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Abstract:We demonstrate the fabrication of a high performance multimode (MM) to single-mode (SM) splitter or "photonic lantern", first described by Leon-Saval et al. (2005). Our photonic lantern is a solid allglass version, and we show experimentally that this device can be used to achieve efficient and reversible coupling between a MM fiber and a number of SM fibers, when perfectly matched launch conditions into the MM fiber are ensured. The fabricated photonic lantern has a coupling loss for a MM to SM tapered transition of only 0.32 dB which proves the feasibility of the technology.

Abstract:We demonstrate a novel imaging fiber bundle ("hexabundle") that is suitable for low-light applications in astronomy. The most successful survey instruments at optical-infrared wavelengths use hundreds to thousands of multimode fibers fed to one or more spectrographs. Since most celestial sources are spatially extended on the celestial sphere, a hexabundle provides spectroscopic information at many distinct locations across the source. We discuss two varieties of hexabundles: (i) lightly fused, closely packed, circular cores; (ii) heavily fused non-circular cores with higher fill fractions. In both cases, we find the important result that the cladding can be reduced to ~2μm over the short fuse length, well below the conventional ~10λ thickness employed more generally, with a consequent gain in fill factor. Over the coming decade, it is to be expected that fiber-based instruments will be upgraded with hexabundles in order to increase the spatial multiplex capability by two or more orders of magnitude.

Efficient multi-mode (MM) to single-mode (SM) conversion in a 61 port splitter or "Photonic Lantern" is demonstrated. The coupling loss from a 100 µm core diameter MM section to an ensemble of 61 SM fibers and back to another 100 µm core MM section is measured to be as low as 0.76 dB. This demonstration shows 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.

Abstract-We consider the problem of radiation into free space from the end-facet of a single-mode photonic crystal fiber (PCF). We calculate the numerical aperture NA = sin θ from the half-divergence angle θ ∼ tan −1 (λ/πw) with πw 2 being the effective area of the mode in the PCF. For the fiber first presented by Knight et al. we find a numerical aperture NA ∼ 0.07 which compares to standard fiber technology. We also study the effect of different hole sizes and demonstrate that the PCF technology provides a large freedom for NAengineering. Comparing to experiments we find good agreement.