Comment on 'Counterintuitive Dispersion Violating Kramers-Kronig Relations in Gain Slabs'

TL;DR

This paper critiques a previous study by demonstrating that its conclusions are invalid due to the inappropriate use of linear theory in systems with complex poles, emphasizing the importance of correct theoretical application.

Contribution

It clarifies the limitations of linear theory in analyzing systems with poles in the upper half-plane, correcting misconceptions in prior work.

Findings

Linear theory is not applicable to systems with poles in the upper half-plane.

Previous conclusions about dispersion violations are invalid under proper theoretical analysis.

Highlights the necessity of correct mathematical frameworks in optical system analysis.

Abstract

In this Comment, we refute conclusions made in Phys. Rev. Lett. 112, 233601 (2014) by L.-G. Wang, L. Wang, M. Al-Amri, S.-Y. Zhu, and M. S. Zubairy. These conclusions stem from the use of the linear theory, which is not applicable to systems having poles of the reflection and transmission coefficients in the upper half of the complex frequency plane.