Spatial Aperture-Sampled Mode Multiplexer Extended to Higher Mode Count Fibers

Efficient mode division multiplexing using the spatial aperture sampled concept from single-modefibers to a few-mode fiber is extended to circular step index fibers supporting up to ten spatial modes and to annular refractive index profile fibers supporting nine optical orbital angular momentum modes (mode counts double when considering polarization states for each case). Each sampling beam aperture is spatially shaped for lower average coupling losses and mode dependent losses or a balance thereof. The optimization demonstrates the scalability and consistent low losses for the aperture-sampled mode multiplexer for increasing mode counts, as opposed to the phase hologram-based mode conversion technique. The aperture-sampling approach is also found to be robust to small input fiber alignment errors and fiber geometrical distortions.