Zhongyin Xiao

Multi-band transmissions of chiral metamaterials based on Fabry-Perot like resonators.

In this paper, a multi-layered metallic structure is proposed, which consists of split-ring resonators on both sides of two dielectric substrates. Numerical results reveal that the structure realizes a high magnitude of 0.94, three bands and broadband (more than 8 GHz) asymmetric transmission for linearly polarized wave. These properties are not observed in previous works. In order to better know these transmission properties, the Fabry-Perot like resonance model has been introduced to analyze the enhancement mechanism of asymmetric transmission in the multi-layered structure. The physical mechanism of linearly polarized wave conversion and asymmetric transmission based on electric fields and currents distribution is also analyzed in detail, respectively.

Formation and conversion of defect centers in low water peak single mode optical fiber induced by gamma rays irradiation

The formation and conversion processes of defect centers in low water peak single mode optical (LWPSM) fiber irradiated with gamma rays were investigated at room temperature using electron spin resonance. Germanium electron center (GEC) and self-trapped hole center (STH) occur when the fibers are irradiated with 1 and 5 kGy cumulative doses, respectively. With the increase in irradiation doses, the GEC defect centers disappear, and new defect centers such as E′ centers (Si and Ge) and nonbridge oxygen hole centers (NBOHCs) generate. The generation of GEC and STH is attributed to the electron transfer, which is completely balanced. This is the main reason that radiation-induced attenuation (RIA) of the LWPSM fiber is only 10 dB/km at communication window. The new defect centers come from the conversion of GEC and STH to E′ centers and NBOHC, and the conversion processes cause bond cleavage, which is the root cause that the RIA of the LWPSM fiber significantly increases up to 180 dB/km at working window. Fu...

Gamma irradiation effect on Rayleigh scattering in low water peak single-mode optical fibers

The Rayleigh scattering loss in low water peak single-mode optical fibers under varying Gamma rays irradiation has been investigated. We observed that the Rayleigh scattering coefficient (CR) of the fiber is almost linearly increased with the increase of Gamma irradiation in the low-dose range (< 500 Gy). Based on the electron spin resonance (ESR) spectra analysis, we confirmed that the Rayleigh scattering mainly results from the irradiation-induced defect centers associated with electron transfer or charge density redistribution around Ge and O atoms. This work provides a new interpretation of the optical loss and reveals a new mechanism on irradiation influence on Rayleigh scattering.

Broadband and polarization-insensitive metamaterial absorber based on hybrid structures in the infrared region

Abstract In this work, a new type of metamaterial absorber is proposed in the infrared region. This structure consists of metal-dielectric-metal. But the difference is that a square groove in the dielectric has been dug, and replaced by a metal. The simulated results show that this structure can achieve a broadband absorption. And the absorption bandwidth can be realized from 60.5 to 115.5 THz when the absorption efficiency is larger than 90%. And this structure is polarization-insensitive for incident electromagnetic waves. In addition, the structure can also achieve better absorption effect for a large incident angle, especially for TM polarized wave. What is more, a remarkably enhanced bandwidth can be realized by using a metal to fill the square groove which is dug in the dielectric. To further explain the mechanism of high absorption, the distribution of the electromagnetic field and power loss density at the resonance frequencies are analysed. And these novel properties make the absorbers have many applications including sensor, cloaking, etc.

Dual-band cross polarization converter in bi-layered complementary chiral metamaterial

Abstract In this article, a new chiral metamaterial with giant optical activity (90°) around 225 and 285 THz has been proposed which can be acted as a dual-band cross polarization converter (CPC). During the frequency range of proposed CPC, the maximum transmission coefficient and cross polarization conversion efficiency are up to 0.55 and 0.998, respectively. Importantly, the corresponding ellipticities are almost zero at 225 and 285 THz.

Influence of Irradiation and Annealing on Structural Properties of the Optical Fiber Cladding Material

We experimentally investigate the influences of irradiation and annealing process on the microstructure properties of optical fiber cladding material. The electron spin resonance (ESR) results reveal that the defect concentration significantly decreases after silica fiber cladding material is irradiated by ã-rays with a successive thermal annealing process. Raman analysis show the irradiated microstructure of cladding material change little, after irradiation, which indicates that the three- and four-membered rings (3-MRs and 4-MRs) structures are stable. However, after thermal annealing process, Raman spectrum shows that 3-MRs and 4-MRs are reduced obviously, which means that the ring structures are broken after thermal annealing and new stable structures are formed. X-ray diffraction (XRD) also shows that slight crystallization occurs when the annealing temperature is equal to 1000°C. We conclude that Si-O bonds around 3-MRs and 4-MRs are easier to fracture, where color centers are formed. We also show the microstructure models explained by the theory of quantum chemistry.

Design of a broadband, wide-angle metamaterial absorber base on hybrid structure

Abstract In this paper, we presented and investigated a special metamaterial absorber to achieve broadband absorption. Firstly, we proposed a two-dimensional (2D) structure, which include a hybrid layer on the top, a dielectric layer in the middle, and a metal ground on the bottom. By the hybrid design on the top layer of the absorber, we achieved broadband absorption. The relative bandwidth is 22.57%. Furthermore, in order to improve the absorption bandwidth, we changed the absorber as a three-dimensional (3D) structure. The simulated results show that the absorber can be obtained a broadband absorption, the relative bandwidth up to 82.93%. Compared to the two-dimensional structure, it is clear that the three-dimensional structure has a better absorption. According to the effective medium theory, the relative impedance is calculated to explain the absorption mechanism. Finally, we believe it will have many potential applications in sensing, energy harvest and so on.

Broadband visible metamaterial absorber based on a three-dimensional structure

ABSTRACT In this paper, a broadband metamaterial absorber is successfully designed by a three-dimensional structure. And the three-dimensional absorber is just obtained by a two-dimensional structure which rotates 90°along x-axis. The simulated results show that the absorption of the three-dimensional metamaterial absorber is much better than the two-dimensional absorber. Moreover, the absorber is polarization-sensitive for the incident electromagnetic waves due to the asymmetry of the structure. Compared with the Y-polarization wave, the proposed absorber can realize broadband absorption with greater than 90% from 355.6 to 737.7 THz for X-polarized wave. Finally, based on the analysis of the electric field and surface current distributions, it can demonstrate that the localized surface plasmons and dipoles resonances will play an important role in the broadband absorption. And we believe that the metamaterial absorber will have many potential applications in emitter and energy harvesting.

Luminescence and energy transfer characteristics in silica optical fiber materials with cerium and terbium co-doping

A cerium (Ce) and terbium (Tb) co-doped silica optical fiber (CTDF) is fabricated by the powder-in-tube technique. Its luminescence and energy transfer characteristics are investigated. The experimental results show that a strong excitation peak at 252 nm appears for the Tb-doped fiber materials. Another excitation peak with a similar intensity at 305 nm appears for the CTDF rod. The emission of Tb3+ ions at 542 nm is efficiently excited at 305 nm after Ce3+ ions doping in the silica fiber core. Moreover, the photoluminescence decay of CTDF rod materials at 542 nm is longer than that of Tb-doped fiber materials, from 1709.21 to 2173.17 μs. These results indicate that an obvious energy transfer process from Ce3+ to Tb3+ ions are achieved. Then, an energy level scheme with a local structure model of CTDF is built. Furthermore, numerical simulation results indicate that dipole-dipole interaction is the most-likely energy transfer mechanism. It is significant for the fabrication of Ce/Tb co-doped green emitting fiber lasers and remote fiber-optic radiation dosimeters.

Tunable multiband band-stop filter based on graphene metamaterial in THz frequency

ABSTRACT In this paper, a tunable multiband band-stop filter based on single-layer and few-layer doped periodically graphene rings is designed at THz wavelength. The performance of the proposed structure is calculated by using the finite-difference time-domain method. The metamaterial structure is comprised of the concentric graphene ring resonators printed on substrate layer of silica medium. The multiband band-stop filter can be achieved by adjusting the numbers of graphene ring resonator. More importantly, a dynamically tunable filter can be designed by adjusting the applied voltage or chemical potential doping to manipulate graphene’s Fermi energy. The z-component electric field is investigated to explain the physical mechanism of the transmission. In addition, the proposed filter has the advantage of independence to polarization and insensitivity to the angles of the incident wave. Our design can have potential applications in various fields of tunable photonic devices, sensors and multi-band communication.