Photonic Band Gap Crystals Research Articles

Experimental evidence of the photonic band gap in hybrid one-dimensional photonic crystal based on a mixture of (HMDSO, O2)

Hybrid One-dimensional photonic crystal coated from a mixture of an organic compound (HMDSO) and oxygen (O2) is elaborated by PECVD technique. The originality of the method consists in obtaining layers of different permittivity with the same gas mixture, but with different flow. The change in flow is optimized to obtain organic/inorganic layers of good quality with high and low refractive index of 2.1 and 1.4 corresponding respectively to HMDSO and SiO2 materials as assigned by IR measurement. Evidence of the photonic band gap is obtained by measuring the transmissions and reflections spectra which show that it appears only after 13 periods with a width of 325 nm corresponding to energy 3.8 eV. We have also introduced a defect in this photonic structure by changing the thickness of central layer, and observed the presence of a frequency mode corresponding to this defect. Our results are interpreted by using a theoretical model based on transfer matrix wich well reproduced the experimental data.

Strain control of one-dimensional graphene-based photonic crystal

Motivated by resent experimental realization of a 1D strain-tunable photonic crystals and also increasing successes in strain-engineering in grapehene, we demonstrate the capability of a controllable photonic bandgap of a 1D graphene-dielectric photonic crystal by uniaxial strained graphene exhibiting either shrinkage or broadening along different chain crystalline orientations. Moreover, more analyzing over an electric field deviation angle to the stretching direction shows that the photonic spectrums are more sensitive to stronger deformations. Finally, we address how some resulting locked-up situations provide the measurement of the strain dependence of the chemical potential which is of considerable concern to be detectable as well as different strain states.

A plasma photonic crystal bandgap device

A fully tunable plasma photonic crystal is used to control the propagation of free space electromagnetic waves in the S to X bands of the microwave spectrum. An array of discharge plasma tubes forms a simple square crystal structure with the individual plasma dielectric constant tuned through variation in the plasma density. We show, through simulations and experiments, that transverse electric mode bandgaps exist, arising from the positive and negative dielectric constant regimes of the plasma, and that the respective bandgap frequencies can be shifted through changing the dielectric constant by varying discharge current density.

Study on the properties of photonic band gap and flatbands in the three-dimensional magnetized plasma photonic crystals with a general case

In this paper, the properties of photonic band gap (PBG) and flatbands in the three-dimensional (3D) magnetized plasma photonic crystals (MPPCs) with a general case in face-centered-cubic lattices are theoretically investigated based on the modified plane wave expansion method, in which the homogeneous magnetized plasma spheres are immersed in the homogeneous and isotropic dielectric background, as the magneto-optical Faraday effects are considered. The more general situation has been considered, and the PBG of such MPPCs is for all of the electromagnetic waves. The derivation of the formulas for calculating also is given. Theoretical computing results show that a PBG and two flatbands regions can be obtained. Compared to the conventional dielectric-air photonic crystals with similar structure, the larger PBG can be obtained in such 3D MPPCs. However, the narrower PBG can be achieved compared to that for the right circular polarized (RCP) wave, and the larger upper edge frequency of second flatbands region can be achieved. For the flatbands region, the upper edge only can be tuned by the plasma frequency and plasma cyclotron frequency. The effects of plasma frequency and plasma cyclotron frequency (the external magnetic field) on the properties of PBG also are investigated theoretically in detail. Theoretical simulations show that the PBG can be manipulated by those two parameters. The results show that the properties of PBG are obviously different with those for RCP wave in the similar 3D MPPCs. Those results can hold promise for opening a new scope to design the filters, planar reflectors, omnidirectional mirrors, absorber or waveguides based on the 3D MPPCs.

Band gap of two-dimensional fiber-air photonic crystals

A two-dimensional photonic crystal (PC) composed of textile fiber and air is initially discussed in this paper. Textile materials are so called soft materials, which are different from the previous PCs composed of rigid materials. The plain wave expansion method is used to calculate band structure of different PCs by altering component properties or structural parameters. Results show that the dielectric constant of textile fibers, fiber filling ratio and lattice arrangement are effective factors which influence PCs' band gap. Yet lattice constant and fiber diameter make inconspicuous influence on the band gap feature.

Influence of dielectrics with light absorption on the photonic bandgap of porous alumina photonic crystals

In this work, the influences of dielectrics with light absorption on the photonic bandgaps (PBGs) of porous alumina photonic crystals (PCs) were studied. Transmittance spectra of porous alumina PCs adsorbing ethanol showed that all the PBGs positions red-shifted; however, the transmittance of the PBG bottom showed different trends when the PBGs were located in different wavelength regions. In the near infrared region, liquid ethanol has strong light absorption, and, with the increase in adsorption, the PBG bottom transmittance of porous alumina PCs first increased and then decreased. However, in the visible light region, liquid ethanol has little light absorption, and thus, with the increase in adsorption, the PBG bottom transmittance of porous alumina PCs increased gradually all the time. Simulated results were consistent with the experimental results. The capillary condensation of organic vapors in the pores of porous alumina accounted for the change in the PBG bottom transmittance. The nonnegligible light absorption of the organic vapors was the cause of the decrease in the transmittance. The results for porous alumina PC adsorbing methanol, acetone, and toluene further confirmed the influences of light absorption on the PBG bottomed transmittance.

Two-dimensional function photonic crystal

Photonic crystal is a kind of periodic optical nanostructure consisting of two or more materials with different dielectric constants, which has attracted great deal of attention because of its wide range of potential applications in the field of optics. Photonic crystal can be fabricated into one-, or two-, or three- dimensional one. Among them, the two-dimensional photonic crystal turns into a hot focus due to its fantastic optical and electrical properties and relatively simple fabrication technique. Since the tunable band gaps of two-dimensional photonic crystals are beneficial to designing the novel optical devices, to study their optical and electrical properties for controlling the electromagnetic wave is quite valuable in both theoretical and practical aspects. In this work, we propose a new type of two-dimensional function photonic crystal, which can tune the band gaps of photonic crystals. The two-dimensional function photonic crystal is different from the traditional photonic crystal composed of medium columns with spatially invariant dielectric constants, since the dielectric constants of medium column are the functions of space coordinates. Specifically, the photorefractive nonlinear optical effect or electro-optic effect is utilized to turn the dielectric constant of medium column into the function of space coordinates, which results in the formation of two-dimensional function photonic crystal. We use the plane-wave expansion method to derive the eigen-equations for the TE and TM mode. By the Fourier transform, we obtain the Fourier transform form (G) for the dielectric constant function (r) of two-dimensional function photonic crystal, which is more complicated than the Fourier transform in traditional two-dimensional photonic crystal. The calculation results indicate that when the dielectric constant of medium column is a constant, the Fourier transforms for both of them are the same, which implies that the traditional two-dimensional photonic crystal is a special case for the two-dimensional function photonic crystal. Based on the above theory, we calculate the band gap structure of two-dimensional function photonic crystal, especially investigate in detail the corresponding band gap structures of TE and TM modes. The function of dielectric constant can be described as (r) = kr + b, in which k and b are adjustable parameters. Through comparing the calculation results for both kinds of photonic crystals, we can find that the band structures of TE and TM modes in two-dimensional function photonic crystals are quite different from those in traditional two-dimensional photonic crystal. Adjusting parameter k, we can successfully change the number, locations and widths of band gaps, indicating that the band gap structure of two-dimensional function photonic crystal is tunable. These results provide an important design method and theoretical foundation for designing optical devices based on two-dimensional photonic crystal.

Investigation on the properties of omnidirectional photonic band gaps in two-dimensional plasma photonic crystals

The properties of omnidirectional photonic band gaps (OBGs) in two-dimensional plasma photonic crystals (2D PPCs) are theoretically investigated by the modified plane wave expansion method. In the simulation, we consider the off-plane incident wave vector. The configuration of 2D PPCs is the triangular lattices filled with the nonmagnetized plasma cylinders in the homogeneous and isotropic dielectric background. The calculated results show that the proposed 2D PPCs possess a flatbands region and the OBGs. Compared with the OBGs in the conventional 2D dielectric-air PCs, it can be obtained more easily and enlarged in the 2D PPCs with a similar structure. The effects of configurational parameters of the PPCs on the OBGs also are studied. The simulated results demonstrate that the locations of OBGs can be tuned easily by manipulating those parameters except for changing plasma collision frequency. The achieved OBGs can be enlarged by optimizations. The OBGs of two novel configurations of PPCs with different cross sections are computed for a comparison. Both configurations have the advantages of obtaining the larger OBGs compared with the conventional configuration, since the symmetry of 2D PPCs is broken by different sizes of periodically inserted plasma cylinders or connected by the embedded plasma cylinders with thin veins. The analysis of the results shows that the bandwidths of OBGs can be tuned by changing geometric and physical parameters of such two PPCs structures. The theoretical results may open a new scope for designing the omnidirectional reflectors or mirrors based on the 2D PPCs.

Low loss and narrow-band THz filter based on magnetic photonic crystals

As a key point to applying and studying magnetic photonic crystal technology, communication devices such as the magnetic photonic crystal filters with high performance and easy integration are developed. We investigate the feasibility of ferrite magnetism materials that can be used to make photonic crystal filters. The optical properties of the magnetic materials may be tuned by adjusting the magnetic field or temperature. The band gap of the magnetic photonic crystal can thus be transferred by changing the external magnetic field. This kind of magnetic photonic crystal has a great application prospect. A low insertion loss and narrow-band filter is designed based on a magnetic field-controlled ferrite defect in a photonic crystal for a terahertz (THz) wave. Ferrite is a ferromagnetic metal oxide with high dielectric constant, low saturation magnetization intensity, and high magnetic permeability at high frequencies. According to the crystal structure it can be divided into three categories: spinel, garnet and magnetic rock types. The garnet ferrite crystal can be used to realize THz band transmission, and its absorption coefficient is low (0.05-0.3) in uniform polarization. In this paper, a novel magnetic THz photonic crystal filter is proposed, in which point defects are produced by the introduction of garnet ferrite magnetic materials. Based on the coupling characteristics between the linear defect wave guide and the point defects, THz wave with a certain wave length can be well coupled by changing the radius and arrangement of the resonant cavity, so as to achieve high efficiency filter function. The permeability properties of ferrite magnetic materials are changed with the variation of the intensity of the external magnetic field, and the tuning of the frequency of the resonance mode. The optical properties of the filter are analyzed in detail by using plane waves method(PWM) in finite difference time domain(FDTD). Simulation results show that by changing the point defect structure and the radius of a certain dielectric cylinder, the insertion loss and 3 dB bandwidth of the filter are 0.0997 dB and 8.22 GHz, respectively.

Omnidirectional photonic bandgap of the one-dimensional plasma photonic crystal based on a novel Fibonacci quasiperiodic structure

The binary one-dimensional plasma photonic crystal (1DPPC) based on Fibonacci quasiperiodic structure is studied systematically in this paper. We consider the two simplest cases. In one case, the initial sequences F0 and F1 are both of single layer structure. In another case, one initial sequence (F0 or F1) is of a single layer structure, while the other one (F1 or F0) is of a double layer structure. Thus there are ten different kinds of initial sequences in total. The photonic bandgap characteristics of the 1DPPC with these different initial sequences and numbers of period are analyzed. On these bases, a novel structure of one-dimensional plasma photonic crystal (F3)3 with initial sequence of F0=AP, F1=P and F0=PA, F1=P is proposed in this paper to enlarge the omnidirectional photonic bandgap (OPBG). Compared with previously reported structures in the literature, this structure is simple in configuration with fewer layers and materials, and its OPBG width is wide. The influences of the parameters of the plasma material, such as the thickness, plasma frequency and collision frequency, on the OPBG characteristics of this structure are also discussed. The OPBG width increases with the increase of the thickness and plasma frequency of the plasma layer. Compared with the structures in the literature, the change of OPBG width is the fastest for the proposed structure when the parameters are relatively small. And with the same parameters, the OPBG width for the proposed structure is the widest when the parameters are greater than a certain value. The plasma collision frequency has no effect on the OPBG width for all the structures. But the OPBG width for the proposed structure is the widest when this parameter has the same value. The reason why the proposed structure has an optimal OPBG width is explained by analyzing the dispersion properties of the plasma. The real and imaginary part of the dielectric constant of plasma change with frequency significantly only in the low frequency region. Since the imaginary part of dielectric constant is nearly zero when the frequency is larger than 2 GHz, only the dispersion effect of the real part of dielectric constant needs to be considered in the frequency range we investigate. And its value is much greater than that of conventional medium in the same frequency range. This makes the high-reflectance bands of the 1DPPC broader than those in the case of pure photonic interference phenomena with conventional medium. On the other hand, the corresponding highest proportion of plasma layers in the whole quasiperiodic structure can also be used to explain the broadest band gap of (F3)3. These results can provide important theoretical guidance for designing the novel omnidirectional reflectors.

Silicon On-chip 1D Photonic Crystal Nanobeam Bandgap Filter Integrated with Nanobeam Cavity for Accurate Refractive Index Sensing

A novel method for integration of high-performance 1-D photonic crystal nanobeam bandgap filter (1-D PC-NBF) and high-sensitivity 1-D PC nanobeam cavity sensor (1-D PC-NCS) is proposed on a monolithic silicon chip. The 1-D PC-NBF consists of a simple 1-D PC nanobeam waveguide, in which the bulk air-hole grating radii are kept the same. The 1-D PC-NCS consists of a common 1-D PC nanobeam cavity, in which the air-hole grating radius is parabolically tapered from center to end. By using the 3-D finite-difference time-domain (3-D-FDTD) method, the proposed 1-D PC-NBF with an effective low-pass bandgap ranging from 1533 to 1785 nm (with width > 250 nm) is demonstrated, where the resonant wavelengths lying in the bandgap are not guided. Then, by connecting an additional 1-D PC-NBF to a 1-D PC-NCS in series, a transmission spectrum only containing the specific fundamental mode of the 1-D PC nanobeam cavity for sensing purposes is created, while the other high-order modes are filtered out. Moreover, the additional 1-D PC-NBF has no influence on the properties (e.g., Q-factor, resonance position, and sensitivity) of the fundamental resonant mode of 1-D PC-NCS. In particular, the footprint of the proposed 1-D PC nanobeam integrated sensor is ultracompact around 0.7 μm × 10 μm, which is improved more than three orders of magnitude compared with the integrated sensor devices based on 2-D PC. Thus, the method presented here is promising to build highly parallel integrated sensor arrays for lab-on-a-chip applications and accurate detections.

近红外光谱区光子晶体禁带与KTP缺陷研究

近红外光谱区光子晶体禁带与KTP缺陷研究

近红外光谱区光子晶体禁带与KTP缺陷研究

近红外光谱区光子晶体禁带与KTP缺陷研究

Method for making a single-step etch mask for 3D monolithic nanostructures

Current nanostructure fabrication by etching is usually limited to planar structures as they are defined by a planar mask. The realization of three-dimensional (3D) nanostructures by etching requires technologies beyond planar masks. We present a method for fabricating a 3D mask that allows one to etch three-dimensional monolithic nanostructures using only CMOS-compatible processes. The mask is written in a hard-mask layer that is deposited on two adjacent inclined surfaces of a Si wafer. By projecting in a single step two different 2D patterns within one 3D mask on the two inclined surfaces, the mutual alignment between the patterns is ensured. Thereby after the mask pattern is defined, the etching of deep pores in two oblique directions yields a three-dimensional structure in Si. As a proof of concept we demonstrate 3D mask fabrication for three-dimensional diamond-like photonic band gap crystals in silicon. The fabricated crystals reveal a broad stop gap in optical reflectivity measurements. We propose how 3D nanostructures with five different Bravais lattices can be realized, namely cubic, tetragonal, orthorhombic, monoclinic and hexagonal, and demonstrate a mask for a 3D hexagonal crystal. We also demonstrate the mask for a diamond-structure crystal with a 3D array of cavities. In general, the 2D patterns on the different surfaces can be completely independently structured and still be in perfect mutual alignment. Indeed, we observe an alignment accuracy of better than 3.0 nm between the 2D mask patterns on the inclined surfaces, which permits one to etch well-defined monolithic 3D nanostructures.

Ultra-sensitive and dual-polarization refractive-index biosensors based on annular photonic crystals

We report new refractive-index biosensors with obviously enhanced sensitivity based on annular photonic crystals. Due to the introduction of dielectric rods into the air holes, the upper frequency edge of band gap of annular photonic crystals will be drawn to lower frequencies. This is quite helpful for annular photonic crystals to support as high as 2–3 times relative sensitivity than conventional photonic crystals. Based on this feature, a novel slotted annular photonic crystal waveguide is proposed to show its ultra-sensitive performance. More interesting contribution of this work is that we have proposed a new definition of relative sensitivity by measuring the difference of cross-polarization relative sensitivity of annular photonic crystals. Based on such definition, a novel conception of dual-polarization refractive-index biosensors with ultra-sensitive performance has been proposed and successfully demonstrated in theory.

Enhancement of gas–solid photocatalytic activity of nanocrystalline TiO2 by SiO2 opal photonic crystal

A series of nc-TiO2/SiO2 opal composite photocatalytic membranes were fabricated through coating a nanocrystal TiO2 (nc-TiO2) layer onto a SiO2 opal photonic crystal layer and used as catalysts for photodegradation of gaseous acetaldehyde under 380 nm monochromatic light and white light irradiation. The photonic band gap (PBG) of the SiO2 photonic crystal was designed at the vicinity of the electronic band gap of TiO2 and tuned by the size of SiO2 microspheres constructing the SiO2 opals. It was found that the nc-TiO2/SiO2 opal composite membrane, with the PBG of the SiO2 photonic crystal overlapping with the absorption edge of TiO2, exhibited the highest photocatalytic activity, which was 1.5 times that of a control photocatalytic membrane—the membrane of nc-TiO2 coated on a disordered porous SiO2 film. The farther the photonic PBG is away from the absorption edge of TiO2, the lower the photocatalytic activity of the composite membranes; when the nc-TiO2/SiO2 opal composite membrane catalyst with PBG was completely outside of the absorption edge of TiO2, the photocatalytic enhancement was not found. The photocatalytic enhancement is attributed to the enhanced light harvest of TiO2 resulting from the absorption of reflected light at PBG of photonic crystal and attributed to the light localization of photonic crystal inside the nc-TiO2.

Photonic and omnidirectional band gap engineering in stack of exponential graded index material and negative index material

We have investigated the photonic band gaps (PBG) and omnidirectional band gaps in one-dimensional photonic crystals made up of alternate layer of exponential graded index material and negative index material. We have considered the influence of material properties, geometrical parameters and material composition on the PBG and omnidirectional band gap. Results show that the parameters of exponential graded index material and negative index material can change the photonic and omnidirectional band structures remarkably. Number and bandwidth of PBG increases with increasing the negative index material layer thicknesses while thicknesses of graded index layer only have an effect on the bandwidth of PBGs. The bandwidth of PBG also depends on grading profile parameter of exponential graded index layers and bandwidth can be tuned with increase the value of grading profile parameter. This work can facilitate the design of filters and reflectors, and provide the basic understanding of the influence of graded index materials and metamaterials on the PBG properties.

A tunable microwave plasma photonic crystal filter

The integration of gaseous plasma elements into a microwave photonic crystal band gap cavity structure allows for active tuning of the device. An alumina rod array microwave photonic crystal waveguide resonator is simulated and characterized through finite difference time domain methods. A gaseous plasma element is integrated into the cavity structure and the effect of plasma density on the transmission properties of the structure is investigated. We show, through both simulations and experiments, that the permittivity of the plasma can be adjusted to shift the peak resonance to allow for both switching and tunability of transmission. The experimentally measured peak shifts in transmission are compared to those simulated and the electron density of the gaseous plasma element is calculated and compared to values determined from the measured discharge current density.

Electric Field-Driven Shifting and Expansion of Photonic Band Gaps in 3D Liquid Photonic Crystals

Highly tunable 3D liquid photonic crystals are demonstrated using low-dc-field-driven polymer-stabilized blue-phase liquid crystals. The central wavelength of the photonic band gap can be reversibly shifted to more than 200 nm away from the original position. Besides, by controlling the polymerization-induced morphology variations, the band gap can also be expanded from a bandwidth of around 30 nm to at least 310 nm, the first time a “white” blue phase is observed. Both types of band-gap modulation, namely, shifting and expansion, can be independently manipulated in any crystal axis without affecting the lattice spacings in the other dimensions. We envision polymer-stabilized blue-phase liquid crystals as a fascinating platform for photonic applications, such as 3D lasers, nonlinear optics, and photonic integrated circuits.

Tuning of guided mode in two dimensional chalcogenide based photonic crystal waveguide

A photonic crystal waveguide have been designed by modifying the size of one row of rods. This will allow a guided mode inside the photonic bandgap, which have been studied with modifying the size of row of rods. It is found that the radius of defect rods decide the propagation character of guided mode in photonic crystal bandgap. The effect on the group velocity of defect rods size is also studied.