Experimental Comparison of Adaptive Optics Algorithms in 10-Gb/s Multimode Fiber Systems

We experimentally compare various adaptive algorithms that use a spatial light modulator (SLM) to compensate modal dispersion in 50-µm graded-index multimode fibers. We show that continuous-phase sequential coordinate ascent (CPSCA) gives better bit-error-ratio performance than 2- or 4-phase sequential coordinate ascent, in concordance with simulations in [10]. We then evaluate the bandwidth characteristics of CPSCA, and show that a single SLM is able to simultaneously compensate the modal dispersion in up to 9 wavelength-division-multiplexed 10-Gb/s channels, spaced by 50 GHz, over a total bandwidth of 450 GHz. We also show that CPSCA is able to compensate for modal dispersion in fibers up to 2.2 km long, even in the presence of midspan connector offsets up to 4 µm (simulated in experiment by offset splices). A known non-adaptive launching technique using a fusion-spliced single-mode-to-multimode patchcord is shown to fail under these conditions.