Comment on "Nonreciprocal Light Propagation in a Silicon Photonic Circuit" in Science 333, 729-733 (2011)

TL;DR

This paper critiques a previous study claiming nonreciprocal light propagation in a silicon photonic system, arguing that the original authors used an unconventional definition of reciprocity leading to incorrect conclusions about its use as an optical isolator.

Contribution

It clarifies the proper definition of reciprocity in optical systems and challenges the validity of the original claims about nonreciprocal behavior in the cited work.

Findings

The original system does not exhibit true nonreciprocal light propagation.

The authors' definition of reciprocity is unconventional and leads to incorrect conclusions.

Proper analysis shows the system cannot function as an optical isolator.

Abstract

In the recent article by Feng et al. [Science 333, 729-733 (2011)] a system is proposed with a periodic spatial modulation of refractive index and absorption. It is claimed that this system is nonreciprocal and can be used as an optical isolator. The authors use an unconventional definition of reciprocity and thus make wrong conclusions on the applicability of the described phenomena for optical isolators. (Submitted to Science on October 7, 2011)