Efficient multi-mode to single-mode conversion in a 61 port photonic lantern

We demonstrate the fabrication of a multi-mode (MM) to 61 port single-mode (SM) splitter or "Photonic Lantern". Low port count Photonic Lanterns were first described by Leon-Saval et al. (2005). These are based on a photonic crystal fiber type design, with air-holes defining the multi-mode fiber (MMF) cladding. Our fabricated Photonic Lanterns are solid all-glass versions, with the MMF defined by a low-index tube surrounding the single-mode fibers (SMFs). We show experimentally that these devices can be used to achieve efficient and reversible coupling between a MMF and 61 SMFs, when perfectly matched launch conditions into the MMF are ensured. The total coupling loss from a 100 µm core diameter MM section to the ensemble of 61 SMFs and back to another 100 µm core MM section is measured to be as low as 0.76 dB. This demonstrates the feasibility of using the Photonic Lanterns within the field of astrophotonics for coupling MM star-light to an ensemble of SM fibers in order to perform fiber Bragg grating based spectral filtering.