Width Of Photonic Band Gap Research Articles

Tunability and Sensing Properties of Plasmonic/1D Photonic Crystal

Gold/one-dimensional photonic crystal (Au/1D-PC) is fabricated and applied for sensitive sensing of glucose and different chemical molecules of various refractive indices. The Au layer thickness is optimized to produce surface plasmon resonance (SPR) at the right edge of the photonic band gap (PBG). As the Au deposition time increased to 60 sec, the PBG width is increased from 46 to 86 nm in correlation with the behavior of the SPR. The selectivity of the optimized Au/1D-PC sensor is tested upon the increase of the environmental refractive index of the detected molecules. The resonance wavelength and the PBG edges increased linearly and the transmitted intensity increased nonlinearly as the environment refractive index increased. The SPR splits to two modes during the detection of chloroform molecules based on the localized capacitive coupling of Au particles. Also, this structure shows high sensitivity at different glucose concentrations. The PBG and SPR are shifted to longer wavelengths, and PBG width is decreased linearly with a rate of 16.04 Å/(μg/mm3) as the glucose concentration increased. The proposed structure merits; operation at room temperature, compact size, and easy fabrication; suggest that the proposed structure can be efficiently used for the biomedical and chemical application.

Modelling defect cavities formed in inverse three-dimensional rod-connected diamond photonic crystals

Defect cavities in 3D photonic crystal can trap and store light in the smallest volumes allowable in dielectric materials, enhancing non-linearities and cavity QED effects. Here, we study inverse rod-connected diamond (RCD) crystals containing point defect cavities using plane-wave expansion and finite-difference time domain methods. By optimizing the dimensions of the crystal, wide photonic bandgaps are obtained. Mid-bandgap resonances can then be engineered by introducing point defects in the crystal. We investigate a variety of single spherical defects at different locations in the unit cell focusing on high-refractive-index-contrast (3.3:1) inverse RCD structures; quality factors (Q-factors) and mode volumes of the resonant cavity modes are calculated. By choosing a symmetric arrangement, consisting of a single sphere defect located at the center of a tetrahedral arrangement, mode volumes < 0.06 cubic wavelengths are obtained, a record for high-index cavities.

Full photonic band gap properties of plasma photonic crystals with triangular structure

In this study, we analyse full photonic band gap (PBG) properties of two-dimensional plasma photonic crystals (PCs) with triangular lattice, composed of anisotropic tellurium rods with different geometrical shapes immersed in plasma background. Using the finite-difference time-domain method, we discuss the maximization of the full PBG width as a function of tellurium rods parameters with different shapes and orientations. The numerical results show that our proposed structures represent significant large full PBGs in comparison to previously studied plasma PCs.

Effect of shape of scatterers and plasma frequency on the complete photonic band gap properties of two-dimensional dielectric-plasma photonic crystals

In this study, we analyze complete photonic band gap properties of two-dimensional dielectric-plasma photonic crystals with triangular and square lattices, composed of plasma rods with different geometrical shapes in the anisotropic tellurium background. Using the finite-difference time-domain method we discuss the maximization of the complete photonic band gap width as a function of plasma frequency and plasma rods parameters with different shapes and orientations. The numerical results demonstrate that our proposed structures represent significantly wide complete photonic band gaps in comparison to previously studied dielectric-plasma photonic crystals.

Combining complementary multiple bandgaps in one-dimensional plasma photonic crystal heterostructures

A single bandgap overlapping scheme is often used to enlarge the photonic bandgap (PBG) range in cascaded or hetero one-dimensional photonic crystal (1D PC) structures. In this paper, we design an optimized one-dimensional plasma photonic crystal (1D PPC) heterostructure based on the idea of combining complementary multiple PBGs to enlarge the PBG range. The flexibility of the PBG of a 1D PPC, caused by the frequency-dependent dispersive properties of plasma, is helpful for generating and combining multiple bandgaps. The obtained omni-directional photonic bandgap (ODPBG) width for the 1D PPC heterostructure is dramatically enhanced compared with that of a single 1D PPC alone and is much larger than that of 1D PC heterostructures described in the previous works. Further study shows that the PPC heterostructures are more suitable than other heterostructures (such as a 1D PC heterostructure or heterostructures composed of a 1D PPC and 1D PC) for combining complementary PBGs. The ODPBG ranges for 1D PPC heterostructures can be further extended by adjusting the parameters of the plasma to allow more complementary PBGs to combine with each other.

Optical filters using Cantor quasi-periodic one dimensional photonic crystal based on Si/SiO2

Quasi-periodic one-dimensional Cantor photonic crystals are elaborated by depositing alternating silicon and silica Si/SiO2 layers by radiofrequency magnetron sputtering technique with cold plasma. Transmittance and reflectance spectra of these quasi crystals exhibit a large photonic band gap in the infrared range at normal incidence which is well reproduced by a theoretical model based on the transfer matrix method. The obtained wide photonic band gap reveals the existence of permitted modes depending on the nature and characteristics of the built in system which can constitute optical windows. This effect can be a good alternative for the design of flexible filters used in many areas of applications such as telecommunication and optoelectronic devices.

Fabrication and characterization of two‐dimensional cubic AlN photonic crystal membranes containing zincblende GaN quantum dots

AbstractWe successfully developed a process to fabricate freestanding cubic aluminium nitride (c‐AlN) membranes containing cubic gallium nitride (c‐GaN) quantum dots (QDs). The samples were grown by plasma assisted molecular beam epitaxy (MBE). To realize the photonic crystal (PhC) membrane we have chosen a triangular array of holes. The array was fabricated by electron beam lithography and several steps of reactive ion etching (RIE) with the help of a hard mask and an undercut of the active layer. The r/a‐ ratio of 0.35 was deter‐ mined by numerical simulations to obtain a preferably wide photonic band gap. Micro‐photoluminescence (µ‐PL) measurements of the photonic crystals, in particular of a H1 and a L3 cavity, and the emission of the QD ensemble were performed to characterize the samples. The PhCs show high quality factors of 4400 for the H1 cavity and about 5000/3000 for two different modes of the L3 cavity, respectively. The energy of the fundamental modes is in good agreement to the numerical simulations. (© 2015 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Miniaturized ultra-low loss subwavelength waveguide at terahertz frequency

Compact low-loss terahertz waveguides are crucial in integrating the terahertz devices in the newly emerging field of terahertz photonics. One of the promising structures used for this purpose are photonic crystal waveguides. However, device compactness is limited due to diffraction. This study deals with the possibility of going beyond the diffraction-limited property of a photonic crystal. We demonstrate, numerically, terahertz wave-guiding with up to subwavelength confinement factor of λ2/ (mode surface) = 306 in a 2D structure consisting of square lattice of ionic cylinders in an air matrix. The total loss can be further mitigated due to an increase of spectral width of photonic band gap in a dispersive structure compared to that of an otherwise non-dispersive structure. According to the results, the square-lattice geometry supports TE-polarized guided modes with higher confinement factor compared with that of TM-polarized guided modes.

Slow Light in Square-Lattice Chalcogenide Photonic Crystal Holey Fibers

Slow light in square-lattice chalcogenide photonic-crystal (PC) holey fibers with uniform longitude geometry are proposed and theoretically investigated. By using the planewave-expansion method, a largest normalized complete 2-D photonic bandgap (CPBG) width of about 7.4% is found in an optimized connected-rod square-lattice chalcogenide PC, and the CPBG remains open with a refractive-index contrast as low as 2.48:1. We then consider the PCs as cladding layers to form holey fibers, and group indices up to several hundreds are predicted.

Photonic bandgap compensation and extension for hybrid quasiperiodic heterostructures

Based on the idea of multiple photonic bandgap (PBG) overlapping for a one-dimensional photonic crystal heterostructure, a novel hybrid quasiperiodic heterostructure is proposed to enlarge the omnidirectional photonic bandgap (OPBG). The heterostructure is formed by combining Fibonacci and Thue-Morse quasiperiodic structure. The results show that the OPBG of the heterostructure is enlarged obviously, which increases about three times compared with that of Fibonacci quasiperiodic structure, and twelve times compared with that of Thue-Morse quasiperiodic structure. The influences of structural parameters, such as period number and generation number, on PBGs of Fibonacci and Thue-Morse quasiperiodic structure are studied respectively. The results show that the parameters have little effects on PBG widths of the two quasiperiodic structures. The influences of the refractive indexes and thickness values of the high and low refractive index materials on OPBG of the heterostructure are also investigated. The results show that the OPBG of the heterostructure can be further broadened by increasing the refractive index ratios and thickness values of the high and low refractive index materials. The reason why the quasiperiodic structure can easily realize the multiple band gap overlapping is analyzed by comparing the bandgap properties of periodic structure. The number of PBGs of the quasiperiodic structure in the same wavelength range is more than that of the periodic structure. Moreover, with the increase of generation number of the quasiperiodic structure, due to the occurrence of PBG split, the number of PBGs increases obviously, and each PBG width is less than that of the periodic structure. Owing to this kind of PBG characteristic of the quasiperiodic structure, the heterostructure formed by cascading the two quasiperiodic structures is more prone to realizing the multiple PBG overlapping than other heterostructures, thus more easily achieving the expansion of OPBG. These results lay the design foundation for the compensation and broadening of the more complex bandgap structure.

Omnidirectional photonic band gap in magnetron sputtered TiO2/SiO2 one dimensional photonic crystal

One dimensional photonic crystal (1DPC) of TiO2/SiO2 multilayer has been fabricated by sequential asymmetric bipolar pulsed dc magnetron sputtering of TiO2 and radio frequency magnetron sputtering of SiO2 to achieve wide omnidirectional photonic band in the visible region. The microstructure and optical response of the TiO2/SiO2 photonic crystal have been characterized by atomic force microscopy, scanning electron microscopy and spectrophotometry respectively. The surface of the photonic crystal is very smooth having surface roughness of 2.6nm. Reflection and transmission spectra have been measured in the wavelength range 300 to 1000nm for both transverse electric and transverse magnetic waves. Wide high reflection photonic band gap (∆λ=245nm) in the visible and near infrared regions (592–837nm) at normal incidence has been achieved. The measured photonic band gap (PBG) is found well matching with the calculated photonic band gap of an infinite 1DPC. The experimentally observed omnidirectional photonic band 592–668nm (∆λ=76nm) in the visible region with band to mid-band ratio ∆λ/λ=12% for reflectivity R>99% over the incident angle range of 0°–70° is found almost matching with the calculated omnidirectional PBG. The omnidirectional reflection band is found much wider as compared to the values reported in literature so far in the visible region for TiO2/SiO2 periodic photonic crystal.

Unfolding the band structure of non-crystalline photonic band gap materials.

Non-crystalline photonic band gap (PBG) materials have received increasing attention, and sizeable PBGs have been reported in quasi-crystalline structures and, more recently, in disordered structures. Band structure calculations for periodic structures produce accurate dispersion relations, which determine group velocities, dispersion, density of states and iso-frequency surfaces, and are used to predict a wide-range of optical phenomena including light propagation, excited-state decay rates, temporal broadening or compression of ultrashort pulses and complex refraction phenomena. However, band calculations for non-periodic structures employ large super-cells of hundreds to thousands building blocks, and provide little useful information other than the PBG central frequency and width. Using stereolithography, we construct cm-scale disordered PBG materials and perform microwave transmission measurements, as well as finite-difference time-domain (FDTD) simulations. The photonic dispersion relations are reconstructed from the measured and simulated phase data. Our results demonstrate the existence of sizeable PBGs in these disordered structures and provide detailed information of the effective band diagrams, dispersion relation, iso-frequency contours, and their angular dependence. Slow light phenomena are also observed in these structures near gap frequencies. This study introduces a powerful tool to investigate photonic properties of non-crystalline structures and provides important effective dispersion information, otherwise difficult to obtain.

Study of bandgap characteristics of three-dimensional photonic crystal with typical structures

The aim of this study was to investigate the bandgap characteristics of three-dimensional photonic crystals of SIC, GaP, InP, GaAs, InAs, InSb, HgTe, and HgSe materials with typical structures under the following different conditions: diamond, face-centered cubic (fcc), and wood. Based on the plane wave expansion method, the influence of factors such as the dielectric constant, density on the upper and lower boundary, and width on the bandgap characteristics of three-dimensional photonic crystals was studied, in addition to the influence of factors such as the filling ratio and the radius of the ball on the bandgap variation in three-dimensional photonic crystals. The results show that the bandgap width of diamond and fcc structures can be improved by increasing the dielectric constant and density. However, the bandgap width of wood structures decreases, as they have wider photonic bandgaps when the filling rate is 0.325 and the ball radius is highly symmetrical. These results provide the theoretical basis for the design of three-dimensional photonic crystal devices.

Photonic band gaps of two-dimensional square-lattice photonic crystals based on 8-shaped scatters

A novel photonic crystals (PhC) based on 8-shaped scatters with two-dimensional (2-D) square-lattice is presented. By employing the MIT photonic bands (MPB), the relationship between the structural parameters of the PhC and the properties of photonic band gaps (PBG) are investigated. The calculation results of 8-shaped scatters with 2-D square-lattice demonstrate that the reduction of scatters’ symmetry can produce larger number of PBG and broaden the width of PBG only for TM mode, and reversely for TE mode. The peculiarity would meet the distinguish employment of different mode. By optimizing the structural parameters, the maximum absolute PBG 0.1028(ωa/2πc) at R=0.3, ɛr=11.56, θ=45° is obtained and six absolute PBGs is got at R=0.3, θ=115°, ɛr∈[32.3, 33.5].

Temperature-tunable lasing in negative dielectric chiral nematic liquid crystal**Project supported by the National Natural Science Foundation of China (Grant No. 61378042), the Outstanding Young Scholars Growth Plans of Colleges and Universities in Liaoning Province, China (Grant No. LJQ2013022), the Science and Technology Research of Liaoning Province, China (Grant No. L2010465), the Open Funds of Liaoning Province Key Laboratory of Laser

In this work, negative dielectric nematic liquid crystal SLC12V620-400, chiral dopant S811, and laser dye DCM are used to prepare dye-doped chiral nematic liquid crystal laser sample. In order to investigate temperature-tunable lasing in negative dielectric chiral nematic liquid crystal, we measure the transmission and lasing spectrum of this sample. The photonic band gap (PBG) is observed to red shift with its width reducing from 71.2 nm to 40.2 nm, and its short-wavelength band edge moves 55.3 nm while the long-wavelength band edge only moves 24.9 nm. The wavelength of output laser is found to red shift from 614.4 nm at 20 °C to 662.8 nm at 67 °C, which is very different from the previous experimental phenomena. The refractive indices, parallel and perpendicular to the director in chiral nematic liquid crystal have different dependencies on temperature. The experiment shows that the pitch of this chiral nematic liquid crystal increases with the increase of temperature. The decrease in the PBG width, different shifts of band edges, and the red shift of laser wavelength are the results of refractive indices change and pitch thermal elongation.

Investigation of defect cavities formed in three-dimensional woodpile photonic crystals

We report the optimisation of optical properties of single defects in three-dimensional (3D) face-centred-cubic (FCC) woodpile photonic crystal (PC) cavities by using plane-wave expansion (PWE) and finite-difference time-domain (FDTD) methods. By optimising the dimensions of a 3D woodpile PC, wide photonic band gaps (PBG) are created. Optical cavities with resonances in the bandgap arise when point defects are introduced in the crystal. Three types of single defects are investigated in high refractive index contrast (Gallium Phosphide-Air) woodpile structures and Q-factors and mode volumes ($V_{eff}$) of the resonant cavity modes are calculated. We show that, by introducing an air buffer around a single defect, smaller mode volumes can be obtained. We demonstrate high Q-factors up to 700000 and cavity volumes down to $V_{eff}<0.2(\lambda/n)^3$. The estimates of $Q$ and $V_{eff}$ are then used to quantify the enhancement of spontaneous emission and the possibility of achieving strong coupling with nitrogen-vacancy (NV) colour centres in diamond.

Theoretical Investigation of Transmission and Dispersion Properties of One Dimensional Photonic Crystal

In this work, we demonstrate via numerical simulation the general design for one dimensional photonic crystal (1D- PC). In the design procedure, the transfer matrix method and Bloch theorem are used to determine the transmission coefficient and dispersion relation of (1D- PC) structure for both TE (transverse electric) and TM (transverse magnetic) modes. Results obtained showing the effect of the filling factor as well as the incident angle on the photonic band gap width. The analysis is carried out using MATLAB software tool. The accuracy of the analysis is tested by comparing the computed results with measurements published data.

Topology optimization of simultaneous photonic and phononic bandgaps and highly effective phoxonic cavity

By using the non-dominated sorting-based genetic algorithm II, we study the topology optimization of the two-dimensional phoxonic crystals (PxCs) with simultaneously maximal and complete photonic and phononic bandgaps. Our results show that the optimized structures are composed of the solid lumps with narrow connections, and their Pareto-optimal solution set can keep a balance between photonic and phononic bandgap widths. Moreover, we investigate the localized states of PxCs based on the optimized structure and obtain structures with more effectively multimodal photon and phonon localization. The presented structures with highly focused energy are good choices for the PxC sensors. For practical application, we design a simple structure with smooth edges based on the optimized structure. It is shown that the designed simple structure has the similar properties with the optimized structure, i.e. simultaneous wide phononic and photonic bandgaps and a highly effective phononic/photonic cavity, see Figures 8(b) and 8(c).

Wide Absolute-Photonic-Bandgap 2D Square-Lattice Photonic Crystal Based on Hollow Cylinders and Cross Connecting Plates

Looking for photonic crystals with wide absolute bandgaps is always a challenging, attractive and significant task for optics scientists and optics engineers. In this paper, a new square-lattice photonic crystal structure is proposed based on a unit cell with a hollow cylinder and cross connecting plates. It is demonstrated through plane wave expansion method to have wider absolute photonic bandgaps compared with others reported.

A Two-Dimensional Square-Lattice Photonic Crystal with Rotated Square Cylinders and Cross Thin Plates Exhibiting Wide Photonic Bandgap

A new type of two-dimensional square-lattice photonic crystal structure made of rotated square cylinders and cross thin plates is presented and numerically investigated using the plane-wave expansion method. The largest absolute photonic bandgap (APBG) reaches 14.3%. The proposed structure can have promising application for its large APBG and convenience in designing optical circuits.