1D Photonic Bandgap Structures Research Articles

Realization of all-optical logic gates using a single design of 2D photonic band gap structure by square ring resonator

The interference method is used to achieve all-optical logic gate operations. This has been realized with a single design of photonic crystal ring resonator at different wavelengths rather than designing separate for all the logic gates. Such a single design can be used to perform all optical operations as AND, OR, and XOR logic gates at different wavelengths. Further operating wavelength, contrast ratio (CR), response time (RT), and bit rate have been analyzed for all three logic gates. The highest CR is obtained as about 22.06 dB with fast RT about 0.14 ps and high bit rate of 7.14 Tb / s for proposed XOR logic gate in comparison to all the other logic gates with single-design structure, which may lead us to construct on-chip logic circuits.

Video-Rate Identification of High-Capacity Low-Cost Tags in the Terahertz Domain.

In this article, we report on video-rate identification of very low-cost tags in the terahertz (THz) domain. Contrary to barcodes, Radio Frequency Identification (RFID) tags, or even chipless RFID tags, operate in the Ultra-Wide Band (UWB). These THz labels are not based on a planar surface pattern but are instead embedded, thus hidden, in the volume of the product to identify. The tag is entirely made of dielectric materials and is based on a 1D photonic bandgap structure, made of a quasi-periodic stack of two different polyethylene-based materials presenting different refractive indices. The thickness of each layer is of the order of the THz wavelength, leading to an overall tag thickness in the millimetre range. More particularly, we show in this article that the binary information coded within these tags can be rapidly and reliably identified using a commercial terahertz Time Domain Spectroscopy (THz-TDS) system as a reader. More precisely, a bit error rate smaller than 1% is experimentally reached for a reading duration as short as a few tens of milliseconds on an 8 bits (~40 bits/cm2) THID tag. The performance limits of such a tag structure are explored in terms of both dielectric material properties (losses) and angular acceptance. Finally, realistic coding capacities of about 60 bits (~300 bits/cm2) can be envisaged with such tags.

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.

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 ...

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.

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

Asymmetric one-dimensional photonic crystal for optical sensing in the visible spectral range

A gas sensor based on an asymmetric one-dimensional (1D) photonic band gap structure with one defect layer was designed and fabricated through layer-by-layer deposition of spin-coated poly methyl methacrylate (PMMA) and vacuum-deposited As2S3. Initially, the thickness variations, Δd, were determined of the thin films resulting from the poly methyl methacrylate exposure to chloroform vapor in the concentration range 100 – 9000 ppm. It was found that the value of Δd depends on the gas concentration and the exposure time. A two-layer structure was prepared consisting of PMMA and vacuum-deposited As2S3. Further, the permeability of thin As2S3 films to chloroform vapors was investigated. The asymmetric photonic structure consisted of 11 alternating layers of As2S3 and PMMA. The defect PMMA layer was located before the last high-refractive-index film of chalcogenide glass. The thickness of the defect layer of PMMA was pre-calculated so that the pass band be centered at the wavelength of 550 nm. An offset was observed of the position of the pass band to the larger wavelengths after exposure to chloroform vapor. The multilayered structure proposed is promising for optical sensor applications.

Extraction Length Determination in Patterned Luminescent Sol-Gel Films

Optimization of light emitting devices when light is trapped within the dielectric structures opens the question of the management of light propagation and of control of the directionality of extracted light. These phenomena are closely connected to the so-called extraction length of light propagating within the device, a parameter that is poorly discussed when considering the design and architecture of devices. In this work, a straightforward method for the measurement of the extraction length in the case of luminescent sol–gel films patterned with a 2D photonic bandgap structure is presented. Quantitative information usually obtained by spectro-angular measurements can be retrieved from simpler standard spectrometry, allowing discussion of the influence of pattern depth, which determines the extraction by the photonic structure as compared to other uncontrolled pathways such as diffusion from defects in the film coating. These assessments provide a quick and safe method for the quantitative evaluation of light extraction strategies toward a rational design of light emitting devices with optimized properties.

Adjustable YAG : Ce3+ photoluminescence from photonic crystal microcavity

Four different photonic bandgap (PBG) structures embedding a YAG : Ce3+ layer inside two three-period Bragg mirrors were prepared by sol–gel processing, forming Fabry–Perot microcavities whose defect peaks moved from red to green. Under irradiation of blue Ar+ laser light, the typical broad YAG : Ce3+ photoluminescence (PL) emission band was highly narrowed in these four samples, with the new position of the modified PL peaks corresponding to the resonance wavelength of each microcavity sample, while the simultaneous colour changes could be easily observed by the human eye. The adjustable range demonstrated here was wide enough to generate white light with colour temperatures from warm white (∼2700 K) to daylight white (∼5600 K), by mixing the modified PL with light from any usual blue LED excitation source. This result provides a novel technique to solve the red-deficiency problem in the white LED industry: instead of relying on the development of new phosphors, the well-known PL of YAG : Ce3+ can be conveniently adjusted by 1D PBG structures.

Dispersion characteristics of 1D PBG structures composed of subwavelength dipole elements

In this article, an innovative approach for characterization of one dimensional photonic band gap (PBG) structures comprised of subwavelength dipole elements is presented.Through an efficient S- to T-parameters conversion technique, polarization sensitivity of the subwavelength cell element was exploited to propose a novel combination of elements which allows achieving PBGs with simultaneous frequency and polarization selectivity. The proposed approach demonstrated that dispersion characteristics of each orthogonal polarization can be independently adjusted with dipole elements parallel to that same polarization. The structure has potential application in orthomode transducer and generally whenever the polarization of the incoming signal is to be used as a means of separating it from another signal in the same frequency band that is of orthogonal polarization. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:611–615, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27378

Simulations and Analysis of Nano Scale Porous Silicon Structures for Optical Sensor Applications

Recently, Porous Silicon (PS) is emerged as novel and unique material as a stable nano scale optical sensor device. In this work, one dimensional (1D) Photonic Bandgap (PBG) structures such as single layer (SL), Distributed Bragg Reflector (DBR) and Microcavity (MC) using PS material are suggested as optical sensor applications. Design and simulations are relying on the Bruggeman’s Effective Medium Approximation (BEMA) and the Transfer Matrix Method (TMM) to predict the optical properties of 1DPSPBG sensor device structures. By analyzing the reflectance spectra, wavelength shift (Δλ) has been obtained, which showed good linear relationship with refractive index of the void. Sensitivity analysis showed that MC structure performs best as 1D-PSPBG optical sensor device due to its structural and optical properties. The results reported here are useful for the design and prediction of the response of optical sensor devices using 1D-PSPBG structures.

Continuous wave mirrorless lasing in cholesteric liquid crystals with a pitch gradient across the cell gap

Despite numerous efforts, continuous wave (CW) lasing in dye doped, one-dimensional (1D) photonic bandgap cholesteric liquid crystal (CLC) structures has not been previously reported, to our knowledge. Here we report on the observation of lasing in such structures under both coherent (laser) and incoherent (LED) CW light excitation. To achieve this effect, we used a 1D-photonic bandgap structure made of a polymer stabilized CLC with a pitch gradient across the cell thickness. A spectral reflectivity profile of such a CLC structure reveals local minima in the area within a photonic stopband and close to it. The realization of lasing pumped by low power CW light sources opens the possibility of all-organic, compact, tunable CW lasers for display and medical applications.

High quality factor Er-doped Fabry–Perot microcavities by sol–gel processing

An optimized sol–gel process was developed to fabricate 1D photonic bandgap structures. Several erbium-doped Fabry–Perot microcavities were prepared and characterized. The thickest sample contained two Bragg mirrors, each having 12 distributed Bragg reflector periods of alternating silicate glass and titania layers. The total thickness of this sample reached ∼12 µm. The Er3+ photoluminescence spectra at 1.5 µm were measured for the microcavities. A quality factor of 250 and an Er3+ photoluminescence enhancement of 96 times at 1.5 µm have been reached. The sol–gel processing details, the crystallization of the titania films and the refractive index of the deposited materials are discussed in detail. The simulated optical spectra of the microcavities were found to agree well with the actually measured curves. These results demonstrate that the present sol–gel processing technique is of potential interest for low cost fabrication of 1D photonic bandgap devices.

Quasi-normal-modes description of transmission properties for photonic bandgap structures

We use the quasi-normal-modes (QNM) approach for discussing the transmission properties of double-side opened optical cavities: in particular, this approach is specified for one-dimensional (1D) photonic bandgap (PBG) structures. Moreover, we conjecture that the density of the modes is a dynamical variable that has the flexibility of varying with respect to the boundary conditions as well as the initial conditions; in fact, the electromagnetic (e.m.) field generated by two monochromatic counterpropagating pump waves leads to interference effects inside a quarter-wave symmetric 1D-PBG structure. Finally, here, for the first time to the best of our knowledge, a large number of theoretical assumptions on QNM metrics for an open cavity, never discussed in literature, are proved, and a simple and direct method to calculate the QNM norm for a 1D-PBG structure is reported. (c) 2009 Optical Society of America

Functionalized Photonic Crystal Sensor Elements based on Nanoporous Polymers

ABSTRACTWe report the development of oxygen sensors using polymer photonic bandgap structure and CMOS chips. These integrated sensors provide a new platform for the development of low cost, low (battery) powered, light weight, robust, fast and small sensors. We demonstrate an approach to encapsulation of chemical and biological recognition elements within the porous structures. This sensing platform is built on our recently demonstrated nanofabrication technique using holographic interferometry of a photo-activated mixture that includes a volatile solvent as well as monomers, photoinitiators, and co-initiators. Resulting structure is nanoporous polymer 1D photonic bandgap structures that has reflection grating property and can be directly integrated into optical sensor systems that we have previously developed. For optical sensor system, CMOS (Complementary Metal Oxide Semiconductor) detectors that include phototransistors, trans impedance amplifier, and other signal processing units are used. Combining CMOS chip and nano-porous polymer reflection grating, we demonstrate an oxygen sensor as a prototype by encapsulating the fluorophore (tris(4,7-diphenyl-1,10-phenathroline)ruthenium(II) using fluorescence intensity.

Defect-mode mirrorless lasing in dye-doped organic/inorganic hybrid one-dimensional photonic crystal

We have developed a dye-doped organic/inorganic hybrid one-dimensional (1D) photonic crystal containing a dye-doped defect layer for defect-mode photonic band gap lasing. The multilayer laser structure consists of alternating layers of titania nanoparticles and polymethylmethacrylate (PMMA) with an active emission layer of organic dyes in PMMA. Low threshold lasing has been demonstrated at a single defect-mode wavelength of the 1D photonic band gap structure resulting from the inhibited density of states of photons within the stop band and the enhanced rates of spontaneous emission at the localized resonant defect mode.

Fabrication-induced disorder in structures for nanophotonics

We investigated the influence of nanoscale technological imperfections to the macroscopic behavior of ordered composite structures for photonic applications. A connection between the deviations from the designed geometry on nanoscopic level and macroscopic behavior was established using amplitude and frequency noise as the primary figures of merit. We calculated the influence of nanoscale deviations by transfer matrix technique, while surface roughness was taken into account by using the effective medium theory. As an example we considered our nonuniform silicon/silica 1D photonic bandgap structures fabricated by rf sputtering, which contained defect layers with spatially varying thickness. The cross-sections and surface morphology of the samples were analyzed by scanning electron microscopy and atomic force microscopy while spectral transmission was measured by FTIR spectrometry. It was established that thickness deviations of 5–7 nm caused scattering losses of 20–40%, while lattice parameter change of 70 nm resulted in spectral transmission shift of about 70 nm. The approach is applicable to other mesoscopic and subwavelength structures, including those with higher dimensional (2D and 3D) geometries and could be used as a means for fast assessment of optical nanodevice fabrication systems.

Analysis of photonic band‐gap structures in stratified medium

PurposeTo demonstrate the flexibility and advantages of a non‐uniform pseudo‐spectral time domain (nu‐PSTD) method through studies of the wave propagation characteristics on photonic band‐gap (PBG) structures in stratified mediumDesign/methodology/approachA nu‐PSTD method is proposed in solving the Maxwell's equations numerically. It expands the temporal derivatives using the finite differences, while it adopts the Fourier transform (FT) properties to expand the spatial derivatives in Maxwell's equations. In addition, the method makes use of the chain‐rule property in calculus together with the transformed space technique in order to make the algorithm flexible in terms of non‐uniform spatial sampling.FindingsThrough the studies of the wave propagation characteristics on PBG structures in stratified medium, it has been found that the proposed method retains excellent accuracy in the occasions where the spatial distributions contain step of up to five times larger than the original size, while simultaneously the flexibility of non‐uniform sampling offers further savings on computational storage.Research limitations/implicationsResearch has been mainly limited to the simple one‐dimensional (1D) periodic and defective cases of PBG structures. Nevertheless, the findings reveal strong implications that flexibility of sampling and memory savings can be realized in multi‐dimensional structures.Practical implicationsThe proposed method can be applied to various practical structures in electromagnetic and microwave applications once the Maxwell's equations are appropriately modeled.Originality/valueThe method validates its values and properties through extensive studies on regular and defective 1D PBG structures in stratified medium, and it can be further extended to solving more complicated structures.

Spectroscopic assessment of rare-earth activated planar waveguides and microcavities

This paper deals with glass-based photonic structures, used to control and modify the optical and spectroscopic properties of rare earth ions. The spectroscopic assessment of sol–gel-derived planar waveguides and 1D photonic band gap structures is reported. The spectroscopic, optical, and structural properties of planar waveguides with (100 − x)SiO 2– xHfO 2– yErO 1.5 with y = 0.3, 0.01; and x = 10, 20, 30, 40 have been investigated by photoluminescence and Raman spectroscopy. The radiative quantum efficiency of the 4I 13/2 metastable state of Er 3+ ions is between 84 and 88% depending on the Si/Hf molar ratio. The sol–gel-derived one-dimensional cavity was realized by a Eu 3+-activated dielectric layer placed between distributed Bragg reflectors (DBRs).

Bragg waveguide grating as a 1d photonic band gap structure: COST 268 modelling task

Modal reflection, transmission and loss of deeply etched Bragg waveguide gratings were modelled by six European laboratories using independently developed two-dimensional (2D) numerical codes based on four different methods, with very good mutual agreement. It was found that (rather weak) material dispersion of the SiO2/Si3N4 system does not significantly affect the results. The existence of lossless Floquet-Bloch modes in deeply etched gratings was confirmed. Based on reliable numerical results, the physical origin of out-of-plane losses of 1D or 2D photonic band gap structures in slab waveguides is briefly discussed.