Is one-way modal conversion sufficient for optical isolation

TL;DR

This paper argues that one-way photonic modal conversion alone cannot achieve optical isolation because the underlying structure's symmetric scattering matrix prevents true isolation, requiring additional design modifications.

Contribution

It demonstrates that the existing one-way modal conversion effect is insufficient for optical isolation due to symmetric scattering properties, highlighting the need for non-symmetric scattering in system design.

Findings

One-way modal conversion does not break symmetry of the scattering matrix.

Symmetric scattering matrices prevent true optical isolation.

Additional design modifications are necessary for effective isolation.

Abstract

We show that the novel one-way photonic modal conversion effect, as demonstrated by Feng et al (Reports, 11 August, 2011, p. 729), is insufficient in itself to enable optical isolation, since the underlying dielectric structure possesses a symmetric scattering matrix. Moreover, one cannot construct an optical isolator, by enclosing this structure with a system containing any combination of components or signal processing elements, as long as the overall system is linear, and is described by a static scalar dielectric function. Instead, to achieve complete optical isolation, one would need to augment the present design so that the final system is described by a non-symmetric scattering matrix.