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.

Detection of Reproductive Hormones in Females by Using 1D Photonic Crystal-Based Simple Reconfigurable Biosensing Design

In this manuscript, we have explored the photonic biosensing application of the 1D photonic crystal (PhC) (AB)NCDC(AB)N, which is capable of detecting reproductive progesterone and estradiol hormones of different concentration levels in blood samples of females. The proposed structure is composed of an air cavity surrounded by two buffer layers of material MgF2, which is sandwiched between two identical 1D sub PhCs (AB)N. Both sub PhCs are made up of alternate layers of materials, SiO2 and Si, of period 5. MATLAB software has been used to obtain transmission characteristics of the structure corresponding TE wave, only with the help of the transfer matrix method. The mainstay of this research is focused on the dependence of the intensity and position of the defect mode inside the photonic bandgap with respect to reproductive hormone concentrations in blood samples, change in the thickness of the cavity region and change in angle of incidence corresponding to TE wave only. The proposed design shows high sensitivity of 98.92 nm/nmol/L and 96.58 nm/nmol/L when the cavity of a thickness of 340 nm is loaded with progesterone and estradiol hormones of concentrations of 80 nmol/L and 11 nmol/L, respectively, at an incident angle of 20°. Apart from sensitivity, other parameters such as quality factor and figure of merit have also been computed to gain deep insight about the sensing capabilities of the proposed design. These findings may pave the path for the design and development of various sensing devices capable of detecting gynecological problems pertaining to reproductive hormones in females. Thus, the simple design and excellent performance makes our design most efficient and suitable for sensing applications in industrial and biomedical fields.

Photonic Crystals with a Defect Fabricated by Two-Photon Polymerization for the Infrared Spectral Range

One-dimensional photonic crystals composed of alternating layers with high- and low-density were fabricated using two-photon polymerization from a single photosensitive polymer for the infrared spectral range. By introducing single high-density layers to break the periodicity of the photonic crystals, a narrow-band defect mode is induced. The defect mode is located in the center of the photonic bandgap of the one-dimensional photonic crystal. The fabricated photonic crystals were investigated using infrared reflection measurements. Stratified-layer optical models were employed in the design and characterization of the spectral response of the photonic crystals. A very good agreement was found between the model-calculated and measured reflection spectra. The geometric parameters of the photonic crystals obtained as a result of the optical model analysis were found to be in good agreement with the nominal dimensions of the photonic crystal constituents. This is supported by complimentary scanning electron microscope imaging, which verified the model-calculated, nominal layer thicknesses. Conventionally, the accurate fabrication of such structures would require layer-independent print parameters, which are difficult to obtain with high precision. In this study an alternative approach is employed, using density-dependent scaling factors, introduced here for the first time. Using these scaling factors a fast and true-to-design method for the fabrication of layers with significantly different surface-to-volume ratios. The reported observations furthermore demonstrate that the location and amplitude of defect modes is extremely sensitive to any layer thickness non-uniformities in the photonic crystal structure. Considering these capabilities, one-dimensional photonic crystals engineered with defect modes can be employed as narrow band filters, for instance, while also providing a method to quantify important fabrication parameters.

Design and Optimization of a Novel SAW Gyroscope Structure Based on Amplitude Modulation with 1-D Phononic Crystals

Surface acoustic wave gyroscopes (SAWGs), as a kind of all-solid-state micro-electro-mechanical system (MEMS) gyroscopes, can work normally under extremely high-impact environmental conditions. Among the current SAWGs, amplitude-modulated gyroscopes (AMGs) are all based on the same gyro effect, which was proved weak, and their sensitivity and intensity of the output are both lower than frequency-modulated gyroscopes (FMGs). However, because FMGs need to process a series of frequency signals, their signal processing and circuits are far less straightforward and simple than AMGs. In order to own both high-sensitivity and simple signal processing, a novel surface acoustic traveling wave gyroscope based on amplitude modulation is proposed, using one-dimensional phononic crystals (PCs) in this paper. In view of its specific structure, the proposed gyroscope consists of a surface acoustic wave oscillator and a surface acoustic wave delay line within a one-dimensional phononic crystal with a high-Q defect mode. In this paper, the working principle is analyzed theoretically through the partial wave method (PWM), and the gyroscopes with different numbers of PCs are also designed and studied by using the finite element method (FEM) and multiphysics simulation. The research results demonstrate that under a 1 V oscillator voltage output, the higher sensitivity of −23.1 mV·(rad/s)−1 in the linear range from −8 rad/s to 8 rad/s is reached when the gyro with three PC walls, and the wider linear range from −15 rad/s to 17.5 rad/s with the sensitivity of −6.7 mV·(rad/s)−1 with only one PC wall. Compared with the existing AMGs using metal dots to enhance the gyro effect, the sensitivity of the proposed gyro is increased by 15 to 112 times, and the linear range is increased by 4.6 to 186 times, even without the enhancement of the metal dots.

Designing a phononic crystal with large-size defect to enhance elastic wave energy localization and harvesting

Phononic crystal (PnC) has been proved for its manipulation and amplification of elastic waves. Using this characteristic of PnC to assist energy harvesting has remarkable effect. Generally, defect occurs when unit cell in PnC is replaced by another cell with different geometric or material properties, the output electric power of piezoelectric energy harvesting (PEH) devices will be significantly enhanced. In this study, a cross hole-type PnC-assisted PEH device with a large-size defect is presented by replacing several adjacent multiple cells with other cells. It is found that multiple peak voltages can be created within BG and multimodal energy harvesting can be performed. Compared with the defect mode composed of a small-size defect, energy localization and amplification of the proposed PnC leads to substantially enhancement of harvesting power after tailoring geometric parameters of a PEH device. This work will be expected to design PnC-assisted PEH devices in a reasonable way.

High Sensitivity Terahertz Biosensor Based on Mode Coupling of a Graphene/Bragg Reflector Hybrid Structure

In this work, a high-sensitivity terahertz (THz) biosensor is achieved by using a graphene/Bragg reflector hybrid structure. This high-sensitivity THz biosensor is developed from the sharp Fano resonance transmission peak created by coupling the graphene Tamm plasmons (GTPs) mode to a defect mode. It is found that the proposed THz biosensor is highly sensitive to the Fermi energy of graphene, as well as the thickness and refractive index of the sensing medium. Through specific parameter settings, the composite structure can achieve both a liquid biosensor and a gas biosensor. For the liquid biosensor, the maximum sensitivity of >1000°/RIU is obtained by selecting appropriate parameters. We believe the proposed layered hybrid structure has the potential to fabricate graphene-based high-sensitivity biosensors.

Simulation Research on Blood Detection Sensing with Parity-Time Symmetry Structure

To realize the design of a medical sensor with excellent comprehensive performance indexes, herein, a plasma concentration sensing model satisfying the Parity-Time (PT) symmetric condition is proposed. In this paper, the transfer matrix method was used to simulate the transmittance spectrum of the structure, according to the amplification effect on defect mode transmission and various detection performance indexes of the structure. We numerically optimized the parameters of the structure, such as the number of PT-symmetry unit cell N, the sample layer thickness dD as well as the macroscopic Lorentz oscillation intensity α in the PT-symmetry unit cell. The calculation results demonstrate that when the sample concentration changes from 0 g/L to 50 g/L, the wavelength of defect peak shifts from 1538 nm to 1561 nm, and the average quality factor, sensitivity, average figure of merit, average detection limit and average resolution of the structure can reach 78,564, 0.4409 nm/(g/L) (or 227.05 nm/RIU), 11,515 RIU−1, 5.1 × 10−6 RIU and 0.038 g/L, respectively. Not only the sensitivity and resolution of the PT-symmetry structure are better than that of the similar sensors, but it also has excellent comprehensive detection performance, which indicates that the developed sensor can be used in high-precision biomedical detection devices.