Miniaturization: The Next Wave in Astronomical Instrumentation

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A spectrograph is an astronomical instrument that divides starlight into colors and makes precise, quantitative measurements of them. It is essential for a broad range of astronomical observations; but it is complex, bulky, and expensive. This project uses photonics technology adapted from the telecommunications industry to develop a novel kind of astronomical spectrograph. Photonics technology offers the potential to reduce the size by orders of magnitude while also lowering cost. Veilleux and collaborators are developing such a miniaturized, photonic spectrograph for deployment on a telescope. This demonstration instrument has the potential to transform the traditional spectrograph, workhorse of any astronomical observatory, into a lithe 21st century discovery engine.These investigators borrow several innovations from the telecommunications industry to miniaturize a spectrograph. The essential one is a photonic lantern, which is a method of efficiently coupling light from a multi-mode fiber into a single mode fiber. Multi-mode fibers are the only type that can be used at an astronomical focal plane. However, coupling to single mode fibers enable using other photonics innovations: fiber Bragg gratings and complex waveguide Bragg gratings, which filter out specific wavelengths and suppress unwanted noise. Noise arises from water vapor / OH sky emission and is the major source of unwanted background in an astronomical IR spectrograph. The final innovation is an arrayed waveguide grating -- a lightwave circuit fabricated on silicon that forms the dispersive element. Each of these individual components has been developed and tested by the investigators using their institutional access to fabrication facilities. This project will complete the instrument and deploy it at the 4.3 m Discovery Channel Telescope. The science goals identified for the instrument included follow-up investigations of gamma-ray burst afterglows. This field has seen tremendous advance over the past two decades and will be relevant for years to come.