# Strong self-induced nonreciprocal transmission by using nonlinear PT-symmetric epsilon-near-zero metamaterials

**Authors:** Boyuan Jin, Christos Argyropoulos  
**arXiv:** [2003.01608](https://arxiv.org/abs/2003.01608)  
**Date:** 2020-03-03  
**Summary page:** https://www.summarizepaper.com/en/paper/2003.01608v1/

## Key points

- Investigate nonreciprocal transmission for unidirectional wave propagation
- Propose a compact and practical metamaterial based on SiC media separated by an air gap
- Photonically dope SiC media with gain and loss defects to achieve PT symmetry
- Exceptional point formed in the PT-symmetric system when SiC operates as ENZ material with moderate optical loss
- Strong self-induced nonreciprocal transmission excited due to nonlinear Kerr effect at slightly shifted frequency off the EP without breaking PT-symmetric phase
- Transmittance from one direction becomes unity while transmittance from other direction decreases to low values, allowing effective control of wave propagation
- Proposed active nonlinear metamaterial surpasses limitations of passive nonlinear nonreciprocal resonators enabling stronger nonreciprocity
- Enhancement of electric field in defects leads to extreme asymmetric field distribution upon excitation from opposite incident directions, contributing to strong self-induced nonreciprocal transmission and reducing required optical power
- Potential applications include developing nonreciprocal ultrathin coatings, circulators and isolators for controlling wave propagation.

## Summary

In this study, Jin and Argyropoulos investigate the phenomenon of nonreciprocal transmission which is essential for unidirectional wave propagation. They propose a compact and practical metamaterial based on two Silicon Carbide (SiC) media separated by an air gap. The SiC media are photonically doped with gain and loss defects to achieve parity-time (PT) symmetry. The researchers demonstrate that when SiC operates as a practical epsilon-near-zero (ENZ) material with moderate optical loss, an exceptional point (EP) is formed in the PT-symmetric system. Importantly, they show that strong self-induced nonreciprocal transmission can be excited in this system due to the nonlinear Kerr effect at a frequency slightly shifted off the EP without breaking the PT-symmetric phase. The team observes that the transmittance from one direction becomes exactly unity while the transmittance from the other direction decreases to very low values. This high level of optical isolation allows for effective control of wave propagation. The proposed active nonlinear metamaterial surpasses the limitations of passive nonlinear nonreciprocal resonators enabling stronger nonreciprocity. The significant enhancement of electric field in the defects leads to an extreme asymmetric field distribution upon excitation from opposite incident directions which contributes to the strong self-induced nonreciprocal transmission observed in the system and reduces the required optical power to trigger this response. The findings of this research have various potential applications such as developing nonreciprocal ultrathin coatings to protect sources or sensitive equipment from external pulsed signals or using these advancements for circulators and isolators in controlling wave propagation. Overall, this study presents a novel approach to achieving strong self-induced nonreciprocal transmission using PT-symmetric epsilon-near-zero metamaterials offering valuable insights into designing efficient and practical devices for controlling wave propagation in various applications.