Photonic Band Gap Region Research Articles

Data analysis on the three defect wavelengths of a MoS2-based defective photonic crystal using machine learning

To reduce the dimension of optoelectronic devices, recently, Molybdenum disulfide (MoS2) monolayers with direct bandgap in the visible range are widely used in designing a variety of photonic devices. In these applications, adjustability of the working wavelength and bandwidth with optimum absorption value plays an important role. This work proposes a symmetric defective photonic crystal with three defects containing MoS2 monolayer to achieve triple narrowband defect modes with wavelength adjustability throughout the Photonic Band Gap (PBG) region, 560 to 680 nm. Within one of our designs remarkable FWHM approximately equal to 5 nm with absorption values higher than 90% for the first and third defect modes are achieved. The impacts of varying structural parameters on absorption value and wavelength of defect modes are investigated. Due to the multiplicity of structural parameters which results in data plurality, the optical properties of the structure are also predicted by machine learning techniques to assort the achieved data. Multiple Linear Regression (MLR) modeling is used to predict the absorption and wavelength of defect modes for four datasets based on various permutations of structural variables. The machine learning modeling results are highly accurate due to the obtained R2-score and cross-validation score values higher than 90%.

Ultra-compact dual-purpose photonic crystal slab waveguide for both generating and isolating optical frequency comb

In this article, we present a novel approach to achieve a highly compact Si3N4 photonic crystal waveguide by incorporating air holes. This structure is developed in two functional applications that simultaneously perform the functions of generating optical frequency combs and demultiplexing them. The presence of air holes enhances control and precision in the dispersion engineering process. At the same time, the light conduction, based on the refractive index contrast between the core and cladding, along with the conduction occurring in the photonic bandgap region of the structure, leads to enhanced trapping of light within the core of the structure. As a result, a nonlinear coefficient of 4.2 m-1W−1 is obtained, which originates from the small effective mode area of 0.67 µm2. By employing four-wave mixing, a total of 40 comb lines are generated with a frequency spacing range of 10 GHz, 50 GHz, 60 GHz, and 100 GHz over a 6 mm length waveguide. The same waveguide structure is also developed for demultiplexing the comb lines, with four filters at the end which, individually extract the optical combs possessing wavelengths of 1317.8 nm, 1318.5 nm, 1319.2 nm, and 1319.9 nm. This demultiplexer has a Q-factor, average transmission efficiency, channel spacing, and spectral linewidth of 7209.35, 99.2 %, 0.7 nm, and 0.185 nm, respectively. The suggested design can significantly advance integrated photonic circuits, optical communications, and remote sensing applications requiring simultaneous information delivery, such as remote surgical operations and sensing, because of its substantial compactness.

Exploring the potential of broadband Tamm plasmon resonance for enhanced photodetection.

Tamm plasmon polaritons (TPPs) have emerged as a promising platform for photodetector applications due to their strong light-matter interaction and potential for efficient light absorption. In this work, a design for a broadband photodetector (PD) based on the optical Tamm plasmon (OTS) state generated in a periodic metal-semiconductor-distributed Bragg reflector (DBR) geometry is proposed. The transfer matrix method (TMM) was used to study the propagation of electromagnetic waves through the proposed structure. By exciting the structure with incident light and analyzing the electric field profile within the multilayer structure at the resonant wavelength, we observe a distinctive electric field distribution that indicates the presence of Tamm plasmon modes. A comparative study was conducted to investigate the optical properties of a photodetector in the near-infrared (NIR) range by varying parameters such as thickness. By optimizing the thickness, we successfully achieved a broadband photoresponse in the photodetector, with a maximum responsivity of 21.8mA/W at a wavelength of 1354nm, which falls within the photonic bandgap region. FWHM was found to be 590nm for the responsivity spectrum. The geometry also presents maximum absorption with FWHM calculated to be about 871.5nm. The proposed geometry offers a broadband photoresponse, which is advantageous for the advancement of Tamm-based detector technologies. The ability to detect light over a wide operation range makes this mechanism highly beneficial for various applications.

Incident-side-dependent mirror based on 1D photonic crystals containing VO2 nanoparticles

The optical properties of an incident-side-dependent mirror based on a one-dimensional photonic crystal composed of nanocomposite layers containing vanadium dioxide nanoparticles were investigated theoretically using the transfer matrix method in the near-infrared spectral range. The influence of the incident angle and filling fraction of the vanadium dioxide nanoparticles on the reflectance and transmittance of the structure were studied. We found that the mirror is an incident-side-dependent reflector with nearly zero transmittance in the photonic bandgap regions. The incident-side-dependent properties of the mirror are more pronounced when the vanadium dioxide nanoparticles are in their metal phase. In addition, the mirror is a perfect reflector for incoming rays from one side and a perfect absorber for incoming rays from the opposite side. Such temperature-controlled and incident-dependent mirrors may find application in the design of various intelligent windows.

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.

Performance analysis of the salinity based on hexagonal two-dimensional photonic crystal: computational study

We have designed a unique structure for a liquid sensor based on two-dimensional PCs with a triangular lattice constant in the periodicity by drilling a hexagonal cylinder in a dielectric host material. Using the COMSOL multiphysics approach, we investigated the given structure and sensing performance based on the finite element method. We will optimize two-dimensional hexagonal photonic crystals to localize the photonic band gap region in the mid and far infra-red frequency range, as water is a good absorber for this range of frequencies. Then, we inject the central hexagonal cylinder with saline water and calculate the sensor parameters for different values of the refractive index of saline water at different frequencies related to photonic band gaps. We could reach the optimum conditions of the salinity sensor as the half diagonal of the hexagonal shape (R) = 500 nm, the perpendicular distance between the two diagonal hexagonal (D) = 250 nm, and the number of periods (N) = 5, which gives a high efficiency with sensitivity (S) = 525 nm/RIU, figure of merit (FOM) = 80.7 RIU−1, and quality factor (Q) = 375. The effects of structural characteristics on sensing performance are investigated, with new approaches for improving salinity sensors proposed. Furthermore, traditional salinity sensors may be replaced by the proposed method in the photo-sensing application, which is simple and practical for use in the thermal desalination techniques.

Study of photonic band gap robustness in disordered polymer photonic crystals under hydrostatic pressure

Transmission properties of light through disorder polymeric photonic crystals have been studied. The photonic crystals made of polymeric multilayers with Gaussian distribution of layer thickness are found to exhibit robust photonic bandgap (PBG). The transmission characteristics of different random structures starting from periodic to gradually perturbed structures have been systematically investigated. The numerical examples illustrate that the photonic structure can sustain its PBG for a large range of disorder up to σ = 100 nm, which is nearly equal to 15% of the layer thickness calculated from the quarter wavelength condition for a normal incidence of light. It also quantitatively demonstrates the average transmission of the PBG region is becomes flatter due to the random nature of the structure. The proposal provides that the polymeric photonic crystal may be employed for potential applications for robust integrated photonic devices and optical communication systems.

Terahertz Band Communications With Topological Valley Photonic Crystal Waveguide

The sixth generation (6 G) communication standard is expected to include support for very-high data rates (over 100 Gbit/s) and device electronics will require processors with on-chip communications able to support such high bandwidths. Although the terahertz band possesses ample bandwidth, conventional THz waveguides suffer from high bending losses and are sensitive to process defects. The recent revelation of the topological valley photonic crystal (VPC), which exhibits near zero-loss bends, zero back-scattering and zero junction-area, holds much promise for future high speed inter-device communications. Low dispersion in the photonic bandgap region as the number of bends increase is demonstrated through simulation and experiment of the transmission and group delay characteristics. Through comprehensive communications experiments we demonstrate online results below the forward error correction level including an 108-Gbit/s bit rate using multi-level modulation for a 10 mm straight VPC waveguide and a 62.5-Gbit/s bit-rate for a ten sharp bended structure.

Hybrid all-optical infrared metal-insulator-metal plasmonic switch incorporating photonic crystal bandgap structures

A novel hybrid all-optical infrared switch based on metal-insulator-metal plasmonic and one dimensional photonic crystal structures is introduced in this paper. A photonic crystal lattice composed of two different (low and high refractive index) Kerr materials is located at the center of the switch. Two plasmonic metal-insulator-metal waveguides are used to transfer the data signal. Also, two dielectric waveguides are used as input and output pump ports. The existence of two separate paths for data and pump signals results in good isolation between such signals. The photonic crystal lattice creates a photonic bandgap region with sharp transmission edges in the data signal path. The created edges in data signal path can be used for the switching mechanism. The proposed structure can operate as an all-optical switch using different Kerr materials. The benefits of the proposed switch are having isolated signal and control ports and also its versatile topology. The switch can easily be redesigned and adapted with different Kerr materials for different applications. Furthermore, since a hybrid photonic crystal-plasmonic topology is used, it benefits both from the advantages of plasmonic and PhC structures. Based on the mentioned advantages, the proposed switch can be used as a basis to design other complex optical circuits.

Photonic bandgaps engineering in double graded hyperbolic, exponential and linear index materials embedded one-dimensional photonic crystals

We present the structuring of different double graded-index materials in the form of one-dimensional (1D) photonic crystals (PCs) for highly efficient light trapping and controlling photonic devices in terms of tuned and controlled photonic bandgap (PBG) performances. Considered 1D graded photonic crystal (GPC) structures are stacked of hyperbolic, exponential, and linear double graded index layers. In the graded index layers, the refractive indices vary in hyperbolic, exponential, and linear fashions as a function of the layer thickness. These configurations show that the operating frequencies and the number of PBGs can be tuned by controlling layer thickness, grading profiles, and grading parameters of the constituted graded layers. The changes in the grading profiles of the graded layers modulate the operation frequencies and also the number of PBGs. We also found that the operating frequencies and bandwidth of PBGs can be tuned by changing the values of initial and final refractive indices of the graded layer. Therefore, the desirable PBG regions and bandwidths can be achieved and controlled by selecting appropriate parameters of the systems. Results can be implemented to design tunable reflectors, multi-channel filters, sensors, and optical detectors. Also, this work may provide an understanding of the effect of different double graded-index materials on PBG characteristics in the GPCs.

Analysis of Bragg fiber waveguides having a defect layer for biosensing application

A novel hollow core Bragg fiber waveguides having a defect layer are proposed and analyzed theoretically for sensing application. Matching the electric and magnetic fields at various interfaces, a relation between fields of first layer with final layer has been stabilized; hence, the equations for reflectance and transmittance of proposed structure are derived. Due to periodicity of concentric cylindrical structure, a perfect photonic band gap is observed in considered wavelength range. The presence of defect layer in cylindrical periodic structure shows a peak corresponding to defect mode in perfect photonic band gap region. The full width at half maxima of this peak depends on the periodicity of the cladding layers. Also, the spectral position and shift of peak of defect mode depend on the angle of incidence of light, refractive index of core material and design wavelength of structure. Therefore, it is more appropriate to consider this peak of defect mode as sensing signal instead of considering whole photonic band gap as sensing signal.

Excellent Quality Factor Ultra-Compact Optical Communication Filter on Ring-Shaped Cavity

Abstract In this paper, we propose a high-quality factor (QF) ultra-compact structure for designing all optical filter based on two dimensional (2D) photonic crystals that can operate in third communication window range (1550 nm). The simulation results calculated by using 2D finite difference time domain (FDTD) method and photonic band gap (PBG) region are calculated by plane wave expansion (PWE) method. The average transmission efficiency, average QF and optical full width at half maximum (FWHM) bandwidth more than 95 %, 4300 and 0.4 nm obtained, respectively. The value of QF for the proposed structure is a major QF for ring resonator-based filters. We studied the effect of changing the air background to liquid crystal (LC) surrounding the dielectric rods. Results showed that by increasing LC refractive index (n) peak of wavelengths red shifted. The footprint of proposed filter is 160 ${{\mu}}{{\rm{m}}^{\rm{2}}}$ which make the proposed structure promising candidate for optical integrated circuits.

Voltage-tunable pass band in cylindrical multilayered structure containing PMMA and 0.67PMN–0.33PT single crystal as a defect layer

In present paper, an inline optical demultiplexer through cylindrical multilayered structure having a cavity of Poly-methyl methacrylate surrounded with single crystal 0.67PMN–0.33PT is presented. The required transmission of the proposed structure is obtained by transfer matrix method using cylindrical coordinate system. It is observed that the multilayer cylindrical structure is able to provide the photonic band gap, where groups of wavelengths are stopped from propagation through the waveguide. The insertion of cavity in considered structure also provides a pass band in the photonic band gap region. The 0.67PMN–0.33PT crystal in the present structure is used to control the thickness of cavity by applying an external DC voltage. Hence, the obtained shift of pass band is approximately 6 nm/V in the proposed structure.

Safe and simple detection of sparse hydrogen by Pd-Au alloy/air based 1D photonic crystal sensor

A simple integrated hydrogen sensor using Pd-Au alloy/air based one dimensional photonic crystal with an air defect layer is theoretically modeled. Structural parameters of the photonic crystal are delicately scaled to generate photonic band gap frequencies in a visible spectral regime. An optimized defect thickness permits a localized defect mode operating at a frequency within the photonic band gap region. Hydrogen absorption causes modification in the band gap characteristics due to variation of refractive index and lattice parameters of the alloy. As a result, the transmission peak appeared due to the resonant defect state gets shifted. This peak shifting is utilized to detect sparse amount of hydrogen present in the surrounding environment. A theoretical framework is built to calculate the refractive index profile of hydrogen loaded alloy using density functional theory and Bruggeman's effective medium approximation. The calculated refractive index variation of Pd3Au alloy film due to hydrogen loading is verified experimentally by measuring the reflectance characteristics. Lattice expansion properties of the alloy are studied through X-ray diffraction analyses. The proposed structure shows about 3 nm red shift of the transmission peak for a rise of 1% atomic hydrogen concentration in the alloy.

Investigation Effects of Filling Rate on the Bands Gaps of Two Dimensional Photonic Crystals

The influences of the filling rate on the photonic band gap properties of the two dimensional hex photonic crystals are investigated using the finite-difference time-domain method. When the filling rate f varies from 0.227 to 0.735 reminding the refractive index as 5, the number of the photonic band gaps decreases from 5 to 2 bands, the width of the photonic band gap between the transmit peaks become narrow; but for larger f >0.445, the transmit intensity is very low in the high frequency region, it can be consider as a larger photonic band gap region, the onset of this larger photonic band gap shifts toward low frequency. At the same time, the onset transmit peaks shift toward low frequency also. The simulation results show that the photonic band gap can be effectively changed by the filling rate.

An optical demultiplexer based on photonic crystal ring resonators

A 4-channel wavelength division demultiplexer based on photonic crystal ring resonators suitable for WDM applications is proposed in this paper. For performing the demultiplexing task, we used four resonant rings with different geometrical parameters. A square lattice of two dimensional photonic crystal structure composed of dielectric rods was used as fundamental structure for designing the demultiplexer, which has two photonic band gap regions. The first band gap covers the optical communication wavelengths. For this demultiplexer, the minimum transmission efficiency is more than 92% and average channel spacing is 3.2nm.

Performance enhancement of aqueous dye-sensitized solar cells via introduction of a quasi-solid-state electrolyte with an inverse opal structure

To bridge the gap in the power conversion efficiencies (PCEs) of aqueous and organic-solvent based dye-sensitized solar cells (DSCs), water-based electrolytes are exploited for a new role to enhance DSC performance. Hydrogels with an inverse opal structure (IOS) were prepared using various SiO2 opal films as templates. The gels were further used as a host for preparing fully water-based gel electrolytes with a photonic band gap (PBG) on which quasi-solid-state DSCs were fabricated. The current–voltage curves indicate that PCEs for the gel electrolytes with the IOS are superior to those for the reference gel electrolyte without the structure, and a maximum average PCE of 1.80% is achieved for the gel electrolytes with the PBG around 624nm, which is approximately 22% higher than the value for the reference gel electrolyte (1.48%). The action spectra reveal increases of the incident photo-to-current conversion efficiencies both in and beyond the PBG region, indicating that the back reflection and scattering of photons as a result of the IOS are significant for light-harvesting and PCE enhancement. The electrochemical impedance spectra further demonstrate that the IOS lowers the Warburg impedance and the resistance at the TiO2/electrolyte interface compared to the reference gel electrolyte. Furthermore, the durability of DSCs is improved by the gel electrolyte/TiO2 interface and the IOS.

Theoretical modelling of one dimensional photonic crystal based optical demultiplexer

An optical demultiplexer through one-dimensional Si–SiO2 photonic crystal structure in the presence of air cavity with a single crystal PMN-0.38PT material is presented. The transmittance of this structure is obtained using the transfer matrix method. The transmittance of this structure shows a sharp passband in the band gap region. It is observed that by introducing PMN-0.38PT layer in both sides of the air cavity, the existing band gap region of Si–SiO2 structure is slightly increased. Here, PMN-0.38PT material is working as a tunable element for passband. By applying some external potential on PMN-0.38PT crystal, the thickness of cavity layer can be tuned and the passband can be placed at any desired wavelength in the band gap region. Since the photonic band gap region contains a range of wavelengths which are not allowed to pass through the structure can be considered as a multiplex signal for the proposed demultiplexer. Therefore, any optical signal that lies in the band gap region of the structure can be separated into its components as a pass band. Hence, the proposed structure will work as an optical demultiplexer.

Analysis of Asymmetric Cantor Set Multi-Layered Structure

The word fractal is derived from the latin word fractus , meaning broken. In more scienti c terms, fractal is used to describe geometries that present selfsimilar patterns, such as the small patterns are replicas of the large ones [1]. Fractal theory is applied to a wide range of areas including chemistry, biology, physics and engineering. In electromagnetics, fractals have been used to produce antennas [2], optical devices [3 5] and nanoparticles [6]. In particular, one-dimensional structures such as the Cantor set can be easily constructed and has been used to create broadband devices and enhancing nonlinear effects. The Cantor set has a Hausdor dimension of log (2)/log (3) [1]. A standard Cantor set is created by initially removing the middle third of a segment, creating a Cantor set of order 1. The next order is obtained by removing the middle third of the rst and third remaining segments the procedure could be, in principle, repeated at exhaustion. On the other hand, photonic crystals have been used in a wide variety of applications in ltering, sensors, lasers and multiplexing [7 17]. Photonic crystals are periodic structures of high refractive index contrast (e.g. GaAs and air): in a certain wavelength range (photonic bandgap region), light cannot propagate through the structure. In addition to producing re ectors that are used in lasers [10] and optical lters, defects introduced in the photonic crystal lattice can be used to create microcavities and waveguides. In fact, photonic crystal waveguides can exhibit very interesting properties such as very low group velocities. In this paper, we analyze one-dimensional photonic crystal structures that are based on the Cantor set structures: we modify the traditional Cantor set structure by adding asymmetries in the formation of the Cantor set and study the re ectivity properties of these photonic

A polymer gel electrolyte with an inverse opal structure and its effects on the performance of quasi-solid-state dye-sensitized solar cells

To make the use of dye-sensitized solar cells (DSCs) practical, improvements in their light harvesting and power conversion efficiencies (PCEs) are needed. Hybrid polymer gels with an inverse opal structure (IOS) are prepared using various SiO2 opal films as templates and subsequent template etching. The polymer gel is further used as a host to prepare gel electrolytes with a photonic band gap (PBG), based on which quasi-solid-state DSCs are fabricated. The current–voltage curves indicate higher PCEs for the gel electrolytes with IOS than for reference gel electrolytes. A maximum average PCE of 3.85% is achieved for the gel electrolytes with a PBG around 690 nm, which is ca. 10% higher than the value for the reference gel electrolyte (3.48%). The action spectra reveal increases in the incident photo-to-current conversion efficiencies in and/or away the PBG region, indicating the significance of IOS for light-harvesting and PCE enhancement by back scattering and reflection of light. The electrochemical impedance spectra further demonstrate that the gel electrolytes with IOS have a lower Warburg impedance value than the reference gel electrolyte, which may also have contributed to the observed PCE enhancement. Besides, the IOS is found to give more stable performance of DSCs.