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Efficient photonic reformatting of celestial light for diffraction-limited spectroscopy

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

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D.G. MacLachlan

R.J. Harris

I. Gris-Sánchez

D. Choudhury

E. Gendron

I. Spaleniak

A. Arriola

T.A. Birks

J.R. Allington-Smith

R.R. Thomson


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.


MacLachlan, D., Harris, R., Gris-Sánchez, I., Morris, T., Choudhury, D., Gendron, E., …Thomson, R. (2017). Efficient photonic reformatting of celestial light for diffraction-limited spectroscopy. Monthly Notices of the Royal Astronomical Society, 464(4), 4950-4957.

Journal Article Type Article
Acceptance Date Oct 6, 2016
Online Publication Date Oct 6, 2016
Publication Date Feb 1, 2017
Deposit Date Jul 26, 2017
Publicly Available Date Jul 26, 2017
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 464
Issue 4
Pages 4950-4957


Published Journal Article (1.8 Mb)

Copyright Statement
This article has been accepted for publication in Monthly notices of the Royal Astronomical Society ©: 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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