Negative index of refraction, perfect lenses and transformation optics -- some words of caution

TL;DR

This paper clarifies that negative refraction in transformation optics arises from sign choices rather than the fundamental theory, and challenges the notion of perfect imaging by transformation-designed lenses.

Contribution

It demonstrates that negative index does not directly follow from transformation optics and shows that such lenses do not amplify evanescent modes for perfect imaging.

Findings

Negative index is due to sign choice, not transformation optics itself.

Transformation-designed lenses do not amplify evanescent modes.

No true near-field imaging occurs with these lenses.

Abstract

In this paper we show that a negative index of refraction is not a direct implication of transformation optics with orientation-reversing diffeomorphisms. Rather a negative index appears due to a specific choice of sign freedom. Furthermore, we point out that the transformation designed lens, which relies on the concept of spacetime folding, does not amplify evanescent modes, in contrast to the Pendry-Veselago lens. Instead, evanescent modes at the image point are produced by a duplicated source and thus no imaging of the near field (perfect lensing) takes place.