2D Photonic Crystals Research Articles

Analysis of GaN-based 2D Photonic Crystal Sensor for Real-time Detection of Alcohols

The present research proposes an extensive assay of photonic band gap (PBG) characteristics for transverse electric field polarization in two-dimensional (2D) photonic crystal (PhC) structures, with a vision to sense different groups of alcohol like methanol, ethanol, propanol, butanol and phenol. The plane wave expansion (PWE) technique is implemented for realization of PBG in two types of lattice configurations such as square lattice and triangular lattice with circular air holes. Various structure parameters like radius of the circular air holes, lattice constant, nature of the background material, arrangement of air holes and period of air holes are meticulously optimized for envisaging a complete band gap. A variety of unpredicted trends are observed in the simulation outcomes, which include a substantial shift in band gap width, band gap size, reflected wavelength, reflected light intensity and transmitted light intensity for different types of alcohols. Also, the effect of air filling fraction on the band gap size has been investigated by selecting different radius of circular air holes. Apart from this, high sensitivity of 1645 nm/RIU and resolution of $$6.07\times {10}^{-5}$$ RIU is attained with the proposed structures, which pave the path for different bio-sensing applications.

Landau levels in strained two-dimensional photonic crystals

The principal use of photonic crystals is to engineer the photonic density of states, which controls light-matter coupling. We theoretically show that strained 2D photonic crystals can generate artificial electromagnetic fields and highly degenerate Landau levels. Since photonic crystals are not described by tight-binding, we employ a multiscale expansion of the full wave equation. Using numerical simulations, we observe dispersive Landau levels which we show can be flattened by engineering a pseudoelectric field. Artificial fields yield a design principle for aperiodic nanophotonic systems.

Light Propagation in an Imperfect 1D Photonic Crystal

The virtual crystal approximation is used for numerical simulation of a polariton spectrum transformation in 1D photonic crystal, consisting of alternating silicon and liquid crystal layers and randomly included admixture layers. The character of dependence of the band gap width and the refractive index upon the concentration of admixture layers is discussed. It is shown that the energy structure of the imperfect superlattice can be significantly altered by implantation of appropriate defect layers.

Analysis of a photonic crystal temperature sensor based on Z-shaped ring resonator

A 2D photonic crystal (PC) sensor based on optical filter has been designed using a PC ring resonator (PCRR). The sensor used a 2D-PCRR triangular lattice with circular silicon rods placed in air background. We employed a ring resonator with Z-shaped core in the investigated structure, which is designed as temperature sensor and investigated theoretically along with high quality factor, transmission and sensitivity parameters. For sensing analysis, the 2D finite-difference time-domain method and the plane-wave expansion approach have been applied. A temperature variation from 0 to 20 °C causes a defect mode shifting and the channel filter wavelength shift was used as sensing mechanism. Using the number of the functionalized rods N = 36 at the temperature of 5 °C, the quality factor, the temperature sensitivity, the refractive index sensitivity and the detection limit of the studied structure were found to be 57,104, 96 pm/°C, 400 nm/RIU and 6.16 × 10–6 RIU, respectively.

Properties of defect modes and band gaps of mirror symmetric metal-dielectric 1D photonic crystals

Inserting of any sort of irregularity in a photonic crystal (PC) with a perfect periodicity can produce defect modes. Great interest has been directed towards defect modes due to many potential applications. In this work, a binary PC consisting of silica (SiO2) and silver (Ag) is assumed. The PC is supposed to have a mirror symmetry with the structure (SiO2/Ag)N(Ag/SiO2)N, where 2 N is the number of periods of the PC. The transmission spectra of the PC are investigated in the visible and IR wavelengths. It is found that when the thickness of Ag layer increases, band gaps are broadened, more band gaps appear starting at low wavelengths and all these band gaps are shifted toward loner wavelengths. Defect modes appear at certain thicknesses of Ag, diminish gradually and then entirely disappear. When the incidence angle increases, band gaps are blue shifted in contrary to their behavior with the increase of the thickness of the metal and SiO2 layers.

Spectral Characterization of Mid-Infrared Bloch Surface Waves Excited on a Truncated 1D Photonic Crystal.

The many fundamental roto-vibrational resonances of chemical compounds result in strong absorption lines in the mid-infrared region (λ ∼ 2–20 μm). For this reason, mid-infrared spectroscopy plays a key role in label-free sensing, in particular, for chemical recognition, but often lacks the required sensitivity to probe small numbers of molecules. In this work, we propose a vibrational sensing scheme based on Bloch surface waves (BSWs) on 1D photonic crystals to increase the sensitivity of mid-infrared sensors. We report on the design and deposition of CaF2/ZnS 1D photonic crystals. Moreover, we theoretically and experimentally demonstrate the possibility to sustain narrow σ-polarized BSW modes together with broader π-polarized modes in the range of 3–8 μm by means of a customized Fourier transform infrared spectroscopy setup. The multilayer stacks are deposited directly on CaF2 prisms, reducing the number of unnecessary interfaces when exciting in the Kretschmann–Raether configuration. Finally, we compare the performance of mid-IR sensors based on surface plasmon polaritons with the BSW-based sensor. The figures of merit found for BSWs in terms of confinement of the electromagnetic field and propagation length puts them as forefrontrunners for label-free and polarization-dependent sensing devices.

Optimized bio-photonic sensor using 1D-photonic crystals as a blood hemoglobin sensor

In this paper, a blood hemoglobin sensor is designed and analyzed by using a defected one-dimensional photonic crystal (1DPhCs). A structure of a binary defected 1D-PC is proposed. The structure is optimized by considering the effect of the angle of incidence, the defect layer thickness, and the refractive index of the first layer. The average sensitivity of the optimized sensor (Si/SiO2)N/Dd/(Si/SiO2)N is about 1025 nm/RIU. We have used the transfer matrix method in our study by using the MATLAB code to achieve the present results.

Design of asymmetric transmission of photonic crystal heterostructure based on two-dimensional hexagonal boron nitride material

Two-dimensional (2D) hexagonal boron nitride (hBN) possesses many unique properties such as high mechanical strength and excellent chemical and thermal stability. The 2D hBN exhibits a wide bandgap in the UV region and optically-stable ultra-bright quantum emitters that make hBN a promising nanophotonic platform for quantum computing and information processing, especially in the visible wavelength range. Therefore, it is greatly important to build up different nanophotonic devices with different functionalities based on this material platform to achieve the integrated photonic chips. Among the devices, the integratable optical asymmetric transmission devices are important elements for functional quantum computing chips. Since hBN is a dielectric material, photonic crystal (PhC) structure is the most suitable in principle and allows on-chip integration with other photonic devices. In this study, we theoretically design an asymmetric transmission device based on 2D hBN PhC heterostructures in the visible wavelength range for the first time. Due to the relatively low refractive index of 2D hBN material (<i>n</i> < 2.4), we design a free-standing hBN PhC heterostructure to maximize the light trapping in the structure and minimize the propagation loss. The asymmetric transmission device is composed of two square-lattice 2D PhC structures, namely PhC 1 and PhC 2. We use the plane wave expansion method (PWM) to calculate the iso-frequency contours (EFCs) of the PhC structures to study the light propagation inside of the PhCs, which will propagate along the gradient of direction of the EFCs. We design the PhC structure in the way that the incident light beams from different angles can be self-collimated along the <i>Г-X</i> direction of the PhC 2 and coupled out. On the other hand, the backward incident light is blocked by the bandgaps of PhC 2. In this way, asymmetric optical transmission is achieved with high forward transmittance and contrast ratio. In addition, we further finely tune the structural parameters, including the lattice constant and column radius of the PhCs to optimize the performance by using the finite difference time domain (FDTD) method. The resulting 2D hBN PhC heterostructure achieves an asymmetric transmission in a wavelength range of 610–684 nm with a peak forward transmittance of 0.65 at a wavelength of 652 nm. Meanwhile, the backward transmittance is controlled to be 0.04. As a result, the contrast ratio can reach up to 0.95. The working bandwidth of the hBN PhC is 74 nm (<i>T</i><sub>F</sub> > 0.5). In addition, the designed asymmetric transmission device has a small size of 11 μm × 11 μm, thus it is suitable for on-chip integration. Our results open up possibilities for designing new nanophotonic devices based on 2D hBN material for quantum computing and information processing. The design principle can be generally used to design other photonic devices based on 2D hBN material.

Optimized high-speed all-optical 2-bit ADCbased on two-dimensional photonic crystal nanoresonators.

In the present paper, a new 2-bit analog-to-digital converter (ADC) was designed and simulated by using 2D photonic crystal (PC) structures to create a relatively faster and smaller structure. For this purpose, a PC structure with a square lattice and silicon rods in the air bed was used. In the proposed structure, a combination of an optical filter with a linear waveguide, optical nanoresonators, and interference effects was used to create a 2-bit ADC. To create a structure in optimal conditions with maximum output optical power, the size of nanoresonators was scanned to reach the best size. The proposed structure operated at the operating wavelength of 1550 nm with a response time of about 1.63 ps, a sampling rate of about 613 GS/s, and a resolution sampling rate product (RSRP) value of about 2453 ks. Additionally, the size of the structure was about 194µm2, which is small compared with other structures proposed in this field; it also enjoys high simplicity and flexibility like structures with other functions, including 4-bit converters. The amount of power used to create different logic states was at the rate of mW/µm2, which is much lower than the amount used in similar structures and is achieved using nonlinear effects and materials. Therefore, due to the excellent results obtained, this structure is recommended to be used in optical integrated circuits. The plane wave expansion method was used to extract the photonic bandgap, and the finite-difference time-domain method was used to obtain the results related to the output spectrum of the designed structures.

Photonic crystal-based optical sensor for two-phase liquid compounds

In this paper, an ultra-compact sensor based on a one-dimensional (1D) photonic crystal (PC) structure with alternative layers of TiO2 and MgF2 consisting a defect layer in the middle is investigated. Two-phase liquid compounds including heavy oil with various contents of water, ethanol with different contents of water, and sea water with different contents of salt are infiltrated into the defect layer and the reflection spectra are simulated. Simulation results based on the transfer matrix method (TMM) show that the defect mode appearing in the photonic band gap (PBG) of the PC shifts to longer wavelengths by increasing the refractive index of the defect layer. Using the Lichtennecher method, the best average sensitivities of S=0.0188 nm-1, S=0.2911 nm-1, and S=0.0426 nm-1 are obtained respectively for the heavy oil, ethanol, and seawater through which the sample content in each compound can be calculated.

1D porous silicon photonic crystals comprising Tamm/Fano resonance as high performing optical sensors

We theoretically discuss a new design for the sensing and detection of chemical and biomedical fluids based on the change in their indices of refraction in the refractive index range 1−1.5. The transfer matrix method in cylindrical coordinates and the Bruggeman's effective medium approximation represent the theoretical overview of our study. The metallic cap in front of a ternary porous silicon photonic crystal induces Tamm / Fano states inside the photonic band gap that take part of the resonant peaks in conventional defected PCs. Analysis shows that the spectral positions of these states are very sensitive to changes in refractive index of the void fluids. In particular, the proposed sensor could provide higher performance than many previous 1D photonic crystals sensors. At a void refractive index of 1.1, our design exhibits a sensitivity of 6770 nm/RIU and a quality factor of 662. Therefore, the detection and sensing procedures of chemical and biomedical fluids could be investigated in a rather much efficient, stable and novel technique that has not been applied before.

Model of thermo-optic nonlinear dynamics of photonic crystal cavities

The wavelength scale confinement of light offered by photonic crystal (PhC) cavities is one of the fundamental features on which many important on-chip photonic components are based, opening silicon photonics to a wide range of applications from telecommunications to sensing. This trapping of light in a small space also greatly enhances optical nonlinearities and many potential applications build on these enhanced light-matter interactions. In order to use PhCs effectively for this purpose it is necessary to fully understand the nonlinear dynamics underlying PhC resonators. In this work, we derive a first principles thermal model outlining the nonlinear dynamics of optically pumped silicon two-dimensional (2D) PhC cavities by calculating the temperature distribution in the system in both time and space. We demonstrate that our model matches experimental results well and use it to describe the behavior of different types of PhC cavity designs. Thus, we demonstrate the model's capability to predict thermal nonlinearities of arbitrary 2D PhC microcavities in any material, only by substituting the appropriate physical constants. This renders the model critical for the development of nonlinear optical devices prior to fabrication and characterization.

Functionalized Mesoporous Photonic Crystal Film for Ultrasensitive Visual Detection and Effective Removal of Mercury (II) Ions in Water

AbstractMercury ion (Hg2+) contamination is a worldwide serious environment problem; exploring smart sensing and adsorption materials are urgently demanded for Hg2+ monitoring and removal. Herein, a simple 1D photonic crystal to first ever feature capabilities of visually quantitative determination and effective adsorption toward Hg2+ is facilely constructed by integrating a specifically designed thiourea‐functionalized nanocopolymer layer with a mesoporous TiO2 layer. Based on strong chelation and porous structure, Hg2+ is easily adsorbed on the copolymer and triggers vertically volumetric shrinkage, resulting in highlighted wavelength blue‐shifts and color changes in a broad Hg2+ level scope. Utilizing the adsorption characteristic, Hg2+ existing in aqueous media can be effectively removed by the photonic film with a remarkable uptake capacity of 739.6 mg g−1. This portable nanolayered film exhibits full regeneration, facile recovery, desirable selectivity toward Hg2+, and shields interference from other metal ions, which enables future application for environmental determination and remediation. Furthermore, a novel nanopolymer‐based two‐regime Hg2+‐capturing mechanism is first revealed by quartz crystal microbalance with dissipation monitoring, providing valuable references for future relevant adsorption researches.

Theoretical Analysis on Operation Speed of the Circular Defect in 2D Photonic Crystal (CirD) Laser

Herein a circular defect in a 2D photonic crystal (CirD) laser for wavelength division multiplexing (WDM) optical communications is theoretically analyzed. By coupling CirD lasers to a waveguide, a huge communication capacity can be expected. For example, if high‐speed, 50 Gbps laser operations are successfully achieved, WDM devices with 20 CirD lasers could achieve a communication capacity of 1 Tbps. Based on finite‐difference time‐domain (FDTD) simulation results, in this study, both current‐output and high‐frequency characteristics are investigated by solving 2D rate equations, revealing that an excessively high‐quality factor in laser cavities reduces the relaxation‐oscillation frequency. When the photon lifetime is 2 ps, which corresponds to a quality factor of ≈3000, a small threshold current of 5 μA and a high relaxation‐oscillation frequency of 40 GHz can be simultaneously obtained. These results suggest the potential of developing a WDM device using CirD lasers.

All-optical 1 × 2 decoder based on the self-collimated beam method in 2D photonic crystals

The design, analysis, and simulation of a 1 × 2 decoder based on self-collimated beams was the aim of this work. The proposed structure consists of two-dimensional (2D) photonic crystals with their silicon rods in air. The device, of a relatively simple structure with a footprint of 228.71 μm2, comprises two inputs (I and Iref) and three outputs (Q1, Q2, and QI). It, furthermore, contains two beam splitters, produced by point defects. 2D Finite Difference Time Domain (FDTD) and Plane Wave Expansion (PWE) codes have been used for the simulation. Contrast ratio of 2.02 dB and a bit rate of 2.8 Tb/s were obtained for this device - potential candidate for all-optical digital integrated circuits.

Ultracompact all-optical full adders using an interference effect based on 2D photonic crystal nanoring resonators

Given the special place of hybrid logic circuits such as all-optical full adders in next-generation digital systems, a new kind of these structures using two-dimensional (2D) photonic crystals (2D-PC) is designed and simulated herein. The proposed structure is made of a hexagonal nanoring resonator (NRR), a coupling rod, and several waveguides. In this all-optical full adder, the mechanism of the interference effect in the PCs is used to simplify and minimize the structure. To make the structure flexible, the radius of the dielectric rod in the whole structure and the NRR are considered based on a lattice constant of 0.2a and 0.04a, respectively. The structure is operated at a wavelength of 1550 nm, considering the value of the power entering the waveguides and that exiting the Carry and Sum ports. To analyze the all-optical full adder, the plane-wave expansion method and finite-difference time-domain method are applied respectively to calculate the bandgap diagram and obtain the transmission and propagation of the optical field. In the proposed structure, the contrast ratio at the Carry and is been investigated in a unique and novel way, yielding values of 10.68 and 9.03 dB, respectively. In addition, the maximum and minimum response time for the Carry and Sum are obtained as 1.6 and 0.75 ps, respectively. The total footprint of the structure is about 183 µm2. Due to its ultracompact size, low power consumption, fast response time, and simple structure, this all-optical full adder is suitable for use in low-power optical integrated circuits.

Stretchable Freestanding Films of 3D Nanocrystalline Blue Phase Elastomer and Their Tunable Applications

AbstractGiven that it is a potential medium for 3D manipulation of photons in the forward‐looking technology of quantum optics, nonlinear optics, electronics, nanomaterials, and bionics, 3D photonic crystal (PhC) is a promising material of strategic significance and has great impact on scientific development. Blue phase (BP), a liquid crystalline mesophase with unique nanoscaled 3D PhC features, has been shown to contain significant potential values in fundamental studies and technological applications. However, thus far, the environmental stability of BP devices remains a puzzling issue of material exploitation. Therefore, in this study, stretching‐tunable BP elastomer (BPE) photonic bandgap (PBG) free‐standing films are fabricated via full photopolymerization. The BPE films exhibit benefit‐specific features, including sharp PBG with high reflectivity and flexible tunability in the visible region, high thermal stability, and good mechanical ductility and resistance in chemicals. These properties are attributed to the pre‐developed, fully‐reactive mesogenic materials employed, which show BP states in a wide temperature range, including room temperature. Additionally, mirrorless laser applications with flexible tunability are also realized in this study. The freestanding BPE film can be used as a prototype instrumentality to promote the future development of multifunctional intelligent applications in lasers, sensors, displays, intelligent lightings, lidars, micro‐robots and antennas.

Wannier-function expansion of localized modes in 1D photonic crystals without inversion symmetry

The localized modes of one-dimensional photonic crystals without inversion symmetry are calculated by using linear combinations of Wannier functions. A closed form is given for the phase of the Bloch function leading to maximally localized Wannier functions. The defect consists of changing the refractive index of one layer in a single unit cell. The results for the frequencies and magnetic-field profiles of the localized modes are found in good agreement with calculations based on the transfer-matrix method. The need for maximally localized Wannier functions is discussed.

Magnetically controllable transmission spectrum of a 1D photonic crystal with a graphene defect layer in infrared region

Magneto-optical properties of a one-dimensional (1D) photonic crystal with a graphene defect layer is investigated. It is shown that the steady-state behavior of the medium completely depends on the intensities of magnetic and coherent coupling fields. By proper chose of the controllable parameters, it is found that the absorption spectrum of 1D photonic crystal can be adjusted easily. In addition, by controlling the magnetic field and Rabi-frequencies of applied lights, the transmitted and reflected light pulses at the infrared region can be tuned. The effect of magnetic and coupling fields on the transmission and reflection properties of the laser pulse at $$\lambda_{0} = 9\;\upmu\hbox{m}$$ of the medium is also studied. It is found that optical bistability in reflection and output fields can be controlled by applying the magnetic and coupling fields. The proposed model may provide some new possibilities for technological applications in optoelectronics, solid-state quantum information science and systems, due to vast applications in signal processing.

Investigation of optical and physical property in opal films prepared by colloidal and freeze-dried microspheres

Nowadays, the application of colloidal crystals as a photonic crystal template to prepare invers opal structures has been considerable in developing biosensors. The particle size distribution and polydispersity index (PDI) of polymer microspheres are highly important physical characteristics in optical properties of prepared opal films for invers opal sensors. In this study, the freeze-drying (lyophilization) effect was investigated in two different types of polymer microspheres, including polymethylmethacrylate (PMMA) and polystyrene (PS) synthesized with soap-free and surfactant agent methods with various diameters. The microspheres and three-dimensional (3D) photonic crystals (PC) opal films grown using vertical deposition method were fabricated and characterized using FTIR, DLS, SEM, and UV–vis spectral measurements. The particle sizes, PDI, SEM images and optical spectra of colloidal and freeze dried microspheres were compared. The freeze-drying process resulted in particle size and PDI increase in DLS analyses. The opal films prepared by colloidal microspheres had a more uniformity. Freeze-drying did not have significant effects on morphology of microspheres, but led to a wider stop bandwidth in the optical measurements of opal films in comparison with opal films prepared by colloidal microspheres.