High tunability and sensitivity of 1D topological photonic crystal heterostructure

A modality to high tunability and sensing performance of one-dimensional (1D) topological photonic crystal (PC) heterostructure is realized based on a new mechanism through 1D topological PC. With inserting a defect aqueous layer as a sandwich between two 1D PCs, the transmittance gradually decreases with the increasing thickness of the defect layer. When the two layers of the topological heterostructure interface are replaced by the defect layer, the tunability, all sensing capabilities have been improved and the principle of topology is preserved. A topologically protected edge state is formed at the heterostructure interface with a highly localized electric field. For glucose sensing, high sensitivity S = 603.753 nm/RIU is obtained at the low detection limit of about DL = 1.22×10^(-4) RIU with high-quality factor Q = 2.33×10^4 and a high figure of merit FOM = 8147.814 RIU^(-1). Besides, the transmittance can be maintained more than 99% at low and/or high glucose concentrations, due to the coupling topological edge mode between defect mode and topological edge state. An excellent platform is examined for the design of a topological photonic sensor which is a flexible platform that can be used for any type of sensor solely by replacing the interface layers with the sensor materials. Thus, our results will promote the development of 1D topological photonic devices.

Tailoring Optical Bistability In Nonlinear Photonic Crystals Based on Metallic Nanoparticles And Graphene

In this work, we revisit the optical response of a one-dimensional photonic crystal consisting of graphene monolayers and a plasmonic nanocomposite as a defect layer in the structure. By taking advantage of the modified transfer matrix approach, the analytical solution of the light transmission and field distribution of the photonic crystal are evaluated. Besides, by considering one of the layers as a Kerr-nonlinear medium, we delve into optical bistability phenomenon in the model for two different cases. Our numerical results reveal that the proposed photonic crystal can enhance the field distribution and reduce the optical bistability’s threshold in comparison to the conventional photonic crystals. Furthermore, the optical bistable switch-up and switch-down thresholds of the proposed resonator can be tailored flexibly by plasmon-plasmon interactions in the defect layer. Finally, the electric field distribution amelioration and optical bistability by means of graphene layers in the structure are attainable. The influences of the parameters such as the graphene and the nanocomposite on the performance of OB are analyzed and compared in the two different cases. Therefore, present approach can lay the groundwork for designing highly sensitive surface plasmon resonance biosensors and switches where the proposed technique may find unprecedented capabilities.

Sensitivity Enhancement of an Optical Sensor Based on A Binary Photonic Crystal for The Detection of Escherichia Coli by Controlling the Central Wavelength and The Angle of Incidence

The detection process of Escherichia coli (E. coli) bacteria in drinking water is a global problem as they can lead to hazardous conditions in the human body. In this work, a one-dimensional binary photonic crystal with the structure air/(GaAs,SiO2)N/D/(GaAs,SiO2)N/glass is proposed as an optical sensor to detect E. coli bacteria, where D is the defect layer. Water and E. coli bacteria are treated as the defect layer. The sensing mechanism of the proposed detector is based on the refractive index difference between pure water and waterborne bacteria samples. The transmission spectra of the photonic crystal are investigated and the sensitivity to E. coli bacteria is calculated. The effects of the central wavelength and the angle of incidence on the sensitivity and sensor performance parameters are studied. It is found that the central wavelength increase can enhance the sensor sensitivity and most of the performance parameters. Increasing the incidence angle can improve the sensitivity and all the performance parameters such as full width at half maximum, quality factor, detection limit, sensor resolution, signal-to-noise ratio, dynamic range, detection accuracy and figure of merit.

Photonic Crystal Enhanced by Metamaterial for Measuring Electric Permittivity in GHz Range

The rise of broadband cellular networks and 5G networks enable new rates of data transfer. This paper introduces a new design to measure the permittivity in the GHz range of non-magnetic materials. We tested the proposed design with a wide range of materials such as wood, glass, dry concrete, and limestone. The newly proposed design structure has a maximum sensitivity of 0.496 GHz/RIU. Moreover, it can measure permittivities in the range from 1 up to 9. The main component of the designed structure is a defective one-dimensional photonic crystal with a unit cell consisting of metamaterial and silicon. In addition, we demonstrate the role of the metamaterial in enhancing the proposed design and examine the impact of the defect layer thickness on the proposed structure.

Tunable Temperature Characteristic of Terahertz Bragg Fiber Filled with Liquid Water

Hollow-core terahertz (THz) fibers have attracted a lot of research interest due to the low loss and easy inner modification with functional materials. Liquid water has unique properties in the THz region and has been widely investigated in THz emission, sensing, and devices. In this paper, a hollow-core THz Bragg fiber with a water defect layer is proposed. The finite element method is used to verify and analyze the tunable temperature characteristic of the water-filled THz fiber. The numerical analysis results show that the confinement loss and the low-frequency side of the dip near 0.5 THz can be controlled by the temperature of the liquid water. The temperature sensitivity of the THz fiber is obtained at 0.09614 dB·m−1/K at 0.45 THz with a high core power fraction up to 98%. The proposed THz fiber has potential applications in THz interaction with liquid and THz tunable devices.

Study Design of Optical Sensor 1D Photonic Crystal by Introducing Metal/Defect/Metal Multilayer Defect: Malaria Diagnosis

We introduce a defect layer between two metal layers at middle of a one-dimensional photonic crystal. This structure is used to study the tunable characteristic of proposed structure. The transmission, reflection and absorption are calculated using transfer matrix method. The influence of metal layer width, incident angle and defect layer refractive index has been investigated to analyze the tunable characteristic. The shifting of defect mode is improved with metal layer width and incident angle too. Due to metal layer, the localized surface plasmon wave causes decrease in transmission and appearance of absorption. For TE and TM polarization, the localized defect mode shows a blue shift with incident angle, but the transmission peak reduces with incident angle in TE polarization. Therefore, the proposed structure can be used as optical sensor with high sensitivity for malaria diagnosis compared with previous result.

Induced defect layer method to characterize the effect of fiber tow gaps for the laminates manufactured by automated fiber placement technique

Automated manufacturing defects are new types of composite structure defects induced during fiber deposition by robots. Fiber tow gap is one of the most probable types of defects observed in the Automated Fiber Placement (AFP) technique. This defect can affect the structural integrity of structures by reducing structural strength and stiffness. The effect of this defect on the mechanical response of the composite laminates has been investigated experimentally in the literature. However, there is still no efficient numerical/analytical method for damage assessment of composite structures with distributed induced gaps manufactured by the AFP technique. The present paper aims to develop the Induced Defect Layer Method (IDLM), a new robust meso-macro model for damage analysis of the composite laminates with gaps. In this method, a geometrical parameter, Gap Percentage (GP), is implemented to incorporate the effect of induced-gaps in the elastic, inelastic, and softening behavior at the material points. Thus, while the plasticity and failure of the resin pockets in conjunction with intralaminar composite damages can be evaluated by this method, the defective areas are not required to be defined as resin elements in the Finite Element (FE) models. It can also be applied for any arbitrary distributions of the defects in the multi-layer composite structures, making it a powerful tool for continuum damage analysis of large composite structures. Results indicate that the proposed method can consider the effect of gaps in both elastic and inelastic behavior of the composite laminate with defects. It also provides good agreement with the experimental results.