Photonic Bandgap Structures Research Articles

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 ...

Design and analysis of concave diffraction grating with one-dimensional photonic bandgap structure

Matching one-dimensional photonic bandgap theory with the grating condition, a novel design approach of the etched diffraction grating for the demultiplexer was proposed. With a stack of eight alternating dielectric layers per grating tooth, a computed reflection efficiency of 98% around the central wavelength was achieved by this method. The grating efficiency approached −0.78 dB with a channel uniformity of 0.06 dB over 120 nm bandwidth, and the neighbor channel crosstalk was better than −20 dB. An analysis of etching deviation suggests that the diffraction grating designed by this approach is very tolerant concerning fabrication imperfections.

Effect of defected ground plane on the bandwidth of parallel line-coupled bandpass filter at 3.3 GHz

The effect of a defected ground plane made up of photonic band-gap structure of circular slots or patches of the radii r on the bandwidth of a parallel line- coupled bandpass filter, realized on a dielectric substrate and of 3.3 GHz center, frequency is highlighted in this study. The use of defected ground plane increases the filter bandwidth and allows its use on a broad-band frequency.

Propagation of optical vortices in a nonlinear atomic medium with a photonic band gap.

We experimentally generate a vortex beam through a four-wave mixing (FWM) process after satisfying the phase-matching condition in a rubidium atomic vapor cell with a photonic band gap (PBG) structure. The observed FWM vortex can also be viewed as the reflected part of the launched probe vortex from the PBG. Further, we investigate the propagation behaviors, including the spatial shift and splitting of the probe and FWM vortices in the medium with enhanced Kerr nonlinearity induced by electromagnetically induced transparency. This Letter can be useful for better understanding and manipulating the applications involving the interactions between optical vortices and the medium.

Local self-uniformity in photonic networks

The interaction of a material with light is intimately related to its wavelength-scale structure. Simple connections between structure and optical response empower us with essential intuition to engineer complex optical functionalities. Here we develop local self-uniformity (LSU) as a measure of a random network’s internal structural similarity, ranking networks on a continuous scale from crystalline, through glassy intermediate states, to chaotic configurations. We demonstrate that complete photonic bandgap structures possess substantial LSU and validate LSU’s importance in gap formation through design of amorphous gyroid structures. Amorphous gyroid samples are fabricated via three-dimensional ceramic printing and the bandgaps experimentally verified. We explore also the wing-scale structuring in the butterfly Pseudolycaena marsyas and show that it possesses substantial amorphous gyroid character, demonstrating the subtle order achieved by evolutionary optimization and the possibility of an amorphous gyroid’s self-assembly.

Effects of noncircular inner scatterers on absolute photonic band gap of 2D triangular annular photonic crystals

Using the plane wave expansion method, the photonic band gap (PBG) structures of quasi 2D triangular annular photonic crystals (PCs) with square and hexagonal inner scatterers have been calculated. We investigate the effects of structural parameters on absolute PBGs for silicon (Si)-based and germanium (Ge)-based annular PCs. The results reveal that the optimal inner scatterer shape is hexagonal. Moreover, we discuss the PBGs as a function of inner scatterer orientation. As for silicon annular PCs, utilization of high refractive index or anisotropic tellurium (Te) rods can lead to the formation of larger absolute PBGs.

Photonic band gaps structure properties of two-dimensional function photonic crystals

The tunable two-dimensional photonic crystals band gap, absolute photonic band gap and semi-Dirac point are beneficial to designing the novel optical devices. In this paper, tunable photonic band gaps structure was realized by a new type two-dimensional function photonic crystals, which dielectric constants of medium columns are functions of space coordinates. However for the two-dimensional conventional photonic crystals the dielectric constant does not change with space coordinates. As the parameter adjustment, we found that the photonic band gaps structures are dielectric constant function coefficient, medium columns radius, dielectric constant function form period number and pump light intensity dependent, namely, the photonic band gaps position and width can be tuned. we also obtained absolute photonic band gaps and semi-Dirac point in the photonic band gaps structures of two-dimensional function photonic crystals. These results provide an important theoretical foundation for design novel optical devices.

Photonic bandgap structure with plasmonic inclusions for refractive index sensing in optofluidics at terahertz frequencies.

We propose a refractive index sensor in the terahertz domain for optofluidics comprising a one-dimensional photonic bandgap structure with plasmonic inclusions. The central defect layer of the photonic bandgap structure is the fluid channel and acts as the sensing region wherein the embedded plasmonic inclusions provide the enhanced fields. The simultaneous excitation of the plasmonic resonances within the photonic bandgap defect mode results in an enhanced fluid-field interaction. The effective medium parameters of this composite sensing region become extremely sensitive to refractive index variations of the fluid within the channel and lead to significant spectral shifts. The sensitivity of this sensor increases with the volume fraction of the plasmonic inclusions and also provides self-referenced spectral measurement. This is an improved alternative to conventional refractive index sensors, which are based exclusively on either photonic or plasmonic effects.

An Improved Full-Wave Multilevel Green’s Function Interpolation Method With RBF-QR Technique for Fast Field Evaluation

An improved full-wave multilevel Green’s function interpolation method (MLGFIM) with RBF-QR technique is proposed for the fast evaluation of electromagnetic field. The difficulty in applying the interpolation approach with radial basis functions (RBFs) lies in solving the increasingly singular matrix equation with the increase of the number of interpolation points. The compromise of making the basis functions relatively less smooth was used in the previous RBF implementations to address this problem. In this paper, a new interpolation scheme, the RBF-QR technique is applied to the interpolation of Green’s function to resolve the ill-conditioning issue without such a compromise. A better conditioned basis function is generated by the QR-factorization technique, and it also solves the sensitivity of the basis function to the value of shape parameter. Moreover, a new hybrid interpolation pattern is adopted to optimize the grid pattern, e.g., reduce the number of interpolation points required and the boundary interpolation errors. The employment of the proposed RBF-QR technique in conjunction with hybrid interpolation pattern makes the efficiency of the MLGFIM greatly improved. The proposed algorithm is used for the analysis of problems involving objects, such as patch arrays, photonic bandgap structures, metasurface structures, double negative metamaterial and so on. Five numerical examples are given to validate this new algorithm, and show the accuracy and efficiency of the improved MLGFIM.

Trapping of coherence and entanglement in photonic band-gaps

We investigate the coherence trapping of a two-level atom transversally interacting with a reservoir with a photonic band-gap structure function. We then focus on the multipartite entanglement dynamics via genuinely multipartite concurrence among N independent atoms each locally coupled with its own reservoir. By considering the Lorentzian width and the system size, we find that for the resonant and near-resonant conditions, the increase of Lorentzian width and the decrease of system size can lead to the occurrence of coherence trapping and entanglement trapping. By choosing the multipartite GHZ state as atomic initial state, we show that the multipartite entanglement may exhibit entanglement sudden death depending on the initial condition and the system size. In addition, we also analyze how the crossover behaviors of two dynamical regimes are influenced by the Lorentzian width and the weight ratio, in terms of the non-Markovianity.

Photonic bandgap structure and long-range periodicity of a cumulative Fibonacci lattice

In this work, we study the photonic band of cumulative Fibonacci lattices, of which the structure is composed of all generated units in a Fibonacci sequence. The results are compared with distributed Bragg reflector (DBR) structures with the same numbers of layers. Photonic bandgaps are found at two characteristic frequencies, symmetrically separated from the central bandgap in the DBR counterpart. Field amplitude and phase distribution in the Fibonacci lattice indicates an interferential origin of the bandgaps. Fourier transform on the refractive index profile is carried out, and the result confirms a determinate long-range periodicity that agrees well with the photonic band structure.

Design and fabrication of energy efficient film based on one-dimensional photonic band gap structures

A photonic band gap structure of (SiO2/TiO2)5 with Ag system for energy efficient film was proposed theoretically and experimentally. The calculated transmittance spectra show high transmittance in the visible range, but ultra-low transmittance in the wavelength ranges of ultraviolet and infrared. Besides, the effects of the incident angle and two opposite directions on the optical characteristics were studied. The results demonstrate that the structure can simultaneously satisfy the demands of lighting and heat insulating as energy efficient window film. The cross-section morphology indicates that the sample has good periodicity in accordance with the design, whereas the experimentally measured transmittance spectra are well matched with the theoretical calculation.

Fabrication and Characterization of an MOEMS Gyroscope Based on Photonic Bandgap Materials

This paper focuses on a micro-optoelectro-mechanical vibratory gyroscope that provides an optical output and operates in a resonant condition. A custom fabrication technology, based on a silicon-on-insulator substrate, has been considered for the development of the inertial sensor. The optical readout has been accomplished using a metal–dielectric multilayer photonic bandgap (PBG) material. Such an optical structure, composed of alternated layers of one metal and one dielectric material, is embedded in the micromachined device, thus obtaining reflection properties correlated with the displacement of the proof mass induced by the external angular velocity. The principle of the micromachined gyroscope is first introduced, and then, the microelectromechanical gyroscope structure, the materials properties, and the fabrication technology are illustrated. Numerical analyses have also been performed in order to gain insight into the micromachined device. Furthermore, the optical transduction principle that exploits metal–dielectric 1-D PBG structures has been investigated from both a theoretical and an experimental point of view.

High power experimental studies of hybrid photonic band gap accelerator structures

This paper reports the first high power tests of hybrid photonic band gap (PBG) accelerator structures. Three hybrid PBG (HPBG) structures were designed, built and tested at 17.14 GHz. Each structure had a triangular lattice array with 60 inner sapphire rods and 24 outer copper rods sandwiched between copper disks. The dielectric PBG band gap map allows the unique feature of overmoded operation in a ${\mathrm{TM}}_{02}$ mode, with suppression of both lower order modes, such as the ${\mathrm{TM}}_{11}$ mode, as well as higher order modes. The use of sapphire rods, which have negligible dielectric loss, required inclusion of the dielectric birefringence in the design. The three structures were designed to sequentially reduce the peak surface electric field. Simulations showed relatively high surface fields at the triple point as well as in any gaps between components in the clamped assembly. The third structure used sapphire rods with small pin extensions at each end and obtained the highest gradient of $19\text{ }\text{ }\mathrm{MV}/\mathrm{m}$, corresponding to a surface electric field of $78\text{ }\text{ }\mathrm{MV}/\mathrm{m}$, with a breakdown probability of $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}1}$ per pulse per meter for a 100-ns input power pulse. Operation at a gradient above $20\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ led to runaway breakdowns with extensive light emission and eventual damage. For all three structures, multipactor light emission was observed at gradients well below the breakdown threshold. This research indicated that multipactor triggered at the triple point limited the operational gradient of the hybrid structure.

Liquid-crystal-droplet optical microcavities

ABSTRACTThe use of liquid-crystal droplets as optical microcavities and lasers is reviewed and possible applications are discussed. Liquid-crystal droplets are prepared by simple methods that enable scalable production since their internal structure is formed by self-assembly. Light is trapped in droplets due to total internal reflection on the surface due to refractive index mismatch or because of a photonic bandgap structure in cholesteric liquid crystals (CLCs). Light confinement gives rise to a variety of optical modes and by employing a fluorescent dye end external optical pumping, lasing can be achieved. Liquid-crystal-droplet cavities are largely tunable by applying an electric field or a temperature change. Such cavities can be used as temperature and chemical sensors, and tunable light sources and filters in future integrated soft photonic circuits.

Identification of zero density of states domains in band gap fibers using a single binary function.

Here we introduce a new calculation method to find the domains of zero density of states for photonic band gap guiding fibers consisting of arrays of high refractive index strands in a low refractive index cladding. We find an analytic expression that associates any combination of geometric parameter, effective index, material and wavelength with a single binary function which allows direct determination whether the density of cladding states is zero or not. The method neither requires the typically used root finding procedure for dispersion tracking nor simulation volume discretization. We verify the validity of our approach on well-established results and reveal as example that band gap regions are mainly determined by the two lowest order Bessel function orders. Our method allows for extensive parameter scans and evaluation of photonic band gap structures against structural and material inaccuracies with substantially reduced simulation effort.

Phase Modulation of Photonic Band Gap Signal.

We first investigate the probe transmission signal (PTS) and the four wave mixing band gap signal (FWM BGS) modulated simultaneously by the relative phase and the nonlinear phase shift in the photonic band gap (PBG) structure. The switch between the absorption enhancement of PTS and the transmission enhancement of PTS with the help of changing the relative phase and the nonlinear phase shift is obtained in inverted Y-type four level atomic system experimentally and theoretically. The corresponding switch in PTS can be used to realize all optical switches. On other hand, the relative phase and the nonlinear phase shift also play the vital role to modulate the intensity of FWM BGS reflected from the PBG structure. And it can be potentially used to realize the optical amplifier.

Optical processes of photonic band gap structure with dressing field in atomic system

We experimentally investigate probe transmission signals (PTS), the four-wave mixing photonic band gap signal (FWM BGS), and the fluorescence signal (FLS) in an inverted Y-type four level atomic system. For the first time, we compare the FLS of the two ground-state hyperfine levels of Rb 85. In particular, the second-order and the fourth-order fluorescence signals perform dramatic dressing discrepancies under the two hyperfine levels. Moreover, we find that the dressing field has some dressing effects on three such types of signals. Therefore, we demonstrate that the characteristics of PTS, FWM BGS, and FLS can be controlled by frequency detunings, the powers or phases of the dressing field. Such research could have potential applications in optical diodes, amplifiers, and quantum information processing.

Liquid crystal-based tunable photonic crystals for pulse compression and signal enhancement in multiphoton fluorescence

A unique device to enhance the fluorescence excitation with a maximum signal gain of 15-fold is demonstrated here. A one-dimensional photonic crystal infiltrated with liquid crystal as a central defect layer is designed for the enhancement of multiphoton fluorescence. Based on the linear dispersion properties near the edge of photonic bandgap, compression of femtosecond laser pulses can be realized. In comparison to the typical fluorescence enhancement techniques, this novel method has easy on-chip compression of an excitation pulse, tunable device, bio-friendly design, low damage, and compensation-free characteristics. The photonic bandgap structure employed in this approach has tunable and strong enhancements in fluorescence that enable these devices to find a place in bio-imaging and biophotonic technologies.

Effect of CdSe/ZnS quantum dots on color purity and electrical properties of polyfluorene based hybrid light emitting diode

We report enhanced color purity of hybrid organic-inorganic light emitting diode based on polyfluorene-CdSe/ZnS quanum dot (QD) blend as emissive layer. Effect on structural, optical and electrical properties of different doping concentration (0–100 wt.%) of QD in polyfluorene (PFO) was studied. Photoluminescence and electroluminescence spectra confirm the β-formation of PFO by incorporation of CdSe/ZnS QD. Photoluminescence (PL) of blend film was also compared with another method based on one dimensional photonic band gap (1D-PBG) structure that has been used for color purity. In both the cases, that is, QD doped device and 1D-PBG based structures the narrowing of PL spectra was observed. But the fabrication of QD-doped device for color purity is easier than fabricating 1D-PBG structure using multilayer dielectric coating. The present study might find application for QD based color displays, where color purity is an important requirement.