to be captured using only 3 coherent receivers and real-time oscilloscopes in comparison with 10 for conventional methods. The spatial channels were unraveled using 20 × 20 multiple-input multiple-output digital signal processing. By employing a novel round-robin encoding technique, stable performance over a long measurement period demonstrates the feasibility of 10x increase in single-core multi-mode transmission.
Highlights
Demand for more bandwidth continues at a phenomenal pace mainly attributed to emerging applications and services
We investigate a potential route to increasing the number of spatial mode channels within a single core few-mode fiber
Key for longer transmission distances and low computational complexity is the fabrication of fibers with low differential mode group delays
Summary
Demand for more bandwidth continues at a phenomenal pace mainly attributed to emerging applications and services. As the number of guided mode groups is increased, a key challenge is managing the differential mode group delay, caused by the different propagation constant of the respective guided linear polarized modes. This can be ascertained from the impulse response associated with each mode. Transmission over a high DMGD fiber requires larger processing effort in terms of the multiple input multiple output (MIMO) digital signal processing (DSP) required to unravel the mixed spatial channels, resulting in higher computational efforts and energy consumption at the receiver. In addition to DMGD, low mode dependent loss (MDL) is desired, as high MDL between spatial channels limits the theoretical throughput capacity of the system and increases the outage probability [9, 10]. We report a minimum DMGD of 0.2 ns (~0.05 ns/km) and maximum DMGD of 0.357 ns (~0.08 ns/km) after 4.45 km and MDL < 10 dB
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