Type II Perfect Absorption and Amplification Modes with Controllable Bandwidth in PT-Symmetric/Traditional Bragg Grating Combined Structures

TL;DR

This paper uncovers Type II perfect absorption and amplification modes in PT-symmetric and traditional Bragg grating structures, enabling controllable bandwidths and novel nonreciprocal optical behaviors for versatile photonic devices.

Contribution

It introduces the concept of Type II modes in optical systems and demonstrates their realization in combined PT-symmetric/traditional Bragg gratings, expanding the understanding of perfect absorption and amplification.

Findings

Type II modes appear along the real frequency axis at any frequency.

Exotic nonreciprocal absorption and amplification behaviors are observed.

Structures with controllable bandwidths for perfect absorption and amplification are proposed.

Abstract

We reveal previously unnoticed Type II perfect absorption and amplification modes of optical scattering system. These modes, in contrast to the counterparts in recent works [Phys. Rev. A 82, 031801 (2010); Phys. Rev. Lett. 106, 093902 (2011).] which could be referred as Type I modes, appear at a continuous region along the real frequency axis with any frequency. The Type II modes can be demonstrated in the PT-symmetric/traditional Bragg grating combined structures. A series of exotic nonreciprocal absorption and amplification behaviours are observed in the combined structures, making them have potential for versatile devices acting simultaneously as a perfect absorber, an amplifier, and an ultra-narrowband filter. Based on the properties of Type II modes, we also propose structures with controllable perfect absorption and amplification bandwidth at any single or multiple wavelengths.