Uniform amplitude multi-wavelength single-longitudinal-mode Brillouin–erbium fiber lasers

A multi-wavelength single-longitudinal-mode (SLM) Brillouin–erbium fiber laser has been proposed and demonstrated by using the broadband linear gain and the narrow band gain of stimulated Brillouin scattering both in Er-doped fiber. Eight orders of lased Stokes have been observed with relatively uniform amplitudes and rigid spacing of 11?GHz. Each Stokes frequency works on SLM operation owing to very short oscillating cavity. The output signal-to-noise ratio is as high as 50?dB. The hybrid gain of two mechanisms in Er-doped fiber is helpful to improve the flatness of the multi-wavelength combs.     

L-Band multi-wavelength erbium-doped fibre laser based on non-linear optical loop mirror and dual-channel Mach–Zehnder interferometer

In this letter, we propose and demonstrate an L-Band linear cavity tunable multi-wavelength erbium-doped fibre laser based on non-linear optical loop mirror (NOLM) and dual-channel Mach–Zehnder interferometer (MZI) . The NOLM provides the intensity-dependent transmissivity, can effectively alleviate the mode competition and beating caused by the homogeneous gain broadening, so that the multi-wavelength lasing can be achieved at room temperature. The dual-channel MZI, configured by linking the two outputs of the single-channel MZI, serves as comb filter. By adjusting the polarization controller in NOLM and pump power, the tunable multi-wavelength output at 1600 nm can be achieved. Moreover, the output stability of the laser has also been accomplished .     

Switchable triple-wavelength thulium-doped fibre laser based on a Mach–Zehnder interferometer and fibre ring filter

A switchable triple-wavelength thulium-doped fibre laser based on an all-fibre Mach–Zehnder interferometer and fibre ring filter with a polarization-maintaining fibre is proposed and experimentally demonstrated. In the proposed fibre laser, a Mach–Zehnder interferometer comprising two 1 × 2 optical couplers is inserted into the optical cavity to produce the comb filter effect. The fibre ring filter comprises two optical couplers with a 3:7 splitting ratio and a 2-m-long polarization-maintaining fibre to improve lasing stability. Single-wavelength lasing can be tuned continuously from 1864.4 to 1884.5 nm, and five different modes of dual-wavelength and switchable triple-wavelength lasers can be realized by changing the polarization state. The signal-to-noise ratios of all lasers are more than 33 dB. The maximum power fluctuations and wavelength variations are less than 1.5 dB and 0.3 nm at room temperature, respectively, and the 3 dB bandwidth is less than 0.2 nm. The results demonstrate that stable and switchable single- or dual-wavelength lasers can be generated using the designed fibre laser.     

Tough–brittle transition in unidirectional composites with fibre breakage and fibre–matrix interfacial failure

International Journal of Fracture - Fracture of three-dimensional unidirectional composites is studied through Monte Carlo fracture simulations on model composites. Fracture develops in the model...     

Manufacturing sisal–polypropylene composites with minimum fibre degradation

Natural fibres, such as sisal, flax and jute, possess good reinforcing capability when properly compounded with polymers. These fibres are relatively inexpensive, originate from renewable resources and possess favourable values of specific strength and specific modulus. Thermoplastic polymers have a shorter cycle time as well as reprocessability despite problems with high viscosities and poor fibre wetting. The renewability of natural fibres and the recyclability of thermoplastic polymers provide an attractive eco-friendly quality to the resulting natural fibre-reinforced thermoplastic composite materials. Common methods for manufacturing natural fibre-reinforced thermoplastic composites, injection moulding and extrusion, tend to degrade the fibres during processing. Development of a simple manufacturing technique for sisal fibre-reinforced polypropylene composites, that minimises fibre degradation and can be used in developing countries, is the main objective of this study. Composite sheets with a fibre length greater than 10 mm and a fibre mass fraction in the range 15% to 35% exhibited good mechanical properties.     

Critical analysis of frequency selective surfaces embedded composite microwave absorber for frequency range 2–8 GHz

Radar wave absorbers are important for the reduction of radar cross section of the target for stealth applications. Earlier the radars were available in the frequency range 8–12 GHz (X-band) and 12–18 GHz (Ku-Band). Due to recent advancement in radar technology, radars are now available from 2 to 18 GHz frequency range. So there is an urgent need to develop such a material that can work as radar wave absorber in the lower frequency band of the microwave spectrum i.e., 2–8 GHz. For this purpose the selection of material is an important criterion as the radar wave absorption depends primarily upon the material characteristics i.e., complex permittivity and complex permeability. For lower frequency radar wave absorption, the material must also possess the conducting property along with dielectric and magnetic properties. Therefore, an attempt has been made to develop a radar wave absorbing nano-composite material by selecting constituent materials with such inherent properties that can work for the absorption of radar wave in the lower frequency range. It is observed that the developed composite give good absorption in the lower frequency range but with narrow radar wave absorption bandwidth (4–7 GHz). So we have explored the possibility of the efficient use of an advanced electromagnetic technique like frequency selective surface to enhance the radar wave absorption bandwidth in the lower frequency region of the microwave frequency spectrum and precaution has been taken such that complexity due to FSS can be avoided. It has been observed that the synthesised single layer absorber with single square loop, cross dipole and Jerusalem cross FSSs provides radar wave absorption bandwidth in the frequency range 2–8 GHz.     

Wavelength-switchable C-band erbium-doped fibre laser incorporating all-fibre Fabry–Perot interferometer fabricated by chemical etching

A switchable and stable triple-wavelength, ring-cavity, erbium-doped fibre laser incorporating an all-fibre Fabry–Perot interferometer (FPI) is designed and experimentally demonstrated. In the proposed fibre laser, the all-fibre FPI is fabricated using the chemical etching method and is used to generate the filter effect. The laser threshold is 88 mW. Switchable single-wavelength lasing at 1529.9, 1545.1 and 1560.2 nm can be realized with a power fluctuation less than 0.64 dB under 20 min of scanning time at room temperature. In addition, the wavelength-switchable dual-wavelength lasers can be tuned by changing the polarization state in the experiment, and the maximum power fluctuations for the 1545.1 and 1560.2 nm lasers are less than 1.19 and 1.57 dB at 26 °C, respectively. Furthermore, a triple-wavelength laser is obtained by adjusting the polarization controller. The results demonstrate that switchable single-, dual-, or triple-wavelength lasers can be generated through the proposed fibre laser.     

Effect of beam interaction time on laser alloying with pulsed Nd–YAG laser

Abstract

Surface alloying of aluminium with nickel was carried out using a pulsed Nd–YAG laser. The effect of beam interaction time on laser alloying of aluminium with pulsed Nd–YAG laser has been studied. It was found that the beam interaction time of a pulsed laser has a significant effect on microstructure and properties of alloyed layers. The results indicated that with changes in the beam diameter, higher thickness of alloyed layer and higher microhardness are both obtained at a lower effective interaction time. When travel speed changes, the same conditions are obtained at a higher effective interaction time.     

Supercritical carbonation treatment on extruded fibre–cement reinforced with vegetable fibres

The objective of this research was to evaluate the effects of supercritical carbonation treatment for 2 h on the main hydrated phases of the cement matrix (calcium hydroxide and calcium silicate hydrate) and durability of extruded fibre–cement reinforced with bleached eucalyptus pulp and residual sisal chopped fibres. The thermal analysis, bulk density, porosity, physical characteristics and mechanical performance were evaluated before and after 200 soaking and drying cycles for following the degradation of the material under accelerated ageing conditions. The higher carbonation rate during the early stage of curing period decreased the porosity by sealing the opened pores around vegetable fibres and, consequently, led to lower water absorption and higher bulk density in the composites. The average MOR-values showed a significant increase in the case of the supercritical carbonated extruded fibre–cement in the initial age and after accelerated ageing. Besides, after 200 soaking and drying ageing cycles, the average values of energy of fracture (γ_WoF) of the carbonated composites decrease only 28%, showing evidences of the preservation of microstructural stability and toughness of the fibre–cement composites after supercritical CO₂ treatment.     

Fire structural modelling of fibre–polymer laminates protected with an intumescent coating

This paper presents a new modelling approach to analyse the fire structural response of fibre–polymer laminates protected with an intumescent surface coating. The model is designed to predict the temperature, decomposition, softening and failure of laminates with an intumescent coating in fire. The modelling involves a three-stage analytical approach: (i) thermal-chemical analysis of the intumescent coating, (ii) thermal-chemical analysis of heat transfer through the laminate substrate (beneath the intumescent coating), and (iii) thermal-mechanical analysis of the softening and failure of the laminate under tension or compression loading. Fire structural tests were performed on a woven glass/vinyl ester laminate coated with an organic intumescent material to validate the modelling approach. It is shown the model can predict with good accuracy the temperature distribution and swelling of the intumescent coating with increasing exposure time to a constant heat flux. The model can approximate the temperature, softening and failure of the laminate substrate.     

Dispersion-managed dark–bright vector soliton propagation and interaction in fibre with randomly varying birefringence

Coupled dark–bright vector solitons are considered in four dispersion-managed maps with three sorts of randomly varying birefringence, and the effects of the birefringence on the soliton propagation and interaction are investigated by the numerical method. The birefringence leads to the disintegration of the bright soliton and the submergence of the dark soliton, and enhances the soliton interaction. The effects depend strictly on the dispersion-managed maps and the birefringence, and the dark solitons have robust features compared with the bright solitons. Finally, the effective controls for the soliton propagation and interaction are discussed.     

Toughening performance of glass fibre composites with core–shell rubber and silica nanoparticle modified matrices

The fracture energies of glass fibre composites with an anhydride-cured epoxy matrix modified using core–shell rubber (CSR) particles and silica nanoparticles were investigated. The quasi-isotropic laminates with a central 0°/0° ply interface were produced using resin infusion. Mode I fracture tests were performed, and scanning electron microscopy of the fracture surfaces was used to identify the toughening mechanisms.The composite toughness at initiation increased approximately linearly with increasing particle concentration, from 328 J/m² for the control to 842 J/m² with 15 wt% of CSR particles. All of the CSR particles cavitated, giving increased toughness by plastic void growth and shear yielding. However, the toughness of the silica-modified epoxies is lower as the literature shows that only 14% of the silica nanoparticles undergo debonding and void growth. The size of CSR particles had no influence on the composite toughness. The propagation toughness was dominated by the fibre toughening mechanisms, but the composites achieved full toughness transfer from the bulk.     

Microstructural characterisation and corrosion behaviour of laser cladded Al–12Si alloy onto magnesium AS41/carbon fibre composite

Abstract

The quality and properties of laser clad layers are dependent on the microstructure and properties of the interfaces with the substrate. The present paper reports, in details, on the characterisation of microstructure of the coating and interfacial layers evolved as a result of the CO₂ laser remelting of previously plasma sprayed Al–12Si alloy onto C short fibres reinforced AS41–Mg composite. Scanning electron microscopy (SEM), wavelength dispersive X-ray (WDX) analysis and X-ray diffraction (XRD) were employed to identify the phases arising in the interfacial layers. The latter are composed mainly of Mg₁₇Al₁₂ and Mg₂Si phases. XRD was conducted on the clad layers at different distances from the interface. At the same layers, the potentiodynamic polarisation in sodium chloride solution was measured and it was found that as the Mg content increases in the clad coating, the corrosion resistance decreases. However, the corrosion current of the clad coating is around two orders of magnitude lower than that of the C/Mg composite.     

Analysis of shear transfer and gap opening in timber–concrete composite members with notched connections

In timber–concrete composite members with notched connections, the notches act as the shear connections between the timber and the concrete part, and have to carry the shear flow necessary for composite action. The shear transfer through the notches generates shear and tensile stresses in both parts of the composite member, which may lead to brittle failure and to an abrupt collapse of the structure. Although simplified design formulas already exist, some structural aspects are still not clear, and a reliable design model is missing. This paper summarizes current design approaches and presents analytical models to understand the shear-carrying mechanism, to estimate the shear stresses acting in the timber and concrete, and to predict failure. The analysis concentrates on three problems: the shearing-off failure of the timber close to the notch, the shear failure of the concrete, and the influence of the shear flow on the gap opening between the timber and concrete. Parts of the model calculations could be compared to experimental observations. The conclusions of this paper contribute to improving current design approaches.     

Osteoblast interaction with laser cladded HA and SiO2-HA coatings on Ti–6Al–4V

In order to improve the bioactivity and biocompatibility of titanium endosseous implants, the morphology and composition of the surfaces were modified. Polished Ti–6Al–4V substrates were coated by a laser cladding process with different precursors: 100 wt.% HA and 25 wt.% SiO₂-HA. X-ray diffraction of the laser processed samples showed the presence of CaTiO₃, Ca₃(PO₄)₂, and Ca₂SiO₄ phases within the coatings. From in vitro studies, it was observed that compared to the unmodified substrate all laser cladded samples presented improved cellular interactions and bioactivity. The samples processed with 25 wt.% SiO₂-HA precursor showed a significantly higher HA precipitation after immersion in simulated body fluid than 100 wt.% HA precursor and titanium substrates. The in vitro biocompatibility of the laser cladded coatings and titanium substrate was investigated by culturing of mouse MC3T3-E1 pre-osteoblast cell line and analyzing the cell viability, cell proliferation, and cell morphology. A significantly higher cell attachment and proliferation rate were observed for both laser cladded 100 wt.% HA and 25 wt.% SiO₂-HA samples. Compared to 100 wt.% HA sample, 25 wt.% SiO₂-HA samples presented a slightly improved cellular interaction due to the addition of SiO₂. The staining of the actin filaments showed that the laser cladded samples induced a normal cytoskeleton and well-developed focal adhesion contacts. Scanning electron microscopic image of the cell cultured samples revealed better cell attachment and spreading for 25 wt.% SiO₂-HA and 100 wt.% HA coatings than titanium substrate. These results suggest that the laser cladding process improves the bioactivity and biocompatibility of titanium. The observed biological improvements are mainly due to the coating induced changes in surface chemistry and surface morphology.     

Microstructure and mechanical properties of laser beam welded Al–Li alloy 2060 with Al–Mg filler wire

Alloy 2060-T8 is a newly developed high-strength Al–Li alloy for applications in aircraft industry. Crack-free welds were obtained in laser beam welding with 5087 filler wire under optimized welding conditions. In this paper, fusion zone microstructure and joint mechanical properties were investigated. Microstructure typical for the weld metal consists of α-Al matrix with a few nanoscale precipitates inside and a coarse icosahedral quasicrystalline T₂ phase at the dendritic and grain boundaries. The quasicrystalline occurred normally in Al–Li–Cu alloys with higher Li contents. Our investigations show that the icosahedral quasicrystalline phase T₂ phase forms in the laser-welded Al–Li alloy 2060 with lower Li content as a result of segregation and replacement of Mg element. The joint tensile strength in as-welded condition is around 317 MPa, about 63% of that of the base metal, and fracture occurs within the fusion zone.     

Cholesterol biosensor based on a plastic optical fibre with sol–gel: structural analysis and sensing properties

In this paper, we report the design and characterization of an optical fibre cholesterol biosensor by using sol–gel immobilization technique. The cholesterol enzyme is encapsulated inside of the sol–gel film onto an end of a plastic optical fibre. Two film deposition methods (Dip-Coating and Immersion) were studied. The morphology analysis and sensing properties permit us to determine the best film deposition to sense cholesterol concentration. The range of measured is 4.4–5.2 mM in real time and our results were validated by comparing them with other previously published results. The biosensor is portable, simple cheap, and easy to use.     

Selective laser melting of in situ TiN–Ti5Si3 composites with RE–Si–Fe addition: comparative study

Abstract

A comparative study was conducted to investigate the influence of rare earth (RE)–Si–Fe addition on the microstructures and tribological properties of in situ TiN–Ti₅Si₃ composites prepared by selective laser melting (SLM). With the addition of 3 wt-% RE–Si–Fe, the shape of in situ TiN reinforcing particles became rounded and smoothened, the particle size was refined and the dispersion state was homogenised. Relative to TiN–Ti₅Si₃ composites without RE addition, the average friction coefficient of SLM processed RE containing composites decreased from 0·85 to 0·55, and the resultant wear rate decreased from 3·79×10^?4 to 2·65×10^?4 mm³ N^?1m^?1. Metallurgical functions of the RE elements in improving the SLM processability and the resultant wear performance of in situ composites were elucidated.     

Low-temperature sintered Mg2SiO4–CaTiO3 ceramics with near-zero temperature coefficient of resonant frequency

The microwave dielectric properties and the microstructures of (1 ? x)Mg₂SiO₄–xCaTiO₃ composite ceramics with Bi₂O₃–Li₂CO₃–H₃BO₃ (BLB) additions prepared by solid-state reaction method have been investigated. The crystalline phases were studied systematically by using the X-ray diffraction, microstructures by the scanning electron microscopy and composition analysis by the energy-dispersive spectroscopy. The results showed that the τ _f of (1 ? x)Mg₂SiO₄–xCaTiO₃ was related to the amount of CaTiO₃ phase constitutions. When x = 0.08 and 0.09, the τ _f of (1 ? x)Mg₂SiO₄–xCaTiO₃ were about ?3.0 ppm/°C and +6.8 ppm/°C. The microwave dielectric properties of 0.91Mg₂SiO₄–0.09CaTiO₃ ceramics samples with BLB additions sintered at 900–1,000 °C were characterized, and the permittivity and Q × f were associated with the amount of BLB and the sintering temperature. The sintering temperature of ceramics was reduced to 950 °C from about 1,250 °C and the temperature coefficient of resonant frequency (τ _f ) was modified to ?5.0 ppm/ °C with good Q × f. The addition of 12.0 wt% Bi₂O₃–Li₂CO₃–H₃BO₃ in 0.91Mg₂SiO₄–0.09CaTiO₃ ceramics sintered at 950 °C showed excellent dielectric properties of ε _r  = 7.7, Q × f = 11,300 GHz (f = 6.1 GHz) and τ _f  = ?5.0 ppm/ °C. This represented a very promising candidate material for LTCC applications.     

Specifics of electron–ion heat exchange under intense photoexcitation of dielectrics with ultrashort laser pulses

The rate of energy exchange between overheated electrons and the lattice of a dielectric exposed to an ultrashort laser pulse is analyzed in the case of electron scattering by the deformation potential of acoustical phonons and the polarization potential of optical phonons. The temperature and concentration dependences of the emerging heat flux are determined, and analytical approximating expressions are proposed. Estimates for silica are given.