Realizing Nonreciprocal Linear Dichroism and Emission from Simple Media

TL;DR

This paper demonstrates that simple, readily available anisotropic media can exhibit nonreciprocal linear dichroism and emission by leveraging chiral-linear optical interference, challenging the notion that complex metamaterials are necessary for optical nonreciprocity.

Contribution

The authors derive an analytical expression predicting nonreciprocal behavior in simple media and experimentally verify it using solution-processed chiroptic films, revealing new pathways for polarization control.

Findings

Simple materials can support nonreciprocal optical effects.

Experimental validation with CdS, CdSe, and CdTe clusters.

Design rules for nonreciprocal linear dichroism are established.

Abstract

Reciprocity, the principle that a system response is identical in the forward path compared to the backward path, is a fundamental concept across physics, from electrical circuits and optics to acoustics and heat conduction. Nonreciprocity arises when this symmetry is broken, enabling directional-dependent behavior. In photonics, nonreciprocity allows control over the propagation of electromagnetic waves, essential for isolators and circulators. But achieving optical nonreciprocity typically requires complex metamaterials, exotic media, or strong external fields. Because of this, researchers have historically overlooked the possibility that readily available materials could support nonreciprocal optical behavior, assuming that conventional systems lack the ability to produce nonreciprocal behavior. In this work, we challenge that assumption by revisiting the light-matter interactions of chiroptic and linearly anisotropic media. Through Stokes-Mueller formalism we derive a simple analytical expression that predicts a pathway to nonreciprocal absorption and emission of orthogonal linear polarizations. We test this idea experimentally using solution-processed films of CdS, CdSe, and CdTe magic-size clusters that possess commensurate circular dichroism (CD) and linear dichroism (LD)values and find that they can support this effect, engineering films that exhibit nonreciprocal absorption and emission of linearly polarized light. Based on the derived expressions and experiments, several design rules are presented. Our findings reveal that nonreciprocal linear dichroism and emission can be achieved in readily processable, macroscopically symmetric materials by harnessing chiral-linear optical interference. This work opens new opportunities for scalable, polarization-based photonic control for direction-dependent optical routing, optical logic, and polarization-multiplexed information encoding.