Correction to: Nature Photonics https://doi.org/10.1038/s41566-017-0033-z (2017); published online 30 October 2017.

In the version of this Article originally published online, the following statement for the equally contributing authors was missing: “Hongtao Lin, Yi Song, Yizhong Huang and Derek Kita contributed equally to this work.” This has now been corrected in all versions of the Article.