3D Photonic Band Gap Research Articles

Phoamtonic designs yield sizeable 3D photonic band gaps

We show that it is possible to construct foam-based heterostructures with complete photonic band gaps. Three-dimensional foams are promising candidates for the self-organization of large photonic networks with combinations of physical characteristics that may be useful for applications. The largest band gap found is based on 3D Weaire-Phelan foam, a structure that was originally introduced as a solution to the Kelvin problem of finding the 3D tessellation composed of equal-volume cells that has the least surface area. The photonic band gap has a maximal size of 16.9% (at a volume fraction of 21.6% for a dielectric contrast [Formula: see text]) and a high degree of isotropy, properties that are advantageous in designing photonic waveguides and circuits. We also present results for 2 other foam-based heterostructures based on Kelvin and C15 foams that have somewhat smaller but still significant band gaps.

High-sensitivity broad free-spectral-range two-dimensional three-slot photonic crystal sensor integrated with a 1D photonic crystal bandgap filter.

We present a novel high-sensitivity broad free-spectral-range (FSR) two-dimensional three-slot photonic crystal sensor integrated with a 1D photonic crystal tapered nanobeam bandgap filter (1DPC-TNBF) based on thin-film silicon. Designed to lie in the wavelength at around 1550nm, the resonance of the two-dimensional photonic crystal three-slot cavity (2DPC-TSC) shows strong light-matter interaction in the slot region, which enhances the bulk refractive index sensitivity of the sensor significantly. The simulated sensitivity is over 900nm/refractive index unit (RIU). By connecting an additional 1DPC-TNBF to a 2DPC-TSC in series, the high-order modes are suppressed, which means only a fundamental mode exists with a broad FSR over 200nm. Thus, the proposed structure is promising in designing lab-on-a-chip applications, especially in compact parallel-integrated sensor arrays.

Experimental study of an evanescent-field biosensor based on 1D photonic bandgap structures.

A photonic bandgap (PBG) biosensor has been developed for the label-free detection of proteins. As the sensing in this type of structures is governed by the interaction between the evanescent field going into the cladding and the target analytes, scanning near-field optical microscopy has been used to characterize the profile of that evanescent field. The study confirms the strong exponential decrease of the signal as it goes into the cladding. This means that biorecognition events must occur as close to the PBG structure surface as possible in order to obtain the maximum sensing response. Within this context, the PBG biosensor has been biofunctionalized with half-antibodies specific to bovine serum albumin (BSA) using a UV-induced immobilization procedure. The use of half-antibodies allows one to reduce the thickness of the biorecognition volume down to ca. 2.5 nm, thus leading to a higher interaction with the evanescent field, as well as a proper orientation of their binding sites towards the target sample. Then, the biofunctionalized PBG biosensor has been used to perform a direct and real-time detection of the target BSA antigen.

Cartesian light: Unconventional propagation of light in a three-dimensional superlattice of coupled cavities within a three-dimensional photonic band gap

We explore the unconventional propagation of light in a three-dimensional (3D) superlattice of coupled resonant cavities in a 3D photonic band gap crystal. Such a 3D cavity superlattice is the photonic analogue of the Anderson model for spins and electrons in the limit of zero disorder. Using the plane-wave expansion method, we calculate the dispersion relations of the 3D cavity superlattice with the cubic inverse woodpile structure that reveal five coupled-cavity bands, typical of quadrupole-like resonances. For three out of five bands, we observe that the dispersion bandwidth is significantly larger in the $(k_x, k_z)$-diagonal directions than in other directions. To explain the directionality of the dispersion bandwidth, we employ the tight-binding method from which we derive coupling coefficients in 3D. For all converged coupled-cavity bands, we find that light hops predominantly in a few high-symmetry directions including the Cartesian $(x, y, z)$ directions, therefore we propose the name "Cartesian light". Such 3D Cartesian hopping of light in a band gap yields propagation as superlattice Bloch modes that differ fundamentally from the conventional 3D spatially-extended Bloch wave propagation in crystals, from light tunneling through a band gap, from coupled-resonator optical waveguiding, and also from light diffusing at the edge of a gap.

Three-dimensional photonic band gap cavity with finite support: Enhanced energy density and optical absorption

We study numerically the transport and storage of light in a 3D photonic band gap crystal doped by a single embedded resonant cavity. The crystal has finite support since it is surrounded by vacuum, as in experiments. Therefore, we employ the finite element method to model the diamond-like inverse woodpile crystal that consists of two orthogonal arrays of pores in a high-index dielectric such as silicon and that has experimentally been realized by CMOS-compatible methods. A point defect that functions as the resonant cavity is formed in the proximal region of two selected orthogonal pores with a radius smaller than the ones in the bulk of the crystal. We present a field-field cross-correlation method to identify resonances in the finite-support crystal with defect states that appear in the 3D photonic band gap of the infinite crystal. Out of 5 observed angle-independent cavity resonances, one is s-polarized and 4 are p-polarized for light incident in the X or Z directions. It is remarkable that quality factors up to Q = 1000 appear in such thin structures (3 unit cells). We find that the optical energy density is remarkably enhanced at the cavity resonances by up to 2400x the incident energy density in vacuum or up to 1200x the energy density of the equivalent effective medium. We find that an inverse woodpile photonic band gap cavity with a suitably adapted lattice parameter reveals substantial absorption in the visible range. Below the 3D photonic band gap, Fano resonances arise due to interference between the discrete fundamental cavity mode and the continuum light scattered by the photonic crystal. We argue that the five eigenstates of our 3D photonic band gap cavity have quadrupolar symmetry, in analogy to d-like orbitals of transition metals. We conclude that inverse woodpile cavities offer interesting perspectives for applications in optical sensing and photovoltaics.

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.

Biomaterial-Based "Structured Opals" with Programmable Combination of Diffractive Optical Elements and Photonic Bandgap Effects.

Naturally occurring iridescent systems produce brilliant color displays through multiscale, hierarchical assembly of structures that combine reflective, diffractive, diffusive, or absorbing domains. The fabrication of biopolymer-based, hierarchical 3D photonic crystals through the use of a topographical templating strategy that allows combined optical effects derived from the interplay of predesigned 2D and 3D geometries is reported here. This biomaterials-based approach generates 2D diffractive optics composed of 3D nanophotonic lattices that allow simultaneous control over the reflection (through the 3D photonic bandgap) and the transmission (through 2D diffractive structuring) of light with the additional utility of being constituted by a biocompatible, implantable, edible commodity textile material. The use of biopolymers allows additional degrees of freedom in photonic bandgap design through directed protein conformation modulation. Demonstrator structures are presented to illustrate the lattice multifunctionality, including tunable diffractive properties, increased angle of view of photonic crystals, color-mixing, and sensing applications.

Multi-resonant photonic band-gap/saddle coil DNP probehead for static solid state NMR of microliter volume samples.

The most critical condition for performing Dynamic Nuclear Polarization (DNP) NMR experiments is achieving sufficiently high electronic B1e fields over the sample at the matched EPR frequencies, which for modern high-resolution NMR instruments fall into the millimeter wave (mmW) range. Typically, mmWs are generated by powerful gyrotrons and/or extended interaction klystrons (EIKs) sources and then focused onto the sample by dielectric lenses. However, further development of DNP methods including new DNP pulse sequences may require B1e fields higher than one could achieve with the current mmW technology. In order to address the challenge of significantly enhancing the mmW field at the sample, we have constructed and tested one-dimensional photonic band-gap (PBG) mmW resonator that was incorporated inside a double-tuned radiofrequency (rf) NMR saddle coil. The photonic crystal is formed by stacking ceramic discs with alternating high and low dielectric constants and thicknesses of λ/4 or 3λ/4, where λ is the wavelength of the incident mmW field in the corresponding dielectric material. When the mmW frequency is within the band gap of the photonic crystal, a defect created in the middle of the crystal confines the mmW energy, thus forming a resonant structure. An aluminum mirror in the middle of the defect has been used to substitute one-half of the structure with its mirror image in order to reduce the resonator size and simplify its tuning. The latter is achieved by adjusting the width of the defect by moving the aluminum mirror with respect to the dielectric stack using a gear mechanism. The 1D PBG resonator was the key element for constructing a multi-resonant integrated DNP/NMR probehead operating at 190-199 GHz EPR/300 MHz 1H/75.5 MHz 13C NMR frequencies. Initial tests of the multi-resonant DNP/NMR probehead were carried out using a quasioptical mmW bridge and a Bruker Biospin Avance II spectrometer equipped with a standard Bruker 7 T wide-bore 89 mm magnet parked at 300.13 MHz 1H NMR frequency. The mmW bridge built with all solid-state active components allows for the frequency tuning between ca. 190 and ca. 199 GHz with the output power up to 27 dBm (0.5 W) at 192 GHz and up to 23 dBm (0.2 W) at 197.5 GHz. Room temperature DNP experiments with a synthetic single crystal high-pressure high-temperature (HPHT) diamond (0.3 × 0.3 × 3.0 mm3) demonstrated dramatic 1500-fold enhancement of 13C natural abundance NMR signal at full incident mmW power. Significant 13C DNP enhancement (of about 90) have been obtained at incident mmW powers of as low as <100 μW. Further tests of the resonator performance have been carried out with a thin (ca. 100 μm thickness) composite polystyrene-microdiamond film by controlling the average mmW power at the optimal DNP conditions via a gated mode of operation. From these experiments, the PBG resonator with loaded Q ≃ 250 and finesse F≈75 provides up to 12-fold or 11 db gain in the average mmW power vs. the non-resonant probehead configuration employing only a reflective mirror.

Calculation of photonic bandgap for 2D hexagonal and square structure base on hybrid polymer material

We have calculated 2D photonic crystal band gap using plane-wave expansion method. The studied model of structures is hexagonal lattice and square lattice of rod cylinder in air. We have simulated the dispersion relation of it structure using hybrid polymer as rod material. The parameter structures are nrod = 1.5, nhole = 1, and rrod = 0.25a, where a is lattice constant. We found the distributed feedback occurs at the edge of upper band or frequency at 0.66 (a/λ). In our experimental work, we have successfully fabricated the 2D photonic crystal from hybrid polymer incorporated with organic dye laser. The lasing characteristics ware investigated using strip-line excitation light of SHG Nd-YAG laser (λ=532 nm). The lasing wavelengths for hexagonal structure are observed at 606 nm and 621 nm for photonic crystal period of 400 nm and 410 nm, respectively. λ=532 nm). Whereas the square structure, the lasing wavelengths are observed at (588 nm ± 2) and (606 nm ± 2 nm) for grating period of 391 nm and 405 nm.

(Invited) SURMOFs and CCNCs As Novel Tuneable Materials for Electronic Devices and Applications

Here we present a particularly interesting class of surface-anchored (metal-organic frameworks andcoordination network compounds) materials SURMOFs and (conductive coordination network compounds) CCNCs for the fabrication e.g. of 1D (Photonic Band Gap) PBG materials [1,2] as optical sensors, low-k dielectric thin films [3],optoelectronic/electrochromic switchable coatings/devices [4] microelectronic devices, e.g. RRAM devices [5] or Hybrid-Materials NPs@SURMOFs for future artificial Light-Harnessing (LH) assemblies and photocatalysts.[6] Since these materials are highly porous and the size of their pores are highly adjustable, they can be further functionalized and further tailor to electrically load and unload small ions (optoelectronic applications) or act as photon traps, which are able to efficiently absorb, transport and harness light energy over an artificial LH antenna array.[7] An outlook will be given for highly conductive and porous CCNCs thin film materials as well as further electronic characterization of SURMOFs and CCNCs.

Optically Active Elastomers from Liquid Crystalline Comb Copolymers with Dual Physical and Chemical Cross-Links

We report on the synthesis and properties of cholesteric liquid crystalline random terpolymers with comblike architecture as a modular platform for preparation of stimuli-responsive photonic elastomers. Ring-opening metathesis of norbornene monomers bearing n-alkyloxy cholesteryl (Ch9), n-alkoxy cyanobiphenyl (CB6 or CB12), and poly(ethylene glycol) (PEG) side chains is efficient and quantitatively yields low polydispersity random terpolymers. This terpolymer scaffold self-assembles to form cholesteric mesophases (N*) in which microphase-segregated domains of PEG side chains are randomly embedded. The cholesteric mesophase provides a 1D photonic band gap structure at optical wavelengths, which is maintained during chemical cross-linking of the norbornene backbone to form elastomers. The presence of cyanobiphenyl mesogens leads to an increase in the helical pitch of the cholesteric mesophase, resulting in a red-shift of the reflectivity relative to the pure cholesteric mesophase. By contrast, the presence ...

Reflectivity calculated for a three-dimensional silicon photonic band gap crystal with finite support

We study numerically the reflectivity of three-dimensional (3D) photonic crystals with a complete 3D photonic band gap, with the aim to interpret recent experiments. We employ the finite element method to study crystals with the cubic diamond-like inverse woodpile structure. The high-index backbone has a dielectric function similar to silicon. We study crystals with a range of thicknesses up to ten unit cells ($L \leq 10 c$). The crystals are surrounded by vacuum, and have a finite support as in experiments. The polarization-resolved reflectivity spectra reveal Fabry-P{\'e}rot fringes related to standing waves in the finite crystal, as well as broad stop bands with nearly $100~\%$ reflectivity, even for thin crystals. From the strong reflectivity peaks, it is inferred that the maximum reflectivity observed in experiments is not limited by finite size. The frequency ranges of the stop bands are in excellent agreement with stop gaps in the photonic band structure, that pertain to infinite and perfect crystals. The frequency ranges of the observed stop bands hardly change with angle of incidence, which is plausible since the stop bands are part of the 3D band gap. Moreover, this result supports the previous assertion that intense reflection peaks measured with a large numerical aperture provide a faithful signature of the 3D photonic band gap. The Bragg attenuation lengths $L_{B}$ exceed the earlier estimates based on the width of the stop band by a factor $6$ to $9$. Hence crystals with a thickness of $12$ unit cells studied in experiments are in the thick crystal limit ($L >> L_{B}$). In our calculations for p-polarized waves, we also observe an intriguing hybridization of the zero reflection of Fabry-P{\'e}rot fringes and the Brewster angle, which has not yet been observed in experiments.

Surmofs and Cncs As Novel Tuneable Materials for Optical, Photonic and Solar Energy Materials

Here, I will present a particularly interesting class of surface-anchored (metal-organic frameworks and coordination network compounds) materials SURMOFs and CNCs for the fabrication e.g. of 1D (Photonic Band Gap) PBG materials [1] as optical sensors, low-k dielectric thin films [2], optoelectronic/ electrochromic switchable coatings/devices [3] PV devices [4] or as future artificial Light-Harnessing (LH) antenna array assemblies as well as novel hybrid-photocatalyst.[5] Since these materials are highly porous and the size of their pores are highly adjustable, they can be further functionalized (e.g. with different metal/oxo connectors or clusters linked with various organic linkers) e.g. in order to specifically bind target analytes (optical sensing), to electrically load and unload small ions (optoelectronic applications) as well as to act as photon traps, which are able to efficiently absorb, transport and harness light energy over an artificial LH antenna array. In addition, the RI (Refractive Index) as well as the optical properties of SURMOF and CNC materials can be tailored – a fact which makes these materials ideally suited for photonic, optical, optoelectronic, light-harnessing as well as for future solar energy systems like photocatalytic and PV applications. Keywords: SURMOFs, porous thin films, artificial light harnessing, optics and photonics, PV applications, photocatalysis.

All-optical dynamical Casimir effect in a three-dimensional terahertz photonic band gap

We identify an architecture for the observation of all-optical dynamical Casimir effect in realistic experimental conditions. We suggest that by integrating quantum wells in a three-dimensional (3D) photonic band-gap material made out of large-scale ($\ensuremath{\sim}200\ensuremath{-}\ensuremath{\mu}\mathrm{m}$) germanium logs, it is possible to achieve ultrastrong light-matter coupling at terahertz frequencies for the cyclotron transition of a two-dimensional electron gas interacting with long-lived optical modes, in which vacuum Rabi splitting is comparable to the Landau level spacing. When a short, intense electromagnetic transient of duration $\ensuremath{\sim}250\phantom{\rule{0.28em}{0ex}}\mathrm{fs}$ and carrying a peak magnetic field $\ensuremath{\sim}5\phantom{\rule{0.28em}{0ex}}\mathrm{T}$ is applied to the structure, the cyclotron transition can be suddenly tuned on resonance with a desired photon mode, switching on the light-matter interaction and leading to a Casimir radiation emitted parallel to the quantum well plane. The radiation spectrum consists of sharp peaks with frequencies coinciding with engineered optical modes within the 3D photonic band gap, and its characteristics are extremely robust to the nonradiative damping which can be large in our system. Furthermore, the absence of continuum with associated low-energy excitations for both electromagnetic and electronic quantum states can prevent the rapid absorption of the photon flux which is likely to occur in other proposals for all-optical dynamical Casimir effect.

Testing multilayer structures for optical filtering in temperature unstable environments

Two multilayer structures are taken, the first multilayer is having a sequence LHLHLHLHLHLHLHLH of low (denoted by L) and high refractive index (denoted by H) material layers in the structure and the second multilayer is having a sequence LLLHHLHHLLLHHLHH. These two multilayer structures were tested for optical filtering in temperature unstable environments. The first multilayer structure shows a large shift in the output spectrum, even for a slightest temperature change. While the second multilayer structure shows a negligible shift in the output spectrum even for large changes in the environmental temperature. The transmission spectrum shift observed per degree rise in temperature in the second multilayer structure was 62.5% less than the shift observed in first multilayer. Second multilayer structure is a superior substitute to conventional LHLHLHLHLHLHLHLH sequence 1D Photonic Band Gap structure.

Vacancy-induced transmission in three-dimensional photonic crystal slabs.

The transmission spectra of finite-thickness slabs of three-dimensional (3D) diamond-lattice photonic crystals of air spheres in a dielectric background in which various concentrations of randomly located vacancies are present are studied. We find that resonant modes associated with isolated defects couple to form an extended defect band, leading to a significant increase in transmission for frequencies inside the 3D photonic bandgap. Outside the 3D gap, vacancies induce scattering from evanescent to propagating modes, leading to an increase in transmission near the pseudo-gap edges within the gap. The local defect density of states for several concentrations of vacancies is computed; thus, it is shown that the total number of defect states and the range of supported frequencies increase due to increasing vacancy density.

Enhanced photoluminescence from CdS with SiO2 nanopillar arrays.

In this paper, the enhanced photoluminescence from CdS thin film with SiO2 nanopillar array (NPA) was demonstrated. The CdS was prepared using chemical bath deposition in a solution bath containing CdSO4, SC(NH2)2, and NH4OH. The SiO2 NPA was fabricated by the nanosphere lithography (NSL) techniques. The nanopillar is about 50 nm in diameter, and the height is 150 nm. As a result, the sample with NPA shows an obvious improvement of photoluminescence (PL), compared with the one without NPA. In addition, we also observed that the PL intensity is increased ~5 times if the active layer is deposited on the nanopillar arrays and covered by a thin metal film of Al. It is noteworthy that the enhancement of photoluminescence could be attributed to the roughness of the surface, the 2D photonic band gap (PBG) effect and the surface plasmon resonance (SPR) effects.

Photonic architectures for equilibrium high-temperature Bose-Einstein condensation in dichalcogenide monolayers.

Semiconductor-microcavity polaritons are composite quasiparticles of excitons and photons, emerging in the strong coupling regime. As quantum superpositions of matter and light, polaritons have much stronger interparticle interactions compared with photons, enabling rapid equilibration and Bose-Einstein condensation (BEC). Current realizations based on 1D photonic structures, such as Fabry-Pérot microcavities, have limited light-trapping ability resulting in picosecond polariton lifetime. We demonstrate, theoretically, above-room-temperature (up to 590 K) BEC of long-lived polaritons in MoSe2 monolayers sandwiched by simple TiO2 based 3D photonic band gap (PBG) materials. The 3D PBG induces very strong coupling of 40 meV (Rabi splitting of 62 meV) for as few as three dichalcogenide monolayers. Strong light-trapping in the 3D PBG enables the long-lived polariton superfluid to be robust against fabrication-induced disorder and exciton line-broadening.

Spatial and spectral mode filtration in phase-locked array of injection lasers with volume Bragg grating

High-power edge-emitting lasers with low divergence of the output beam are highly desired for a number of applications. In order to obtain high optical power one needs to expand the emitting area of the laser which usually leads to multi-mode lasing with broad spectrum and poor beam quality. Here we present the study of using a volume Bragg grating (VBG) as a spatial and spectral mode filter for phase-locked arrays of edge-emitting lasers based on 1D photonic bandgap crystals. Emitters in the arrays are synchronized due to the expanded vertical waveguide, which results in the lasing of high order oscillating modes. One lobe of high order mode was used to create an external cavity with VBG. We studied far-fields, spectra and L-I curves of the external cavity lasers and demonstrated that 500 mW of the output optical power could be concentrated in one lobe with the divergence as low as 1° and spectral width of 0.6 nm.

An Effective Method for the Preparation of Stable LC Composites with High Concentration of Quantum Dots

Cholesteric liquid crystals doped with QDs present a special interest because the photonic bandgap structure of cholesteric media when combined with emission properties of QDs provides the opportunity to realize a variety of specifi c photooptical properties. Cholesteric mesophase has a 1D photonic bandgap structure, which stands for its unique optical properties such as Bragg selective light refl ection, huge optical rotation, and so on. [ 20 ] In several recent papers, the optical and photophysical properties of the cholesteric low-molar-mass and polymer liquid crystalline (LC) materials doped with QDs were demonstrated. [ 16‐18 ] For example, in recent publication, [ 16 ] the modulation of recombination lifetimes of CdSe/ZnS QDs (0.01‐0.02 wt%) dispersed in cholesteric low-molar-mass liquid crystal and time-resolved emission from QD ensembles in LC matrices with different alignment were investigated. The difference in decay time characteristics of QD’s emission depending on planar or homeotropic alignment was revealed in the case of overlapping of emission and photonic bandgap peaks. It was shown that coupling between the excitonic and the photonic cavity modes leads to the enhancement and modulation of spontaneous emission. In the papers [ 18,19 ] we have described the novel types of cholesteric QDs-doped materials with photo- and electro-tunable fl uorescence. The possibility of manipulation of fl intensity and degree of circular polarization (dissymmetry factor) was demonstrated for the fi rst time. Despite a great progress in the fi eld of the QD‐LC composites, the introduction of large concentration of QDs into liquid crystal media is still a challenging task. The most successful achievement in the area was published recently. [ 15 ] The authors of this work have offered an approach based on the surface