Lower Cladding Research Articles

A low heat release cladding pump coupler

Few-mode erbium-doped fiber amplifiers (FM-EDFAs) have opened up the possibility of realizing the next generation of high-capacity, high-rate communication systems. However, the leakage of pump light during continuous operation of the FM-EDFA is likely to cause the temperature of the cladding pump coupler to be too high and thus destabilize the amplifier. In this work, a low heat release cladding pump coupler was designed and the corresponding FM-EDFA was constructed. The cladding pump coupler in the 8 hours of continuous operation of the FM-EDFA is at 27.8 °C for maximum, 23.7 °C for minimum, and 26 °C for average temperatures, respectively, which are in a low-temperature safe transmission state. The FM-EDFA performance test was performed on this basis, and the results show that when the input pump power is 7 W, the maximum gain fluctuation of each mode of FM-EDFA at 1550 nm in 0∼8 hours is only 1.5 dB, the gain of all modes is greater than 23 dB and the differential mode gain (DMG) is less than 2 dB. In addition, the FM-EDFA still has good performance in the C-band after 8 hours of continuous operation. The gain for all modes is greater than 21 dB, DMG is less than 2 dB, and wavelength flatness is 3.6 dB. The low heat release cladding pump coupler is conducive to the stable amplification transmission of FM-EDFA, which is of great significance to achieving the upgrading and expansion of the communication system.

Picosecond laser with Yb-doped tapered low birefringent double clad fiber

Abstract In this study, we present results of development fiber picosecond laser by using an active ytterbium tapered double clad optical fiber with mode field diameter of 35 μm and low intrinsic birefringence (1.45 * 10−8 rad m−1). We have demonstrated 1040 nm/50 ps optical source with tunable repetition rate (within range of 1–20 MHz) and an average power of 160 W (peak power 160 kW, 8 μJ per pulse) delivering Gaussian beam with excellent quality (M 2 ∼ 1.11/1.22).

Demonstration of Optical Gain at 1535 nm Based on ErIII Complex‐Doped Polymer Waveguides Under Light‐Emitting Diode Excitation

AbstractA near‐infrared luminescent complex Er(DBTTA)3(DBFDPO) [where DBTTA = dibenzotetrathienoacene; DBFDPO = 4,6‐bis (diphenylphosphoryl) dibenzofuran] is synthesized. Based on the intramolecular energy transfer between organic ligands and Er3+ ions, optical gains at 1535 nm are demonstrated in Er(DBTTA)3(DBFDPO)‐doped polymer waveguides under the excitation of light‐emitting diodes (LEDs) instead of laser pumping. Relative gains of 6.4, 8.2, and 10.6 dB are obtained in 1 cm long waveguides with cross‐sectional dimensions of 6 × 4, 4 × 4, and 2 × 3 µm2 respectively, using the vertical top‐pumping mode of a 365 nm LED with 462 mW. Incorporating an ≈100 nm thick aluminum reflector grown under the lower cladding, enhanced the optical gain to 11.6 dB cm−1 in a waveguide with a cross‐section of 4 × 4 µm2, and an internal gain of ≈7.4 dB cm−1 is achieved. By relying on the intramolecular energy transfer and LED top‐pumping technology, the upconversion luminescence of Er3+ ions and thermal damage to polymer waveguides caused by the high power density of laser pumping can be effectively reduced. The complex Er(DBTTA)3(DBFDPO)‐doped polymer can be spin‐coated on different types of waveguides to compensate for optical losses at 1.5 µm and is expected to have a critical role in planar photonic integration.

Studies on high power laser cladding Stellite 6 alloy coatings: Metallurgical quality and mechanical performances

The present study systematically investigates the effect of powder feeding rates (Vp) on the quality of Stellite 6 alloy coatings with a 20 kW fiber laser. The results demonstrate that the hot cracks in the Stellite 6 coatings can be effectively eliminated by increasing the Vp without preheating substrate or adding buffer layers. It is possible to achieve a single-track coating with a thickness of 2.34 mm, width of 20 mm and dilution rate of 17.3 % with crack-free and densely microstructure when Vp is 90 g/min. Moreover, the build rate (172 mm3/s) surpasses the maximum build rate (133 mm3/s) of low power laser cladding. The heat accumulation of multi-track and double-layer (5.6 mm) under high power laser results in the formation of ε-Co through phase transformation from part of γ-Co. Consequently, the dendrite region primarily consists of γ-Co while a small amount of ε-Co and Cr23C6 dominate in the inter-dendritic region. Although the heat accumulation effect also tends to coarsen the grains in bottom region of the coatings, leading to a slight reduction in mechanical properties, both hardness (485 HV–523 HV) and tensile strength (1131 MPa–1250 MPa) are comparable to those achieved by low power laser cladding, and the break elongation (6.9 %–8.1 %) has significantly surpassed the current level of 3 %. High power laser cladding processes may play a significant role in enhancing the effectiveness of surface modification or remanufacturing for large workpieces, such as the runner of hydroelectric generator set.

Azimuthal confinement: the missing ingredient in understanding confinement loss in antiresonant, hollow-core fibers

Antiresonant, hollow-core optical fibers are currently challenging or even exceeding the loss performance of conventional solid-core fibers. Despite this progress, there are aspects of the guidance mechanism in these fibers that are still not understood. For example, a physical mechanism to explain why negative curvature of the core surround is correlated with low loss remains elusive. It is shown that the glass elements of the cladding structure with an approximately radial orientation play a crucial role in determining the confinement loss by strongly shaping the wave fields in the azimuthal coordinate. This shaping, described as azimuthal confinement, can result in an evanescent field in the radial direction through the cladding, and this leads to a confinement loss that is substantially lower than would be the case without azimuthal confinement. A comprehensive theory of azimuthal confinement is developed, yielding an expression for the confinement loss of any fiber structure with a single antiresonant glass layer between the core and the outer glass jacket. This is tested by comparison with large-scale numerical simulations on two types of cladding structure. It is shown that negative curvature of the core surround has little or no intrinsic role in reducing confinement loss in fibers with a nodeless cladding structure. The power of azimuthal confinement is demonstrated in model structures where the confinement loss drops by more than two orders of magnitude as the radial width of the cladding is increased. It is anticipated that the concept of azimuthal confinement will be valuable in interpreting confinement loss in a wide range of existing antiresonant, hollow-core fibers and in the design of novel, low loss cladding structures.

Experimental investigation on quenching behavior during reflooding in a 3 × 3 dual-cooled annular rod bundle

The internally and externally cooled annular fuel is an innovative fuel geometry proposal for advanced PWR, which could provide a substantial increase of power density while maintaining or improving safety margins. The quenching behavior of annular fuel during reflood phase in LOCA is more complicated than cylindrical solid fuel, owing to the geometrical difference and the coupling effect of dual-cooling. However, the investigation focusing on quenching characteristics in annular fuel geometry is very little. In the present study, an experimental study on quenching behavior of bottom reflood in a 3 × 3 dual-cooled annular rod bundle was carried out under various test conditions (reflood velocities from 0.025 to 0.15 m·s−1, inlet subcooling from 10 to 80°C, peak cladding temperature from 300 to 900°C, and linear power density from 0 to 1.58 kW·m−1). Self-designed indirect-heating annular rods were employed to provide an axial uniform power distribution in this experiment. It was found that the quenching process on external and internal surfaces of annular rod bundle was almost synchronous. The parametric effects on quenching behavior, i.e. precursory cooling rate, quench front propagation velocity (Vqf) and minimum film boiling temperature (Tmin), were investigated in detail. Earlier occurrence of quenching downstream the grid spacer was also observed under low inlet subcooling and high peak cladding temperature conditions. In addition, several correlations for Tmin were assessed against the present results. Kim correlation was in good agreement with the present data, with the mean absolute errors of 7.81% and 7.55% for outer and inner channels respectively.

SPR Sensor Based on a Tapered Optical Fiber with a Low Refractive Index Liquid Crystal Cladding and Bimetallic Ag-Au Layers.

This paper presents a study of the influence of bimetallic layer covers of a tapered optical fiber surrounded by a low refractive index liquid crystal on the properties of light propagation in the taper structure. This research follows previous works on the effect of monometallic thin films (Au and Ag). In this case, the total thicknesses of the bimetallic layers were h = 10 nm, and the participation of gold and silver was equal. The films were deposited on one side of the tapered waist area. The liquid crystal cells were controlled with a voltage U from 0 to 200 V, with and without amplitude modulation at a frequency of fmod = 5 Hz. For the purposes of this research, spectral characteristics were obtained for a wavelength λ ranging from 550 to 1200 nm. Measurements were carried out at room temperature for three types of rubbed layers orientation—orthogonal, parallel, and twist in relation to the fiber axis. Obtained resonant peaks were compared with the previous results regarding the resonant wavelength, peak width, SNR, and maximum absorption. In the presented paper, the novelty is mainly focused on the materials used and their time stability, as well as corresponding changes in the technological parameters used.

Experimental investigation of CMT discontinuous wire arc additive manufacturing of Inconel 625

Additive manufacturing (AM) is a progressive technology which holds promise for manufacturing of heat resistant super alloys. One of the most productive methods is wire arc additive manufacturing (WAAM). In this article, an alternative WAAM strategy is investigated. Experimental clads and material tests were performed to evaluate the material properties obtained through a cold metal transfer (CMT) discontinuous WAAM of Inconel 625 alloy. Using the modern terminology of Fronius Gmbh this method is called CMT cycle step. The difference is that it is automatically controlled by the welding source. CMT discontinuous WAAM has lower productivity and a higher consumption of shielding gas. However, it excels in low heat input and precise material cladding in comparison with a standard CMT continuous WAAM. It enables fabrication of finer details even on thin-walled components or in sections with problematic heat dissipation. Samples manufactured using this strategy were also compared with samples manufactured through a standard CMT continuous WAAM. Two sets of manufactured samples were thus tested. The following material tests were performed: (i) metallographic analysis, (ii) x-ray tomography, (iii) SEM analysis, (iv) hardness, (v) tensile strength (20 °C, 650 °C) and (vi) pin-on-disc (20 °C, 650 °C). The results show that the CMT discontinuous WAAM led to improved material properties in the Inconel 625 samples. Ultimate tensile strength improved by 15% at 20 °C and by 4% at 650 °C. Wear resistance at 650 °C was about two times higher. This paper concludes that the CMT discontinuous WAAM for Inconel 625 is definitely suitable for manufacturing of complex shapes, fine details and thin-walled components.

Fabrication and Characterization of Low-Loss Gaussian-Like Reversed Ridge Optical Waveguides

A Gaussian-like reversed ridge optical waveguide based on the perfluorinated acrylate polymer is fabricated by an improved UV photolithography with the pre-exposure process. A partially cured thin layer is formed on the lower cladding during the pre-exposure process, which will avoid the effect of the oxygen inhibition in the following UV photolithography. A Gaussian-like groove with a smooth surface is obtained after the pattern development process, which is beneficial to the low-loss waveguide. The transmission loss of 0.25 dB/cm at 1310 nm and 0.45 dB/cm at 1550 nm are measured. The fabricated waveguides transmit several modes, and the inter-channel crosstalk with a core pitch of 250 μm is below –40 dB at 1310 nm and –49 dB at 1550 nm, which shows the potential in applications of optical interconnection and communications.

Title Corrosion Behavior of Nitrogenous Low Nickel Weld Cladding in Kcl-Mgcl2 Binary Molten Salt

Title Corrosion Behavior of Nitrogenous Low Nickel Weld Cladding in Kcl-Mgcl2 Binary Molten Salt

Title Corrosion Behavior of Nitrogenous Low Nickel Weld Cladding in Kcl-Mgcl2 Binary Molten Salt

Title Corrosion Behavior of Nitrogenous Low Nickel Weld Cladding in Kcl-Mgcl2 Binary Molten Salt

W-band optical modulators using electro-optic polymer waveguides and patch antenna arrays.

In this study, W-band (75-110 GHz) antenna-coupled optical modulators with a cyclo-olefin polymer (COP) lower cladding, an electro-optic (EO) polymer waveguide, and a gap-embedded patch antenna array were fabricated using a transfer and bonding method of a poled EO polymer film. A carrier-to-sideband ratio (CSR) of 56 dB corresponding to an optical phase shift of 3 mrad was obtained under irradiation with 100 GHz electromagnetic waves with a power of 12.8 W/m2. Our devices have the potential to achieve highly efficient wireless-optical signal conversion in radio-over-fiber (RoF) systems.

On-Chip Broadband Mid-Infrared Supercontinuum Generation Based on Highly Nonlinear Chalcogenide Glass Waveguides

On-chip mid-infrared (MIR) supercontinuum generation (SCG) covering the molecular functional spectral region (3–12 μm) offers the advantages of robustness, simplicity, and compactness. Yet, the spectral range still cannot be expanded beyond 10 μm. In this study, on-chip ultrabroadband MIR SCG in a high numerical aperture chalcogenide (ChG) waveguide is numerically investigated. The ChG waveguide with a Ge-As-Se-Te core and Ge-Se upper and lower cladding is designed to optimize the nonlinear coefficients and dispersion profile. Assisted by dispersive wave generation in both short- and long-wavelength range, broadband SCG ranging from 2 to 13 µm is achieved. Besides, a fabrication scheme is proposed to realize precise manipulation of dispersion design. Such results demonstrate that such sources are suitable for compact, chip-integrated molecular spectroscopy applications.

Analytical and Experimental Study of Multilayer Dielectric Rod Waveguides

This article presents a comprehensive study of the design and performance of a multilayer dielectric rod waveguide (MDRW) with a rectangular cross section. The design is comprised of a high permittivity core encased by a low permittivity cladding. A mathematical model is proposed to predict the fundamental mode cutoff frequency in terms of the core dimensions and the core and cladding permittivity. The model is useful for design purposes and it offers an excellent match to full-wave electromagnetic (EM) simulation results. The MDRW performance is measured for the extended Ku-band (10-18 GHz) considering straight and bent waveguides with different radius of curvatures. The particular multilayer configuration shows a 16.7% and 24% extension of the 1 dB low-band cutoff frequency for a 10×10 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and 20×20 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> cladding area, respectively, when compared to a single layer dielectric rod waveguide (DRW) design of the same core dimensions. MDRW bends also exhibit a significant reduction of the 1 dB low-band cutoff frequency from 20% to 40% when compared to single-layer designs, for the different radius of curvature bends.

Graphene-coated double D-type low loss optical fiber modulator.

A graphene-coated double D-type low loss all-fiber modulator is proposed. The modulator is improved on the basis of standard fiber. Only the cladding is processed without grinding the original core structure. The upper and lower cladding are cut same distance. This can ensure that the mode field does not deviate in one direction, so that most of the mode field is still tied to the core, which greatly reduces the device loss. The existence of the double graphene layer can also ensure a very excellent modulation efficiency. The calculation results show that the mode loss of our proposed dual-D modulator under X polarization is 0.125 dB/mm, and the mode field mismatch loss is 0.25%. The mode loss in Y polarization is 0.033 dB/mm, and the mode field mismatch loss is 0.32%. When the modulation voltage is 5 V, the modulation depth is 78.4% under the condition of five-layer graphene, while the modulation speed can reach 15.38 GHz. Besides maintaining low modulation voltage and higher modulation efficiency, this structure makes full use of the advantages of good fiber coupling, and will be widely used in future fiber communications and all-fiber systems.

A comparative study on microstructure and properties of traditional laser cladding and high-speed laser cladding of Ni45 alloy coatings

High-speed laser cladding technology can significantly improve the efficiency of coating preparation and effectively widen the application range of laser cladding. In this study, the Ni45 powders were deposited on steel substrate by traditional low speed laser cladding and high-speed laser cladding process, respectively. The cladding efficiency, surface forming, cross-sectional microstructure, microhardness, wear and corrosion resistance properties of the traditional and high-speed laser cladded Ni45 alloy coatings were compared. It can be seen that the thickness of the high-speed laser cladding coating was much thinner than that of the traditional laser cladding coating. Compared with traditional laser cladding, high-speed laser cladding could achieve a cladding speed of 76.86 m/min and a cladding efficiency of 156.79 cm2/min. The microstructure of the two kinds of coatings shows the same growth law, but the microstructure in high-speed laser cladding was smaller and denser, and the columnar crystal interval was narrower, only about 6 μm. It is found that the cooling rate of the traditional laser cladding coating was smaller than that of the high-speed laser cladding, and as the cladding speed increased, the cooling rate became higher and higher. The cross-section microhardness of the traditional laser cladding coating was relatively uniform of 337 HV0.2, while the microhardness of high-speed laser cladding surface increased to about 543 HV0.2. In addition, the wear and corrosion resistance of high-speed laser cladded coatings were better than that of traditional laser cladded coatings. As the cladding speed increased, the wear and corrosion resistance of the cladded coatings became better.

Study on microstructure and mechanical properties of Ni60 + WC/Ni35/AISI1040 functional surface gradient structure of remanufacturing chute plate for the mining scraper by a low cost high power CO2 laser cladding technique

CO2 laser cladding is a type of green remanufacturing technology, which is of many technical advantages in repairing and remanufacturing industry, especially for some large-scale key mining equipment or parts due to its characteristics of high quality, high efficiency and environmental protection (e.g. energy and material saving). In this paper, the chute plate of coal mining scraper is fixed and remanufactured by CO2 laser cladding technique. Ni60, WC, Ni35, IG55 and other composite powders are selected to design and build the gradient functional structure for chute plate in order to improve the reproduced lifetime. A lot of high power low cost CO2 laser cladding tests are carried out on the matrix material (AISI 1040 steel plate) of old attrite chute plate. The optical microscope, SEM, XRD, microhardness test and wear experiment are adopted to analyze the relationships among the laser cladding process, the overlaying composite material, gradient functional structure and mechanical properties of the remanufacturing scraper’s chute plate. The research results show that laser power and scanning speed are the dominant cladding process parameters, which have a significant influence on the geometric dimension (including width and height), dilution rate and hardness of the deposited layer. These composite powders (especially including the rare earth metals) are the key factor to form the gradient functional structure. The laser cladding Ni60 + WC/Ni35/AISI1040 composite gradient functional structure has a reasonable toughness and strength of the transition layer structure, and a high hardness and wear-resistant surface functional layer, so the fixed and remanufactured product has formed good ductile plasticity and wear resistance properties as a result of the gradient functional structure. The unique Ni60 + WC/Ni35/AISI1040 gradient functional structure makes sure that the chute plate of mining scraper has excellent comprehensive performance, which is satisfied with the service requirements of mechanical parts or equipment in the harsh working environment of the mining industry. This research work provides technological guidance for the fix and remanufacturing chute plate, and achieves the goal of low cost, high efficiency and long life reproduced chute plate of mining scraper.

Experimental Investigation of Low Density Sound Insulated Concrete Fabricated Wall Cladding Tiles

The growing demand for the need of sound insulation in buildings such as hospitals, recreational institutions and religious buildings is rising in recent years. The material used should be of highly sound insulated as well as easy to install. In this study light weight concrete is used as Wall Cladding tiles in the building, as light weight concrete shows satisfactory sound insulation property. The light weight Wall cladding was fabricated by addition of Fiber glass powder and alccofine as a cement replacement and different sizes of Cenosphere such as Cenosphere 300 micron and Cenosphere 425 micron as a fine aggregate replacement. Various parameters of the light weight concrete Wall Cladding tile both physical and mechanical properties were investigated. The test were conducted to determine the compressive strength, and the sound insulation ability of the fabricated Wall Cladding tile. The experimental investigation shows that Wall Cladding fabricated as a light weight concrete has reliable compressive strength of 6.5 N/mm2 and satisfactory sound insulation property.

Wafer-bonded surface plasmon waveguide sensors with in-plane microfluidic interfaces

Sensors exploiting long-range surface plasmon polariton (LRSPP) waveguides comprised of Au stripes embedded in Cytop with integrated and encapsulated microfluidic channels are fabricated and demonstrated. A fabrication approach was devised where the lower cladding and recessed Au stripes are fabricated on a Si supporting substrate, and the upper cladding and microfluidic channels are fabricated on a glass substrate, followed by wafer bonding to assemble the wafers into complete sealed structures. The bond is centered over the full length of the optical path, yet no evidence of optical scattering or excess loss due to the bond could be observed, and no evidence of a bonding interface could be discerned from high-magnification cross-sectional images. We also demonstrate wafer-scale fabrication of in-plane microfluidic inlets and outlets, along with a fixture for fluidic edge coupling that provides sealed interfaces to external fluidic tubing and components. In-plane microfluidic interfaces are automatically defined along chip facets upon wafer dicing, precluding the need to drill through holes in lids. The performance of the chips was assessed by measuring the attenuation of LRSPPs on fully cladded reference waveguides, on waveguides passing through microfluidic channels, and by measuring the response of sensors to changes in refractive index produced by injecting various sensing solutions. Our fabrication approach based on wafer bonding and in-plane fluidic interfacing is compelling for low-cost high-volume manufacturing.

Design and Analysis of a Dispersion-engineered and Highly Nonlinear Rib Waveguide for Generation of Broadband Supercontinuum Spectra

AbstractIn this paper, a waveguide consisting of a core of As2Se3 chalcogenide glass and the upper and lower claddings of MgF2 with two zero-dispersion wavelengths (ZDW) has been proposed. By optimization of the dimensions of the core and the claddings, their effects on the dispersion curve have been investigated and a suitable structure with a flat dispersion curve, an effective mode area of ​​1.6 μm2 in a pump wavelength of 2.8 μm, and hence, a nonlinear coefficient greater than 34 w−1 m−1 has been obtained. A broadband supercontinuum in a wavelength range of 1.5 μm to 15 μm has been generated by applying an input pulse with duration of 100 fs and a maximum power of 2 kw to this waveguide. Due to the large width of the supercontinuum generated (SCG), the short length of the waveguide (maximum 5 mm), and a low input power, this structure is suitable for use in optical integrated circuits and its various applications.