Defect Modes Research Articles

Temperature tunable Bragg transmission multichannel filters made of two quarter-wave stacks separated by defect layers

We report on simulated temperature-tunable single-channel/multichannel transmission filters with 0.37 nm/K shift in the peak wavelength is observed in the infrared region (1300 nanometers −1650 nanometers) using a one-dimensional photonic crystal structure. A single channel can be selected in the photonic bandgap region based on the thickness of the quarter wave stacks and temperature. The transmission coefficient of the transmitted defect modes is approximately the same as that required for telecommunication. For 20000 defect layers, 4000 channels were created with full width at half maximum of 0.7 picometers at the center wavelength of ∼1550 nm and channel separation of ∼0.18 nanometer between 1500 nanometers-1600 nanometers.

Enhanced piezoelectric energy harvesting based on sandwiched phononic crystal with embedded spheres

In recent years, metamaterial/ phononic crystal (PnC) based energy harvesters are gaining interest due to their excellent elastic wave manipulation and energy trapping capabilities. Here, we propose a novel PnC comprising of Tungsten Carbide (WC) spheres embedded in epoxy resin matrix. The sphere-epoxy composite is encapsulated by Aluminum (Al) holey structure and the device is sandwiched between two Al plates. Numerical analysis of band structure reveals a wide phononic band gap (BG) from 50.65 kHz to 71.12 kHz. These BGs can be engineered by varying geometric parameters of the unit cell viz., the radius of the sphere and thickness of Al plates. A point defect is introduced by removing the central sphere of the 5 × 5 PnC to facilitate the robust localization of evanescent wave defect modes within the bandgap. Moreover, it is observed that, by altering the radius of the defect sphere, the number of defect modes and their shift can be reconfigured. A PnC based energy harvester is implemented by attaching a piezoelectric disk (PZT-5H) onto the defect PnC just above the defect site. This arrangement of PZT disk converts the highly resonant mechanical defect mode into electrical energy, thereby allowing vibration energy harvesting. Finally, we show that the power enhancement can be achieved by ∼12 times with the proposed PnC compared to the bare Al block.

Tunable Fano resonance in coupled topological one-dimensional photonic crystal heterostructure and defective photonic crystal

In this paper, we theoretically investigate the transmission properties of a structure composed of a topological one-dimensional photonic crystal (1D PhC) heterostructure and a conventional 1D PhC containing indium-antimonide (InSb) as a defect layer using the transfer matrix method. The phenomenon of Fano resonance can be achieved by coupling the defect mode with the topological edge state mode, which is supported by the topological PhC. The numerical results show that a narrow Fano resonance is observed in the transmission spectrum of the structure in the presence of the external magnetic field applied to the InSb defect layer. The optical properties of the InSb defect layer, and, therefore, the Fano resonance, can be dynamically controlled by changing the applied external magnetic field. The results obtained with the proposed structure reveal that the magnetic field has the greatest influence on controlling the optical properties of the Fano resonance. These findings could be beneficial for optical devices such as optical filters, sensors, and optical switches.

Effective pressure sensor using the parity-time symmetric photonic crystal

Monitoring the variations in pressure, distribution, and the magnitude of the emitted gases at the ground surface is very important in different applications. Because of the parity-time symmetric mechanism, a novel one-dimensional photonic crystal as a pressure sensor is proposed. The transmittance spectra are calculated and analyzed using the transfer matrix method. The parity-time symmetric property amplifies the transmittance of the defect mode and gives an additional hand to enhance the magnification and performance of the sensor. The optimum conditions are the normal angle of incidence, defect layer thickness of 1400 nm, the porosity of the porous silicon layer of 80%, and macroscopic Lorentz oscillation intensity of 5 × 10-4. The results show that the position and amplitude sensitivities are 4.9 nm GPa−1 and 1844%/GPa. That means in such sensors, by altering pressure, the desired value of magnified transmittance and sensitivity can be achieved as required according to the optical communication devices. Therefore, the proposed device performs better with high precision and accuracy. Consequently, it is much more helpful in optical communication and optoelectronic devices.

Theoretical Demonstration of Tunable Multichannel Midinfrared Optical Filters for Infrared Spectroscopic Gas Detection

A theoretical demonstration of the multichannel midinfrared (MIR) optical filters is proposed, and even-numbered multichannel spectral transmission is obtained by adding 1-D Ge2Sb2Te5 (GST) grating defect layers in a 1-D photonic crystal (1DPhC), which can be attributed to the excitations of defect modes (DMs) and guided mode resonance (GMR). Moreover, the channel numbers of the proposed optical filter can be designed by controlling the number of GST grating layers, and active tunability of the multichannel MIR optical filter can be realized by controlling the GST phase transition. In addition, two theoretically designed examples of optical filters for nondispersive infrared (NDIR) sensing are given for characteristic absorption wavelength acquisitions in single- (CO) and multicomponent (CH4, CH2O, CO2, and CO) gas detections. Our findings may have potential applications in infrared spectroscopic gas detection, material characterization, and biochemical sensing.

Realization of the nonreciprocal thermal radiation by the front and back sides of the Weyl semimetal-dielectric multilayer structures

This work proposes the Weyl semimetal-dielectric multilayer structures (WDMSes), both sides of which can realize nonreciprocal thermal radiation. Utilizing the transfer matrix method, the absorptivity αq and emissivity eq are calculated in the mid-infrared wave range. The absorption can be attributed to the defect modes. For both sides of the WDMSes, it is found the nonreciprocity originates as the incident angle is around 15° and a wider incident angle tends to enhance it. By increasing the angle to 45°, the stronger nonreciprocal thermal radiation for the front side is revealed at the wavelength of 4.692 µm and 3.890 µm. In the same way, for the back side, it is displayed at the wavelength of 4.692 µm and 3.896 µm. The relevant factors including the temperature of the Weyl semimetal, the thickness of the dielectric layer unit, the thickness of the defect layer, and the period of the structure are discussed. They can affect the nonreciprocity, as well as shift the absorption and emission bands in the wave and angular range. This work can be applied to heat radiation transfer media, energy conversion devices, thermal storage and emitter, and so on.

Phononic Crystal Made of Silicon Ridges on a Membrane for Liquid Sensing.

We propose the design of a phononic crystal to sense the acoustic properties of a liquid that is constituted by an array of silicon ridges on a membrane. In contrast to other concepts, the ridges are immersed in the liquid. The introduction of a suitable cavity in the periodic array gives rise to a confined defect mode with high localization in the cavity region and strong solid-liquid interaction, which make it sensitive to the acoustic properties of the liquid. By using a finite element method simulation, we theoretically study the transmission and cavity excitation of an incident flexural wave of the membrane. The observation of the vibrations of this mode can be achieved either outside the area of the phononic crystal or just above the cavity. We discuss the existence of the resonant modes, as well as its quality factor and sensitivity to liquid properties as a function of the geometrical parameters. The performance of the proposed sensor has then been tested to detect the variation in NaI concentration in a NaI-water mixture.

Temperature Sensing Based on Defect Mode of One-Dimensional Superconductor-Semiconductor Photonic Crystals

Based on the transfer-matrix method, we theoretically explore the transmission and reflection properties of light waves in a one-dimensional defective photonic crystal composed of superconductor (HgBa2Ca2Cu3O8+δ) and semiconductor (GaAs) layers. The whole system is centrosymmetric and can generate a defect transmission peak in the photonic band gap. We study the effect of the temperature on the defect mode. Results obtained show that the defect mode shifts to the lower frequency regions as the value of the environmental temperature increases, and the resonance of the defect mode can be strengthened further as the number of periods increases. In addition, our findings reveal that the central wavelength of the defect mode increases with the increase in the environmental temperature and it presents a nearly linear relationship between the central wavelength of the defect mode and the temperature in cryogenic environments. Therefore, we can use the temperature response of the defect mode to detect the temperature. It is hoped that this study has potential applications for the development of cryogenic sensors with high sensitivity.

One-dimensional photonic crystal magnetic sensors based on incomplete surface defect patterns

We propose and study an innovative magnetic sensor of incomplete surface defect one-dimensional (1D) photonic crystal composed of magnetic fluid, SiO2, and TiO2 as defect layers. The magnetic fluid film covers the surface of the 1D photonic crystal, whereas the magnetic fluid penetrates into the array of circular holes with period ∧ inscribed on the dielectric layers of SiO2 and TiO2 to form the incomplete surface defect layer. The sensing characteristics of a 1D photonic crystal magnetic sensor (1D-PCMS) were analyzed using the theory of rigorous coupled wave analysis. The innovative use of the angular interrogation method in magnetic field detection has investigated the effect of defect layer structure parameters, optical dielectric loss on magnetic sensor sensitivity and quality factor at a fixed wavelength. This incomplete surface defect mode 1D-PCMS structure demonstrates the feasibility of scanning angular measurements of magnetic fields and provides a reference for future research on 1D-PCMS based on angular interrogation.

The role of the defect in photonic crystals based on WS2 or WSe2 monolayers: a vision on how to achieve high quality factor and wavelength adjustability in defect modes

The role of the defect in photonic crystals based on WS2 or WSe2 monolayers: a vision on how to achieve high quality factor and wavelength adjustability in defect modes

Enhanced the sensitivity of one-dimensional photonic crystals infiltrated with cancer cells

In this work, we use a one-dimensional photonic crystal as a biosensor composed of alternating GaAs and air layers. Within the cavity where they are infiltrated, the Normal, Jurkat, HeLa, PC-12, MDA-MB-231, and MCF-7 cells are bounded by layers of nanocomposite and graphene to increase biosensor sensitivity. The transmission spectrum was calculated using the transfer matrix method. We observed that, when the structural periodicity is broken, defect modes that characterize each cell are created. These defect modes move at a wavelength as the dielectric constant increases. Additionally, the separation between defect modes and bandwidth determines sensitivity, Q factor, and FOM, in which average values of 406.84 nm/RIU, 1765.53, and 535.44 were obtained, respectively, for normal light incidence. Regarding Transverse-Electric (TE) and Transverse-Magnetic (TM) polarization, the defect modes shift toward shorter wavelengths as the angle of incidence increases. For TE polarization, transmittance decreased and the distance between the modes increased. At a 50° angle, sensitivity, Q factor, and FOM increased up to 497.55 nm/RIU, 3182.02, and 1401.25, respectively. Conversely, at a 50° angle in TM polarization, sensitivity remained constant at a value of 407 nm/RIU, along with increased transmittance and decreased performance. Finally, sensitivity and performance were optimized by modifying the cavity thickness value at an incidence angle of 30° for TE polarization, and at an incidence angle of 10° for TM polarization. In both cases, the increased cavity thickness shifted the defect modes toward longer wavelengths while increasing sensitivity up to 495.75 nm/RIU for TE and 451.33 nm/RIU for TM.

Wide-angle high-efficiency absorption of graphene empowered by an angle-insensitive Tamm plasmon polariton.

In recent years, researchers utilized Tamm plasmon polaritons (TPPs) in conventional heterostructures composed of a metal layer, a dielectric spacer layer and an all-dielectric one-dimensional (1-D) photonic crystal (PhC) to achieve high-efficiency absorption of graphene. According to the Bragg scattering theory, photonic bandgaps (PBGs) in all-dielectric 1-D PhC strongly shift toward shorter wavelengths (i.e., blueshift) as the incident angle increases. Therefore, TPPs in conventional heterostructures also show strongly blueshift property. Such strongly blueshift property of TPPs greatly limits the operating angle range of the high-efficiency absorption of graphene. Herein, we realize an angle-insensitive TPP in a heterostructure composed of a metal layer, a dielectric spacer layer and a 1-D PhC containing hyperbolic metamaterial layers. Empowered by the angle-insensitive property of the TPP, we achieve wide-angle high-efficiency absorption of graphene. The operating angle range (A > 80%) reaches 41.8 degrees, which is much larger than those in the reported works based on TPPs and defect modes. Our work provides a viable route to designing cloaking devices and photodetectors.

Optical Properties of One‐Dimensional Photonic Crystal Composed of Superconductor and Dielectric Layers with Liquid Crystal Layer as Defect

In this article, the optical properties of 1DPC composed of superconductor and dielectric layer with an introduced defect layer of liquid crystal are discussed. To design the 1DPS, the study considers Bi-2223 of Bismuth Strontium Calcium Copper Oxide (BSSCO) and silica (SiO2) materials as superconductor and dielectric layers, and E7 liquid crystal (LC) as a defect layer. For the theoretical study of the considered periodic structure, transfer matrix method (TMM) is employed, which gives the transmittance and reflectance for the structure. The periodic structure shows tunable transmission and reflectance properties under variations of the temperatures of superconductor and LC and incident angle. The variations of temperatures of superconductor and LC show red and blue shifts in the defect mode peak, respectively. Also, the tuning of the photonic bandgap (PBG) with incident angle, in the three-dimensional (3D) reflectance, for both transverse electric (TE) and transverse magnetic (TM) modes, is discussed in the article. The PBG in TM polarization disappears at the incident angle nearly 50°, and reappears with further increase in the incident angle above 60°. Further, the defect mode always exhibits blue shift with increase in the incident angle in TE and TM mode both. This simulation work can be beneficial in analysis of dispersive media and tunable optical devices.

Transmission Properties of a One‐Dimensional Defective Photonic Crystal Structure of Air/Magnetized‐Cold‐Plasma

AbstractIn this paper, the transmission characteristics, of an asymmetric periodic structure of air/LHP‐MCP is considered as LHPPC, are determined. In this study, the same structure with symmetrically introduced defect layer of MCP, as (AB)N/2B(BA)N/2, under same configuration is also analyzed. The authors find that, with an increase in magnitude of magnetizing field, the transmittance in such PCs increase. The transmittance in defect‐introduced PC is low as compared to corresponding LHPPC without defect. It is investigated that the cutoff value of frequency (GHz) for transmission for the defective LHPPC decreases with an increase in magnetic field similar to those of the PC without defect. Here, the complete bandgap obtained at a higher frequency range in the spectra of the defective PC exhibits defect mode and disappears at B = −0.8T, which is disappearing at B = −0.6T in case of the PC without defect. It is demonstrated that both the PCs show broadband reflector behaviors at lower frequency range with low magnetic field, viz. B = −0.2T, while the impact of defect is to further reduce the transmission in MCP‐based PC, for chosen values of the magnetic field. The obtained results under this analysis may be referred in designing broadband reflectors as well as multichannel transmitters and high transmitter with low and high magnetic fields, respectively. The shifting in the cutoff frequency for transmission with magnetic field shows the applications of such PCs in switching devices.

Microwave Propagation Characteristics in Magnetized‐Cold‐Plasma‐Based Binary Photonic Crystal with Defect of MCP Layer

AbstractIn this communication, the TMM for the analysis of transmission characteristics of MCP based PCs is employed. The periodic structure of air/right‐hand‐MCP, in asymmetric form (AB)N, is considered as RHPPC. The transmission characteristics of the same structure are analyzed with symmetrically introduced defect layer of MCP for different values of the magnetizing field. It is observed that this binary RHPPC in both cases acts as good reflectors in low and high frequency ranges for low magnetic field between 0.4T to 1.2T; and the bandgaps vanish at higher magnetic field above 1.2T, in both types of PCs. Further, it is noticed that the transmittance in defect introduced PC is low in comparison to corresponding PC without defect, for a particular value of magnetic field up to 1.2T. The defective RHPPC exhibits defect modes in the bandgap regions. Hence, an increase in magnetic field decreases the bandgaps and consequently increases the transmission in both cases; while impact of defect is to reduce the transmission. The lowest reverse transmission peak for the defective PC obtained with the value of magnetic field from 2.0T to 2.4T shows more transmission as compared to that of the PC without defect. The insights of this comparative analysis can be used in designing tunable microwave transmitters.

Janus Metastructure Based on Magnetized Plasma Material with and Logic Gate and Multiple Physical Quantity Detection

AbstractIn this paper, a Janus metastructure (JMS) is proposed that can act both as a logic gate and detect multiple physical quantities. By adjusting the incident angle of electromagnetic waves, arranging the dielectrics asymmetrically, and using the anisotropy of the plasma, the Janus function can be obtained, which gives the metastructure a multiscale property. Sharp transmission peak (TP) is generated by located defect mode resonance. The AND logic gate on the positive and negative scales can be realized by judging the TP value. By locking the point frequency of the TP, the refractive index, magnetic field strength, incident angle, and plasma density can be detected simultaneously on the two scales in the GHz range, which is rarely studied. Good sensing performances are also owned, and the corresponding optimal sensitivities are 0.095 (2πc/d)/RIU, 9.42 × 10−3 (2πc/d)/T, 1.48 × 10−3 (2πc/d)/°, and 0.035 (2πc/d) m3/1019, respectively. Compared with the traditional sensors, the proposed JMS equipped with two scales not only can realize the logic gate but also measure multiple physical quantities, which has a certain application potential.

Realization of a novel multimode waveguide with photonic band gap hopping based on coupled-resonator optical waveguide theory

Traditionally, in the application of photonic crystals, defect modes are mostly introduced in the photonic band gap to realize high-performance waveguides, and electromagnetic waves beyond the photonic band gap cannot be controlled in photonic crystals. Here we demonstrated a kind of deep subwavelength quasi-photonic crystal waveguide, named 2D closed surface-wave photonic crystal, by combining a photonic crystal with a spoof surface plasmon polaritons-based metal–insulator–metal structure. The closed surface-wave photonic crystal waveguide can realize the introduction of the defect mode in the frequency band where the first-order dispersion curve of the surface-wave photonic crystals is located, instead of being limited to the frequency range of the photonic band gap of surface-wave photonic crystals. At the same time, we confirmed the correctness of the coupled-resonator optical waveguide theory under the conditions of the first-order mode and the multi-order mode based on the closed surface-wave photonic crystal guided-wave mechanism. We have verified our work in 80–130 GHz through experiments, theory, and simulation, which are consistent. The closed surface-wave photonic crystals can be used as a kind of highly integrated waveguide and multi-bandpass/band-elimination filter in integrated optical circuits, and can adjust the working frequency band at very low cost.

Double piezoelectric defects in phononic crystals for ultrasonic transducers

Significant prior research has explored elastic wave-energy localization via defect modes of phononic crystals (PnCs). The integration of defect-introduced PnCs and piezoelectric materials has paved the way for the development of new conceptual products for applications in energy harvesters, wave filters, and ultrasonic sensors. Recently, an attempt has been made to deviate from this paradigm and design an ultrasonic transducer that generates elastic waves. Unfortunately, previous work has been limited to a single-defect situation. Therefore, as an advanced approach, the present work aims to expand the PnC design space into double defects, which will make ultrasonic transducers useful at several frequencies. As a first step, this study targets longitudinal wave generation. To predict the wave-generation performance, a previous analytical model that was built for energy-harvesting purposes under a single-defect situation is modified to be suitable for the present wave-generation purpose under a double-defect situation. Moreover, two parametric studies are executed to analyze how the output responses change based on changes to the input voltage setting and the spacing between the double defects. We hope that these ultrasonic transducers could be potentially applicable for nondestructive testing in structural health monitoring and ultrasonic imaging in medical science.

Damage detection method based on defect mode for orthogonal grid stiffened panels

Orthogonal grid stiffened panels are very useful structures widely utilized in many engineering applications. The nondestructive testing and evaluation (NDT&E) methods for these structures are still limited due to the complex vibration modes induced by stiffeners distributed in two periodic directions. A novel method based on defect modes to localize multiple damage in orthogonal grid stiffened panels is proposed in this research. Instead of utilizing defect modes in periodic structures to control vibration or wave propagation, it is proposed to analyze the influence of defects on the dynamic response properties of orthogonal grid stiffened panels. The damage-related modes can then be used to identify multiple damage. The method is successfully verified both numerically and experimentally and shows great potential for broad engineering applications.

Probing Defects and Spin‐Phonon Coupling in CrSBr via Resonant Raman Scattering

AbstractUnderstanding the stability limitations and defect formation mechanisms in 2D magnets is essential for their utilization in spintronic and memory technologies. Here, defects in mono‐ to multilayer CrSBr are correlated with structural, vibrational, and magnetic properties. Resonant Raman scattering is used to reveal distinct vibrational defect signatures. In pristine CrSBr, it is shown that bromine atoms mediate vibrational interlayer coupling, allowing for distinguishing between surface and bulk defect modes. Environmental exposure is shown to cause drastic degradation in monolayers, with the formation of intralayer defects. This is in contrast to multilayers that predominantly show bromine surface defects. Through deliberate ion irradiation, the formation of defect modes is tuned: these are strongly polarized and resonantly enhanced, reflecting the quasi‐‐1D electronic character of CrSBr. Strikingly, pronounced signatures of spin‐phonon coupling of the intrinsic phonon modes and the ion beam‐induced defect modes are observed throughout the magnetic transition temperature. Overall, defect engineering of magnetic properties is possible, with resonant Raman spectroscopy serving as a direct fingerprint of magnetic phases and defects in CrSBr.