Tailoring Eigenmodes at Spectral Singularities in Graphene-based PT Systems

Weixuan Zhang,Xiangdong Zhang,Tong Wu

doi:10.1038/s41598-017-11231-y

Weixuan Zhang, Xiangdong Zhang + Show 1 more

Open Access

https://doi.org/10.1038/s41598-017-11231-y

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Journal: Scientific Reports	Publication Date: Sep 12, 2017
Citations: 18	License type: open-access

Affiliation: Beijing Institute of Technology

Abstract

The spectral singularity existing in PT-synthetic plasmonic system has been widely investigated. Only lasing-mode can be excited resulting from the passive characteristic of metallic materials. Here, we investigated the spectral singularity in the hybrid structure composed of the photoexcited graphene and one-dimensional PT-diffractive grating. In this system, both lasing- and absorption-modes can be excited with the surface conductivity of photoexcited graphene being loss and gain, respectively. Remarkably, the spectral singularity will disappear with the optically pumped graphene to be lossless. In particular, we find that spectral singularities can exhibit symmetry-modes, when the loss and gain of the grating is unbalanced. Meanwhile, by tuning the loss (gain) of graphene and non-PT diffraction grating, lasing- and absorption-modes can also be excited. We hope that tunable optical modes at spectral singularities can have some applications in designing novel surface-enhanced spectroscopies and plasmon lasers.

Highlights

PT-symmetric systems built using plasmonic elements have attracted increased attention
When we change the real part of the surface conductivity of graphene to be negative (Re[σ/σ0] = −0.137, active, red dot line), the corresponding spectral singularity appears on the absorption-mode
In contrast to the previous method to control the near-field by modifying the geometrical parameters of the plasmonic structures or the surrounding dielectric environment, we can tune the near-field distributions by just varying the surface dynamic conductivity of graphene

Summary

Introduction

PT-symmetric systems built using plasmonic elements have attracted increased attention. We systematically investigate characteristics of the eigenmode at spectral singularity when the electromagnetic field, in terahertz (THz) regime, is incident on an optically pumped monolayer graphene underneath the one-dimensional gain-loss diffractive grating. Such diverse surface dynamic conductivity responses can be used to manipulate optical modes of spectral singularities in graphene-based PT-systems.

Results

Conclusion