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Non-reciprocal propagation versus non-reciprocal control

Nature Photonics volume 14, page 711 (2020)Cite this article

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A Correspondence to this article was published on 20 November 2020

The Original Article was published on 29 May 2020

To the Editor — A recent article1 reports a nonlinear, non-reciprocal device and its application to isolation and routing of signals. Towards the end, the article clearly specifies that the device enables non-reciprocal propagation only for the forward and backward signals that are not coincident in time2. When the signals are coincident, the transmission is fully reciprocal and no isolation takes place. Nevertheless, the accompanying News and Views article3 bears the title no less than ‘Low-loss nonlinear optical isolators in silicon’, and although the body of the article contains a statement about the aforementioned limitation, the device is referred to as an ‘isolator’ throughout the article. This, in my view, is not very helpful to readers, especially casual ones who may get an impression that an optical isolator has been developed, and this impression cannot be further from the truth.

To avoid further confusion, it should be noted that although the nonlinear scheme1 as well as its many progenitors all fail to meet strict criteria for being an optical isolator, it does not mean that a true optical isolator cannot be built using nonlinear optics, for example, by frequency conversion6.

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Fig. 1: Explanation of a non-reciprocally-controlled device and why it’s not an optical isolator.

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  1. Johns Hopkins University, Baltimore, MD, USA

    Jacob B. Khurgin

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  1. Jacob B. Khurgin
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Correspondence to Jacob B. Khurgin.

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Khurgin, J.B. Non-reciprocal propagation versus non-reciprocal control. Nat. Photonics 14, 711 (2020). https://doi.org/10.1038/s41566-020-00723-5

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