Absorption and Scattering Losses in Glasses and Fibers for Light Guidance

Fiber optics for telecommunications applications require very high purity glass. Light loss in glass results primarily from absorption and scattering. Transition metal ions and OH ions cause most of the absorption, whereas scattering is caused by microheterogeneity. Scattering losses vary from 1 to 4 dB/km at 850 nm; absorption losses are high near 630 nm, because of Cr³⁺ and Ni²⁺ impurities, but are lower near 850 nm, making this a preferred wavelength region. Flint glass with a total loss of 50 dB/km at 850 nm, prepared using pure material and special techniques, was used as the core of thin-clad optical fibers 70 μm in diameter; these fibers had an internal loss at 850 nm of ∼450 dB/km.     

Internal Friction of Proton-Exchanged Li2O·Al2O3·2SiO2 Glass

Protons were introduced into the surface of an Li₂O·Al₂O₃·2SiO₂ glass fiber (0.5 mm in diameter) by ion exchange in NH₄HSO₄ at 366°C for 21 h. Infrared absorption measurements established that the protons were associated with bridging oxygen ions. After ion exchange, the magnitude of the alkali internal friction peak decreased and a new peak appeared at ∼220°C. This new peak is attributed to the interaction of alkali and hydrogen ions, independent of the presence of nonbridging oxygen ions.     

玻璃丝形状尺寸对玻璃软化点温度测量影响研究

通过机械拉丝工艺法制备不同直径(Φ0.50~Φ0.90 mm)、不同圆柱度(ΔΦ0.01~ΔΦ0.06mm)和不同圆度(ΔΦ0.01~ΔΦ0.2 mm)3种形态的玻璃丝,采用Littleton法测试玻璃软化点温度,探究玻璃丝直径、圆柱度和圆度对软化点测量结果的影响作用规律。研究结果表明:随着玻璃丝直径增大,测试的玻璃软化点温度逐渐降低;对于不同圆柱度的玻璃丝,上下两端直径差ΔФ增大,软化点温度变化量增大;对于不同圆度的玻璃丝,其软化点温度取决于玻璃丝断面最小直径,最小直径一定时,随着最大直径增大,软化点温度变化不大。     

Extrusion blow molding of long fiber reinforced polyolefins

A 58% (by weight) long glass fiber reinforced (LGF)‐HDPE master batch was blended with a typical blow molding HDPE grade. HDPE composites having between 5% and 20% (by weight) long fiber content were extruded at different processing conditions (extrusion speed, die gap, hang time). The parison swell (diameter and thickness) decreased with increasing fiber content. Although the HDPE exhibited significant shear rate dependence, the LGF/HDPE composites were shear rate insensitive. Both the diameter and weight swell results also indicated very different sagging behavior. The LGF/HDPE parisons did sag as a solid‐body (equal speed at different axial locations) governed by the orientation caused by the flow in the die. Samples taken from blown bottles showed that fiber lengths decreased to 1‐3 mm, from the original 11 mm fiber length fed to the extruder. No significant difference in fiber length distribution was found when samples for different regions of the bottle were analyzed. SEM micrographs corroborate the absence of fiber segregation and clustering or the occurrence of fiber bundles (homogeneous spatial fiber distribution) as well as a preferential fiber orientation with the direction of flow. The blowing step did not change the orientation of the fibers. Five‐percent (5%) and 10% LGF/HDPE composites could be blown with very slight variations to the neat HDPE inflation conditions. However, 20% LGF/HDPE composites could not be consistently inflated. Problems related to blowouts and incomplete weldlines were the major source of problems.     

Multi-component yttrium aluminosilicate (YAS) fiber prepared by melt-in-tube method for stable single-frequency laser

The multi-component glass fibers have demonstrated their unique advantages in the application of single-frequency lasers due to their higher solubility of rare-earth ions and thus a higher gain per unit length in a compact fiber laser cavity. In this study, multi-component yttrium aluminosilicate (YAS) fiber with high doping concentration of Yb³⁺ was prepared by the “melt-in-tube” (MIT) method. A unit-length gain of 3 dB/cm was obtained in a 4.4 cm-long YAS fiber, the laser output slope efficiency reached 23.8% in a 10 cm-long Yb:YAS fiber. Single-frequency laser operation was achieved in a 1.7-cm-long Yb:YAS active fiber. To the best of our knowledge, this is the first demonstration of single-frequency laser with this YAS glass fiber as gain medium. The novel multi-component YAS fiber can be applied as a new gain material to realize single-frequency fiber laser.     

Long fiber reinforcement of polypropylene/polystyrene blends

The recycling of inseparable polymer mixtures usually results in blends with poor mechanical properties. A mixture of PP and PS was taken as a model compound for a recyclate. The effect of adding glass fibers to a mixture of PP/PS (70/30) was studied, with special attention to long glass fiber reinforcement. Test specimens were made in three different ways: by dry blending (direct injection molding), mild compounding with a single screw extruder, and compounding with a twin screw extruder. The fiber concentration was varied from 0 to 30 wt%. The fiber lengths were determined to investigate fiber attrition. The fiber lengths in the samples were 1.09 mm for dry blending, 0.72 mm for single screw compounding, and 0.33 mm for twin screw compounding. The mechanical behavior was studied by unnotched and notched Izod impact and tensile tests. The PP/PS blend had a low fracture strain and low unnotched Izod impact strength compared with a PP homopolymer. With an increasing fiber concentration and fiber length, the modulus, tensile strength, and particularly the impact strength increased. With a 30 wt% glass fiber of the long fiber compound (dry blended), the modulus was raised by a factor of 3.5, the fracture stress by a factor of 2.5 and the unnotched Izod impact strength by a factor of 10. The product quality as judged by the scatter of the data was best for the twin screw compound and poorest for the dry blend. Compounding with a single screw extruder gave fairly constant injection molding product properties, combined with excellent mechanical properties.     

长纤维增强PP-GMT片材膨胀化行为研究

通过膨化率的测量，得到了长纤维增强PP-GMT片材最佳膨化时间为8min；考察了玻纤含量、空隙率、玻纤长度及毡结构对PP-GMT片材膨化的影响，结果发现，随着玻纤含量增加和空隙率减小，片材的膨化率提高；玻纤长度和毡的结构对膨化影响显著，玻纤长度为18nm的短切毡膨化性能最佳；在此基础上，对长纤维增强的PP-GMT片材的膨化机理进行了初步的推理。     

Surface Analysis and Treatment of Extruded Fluoride Phosphate Glass Preforms for Optical Fiber Fabrication

Fabrication of fluoride phosphate glass optical fibers using the extrusion method for preform fabrication has been studied using the commercial Schott N‐FK51A glass. The extrusion step was found to create a surface layer of differing composition from the bulk glass material, leading to defects drawn down onto the optical fiber surface during fiber fabrication, resulting in high loss and fragile fibers. Similar phenomena have also been observed in other fluoride‐based glasses. Removal of this surface layer from preforms prior to fiber drawing was shown to improve optical fiber loss from >5 dB/m to 0.5–1.0 dB/m. The removal of this surface layer is therefore necessary to produce low‐loss fluoride phosphate optical fibers.     

Frequency-doubled short nanosecond fiber lasers for glass drilling and grinding

We developed a fiber laser based 515 nm single-mode green laser with pulse width of 5 ns, peak power of greater than 20 kW, and repetition rates from 100 kHz to 500 kHz, which is suitable for glass drilling and grinding. The lithium triborate (LBO) crystal is used for second harmonic generation of 515 nm laser with efficiency of 68%. Glass drilling speed of 50 mm/s @ 0.5 mm thick glass was achieved for industrial environment continuous operation, which is equivalent to 1 s of time to drill a 4 mm diameter hole on a 2 mm thick glass. The typical chip sizes for the rear and front sides are 80 μm and 120 μm, respectively. Seven thousand holes are drilled in 24 hours in glass product line, and the success rate is larger than 99.7%. This laser glass drilling approach is rapidly accepted by glass industrial. Glass surface grinding was demonstrated by using 1 ns pulse width 515 nm lasers.     

Mechanical and high velocity impact performance of a hybrid long carbon/glass fiber/polypropylene thermoplastic composite

This research explores mechanical and high velocity impact response of hybrid long carbon/glass fiber-reinforced polypropylene thermoplastic composites (HLFT) with different fiber lengths. The work examines three hybrid long fiber thermoplastic composites, i.e., 5, 10 and 20 mm. The HLFTs were prepared by a combination of extrusion and pultrusion processes and using a cross-head die. Tensile and Izod impact tests were carried out to evaluate the mechanical performance of each HLFT compound. A gas gun with a spherical projectile was used to conduct high velocity impact tests at three velocities of 144, 205 and 240 m/s. The results showed that internal mixing operation caused extensive reduction in fiber length of all three LFT lengths. Tensile strength, modulus and Izod impact test results were the indications of higher values with increase in HLFT length. Comparison of these results for the HLFT with that of corresponding glass/PP LFTs, adopted from earlier work by Shayan Asenjan et al. (J Compos Mater 53:353–360, 2019), showed better performance of HLFT. The high velocity impact results showed a steady higher impact performance with the increase in HFLT fiber length for all impact velocities tested. Comparison of HLFT high velocity impact performance revealed better results for all impact velocities tested with that of the corresponding glass/PP LFT composite.     

Surface modification and fabrication of white-light-emitting Tm3+/CdS quantum dots co-doped glass fibers

Due to the widely tunable band gap and broadband excitation, CdS quantum dots (QDs) show great promise for yellow-light luminescence center in white-light-emitting devices. The light intensity of the CdS QD-doped glass was enhanced by doping the Tm³⁺ ions due to the higher absorption rate. The influence of Tm³⁺ ions on the surface structure of CdS QDs was enormous according to the first-principles calculations. Doping Tm³⁺ ions change the surface state of CdS QDs, which will fix the QDs emission peaks and enhance the luminescence of CdS QDs at a lower heat-treatment temperature. White-light emission was obtained by tuning the relative concentration between Tm³⁺/CdS QDs. However, there is a fundamental challenge to fabricate QD-doped glass fibers by rod-in-tube method since uncontrollable QDs crystallization is hard to avoid. Herein, a white-light-emitting borosilicate glass fiber was fabricated by the “melt-in-tube” method using a special designed Tm³⁺/CdS QDs co-doped borosilicate glass with low-melting temperature as fiber core. After heat treatment, ideal white-light emission was observed from the fiber under excitation at single wavelength (359 nm). This finding indicates that Tm³⁺/CdS QDs co-doped glass fiber with white-light-emitting devices has potential application as gain medium of white-light-emitting sources and fiber lasers.     

Manufacturing and testing of long basalt fiber reinforced thermoplastic matrix composites

In this work, long basalt fiber reinforced composites were investigated and compared with short basalt fiber reinforced compounds. The results show that long fiber reinforced thermoplastic composites are particularly advantageous in the respects of dynamic mechanical properties and injection molding shrinkage. The fiber orientation in long basalt fiber reinforced products fundamentally differs from short basalt fiber reinforced ones. This results in more isotropic molding shrinkage in case of long basalt fiber reinforced composites. The main advantage of the used long fiber thermoplastic technology is that the special long fiber reinforced pellet can be processed by most conventional injection molding machines. During extrusion compounding the fibers in the compound containing 30 wt% fibers are fragmented to an average length of 0.48 mm (typical of short fiber reinforced thermoplastic compounds), this length decreases further during injection molding to 0.20 mm. Contrarily using long fiber reinforced pellets and cautious injection molding parameters, an average fiber length of 1.8 mm can be achieved with a conventional injection molding machine, which increased the average length/diameter ratio from 14 to 130. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

Some studies on glass fiber-reinforced polypropylene. Part I: Reduction in fiber length during processing

The reduction in fiber length during extrusion and injection molding of two commercial glass fiber-reinforced polypropylene products containing 30 percent by weight of glass fibers was studied. The first product had very small fibers of average length around 0.5 mm and also contained a coupling agent. The second product contained relatively longer glass fibers of 9 mm length and no coupling agent. In both cases, fiber attrition occurs predominantly at the solid-melt interface in the meiting zone of the extruder. However, in the short fiber granules, the maximum of the length distribution, which for the initial sample is around 0.5 mm, moved to shorter fiber lengths along the screw channels further from the hopper. In the long fiber granules, a bimodal length distribution was obtained in the intermediate channels; the first maximum was around the original length of 9 mm and the second centered around 0.5 mm. Thus, the forces at the solid-melt interface result in fiber breakage to lengths which are predominantly around 0.5 mm. The fiber attrition was observed to be more severe in injection molding apparently because of higher shear rates and also because the fibers had to pass through narrow channels. The measured distributions of fiber length along the screw channels for the two products are presented, and the possible mechanisms of fiber breakage are discussed. The mechanical properties of samples containing different fiber length distributions and the effects of fiber length and interfacial adhesion on properties are presented and discussed in Part II.     

1.8–13 μm supercontinuum generation by pumping at normal dispersion regime of As–Se–Te glass fiber

Mid-infrared (MIR) band supercontinuum (SC) light source has highly important application prospects in aerospace, biomedicine, MIR sensing, and pollutant monitoring. As–Se–Te glass has high nonlinear refractive index, wide MIR transmission range and weak crystallization ability. As₄₀Se₄₀Te₂₀ glass fiber is suitable for producing wide MIR–SC spectrum. In this study, purified As₄₀Se₄₀Te₂₀ glass was prepared and unclad and step-index fibers were drawn. An unclad As₄₀Se₄₀Te₂₀ glass fiber with minimum loss of 1.7 dB/m at 8.8 μm was obtained. By pumping the unclad fiber in the normal dispersion region at 5 μm, we recorded the broadest SC generation spectrum, which covered 1.8–13 μm with a 30 dB spectral flatness, from a fiber with 15 cm length. Besides, As₄₀Se₄₀Te₂₀/As₄₀Se₄₂Te₁₈ step-index fiber with minimum loss of 5.6 dB/m at 5 μm was drawn from isolation extruded preform. The step-index fiber was pumped in the normal dispersion region at 5 μm, and the SC spectrum, covering 2.1–11.2 μm with a 40 dB spectral flatness, was recorded from a fiber with 15 cm length. The SC spectrum, which was achieved by pumping the As₄₀Se₄₀Te₂₀ fiber, covered almost all the transparent range of material.     

Dielectric and microwave absorption properties of CB doped SiO2f/PI double-layer composites

Carbon black (CB) with contents of 5.5?wt% and 15?wt% filled quartz glass fiber reinforced polyimide (SiO_2f/PI) composite were designed and prepared. A double-layer absorbing material was designed using the two composites materials as a matching layer and an absorption layer, respectively. The microwave absorption property of single-layer and double-layer composites is calculated according to transmission line theory. The results show that the microwave absorbing property of double-layer composite is better than that of single-layer at the same thickness. When the 5.5?wt%CB doped SiO_2f/PI composite is used as the matching layer with a thickness of 0.7?mm and 15?wt%CB doped SiO_2f/PI composite is used as the absorption layer with a thickness of 0.9?mm, the RL (reflection loss) of the composite reaches a minimum value of ?46.18?dB at 16.07?GHz. Meanwhile, the bandwidth of RL?≤??5?dB is 5.87?GHz and the bandwidth of RL?≤??10?dB is 3.95?GHz.     

Dry Powder Processing of Fibrous Fumed Silica Compacts for Thermal Insulation

This study proposes a new dry powder processing method to produce fiber reinforced fumed silica compacts for highly efficient thermal insulation. First, mechanical forces such as shear stress and compression were applied into a fumed silica powder (BET SSA 300 m²/g) and glass fibers (3 mm length, 11 μm diameter) using an attrition type milling apparatus without any media balls. In the resultant powder mixture, fumed silica porously coated glass fiber composites were successfully prepared. SiC particles were also integrated as opacifiers. Then, the fibrous fumed silica porous compact was formed by dry pressing of the powder mixture and exhibited fracture strength of 1.58 MPa at room temperature and thermal conductivity of 0.0282 W/mK at 400°C, when its porosity was 80.1%.     

Bending properties of compression molded three-layer long fiber polypropylene composites

The results of studies on bending properties of three-layer long fiber polypropylene composites are presented. Thirteen samples with glass fibers of various lengths (i.e., 13, 25, 50 mm and continuous fiber length) in the laminates were prepared by stamping. Bending properties of shorter lengths exhibited a large scatter. On substitution of the middle layer with a continuous glass fiber the scatter was reduced. These results have been explained on the basis of flow models and X-ray shadowgraphs, which showed that both slippage flow and orientation of the glass fiber during stamping are the major phenomena responsible for the scatter.     

Surface Nucleation and Crystal Orientation in Lithium Silicate Glass Fibers

The effect of inorganic surface treatments on the orientation of lithium disilicate crystals formed in Li₂O·2.75SiO₂ glass fibers was studied. Glass fibers 0.5 mm and 9μ in diameter were subjected to various surface treatments at room temperature and then heated between 550O and 800°C. It was observed that metal salt solutions applied to the fiber surfaces at room temperature decreased the degree of orientation during heating only if the metal entered the glass and formed nucleation sites within the fibers. Orientation could also be decreased by removing lithium from the glass surfaces. Comparison of the crystallization characteristics of untreated and AgNO₃-treated fibers indicated that the crystallization behavior was controlled by either a growth process or a nucleation process, depending on whether the temperature was below or above 625°, respectively.     

Polyamide 6—long glass fiber injection moldings

The injection molding ability of long glass fiber reinforced polyamide pellets was studied. The injection moldable materials were produced by a melt impregnation process of continuous fiber rovings. The rovings were chopped to pellets of 9 mm length. Chopped pellets with a variation in the degree of impregnation and fiber concentration were studied. The injection molded samples were analyzed for fiber concentration, fiber length, and fiber orientation. Dumbbell-shaped tensile bars were made to evaluate the mechanical properties. The fibers in the tensile bars had a high orientation in the flow direction and minor fiber concentration gradients were observed. The fiber lengths decreased with fiber concentration from 1.6 mm for a 2 vol% to 0.6 mm for a 25 vol% system. The tensile and impact properties increased considerably with fiber concentration. A low degree of impregnation in the pellets of the fibers resulted in somewhat lower tensile and impact properties.     

A Method for Measuring the Flow Point of Glass

The need for a new reference point for glasses, at a temperature substantially above the softening point, is discussed from the standpoint of development of. new glasses, control of properties, and behavior in applications where reworking is required. An apparatus and a procedure are described by which a fiber elongation test indicates the "flow point," or temperature at which a glass reaches a viscosity of 10⁵ poises. A short section of a glass fiber, nominally 0.65 mm. in diameter, is heated under specified conditions of load and heat application. The heating time required for the fiber to draw down to a thread indicates the temperature attained. When properly standardized with one or more known glasses, the precision is equivalent to from 1°C. for soft glasses to 5°C. for hard glasses. The effect of infrared absorption by the sample is examined, and a correction curve is given for use when such absorption is abnormally great.