Nature of heterophase inclusions in high-purity optical fiber materials as studied with 3D laser ultramicroscopy

3D laser ultramicroscopy (3D LUM) is intended specially for determining the concentration and size distribution of submicron inclusions in the bulk samples of high-purity materials for visible and IR fiber optics. In this work the 3D LUM technique is shown to be able to identify the nature of individual inclusions detected. The measurement of the light scattered by an inclusion at a varied probe beam wavelength and polarization and at a varied scattered light collection angle makes it possible to determine the inclusion refractive index. The 3D LUM possibilities are illustrated by the example of studying the inclusion nature in the As₂S₃ glass samples prepared by the direct synthesis from elements in a quartz container at elevated temperatures.     

Optical properties and conductivity of PEDOT:PSS films treated by polyethylenimine solution for organic solar cells

We report on conductivity and optical property of three different types of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) films [pristine PH1000 film (PH1000-p), with 5 wt.% ethylene glycol additive (PH1000-EG) and with sulfuric acid post-treatment (PH1000-SA)] before and after polyethylenimine (PEI) treatment. The PEI is found to decrease the conductivity of all the PEDOT:PSS films. The processing solvent of 2-methoxyethanol is found to significantly enhance the conductivity of PH1000-p from 1.1 up to 744 S/cm while the processing solvent of isopropanol or water does not change the conductivity of PH1000-p much. As for the optical properties, the PEI treatment slightly changes the transmittance and reflectance of PH1000-p and PH1000-EG films, while the PEI leads to an substantial increase of the absorptance in the spectral region of 400–1100 nm of the PH1000-SA films. Though the optical property and conductivity of the three different types of PEDOT:PSS films vary with the PEI treatment, the treated PEDOT:PSS films exhibit similar low work function. We demonstrate solar cells with a simple device structure of glass/low-WF PEDOT:PSS/P3HT:ICBA/high-WF PEDOT:PSS cells that exhibit good performance with open-circuit voltage of 0.82 V and fill factor up to 0.62 under 100 mW/cm² white light illumination.     

Residual strain in cadmium telluride/gallium arsenide (001) heterostructures as a function of temperature

Optical studies of residual strain in cadmium telluride (CdTe) films grown using molecular beam epitaxy on gallium arsenide (GaAs) substrate have been performed using photoreflectance techniques. Measurements have been conducted to determine the fundamental transition energy, heavy-hole and light-hole transition energy critical-point parameters in a range of temperatures between 12 and 300 K. There are problems inherent in the fabrication of optoelectronic devices using high-quality CdTe films, due to strain effects resulting from both the lattice mismatch (CdTe: 14.6%) and the thermal expansion coefficient difference. The CdTe film exhibits compressive stress causing valence-band splitting for light and heavy holes. We have used different models to fit the obtained experimental data and, although the critical thickness for the CdTe has been surpassed, the strain due to the lattice mismatch is still significant. However, the strain due to the thermal expansion is dominant. We have found that the fundamental transition energy, E₀, is affected by the compressive strain and the characteristic values are smaller than those reported. In addition, the total strain is compressive for the full measured range, since the strain due to the lattice mismatch is one order of magnitude higher than that calculated from the thermal expansion.     

Photoluminescence properties of novel white phosphor of Dy3+-doped LaBSiO5 glass

A single-phased white emitting phosphor LaBSiO₅:Dy³⁺ was successfully synthesized via a solid state reaction. The X-ray diffraction results confirmed that the doped Dy³⁺ ions did not change the lattice structure. Several strong excitation peaks of LaBSiO₅:Dy³⁺ were found around 300–450 nm. Under excitation of 350 nm, the LaBSiO₅:Dy³⁺ exhibited white emission by combining the two emission peaks at 478 and 574 nm corresponding to the typical ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions. The optimal substitution proportions of Dy³⁺ for La³⁺ was determined to be 1 mol% and the critical distance of Dy³⁺ was 25.9628 Å. Moreover, the CIE chromaticity coordinates of LaBSiO₅:Dy³⁺ phosphor was (0.3116, 0.3474) which is close to the ideal white light coordinates (0.333, 0.333), indicating that the phosphor has a potential application as a single component ultraviolet-convertible white light emitting phosphor.     

An efficient utilization of intermittent surface–satellite optical links by using mass storage device embedded in satellites

Recently, earth observation system by using satellite network has attracted much attention due to its wide coverage and disaster resistance. Although the system is useful for collecting various data, which have an effect on a natural disaster, ecology and so forth, earth observation satellite hardly send the collected observation data to the ground station. This is because that the earth observation satellite needs to orbit near surface of the earth to get high-precision data, and it limited the time that can be used to send the observed data traffic to the ground station. Additionally, the amount of the observed data drastically increase in these days. Thus, we focus on the data relay satellite using optical communication in this network. By relaying observed data to traffic to the relay satellite, which has geostationary orbit, it is possible to increase the chance of sending data for the observation satellite due to the wide coverage of the relay satellite. In addition, laser light that is used in optical communication in satellite network has high frequency and it can deliver large data compared with radio wave. However, laser light is greatly influenced by atmosphere, and optical link capacity between satellite and ground station drastically changes according to weather condition. Therefore, we propose a new data traffic control method to use the network constructed by satellites which has mass storage device effectively according to the condition of optical downlink between satellite and optical ground station. The effectiveness of the proposed method is evaluated with numerical result.     

Design of natural fiber composites utilizing interfacial crystallinity and affinity

Butanediol initiated poly(ε-caprolactone) (PCL) has recently been reported as a toughening agent for cationically curing cycloaliphatic epoxides providing plasticized thermosets with excellent properties (Lützen et al., 2013). In this contribution that promising toughening approach was applied for the first time for the development of novel natural fiber composites (NFC). NFCs based on conventional brittle thermosetting polymers often suffer from poor interfacial adhesion and stress cracking. Composites made up of the novel plasticized thermosets and woven flax fiber preserved the elastomer-like properties and increased tensile strength and elongation at break up to 60 MPa and 5%, respectively. Furthermore, PCL was shown not only to toughen the epoxide but also to modulate the affinity of the matrix to the fiber. In conclusion, improved interfacial adhesion and the resulting excellent mechanical properties of cationically curable NFCs were achieved by both interfacial crystallization and affinity.     

Impact behavior and fractographic study of carbon nanotubes grafted carbon fiber-reinforced epoxy matrix multi-scale hybrid composites

Carbon nanotubes are the most promising reinforcement for high performance composites. Multiwall carbon nanotubes were directly grown onto the carbon fiber surface by catalytic thermal chemical vapor deposition technique. Multi-scale hybrid composites were fabricated using the carbon nanotubes grown fibers with epoxy matrix. Morphology of the grown carbon nanotubes was investigated using field emission scanning electron microscopy and transmission electron microscopy. The fabricated composites were subjected to impact tests which showed 48.7% and 42.2% higher energy absorption in Charpy and Izod impact tests respectively. Fractographic analysis of the impact tested specimens revealed the presence of carbon nanotubes both at the fiber surface and within the matrix which explained the reason for improved energy absorption capability of these composites. Carbon nanotubes presence at various cracks formed during loading provided a direct evidence of micro crack bridging. Thus the enhanced fracture strength of these composites is attributed to stronger fiber–matrix interfacial bonding and simultaneous matrix strengthening due to the grown carbon nanotubes.     

An experimental–numerical investigation of hydrothermal response in adhesively bonded composite structures

Water absorption and thermal response of adhesive composite joints were investigated by measurements and numerical simulations. Water diffusivity, saturation, swelling, and thermal expansion of the constituent materials and the joint were obtained from gravimetric experiments and strain measurements using embedded fiber Bragg grating (FBG) sensors. The mechanical response of these materials at different temperatures and water content was characterized by dynamic mechanical analysis. Thermal loading and water absorption in joint specimens were detected by monitoring the FBG wavelength shift caused by thermal expansion or water swelling. The measured parameters were used in finite element models to simulate the response of the embedded sensor. The good correlation of experimental data and simulations confirmed that the change in FBG wavelength could be accurately related to the thermal load or water absorption process. The suitability of the embedded FBG sensors for monitoring of water uptake in adhesive composite joints was demonstrated.     

Highly transparent terbium gallium garnet crystal fabricated by the floating zone method for visible–infrared optical isolators

Highly transparent terbium gallium garnet (Tb₃Ga₅O₁₂; TGG) single crystal having a large Verdet constant based on the visible and near-infrared region (VIS–NIR) Faraday rotator was grown by Floating Zone (FZ) growth machine. We successfully grew TGG single-crystal rods of 8–10 mm in diameter, which was suitable for the use in optical devices. The crystal showed a full-width at half-maximum as little as 18 arcsec by the X-ray rocking curve measurement. The Faraday rotation (B = 0.55T) was investigated at wavelength of 532, 632.8, 1064 nm at room temperature. The lower weak absorption coefficient, higher Verdet constant, thermal conductivity and laser induced damage threshold (LIDT) compared to the commercial TGG gives the great potential of using this new method to meet the increasing demand of VIS–NIR Faraday rotators (FRs).     

Study of aging behavior of 9/70/30 and 9/65/35 PLZT by optical interferometric technique

In this work Pb_0.91La_0.09(Zr_0.70Ti_0.30)_0.9775O₃ PLZT (9/70/30) and Pb_0.91La_0.09(Zr_0.65Ti_0.35)_0.9775O₃ PLZT (9/65/35) ceramics were prepared at four different sintering temperatures by solid solution method. The samples were aged by keeping at room temperature for 19 days. After the aging process, structural and electrical properties of the samples were studied using Modified Michelson Interferometer, LCR meter and X-ray diffraction. The effect of the Zr/Ti ratios on the dielectric and ferroelectric properties was also investigated. The aged PLZT (9/70/30) showed pinched P–E loop and remnant strain in rhombohedral phase, while PLZT (9/65/35) showed distort s–E shape implying non-180° domain in tetragonal phase.