Exceptional Points in Non-Hermitian Photonic Crystals Incorporated With a Defect

We explored exceptional points (EPs) in one dimensional non-Hermitian photonic crystals incorporated with a defect. The defect was asymmetric with respect to the center. Two EPs could be derived by modulating the normalized frequency and the gain-loss coefficient of defect. The reflection coefficient complex phase changed dramatically around EPs, and the change in complex phase was π at EPs. The electric field of EPs was mainly restricted to the defect, which can induce a giant Goos–Hänchen (GH) shift. Moreover, we found a coherent perfect absorption-laser point (CPA-LP) in the structure. A giant GH shift also existed around the CPA-LP. The study may have found applications in highly sensitive sensors.

Download Full-text

Coherent Perfect Absorption Laser Points in One-Dimensional Anti-Parity–Time-Symmetric Photonic Crystals

Applied Sciences ◽

10.3390/app9132738 ◽

2019 ◽

Vol 9 (13) ◽

pp. 2738 ◽

Cited By ~ 6

Author(s):

Huiling Wang ◽

Weihao Kong ◽

Pu Zhang ◽

Zhongming Li ◽

Dong Zhong

Keyword(s):

Photonic Crystals ◽

Loss Factor ◽

Angular Frequency ◽

Sharp Change ◽

Perfect Absorption ◽

Reflection And Transmission ◽

Coherent Perfect Absorption ◽

Highly Sensitive ◽

Gain Loss ◽

Highly Sensitive Sensors

We investigate the coherent perfect absorption laser points (CPA-LPs) in anti-parity–time-symmetric photonic crystals. CPA-LPs, which correspond to the poles of reflection and transmission, can be found in the parameter space composed of gain–loss factor and angular frequency. Discrete exceptional points (EPs) split as the gain–loss factor increases. The CPA-LPs sandwiched between the EPs are proved to be defective modes. The localization of light field and the bulk effect of gain/loss in materials induce a sharp change in phase of the reflection coefficient near the CPA-LPs. Consequently, a large spatial Goos–Hänchen shift, which is proportional to the slope of phase, can be achieved around the CPA-LPs. The study may find great applications in highly sensitive sensors.

Download Full-text

Coherent perfect absorption in the one-dimensional non-magnetized plasma photonic crystals

Physica Scripta ◽

10.1088/1402-4896/ac3fd2 ◽

2021 ◽

Author(s):

Fupei Wu ◽

Hao Zhang ◽

Baofei Wan ◽

Haifeng Zhang

Keyword(s):

Photonic Crystals ◽

Optical Switching ◽

Absorption Efficiency ◽

Magnetized Plasma ◽

Light Modulation ◽

Perfect Absorption ◽

One Dimensional ◽

Coherent Perfect Absorption ◽

Plasma Photonic Crystals ◽

The One

Abstract Electromagnetic (EM) absorption is the basic characteristic of materials that plays an important role in many applications such as solar cells, EM radiation protection, and stealth technology. However, under normal circumstances, the traditional medium's absorption efficiency of EM waves is limited, but the designer can operate by adjusting the structure of the medium. In this paper, the coherent perfect absorption (CPA) is introduced in the one-dimensional (1-D) non-magnetized plasma photonic crystals. Under the premise that the selected material meets the conditions (appropriate thickness and dielectric constant), the absorption amplitude at the frequency point that meets the coherent absorption conditions is greatly improved. The results show that the forward and backward EM waves that meet the CPA conditions and propagate in PPCs can increase the absorption to 99.94% and change the phase difference of the two coherent beams to control the adjustment range of the absorption efficiency to 12.60%-99.94%. In addition, the effects of plasma and collision frequency on the absorption property, and the effects of the periodic constant of dielectric layers and plasma thickness on the frequency and amplitude of coherent absorption are also presented. It is foreseeable that the idea of tunability of light absorption in photovoltaic cells is proposed in this paper, and the application of absorbers in the field of optical switching and light modulation has been further expanded.

Download Full-text

The exceptional points of non-Hermitian optical systems: Scattering matrix definition, coherent perfect absorption, and lasing

10.1063/5.0031767 ◽

2020 ◽

Author(s):

Denis V. Novitsky ◽

Alexander S. Shalin ◽

Andrey V. Novitsky

Keyword(s):

Scattering Matrix ◽

Optical Systems ◽

Perfect Absorption ◽

Exceptional Points ◽

Coherent Perfect Absorption

Download Full-text

Reflection Enhancement and Giant Lateral Shift in Defective Photonic Crystals with Graphene

Applied Sciences ◽

10.3390/app9102141 ◽

2019 ◽

Vol 9 (10) ◽

pp. 2141 ◽

Cited By ~ 10

Author(s):

Dong Zhao ◽

Fangmei Liu ◽

Peng Meng ◽

Jie Wen ◽

Siliu Xu ◽

...

Keyword(s):

Photonic Crystals ◽

Interband Transition ◽

Single Layer ◽

Defect Layer ◽

Lateral Shift ◽

Single Layer Graphene ◽

Intraband Transition ◽

Highly Sensitive ◽

Highly Sensitive Sensors ◽

Periodic Number

This study investigates the reflectance of the defective mode (DM) and the lateral shift of reflected beam in defective photonic crystals incorporated with single-layer graphene by the transfer matrix method (TMM). Graphene, treated as an equivalent dielectric with a thickness of 0.34 nm, was embedded in the center of a defect layer. The reflectance of the DM was greatly enhanced as the intraband transition of electrons was converted to an interband transition in graphene. The reflectance of the DM could be further enhanced by increasing the Bragg periodic number. Furthermore, a large lateral shift of the reflected beam could also be induced around the DM. This study may find great applications in highly sensitive sensors.

Download Full-text

Unidirectional Invisibility Induced by Complex Anti-Parity–Time Symmetric Periodic Lattices

Applied Sciences ◽

10.3390/app9183808 ◽

2019 ◽

Vol 9 (18) ◽

pp. 3808 ◽

Cited By ~ 4

Author(s):

Hui Cao ◽

Dong Zhao ◽

Ming Fang ◽

Huang Guo ◽

Yonghong Hu ◽

...

Keyword(s):

Reflection Coefficient ◽

Parameter Space ◽

Frequency Band ◽

Angular Frequency ◽

Lateral Shift ◽

The Other ◽

Wide Frequency Band ◽

Highly Sensitive ◽

Highly Sensitive Sensors

Complex anti-parity-time symmetric periodic lattices, in a wide frequency band, can act as unidirectional invisible media. The reflection from one end is suppressed while it is enhanced from the other. Furthermore, unidirectional laser points (ULPs) which correspond to the poles of reflection from one end, arise in the parameter space composed of the permittivity and angular frequency. The phase of the reflection coefficient changes sharply near the ULPs. Subsequently, large lateral shift which is proportional to the slope of phase could be induced for the reflected beam. The study may find great applications in unidirectional invisibility, unidirectional lasers and highly sensitive sensors.

Download Full-text