Efficient photonic reformatting of celestial light for diffraction-limited spectroscopy

D. G. MacLachlan, R. J. Harris, I. Gris-Sánchez, T. J. Morris, D. Choudhury, E. Gendron, A. G. Basden, I. Spaleniak, A. Arriola, T. A. Birks, J. R. Allington-Smith, R. R. Thomson

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The spectral resolution of a dispersive astronomical spectrograph is limited by the trade-off between throughput and the width of the entrance slit. Photonic guided wave transitions have been proposed as a route to bypass this trade-off, by enabling the efficient reformatting of incoherent seeing-limited light collected by the telescope into a linear array of single modes: a pseudo-slit which is highly multimode in one axis but diffraction-limited in the dispersion axis of the spectrograph. It is anticipated that the size of a single-object spectrograph fed with light in this manner would be essentially independent of the telescope aperture size. A further anticipated benefit is that such spectrographs would be free of 'modal noise', a phenomenon that occurs in high-resolution multimode fibre-fed spectrographs due to the coherent nature of the telescope point spread function (PSF). We seek to address these aspects by integrating a multicore fibre photonic lantern with an ultrafast laser inscribed three-dimensional waveguide interconnect to spatially reformat the modes within the PSF into a diffraction-limited pseudo-slit. Using the CANARY adaptive optics (AO) demonstrator on the William Herschel Telescope, and 1530 ± 80 nm stellar light, the device exhibits a transmission of 47-53 per cent depending upon the mode of AO correction applied. We also show the advantage of using AO to couple light into such a device by sampling only the core of the CANARY PSF. This result underscores the possibility that a fully optimized guided-wave device can be used with AO to provide efficient spectroscopy at high spectral resolution.

Original languageEnglish
Pages (from-to)4950-4957
Number of pages8
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Publication statusPublished - 2017
Externally publishedYes

Bibliographical note

Copyright 2016 The Authors. First published in Monthly notices of the Royal Astronomical Society, 464(4), pp.4950–4957. The original publication is available at https://doi.org/10.1093/mnras/stw2558, published by Oxford University Press on behalf of the Royal Astronomical Society. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.


  • Instrumentation: adaptive optics
  • Instrumentation: spectrographs


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