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 ~2 μm 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.
Highlights
Telescopes were used to observe one source at a time on the celestial sphere
We demonstrate a novel imaging fiber bundle (“hexabundle”) that is suitable for low-light applications in astronomy
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
Summary
Telescopes were used to observe one source at a time on the celestial sphere. With advances in optical fibers, it was realized in the early 1980s that many sources could be observed across the telescope focal plane simultaneously by positioning optical fibers across the field [1,2]. With the advent of adaptive optics and ever-increasing telescope apertures, most of the sources studied to date can be spatially imaged with ground-based telescopes This argues for a new photonic imaging device that has the flexibility of an optical fiber and can be positioned over the wide focal plane with existing robotic technology – we refer to such a device as the hexabundle.
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