Optical properties and photonic density of states in one-dimensional and three-dimensional liquid-crystalline photonic crystals

ABSTRACT

Complex optical investigations were performed in one-dimensional (cholesteric) and three-dimensional (Blue Phase II) liquid-crystalline photonic crystals. Spectra of optical transmission and luminescence in the range of the photonic stop band contain information about the local anisotropy, characteristics of the photonic stop band, photonic density of states. We determine the photonic density of states in one-dimensional and three-dimensional liquid-crystalline photonic crystals employing measurements of polarised luminescence. The width of the photonic band gap, density of states and the optical characteristics related to the density of states essentially change with temperature in one-dimensional cholesteric photonic crystal. Drastic transformation of the density of states was found at the transition from one-dimensional to three-dimensional (Blue Phase II) photonic crystal. The results of our investigations demonstrate the possibility to employ the applied method for various types of photonic structures.     

Semiconductor nanowires for subwavelength photonics integration

This article focuses on one-dimensional (1D) semiconductor subwavelength optical elements and assesses their potential use as active and passive components in photonic devices. An updated overview of their optical properties, including spontaneous emission, ultrafast carrier dynamics, cavity resonance feedback (lasing), photodetection, and waveguiding, is provided. The ability to physically manipulate these structures on surfaces to form simple networks and assemblies is the first step toward integrating chemically synthesized nanomaterials into photonic circuitry. These high index semiconductor nanowires are capable of efficiently guiding light through liquid media, suggesting a role for such materials in microfluidics-based biosensing applications.     

One-dimensional random lasing in a single organic nanofiber

One-dimensional light amplification in individual p-sexiphenyl nanofibers is investigated. The influence of fiber morphology on light propagation properties is studied via optical and atomic force microscopy. Isolated nanofibers are shown to yield low-threshold random laser emission in the deep blue. Model calculations of coherent light propagation in one-dimensional random media qualitatively reproduce the experimental results. Implications for photonic nanosensors are briefly discussed.     

Energy transfer in single-molecule photonic wires.

Molecular photonics is a new emerging field of research around the premise that it is possible to develop optical devices using single molecules as building blocks. Truly technological impact in the field requires focussed efforts on designing functional molecular devices as well as having access to their photonic properties on an individual basis. In this Minireview we discuss our approach towards the design and single-molecule investigation of one-dimensional multimolecular arrays intended to work as molecular photonic wires. Three different schemes have been explored: a) perylene-based dimer and trimer arrays displaying coherent exciton delocalisation at room temperature; b) DNA-based unidirectional molecular wires containing up to five different chromophores and exhibiting weak excitonic interactions between neighbouring dyes; and c) one-dimensional multichromophoric polymers based on perylene polyisocyanides showing excimerlike emission. As a whole, our single-molecule data show the importance of well-defined close packing of chromophores for obtaining optimal excitonic behaviour at room temperature. Further improvement on (bio)chemical synthesis, together with the use of single-molecule techniques, should lead in the near future to efficient and reliable photonic wires with true device functionality.     

Integration of gold nanoparticles in optical resonators

The optical absorption of one-dimensional photonic crystal based resonators containing different types of gold nanoparticles is controllably modified by means of the interplay between planar optical cavity modes and localized surface plasmons. Spin-casting of metal oxide nanoparticle suspensions was used to build multilayered photonic structures that host (silica-coated) gold nanorods and spheres. Strong reinforcement and depletion of the absorptance was observed at designed wavelength ranges, thus proving that our method provides a reliable means to modify the optical absorption originated at plasmonic resonances of particles of arbitrary shape and within a wide range of sizes. These observations are discussed on the basis of calculations of the spatial and spectral dependence of the optical field intensity within the multilayers.     

One-dimensional arrays of nanoshell dimers for single molecule spectroscopy via surface-enhanced Raman scattering

The optical properties of one-dimensional arrays of metal nanoshell dimers are studied systematically using the T-matrix method based on Mie theory, within the context of surface enhanced Raman scattering (SERS). It is shown that the local electromagnetic enhancement can be as high as approximately 4.5 x 10(13) for nanoshell dimer arrays with optimal geometry, and sensitive tunability in the resonant frequency can be gained by varying the geometrical parameters, making such structures appealing templates for SERS measurements with single molecule sensitivity. The extraordinarily high enhancement is attributed to a collective photonic effect constructively superposed onto the intrinsic enhancement associated with an isolated nanoshell dimer.     

Optical properties and photonic devices of doped carbon nanotubes

Chemical doping of carbon nanotubes provides a variety of opportunities for tailoring the physical properties of carbon nanotubes. In this review, we discussed the optical properties of doped carbon nanotubes and the related applications as nanoscale photonic devices. The fundamental optical properties of carbon nanotubes with various chemical doping have been summarized. Novel optoelectronic and photonic devices based on doped carbon nanotubes, such as optical nonlinear materials, optical limiting devices, photovoltaic devices, etc., have been discussed.     

Nanoparticle-based one-dimensional photonic crystals

Herein we present a fast, reliable method for building nanoparticle-based 1D photonic crystals in which a periodic modulation of the refractive index is built by alternating different types of nanoparticles and by controlling the level of porosity of each layer. The versatility of the method is further confirmed by building up optically doped photonic crystals in which the opening of transmission windows due to the creation of defect states in the gap is demonstrated. The potential of this new type of structure as a sensing material is illustrated by analyzing the specific color changes induced by the infiltration of solvents of different refractive indexes.     

Dye-integrated cholesteric photonic luminescent solar concentrator

We have developed organic dye-integrated thin-film liquid crystalline photonic luminescent solar concentrators (LSCs), where the chirality of the liquid crystal (LC) results in the formation of a one-dimensional photonic cavity. By varying the different LSC parameters, including dye concentration, spectral position of the photonic band-gap and the LC phase, and by using spectroscopic and electrical characterisation, we have systematically studied the effects of self-absorption, incident absorption and confinement of down-converted emission on optical efficiency. Our results demonstrate that the efficiency of our LSCs is significantly enhanced in the LC phase when the photonic band-gap is at long wavelengths (>600 nm), overcoming associated low incident absorption and higher self-absorption. We reach the significant conclusion that focusing on improving the confinement of dye-emitted photons, rather than on increasing incident absorption, is a more promising route to enhancing thin-film LC-based LSC performance.     

Optical processing with photochromic switches

The absorbance, fluorescence, and refractive index of a photochromic material can be modulated under the influence of optical stimulations. The reversible modification of these macroscopic properties is a result of photoinduced transformations at the molecular level. These processes can be exploited to mediate the interplay of optical signals and offer the opportunity to design and implement photonic devices for optical processing based on molecular components.     

Advances in Photonic Devices Based on Optical Phase-Change Materials

Phase-change materials (PCMs) are important photonic materials that have the advantages of a rapid and reversible phase change, a great difference in the optical properties between the crystalline and amorphous states, scalability, and nonvolatility. With the constant development in the PCM platform and integration of multiple material platforms, more and more reconfigurable photonic devices and their dynamic regulation have been theoretically proposed and experimentally demonstrated, showing the great potential of PCMs in integrated photonic chips. Here, we review the recent developments in PCMs and discuss their potential for photonic devices. A universal overview of the mechanism of the phase transition and models of PCMs is presented. PCMs have injected new life into on-chip photonic integrated circuits, which generally contain an optical switch, an optical logical gate, and an optical modulator. Photonic neural networks based on PCMs are another interesting application of PCMs. Finally, the future development prospects and problems that need to be solved are discussed. PCMs are likely to have wide applications in future intelligent photonic systems.     

Stimuli-responsive 2D polyelectrolyte photonic crystals for optically encoded pH sensing

A versatile photonic crystal sensing motif based on a two-dimensional (2D) inverse opal monolayer of stimuli-responsive polyelectrolyte gel with tunable optical properties is reported. The photonic membrane shows prompt response to pH and can be readily read out from either its optical spectra or interference colours.     

Synthesis and Opto-Electronic Properties of Cholesteric Cellulose Esters

Cholesteric materials display unique optical properties which can be exploited in opto-electronic applications such as light emitting diodes. The key feature is the position of the wavelength of the emitted light relative to the one of the selective reflection band. We have synthesized a set of cellulose derivatives displaying the cholesteric phase with the aim to investigate the correlation between chemical structure and properties. Phase transition temperatures, the chain packing, the wavelength of selective reflection but also absorption and fluorescence spectra were investigated as a function of the degree of substitution (DS), the nature of lateral substituents, the composition of doped systems and blends of different cellulose derivatives. Investigated were furthermore the degree of circular polarization of the emitted light for guest–host systems and for cellulose systems with chromophores linked by covalent bonds to the cellulose backbone as well as their performance in light emitting diodes. The conclusion is that the optical properties can be accounted for on the basis of the model of a one-dimensional photonic crystal. The limiting factor with respect to opto-electronic applications is the poor control of the uniformity of the helix formation and orientation.     

Optically switchable liquid crystal photonic structures

Photo-optic materials offer the possibility of light controlled photonic devices, intelligent and environmentally adaptive optical materials. One strategy for creating these materials is the combination of structure formation through holographic photopolymerization and the variable optical properties of liquid crystals. Holographically patterned, polymer stabilized liquid crystals (HPSLCs) have proven to be useful optical materials. By incorporating photo-optic, azobenzene-derived liquid crystal blends into such material systems, we have generated practical photoresponsive optical materials.     

Gold nanoparticles for the development of clinical diagnosis methods

The impact of advances in nanotechnology is particularly relevant in biodiagnostics, where nanoparticle-based assays have been developed for specific detection of bioanalytes of clinical interest. Gold nanoparticles show easily tuned physical properties, including unique optical properties, robustness, and high surface areas, making them ideal candidates for developing biomarker platforms. Modulation of these physicochemical properties can be easily achieved by adequate synthetic strategies and give gold nanoparticles advantages over conventional detection methods currently used in clinical diagnostics. The surface of gold nanoparticles can be tailored by ligand functionalization to selectively bind biomarkers. Thiol-linking of DNA and chemical functionalization of gold nanoparticles for specific protein/antibody binding are the most common approaches. Simple and inexpensive methods based on these bio-nanoprobes were initially applied for detection of specific DNA sequences and are presently being expanded to clinical diagnosis. Figure Colorimetric DNA/RNA detection using salt induced aggregation of AuNP-DNA nanoprobes.     

FABRICATION OF PHOTONIC CRYSTAL WITH SUPERLATTICES

A novel technique was used to fabricate three-dimensional photonic crystals with superlattices. The super structure was fabricated by assembling monodispersed microspheres in the grooves of the scales of morpho butterfly, which makes the photonic crystal being composed of two kinds of different photonic structures (natural groove structure of butterfly wing and artificial microspherical colloids arrangement). The superstructural photonic crystal exhibits some unique optical properties different from both the butterfly wing and the colloidal crystal. The approach exhibited here provides a new way for fabricate photonic crystals with superlattices.     

流动控制沉积法制备PMMA叠层光子晶体薄膜及其光学性能研究

采用流动控制沉积法,通过调控泵速和聚甲基丙烯酸甲酯(PMMA)胶体微球溶液的浓度,制备出微球排列高度有序且薄膜紧密附着于基底的高质量光子晶体薄膜。获得了制备高质量PMMA光子晶体薄膜的组装条件范围,发现在该条件范围内,当泵速或胶体微球溶液浓度一定时,PMMA光子晶体薄膜的厚度随胶体微球溶液浓度的增加或泵速的降低而增加。研究了组装条件对PMMA光子晶体薄膜光学性能的影响,发现光子禁带位置随光子晶体薄膜厚度增加或减少而红移或蓝移。在此基础上,控制组装条件得到了不同尺寸微球堆叠而成的叠层光子晶体薄膜,并研究了其光学性能的变化规律。结果显示,叠层光子晶体薄膜的光子禁带峰为各层叠层光子晶体禁带峰的简单叠加,且峰强度受光入射角方向影响。     

FABRICATION OF PHOTONIC CRYSTAL WITH SUPERLATTICES

1. INTRODUCTION The very latest subject of physics to surface in biology is the photonic crystal, which is ordered, subwavelength structured material capable of controlling the propagation of light in the similar manner as which atomic crystal control electrons [1,2]. Due to the application of the photonic crystal in laser, integrated optical circuit, it attracted great attention in the past decade. Photonic crystals can be fabricated by microfabrication methods, holographic methods, and c…     

近场光学和纳米粒子生物传感器

评介近场光学生物传感器和纳米粒子生物传感器及其在单细胞的原位活体分析中的应用。     

Templated‐Assembly of CsPbBr3 Perovskite Nanocrystals into 2D Photonic Supercrystals with Amplified Spontaneous Emission

Perovskite nanocrystals (NCs) have revolutionized optoelectronic devices because of their versatile optical properties. However, controlling and extending these functionalities often requires a light‐management strategy involving additional processing steps. Herein, we introduce a simple approach to shape perovskite nanocrystals (NC) into photonic architectures that provide light management by directly shaping the active material. Pre‐patterned polydimethylsiloxane (PDMS) templates are used for the template‐induced self‐assembly of 10 nm CsPbBr₃ perovskite NC colloids into large area (1 cm²) 2D photonic crystals with tunable lattice spacing, ranging from 400 nm up to several microns. The photonic crystal arrangement facilitates efficient light coupling to the nanocrystal layer, thereby increasing the electric field intensity within the perovskite film. As a result, CsPbBr₃ 2D photonic crystals show amplified spontaneous emission (ASE) under lower optical excitation fluences in the near‐IR, in contrast to equivalent flat NC films prepared using the same colloidal ink. This improvement is attributed to the enhanced multi‐photon absorption caused by light trapping in the photonic crystal.