The News & Views 'Backwards Doppler shifts' (Nature Photonics 5, 199–200 (2011); published online 31 March 2011; corrected after print 3 June 2011), should have cited a relevant manuscript that was published in October 1997:

Liu, W. F., Russell, P. St. J. & Dong, L. Opt. Lett. 22, 1515–1517 (1997).

The manuscript describes positive and negative Doppler shifts at optical frequencies in an acousto-optic superlattic modulator using a fibre Bragg grating. Associated amendments have been made to the text and the references have been renumbered accordingly.

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