A Tuneable Multi-Core to Single Mode Fiber Coupler

We demonstrate a low loss, wideband multi-core to single-mode fiber coupler using a modified side-polishing technique. The coupler was designed to access light from a single core of the multi-core fiber without disrupting the signal propagation in the remaining cores. The coupling ratio between the two fibers can be continuously tuned over the entire spectral band via a simple mechanical displacement method. We expect that such couplers will be of use for monitoring, splitting, and multiplexing applications in future multi-core communication and sensing systems.