Long-De Wang

Fabrication and spectroscopic investigation of branched silver nanowires and nanomeshworks

Wide wavelength ranges of light localization and scattering characteristics can be attributed to shape-dependent longitude surface plasmon resonance in complicated nanostructures. We have studied this phenomenon by spectroscopic measurement and a three-dimensional numerical simulation, for the first time, on the high-density branched silver nanowires and nanomeshworks at room temperature. These nanostructures were fabricated with simple light-induced colloidal method. In the range from the visible to the near-infrared wavelengths, light has been found effectively trapped in those trapping sites which were randomly distributed at the corners, the branches, and the junctions of the nanostructures in those nanostructures in three dimensions. The broadened bandwidth electromagnetic field enhancement property makes these branched nanostructures useful in optical processing and photovoltaic applications.

Optical properties of Ag nanoparticle-polymer composite film based on two-dimensional Au nanoparticle array film.

The nanocomposite polyvinyl pyrrolidone (PVP) films containing Ag nanoparticles and Rhodamine 6G are prepared on the two-dimensional distinctive continuous ultrathin gold nanofilms. We investigate the optical properties and the fluorescence properties of silver nanoparticles-PVP polymer composite films influenced by Ag nanoparticles and Au nanoparticles. Absorption spectral analysis suggests that the prominently light absorption in Ag nanowire/PVP and Ag nanowire/PVP/Au film arises from the localized surface plasmon resonance of Ag nanowire and Au nanofilm. The enhanced fluorescence is observed in the presence of Ag nanowire and Au nanofilm, which is attributed to the excitation of surface plasmon polariton resonance of Ag nanowire and Au nanofilm. The gold nanofilm is proven to be very effective fluorescence resonance energy transfer donors. The fabricated novel structure, gold ultrathin continuous nanofilm, possesses high surface plasmon resonance properties and prominent fluorescence enhancement effect. Therefore, the ultrathin continuous gold nanofilm is an active substrate on nanoparticle-enhanced fluorescence.

Two-dimensional ultrathin gold film composed of steadily linked dense nanoparticle with surface plasmon resonance

BackgroundNoble metallic nanoparticles have prominent optical local-field enhancement and light trapping properties in the visible light region resulting from surface plasmon resonances.ResultsWe investigate the optical spectral properties and the surface-enhanced Raman spectroscopy of two-dimensional distinctive continuous ultrathin gold nanofilms. Experimental results show that the one- or two-layer nanofilm obviously increases absorbance in PEDOT:PSS and P3HT:PCBM layers and the gold nanofilm acquires high Raman-enhancing capability.ConclusionsThe fabricated novel structure of the continuous ultrathin gold nanofilms possesses high surface plasmon resonance properties and boasts a high surface-enhanced Raman scattering (SERS) enhancement factor, which can be a robust and cost-efficient SERS substrate. Interestingly, owing to the distinctive morphology and high light transmittance, the peculiar nanofilm can be used in multilayer photovoltaic devices to trap light without affecting the physical thickness of solar photovoltaic absorber layers and yielding new options for solar cell design.

Photoluminescence of MoS 2 prepared by effective grinding-assisted sonication exfoliation

Exfoliation of bulk molybdenum disulfide (MoS2) using sonication in appropriate solvent is a promising route to large-scale preparation of few-layered or monolayered crystals. Grinding-assisted sonication exfoliation was used for preparing monolayered MoS2 nanosheets from natural mineral molybdenite. By controlling the sonication time, larger crystallites could be further exfoliated to smaller as well as thinner nanosheets without damaging their structures. The concentration of 1.6 mg mL-1 of final solution could be achieved. Several microscopic techniques like scanning electron microscopy, transmission electron microscopy, and atomic force microscopy were employed to evaluate the exfoliation results. Strong photoluminescence with the peak centered at 440 nm was also observed in the resulting dispersion which included several small lateral-sized (∼3 nm) nanostructures.

Low half-wave voltage Y-branch electro-optic polymer modulator based on side-chain polyurethane-imide

A Y-branch electro-optic (EO) polymer modulator has been designed and fabricated. High performance side-chain polyurethane-imide (PUI) with a high EO coefficient of larger than 50 pm/V and a moderate glass-transition temperature (Tg) of 206∘C is used as EO polymer core layer of the modulator. The fabricated phase modulator exhibits a low half-wave voltage of 1.94 V at 1550 nm in single arm modulation with 1 cm EO interaction length and 2 cm total length. The results show that the modulator fabricated by side-chain PUI EO materials possesses potential applications in low driving voltage and low cost optical systems.

Synthesis and characterization of electro-optic polyurethane-imide and fabrication of optical waveguide device:

The novel electro-optic (EO) polymers of fluorinated cross-linkable Y-type polyurethane-imides (PUI) were designed and synthesized by polycondensation of second-order non-linear optical azo-based chromophores, phenyl diisocyanate, and aromatic dianhydride. Molecular structural characterization for the resulting polymers was achieved by proton nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, elemental analysis, and gel permeation chromatography. The resulting polymers exhibited good film-forming properties, high glass transition temperature in the range from 186°C to 198°C and thermal stability up to 300°C, high EO coefficient (γ33 = 43–60 pm/V) at 1550 nm wavelength, good stabilization of electrically induced chromophore dipole alignment and low optical propagation losses in the range of 1.5–1.7 dB/cm at 1550 nm, which are suitable for the EO modulators. Using the synthesized EO PUI as the active core material and of a fluorinated polyimide as cladding material, we have designed and fabricated the high-performance polymer waveguide Mach-Zehnder EO modulators. Obvious modulation was observed by application of ac voltage signal to the EO modulators.

Flexible TE-Pass Polymer Waveguide Polarizer With Low Bending Loss

We demonstrate a flexible hybrid transverse electric (TE)-pass polymer waveguide polarizer utilizing the coupling between a lossy infinite-width surface plasmon polariton (LRSPP) waveguide and a dielectric waveguide. The transverse magnetic (TM) nature of the LRSPP waveguide allows for enabling effective attenuation of the TM modes and remarkable reduction of bending loss of the TE mode for a bent dielectric waveguide. Up to 20 times improvement of the bending loss characteristic is achieved compared with the stand-alone dielectric waveguide at a bending radius of 1 mm. Also, less than 19% deration of the extinction ratio is obtained at a bending radius of 1 mm to confirm the functionality of the waveguide polarizer at small bending radius. Such device promises the applications in which the bending directions are predetermined even with very small radii.

Low voltage electro-optic modulator based on side-chain polyurethane-imide

High performance electro-optic (EO) polymers of side-chain polyurethane-imide were designed and synthesized to fabricated EO modulators. The polymers possess a high EO coefficient of larger than 55 pm/V and the fabricated modulator exhibits a low half-wave voltage of 1.875 V at 1550 nm.

Low loss polymeric electro-optic modulator based on disperse red 1 doped fluorinated polyimide

We demonstrate a polymeric electro-optic (EO) modulator with a Mach-Zehnder interferometer (MZI) structure. Low loss fluorinated polyimide (FPI) and low cost nonlinear optical (NLO) chromophores of disperse red 1 (DR 1) were introduced to form the core layer of the modulator. The fabricated EO polymer waveguide exhibits a low propagation loss of 1.14 dB/cm, and the modulating device exhibits a good EO response which indicates a low half-wave voltage of about 5.4 V. The results show that the polymeric EO material of DR 1 doped FPI is a good candidate of high performance EO materials and the modulating device based on the EO polymer possesses potential applications.

Study on the synthesis and optical properties of polyurethane-imide

In this paper, Polyurethane-imide (PUI) which has the advantages of polyurethane and polyimide is synthesized and introduced to apply in the slab optical waveguide devices. The PUI is characterized by infrared spectrum (FT-IR), differential scanning calorimeter (DSC) and thermal gravimetric analysis (TGA). Slab optical waveguide is prepared via spin coating the cyclopentanone solution of PUI on top of K9 glass and cured at 140 °C for 20 minutes to complete removal of the solvent from the film. The film-formability of PUI is characterized by atomic force microscope (AFM). The results of DSC and TGA indicate that the PUI exhibits high thermal stability up to its glass-transition temperature (Tg) of 206 °C and 10% heat loss temperature of 310°C. Optical properties of absorption behavior and propagation loss are investigated in slab waveguides, and propagation loss of 1.782 dB/cm at 1310nm in TE (transverse electric field) mode has been achieved by using prism-coupler method. The results show that polyurethane-imide has distinct merits: good processability, high thermal stability and moderate glass-transition temperature, excellent film-formability, and low propagation loss. These advantages of polyurethane-imides make them suitable as electro-optic polymeric materials in integrated optics.