Preparation of Er3+/Yb3+ co-doped citrate microstructure fiber of large mode field and its 3.0 μm laser performance

The double-cladding Er³⁺/Yb³⁺ co-doped bismuth germanium gallate microstructure fiber of large mode, with the core diameter of 30.6 μm, the inner cladding air pore diameter of about 3.06 μm and a lattice constant of 10.2 μm is prepared by a bundle-drawing method. The spectral characteristics at 975 nm wavelength were studied and the results show that the maximum fluorescence intensity and the high gain quality factor of the fiber core glass can be obtained when the molar ratio of Er³⁺ to Yb³⁺ is 0.5%:2% and its emission cross section is up to 10.9 × 10⁻²¹ cm². A stable laser output with a maximum power of 51.16 mW and a wavelength of 2710 nm was obtained in a microstructure optical fiber with a length of 160 mm employing a independently constructed fiber laser with a cascade structure, whose pump light power was 561 mW, the slope efficiency was 6.89%, the effective mode field area is about 576 μm² and the beam quality factor M² < 1.02. The double-cladding Er³⁺/Yb³⁺ co-doped bismuth germanium gallate microstructure fiber of large mode has excellent laser properties and is an ideal optical fiber material for the development of the 3.0 μm laser.     

Fabrication and amplification of Rhodamine B‐doped step‐index polymer optical fiber

A step‐index polymer optical fiber (SI POF) containing Rhodamine B in poly(methyl methacrylate) (PMMA) has been fabricated by a preform technique. Fluorescence of different fiber lengths were observed and discussed. A high gain (23 dB) for a SI POF with 60‐cm length, 400‐μm diameter was obtained. The Rhodamine B content of the doped SI POF is 5 ppm‐wt. The signal wavelength providing the highest gain for a 60 cm SI POF is around 630 nm, and the optimum fiber length is about 60 cm at 10 kW launched pump power. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 681–685, 2004     

Sol–Gel-Processed SiO2/TiO2/Methylcellulose Composite Materials for Optical Waveguides

SiO₂–TiO₂–methylcellulose (MC) composite materials processed by the sol-gel technique were studied for optical waveguide applications. Dense, crack-free and homogeneous films as thick as 2 μm were obtained via the organic binder MC-assisted sol–gel process and single coating with low-temperature treatment. Light waveguiding in such hybrid film was demonstrated at a wavelength of 650 nm. About 1.1 dB/cm or lower propagation loss for the SiO₂ (80 mol%)–TiO₂ (20 mol%)–MC (22 wt%) film can be achieved. The effects of thermal treatment on the structure and properties of the gel films were also investigated.     

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.     

Fabrication of Arsenic Selenide Optical Fiber with Low Hydrogen Impurities

Arsenic selenide glass optical fibers typically possess extrinsic absorption bands in the infrared wavelength region associated with residual hydrogen and oxygen related impurities, despite using purified precursors. We report a purification process based on the addition of 0.1 wt% tellurium tetrachloride (TeCl₄) to the glass. During melting, the chlorine from TeCl₄ reacts with the hydrogen impurities to produce volatile products (e.g., HCl) that can be removed by subsequent dynamic distillation. The processing conditions have been modified accordingly to give very low H–Se impurity content. Consequently, the H–Se absorption band centered at 4.57 μm has been reduced from tens of dB/m to 0.2 dB/m.     

Spectral Absorption Coefficient of Molten Aluminum Oxide from.0.385 to 0.780 μm

The spectral extinction coefficient, k _λ, and the absorption coefficient, α_λ, of liquid aluminum oxide were determined from emission measurements on partially molten single-crystal sapphire filaments. Measurements were made at wavelengths from 0.385 to 0.780 μm in both argon and oxygen atmospheres and at 0.650 μm in a 10% H₂-90% N₂ mixture. The values of α_λ were found to vary with the time for which the specimen had been molten and achieved different steady-state values in the three processing atmospheres. A decrease in α_λ with wavelength (Urbach tail) was observed from 0.385 μm to about 0.420 μm in argon and 0.490 μm in oxygen, and approximately constant values were obtained at longer wavelengths. Steady-state values of α_λ at the optical pyrometer wavelength of 0.650 μm were 9 ± 2 cm⁻¹ in argon, 41 ± 8 cm⁻¹ in oxygen, and 14 ± 2 cm⁻¹ in the 10% hydrogen-90% nitrogen gas mixture.     

Ultra-large mode area mid-infrared fiber based on chalcogenide glasses extrusion

We have prepared an ultra-large core, high numerical aperture (NA) chalcogenide (ChG) step-index fiber (SIF) with a mode area of >43 600 μm² at the wavelength of 5.5 μm by an improved extrusion method. The fiber based on two ChG glasses with similar softening temperature has a core diameter of 339.0 μm and ultra-thin cladding. The fiber exhibits a minimum loss of 1.75 dB/m at 9.74 μm and an optical loss of <5.0 dB/m from 5.3 to 10.8 μm. Broadband supercontinuum (SC) covering from 1.2 μm to 13.7 μm has been generated in a 17-cm-long ultra-large mode area fiber with large core and high NA. All these show that, the fiber possesses the potential for high-power infrared laser transmission.     

Laminar-Structured YAG/Nd:YAG/YAG Transparent Ceramics for Solid-State Lasers

A laminar-structured YAG/1.0 at.% Nd:YAG/YAG transparent ceramic was fabricated by a solid-state reaction method and vacuum sintering using high-purity α-Al₂O₃, Y₂O₃, and Nd₂O₃ as raw materials with tetraethoxysilane as a sintering aid. The microstructure, the optical property, and the laser performance of the ceramic composite prepared were investigated in this paper. It is found that the sample exhibits a pore-free structure and the average grain size is about 15 μm. There is no secondary phase both at the grain boundary and at the grain matrix. The optical transmittance of the sample (5.0 mm thick) is 80.2% at 1064 nm. The lasing sample is Φ16.2 mm × 5.0 mm in size, mirror polished on both sides and without a coating. A laser diode (808 nm) was used as a pump source with a maximum output of about 1000 mW, and the end-pumped laser experiment was demonstrated. With 658 mW of maximum absorbed pump power, a laser output of 8 mW has been obtained with a slope efficiency of 4.0%.     

Fabrication of Patterned Inorganic–Organic Hybrid Film for the Optical Waveguide by Microfluidic Lithography

Inorganic–organic hybrid materials for the optical waveguide were synthesized by the sol–gel process starting from the acid-catalyzed solutions of phenyltrimethoxysilane, methyltriethoxysilane, and tetraethylorthosilicate. The control of the refractive index in the organically modified silicate films was achieved by varying the content of phenyltrimethoxysilane incorporated as a refractive index modifier. A single spin-coating with the precursor solution produced a crack-free buffer layer of 22-μm thickness with a dense microstructure. For the fabrication of the patterned guiding layer on top of the buffer layer, the microfluidic lithography method was used. The patterned microlines of the linewidth of 20–35 μm with a sharp edge definition could form by filling the precursor solutions into the microchannels associated with the polydimethylsiloxane microfluidic device. The patterned guiding layer was optically transparent as similar as the bare quartz glass at the wavelength above 500 nm and had a low propagation loss of 0.77 dB/cm at 1310 nm.     

Effects of the Weak Absorption Tail on the Transmission Loss of Ge–Sb–Se Optical Fibers

Selenide glass optical fibers were fabricated for Ge₃₀Sb₁₀Se₅₈S₂ and Ge₂₀Sb₁₀Se₇₀ glasses. Their transmission loss has been measured and compared with the theoretical attenuation loss that was calculated taking into account the electronic transition absorption, Rayleigh scattering, and multiphonon absorption. A low attenuation loss of the Ge₂₀Sb₁₀Se₇₀ glass composition in 1.2–1.7 μm range has been expected due to its high optical band gap energy compared with the Ge₃₀Sb₁₀Se₅₈S₂ glass. However, the measured attenuation loss of the Ge₃₀Sb₁₀Se₅₈S₂ glass fiber was ∼13 dB/m at 1.5 μm while Ge₂₀Sb₁₀Se₇₀ glass showed ∼82 dB/m. An enhanced weak absorption tail due to the localized states of the Ge₂₀Sb₁₀Se₇₀ glass was responsible for this behavior. Structural defects are related to the localized states and discussed for the present glass compositions.     

Lower-Temperature Hot-Pressed Dy-α-Sialon Ceramics with an LiF Additive

Hot-pressed Dy-α-sialon ceramics, using LiF as a sintering additive, were fabricated at lower temperatures (≤1650°C). Some of the densified samples possessed higher hardness and fracture toughness up to 19.00–20.00 GPa and 4.00–6.00 MPa·m^1/2, respectively. The amount of LiF had a strong effect on the densification behavior in sialon preparation. As one of the experimental results, the sample with 0.1 wt% of LiF additive sintered at 1600°C produced an optical translucence of about 50% in the range of 1.5–5.0 μm wavelengths. The maximum infrared transmission reached ∼60% at a wavelength of 2.4 μm. It is inferred that these more easily sintered materials would be practical for optical applications in certain fields.     

Populations and Emission Properties of the 5I6 and 5I7 Levels in Ho3+ Doped into PbO–Bi2O3–Ga2O3 Glasses

Emission properties of PbO–Bi₂O₃–Ga₂O₃ glasses doped with Ho³⁺ were investigated for fiber-optic amplification at the 1.18 μm wavelength region. When the glasses were doped with Ho³⁺ ions only, there was a weak emission at 1.18 μm with a lifetime of ∼200 μs. However, when Yb³⁺ ions were codoped, the lifetime of the 1.18 μm emission increased to 630 μs together with a significant increase in intensity. A similar enhancement in the intensity and lifetimes was realized for the 2.05 μm emission. These effects are due to energy transfer from the Yb³⁺:²F_5/2 to the Ho³⁺:⁵I₆ level. Devitrification of the ternary PbO–Bi₂O₃–Ga₂O₃ glasses was efficiently suppressed by adding 10 mol% GeO₂. Optimum Ho³⁺ concentration was ∼0.4 mol%, whereas Yb³⁺ ions can be added up to the solubility limit.     

Refractive Index Dispersion of Sodium Magnesium Silicate Glasses for Ultralow-Loss Fibers

The refractive index dispersion and infrared (IR) reflection spectra of soda magnesium silicate glasses with low Rayleigh scattering were measured to evaluate their potential for use in fabricating ultralow-loss fibers. The zero-material dispersion wavelength (λ₀) was found to be around 1.5 μm, which is one of the key wavelengths in the present telecommunication system. The compositional dependence of λ₀ was found to relate to the population of nonbridging oxygen. Since the oscillation strength and frequency of the Si—O stretching vibrations of the glasses were found to be smaller than those of silica glass, their IR absorption loss was considered to be less than that of silica glass. The minimum loss due to the intrinsic factors, Rayleigh scattering and IR absorption, was estimated to be 0.06 dB/km at 1.6μm.     

Piezoelectric Fibers with Uniform Internal Electrode by Co-Extrusion Process

Piezoelectric fibers with internal electrodes were fabricated by the co-extrusion process. The initial feedrods, which were composed of an outer piezoelectric PZN–PZT layer, a thin conducting PZN–PZT/Ag layer inside, and fugitive carbon black at the center, were co-extruded through a reduction die (1 mm) to form a continuous fiber. After thermal treatment and sintering, the PZN–PZT/Ag layer became the inner electrode, while the carbon black at the center was removed by oxidation to form an empty space. Three different types of fibers were produced: (i) solid fiber filled with an inner electrode, (ii) hollow fiber clad with a uniform inner electrode, and (iii) hollow fiber clad with a partial inner electrode. The piezoelectric properties of the fibers were evaluated in terms of their longitudinal strain (s₃₁) or transverse displacement. When the dimensions of the fiber were 840 μm (outer diameter) × 420 μm (inner diameter) × 40 mm (length), the longitudinal strains of the solid fiber with the inner electrode and hollow fiber clad with the uniform inner electrode were 5.25 × 10⁻⁵ and 8.5 × 10⁻⁵ m/m, respectively, under an applied voltage of 100 V (0.48 kV/mm) at a frequency of 100 Hz. For the hollow fiber clad with a partial inner electrode with the same dimensions, the transverse displacement was 80 μm under the same applied electric field.     

Low Loss,High NA Chalcogenide Glass Fibers for Broadband Mid‐Infrared Supercontinuum Generation

High‐purity Ge–As–Se and Ge–As–S chalcogenide glasses were prepared by modified physical and chemical purification techniques. Using the purified glasses, step‐index fibers with a small core (~5.5 μm) and large numerical aperture (~1.3) were fabricated. When a 13.5‐cm‐long fiber was pumped with 320 fs pulses at a repetition rate of 10.5 MHz at 4.1 μm, supercontinuum spanning from ~1.8 to ~9.8 μm with a dynamic range of ±10 dB and an average power of ~3 mW was generated.     

Fabrication of Transparent Hydroxyapatite Sintered Body with High Crystal Orientation by Pulse Electric Current Sintering

Transparent hydroxyapatite (HAp) sintered body with a high crystal orientation and a relative density of 99.7% was fabricated by the pulse electric current sintering method; the c -axis of HAp crystals with a hexagonal column morphology and ca. 200 μm × 25 μm in size was oriented perpendicular to the pressure direction. The sintered temperature increased to 1200°C at a heating rate of 50°C/min for 10 min and a pressure of 50 MPa was applied. The orientation indexes were calculated from X-ray diffraction patterns of the planes perpendicular and parallel to the pressure direction. The optical transmittance was greater than 70% over the wavelength of 700 nm.     

Preparation and physical properties of functionalized graphene/waterborne polyurethane UV‐curing composites by click chemistry

Functionalized graphene nanoplatelets (f‐GNS) were modified with (3‐mercaptopropyl)trimethoxysilane (MPTMS) to enhance their compatibility with the polyurethane coating matrix. The results of Fourier transform infrared spectroscopy, AFM, Raman and XRD showed that the MPTMS was successfully attached onto the surface of the graphene nanoplatelets. Functionalized graphene/waterborne polyurethane acrylate (f‐GNS/WPUA) nanocomposites were fabricated by UV‐curing technology. The SEM and TEM images indicated that f‐GNS could be well dispersed in the polymer matrix and improved the interfacial adhesion. With the incorporation of 1 wt% f‐GNS, the thermal decomposition temperature of the composites was increased by 25 °C. Meanwhile, the conductivity, hydrophobicity and tensile strength were increased. When the load was further increased, the performance of the composites showed varying degrees of reduction. However, the dielectric loss tangent (tan δ) could be maintained at 0.08 or less and the electromagnetic shielding factor of the composites reached from 5 to 36 dB, showing a good electromagnetic shielding effect at a high content (2.5 wt% f‐GNS). It was considered that f‐GNS could disperse in the waterborne polyurethane well and crosslink with the polyurethane. © 2016 Society of Chemical Industry     

Darkening Kinetics of Photochromic Glass at High Excitation Levels

A conventional copper sensitized photochromic glass was subjected to three excitation intensities, 21 mW/cm², 45 mW/cm², and 108 mW/cm², between 0.3 μm and 0.4 μm. The effect of glass heat treatment as well as excitation intensity on the equilibrium absorption and the darkening rates is described. Results indicated that both the equilibrium absorption and the rate of darkening increase with excitation intensity.     

Fabrication of segmented cladding fiber by bicomponent spinning

Fabrication of segmented cladding fiber (SCF) by bicomponent spinning was proposed in this article. In the new designed spin pack, we considered the high refractive component of cladding and core as a whole to control the cross section of the fiber. Quenching system in current bicomponent melting spinning system was modified according to the requirement of quenching fiber with a large size. The polymer SCF with required cross section was successfully fabricated using polycarbonate and polymethyl methacrylate. The transmission loss in the wavelength of 500–1000 nm was tested by the cut‐back method. The result showed that the transmission loss of the obtained fiber was comparatively high, being up to 30 dB/m. The output light pattern of the obtained fiber of 60 cm was collected by using a charge‐coupled device camera with laser light of 532 nm as the input. The output light pattern for the far field was a uniform circle and that for the near field was similar to the cross‐section designed. The results showed that the obtained fiber was still a multimode optical fiber because of the comparatively large refractive index difference between the two materials used. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

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.