Large Core Size Research Articles

Polarization maintaining single-mode low-loss hollow-core fibres

Hollow-core fibre (HCF) is a powerful technology platform offering breakthrough performance improvements in sensing, communications, higher-power pulse delivery and other applications. Free from the usual constraints on what materials can guide light, it promises qualitatively new and ideal operating regimes: precision signals transmitted free of nonlinearities, sensors that guide light directly in the samples they are meant to probe and so on. However, these fibres have not been widely adopted, largely because uncontrolled coupling between transverse and polarization modes overshadows their benefits. To deliver on their promises, HCFs must retain their unique properties while achieving the modal and polarization control that are essential for their most compelling applications. Here we present the first single-moded, polarization-maintaining HCF with large core size needed for loss scaling. Single modedness is achieved using a novel scheme for resonantly coupling out unwanted modes, whereas birefringence is engineered by fabricating an asymmetrical glass web surrounding the core.

Star-formation in nuclear clusters and the origin of the Galactic center apparent core distribution

AbstractNuclear stellar clusters (NSCs) are known to exist around massive black holes (MBHs) in galactic nuclei. Two formation scenarios were suggested for their origin: build-up of NSCs and Continuous in-situ star-formation. Here we study the effects of star formation on the build-up of NSCs and its implications for their long term evolution and their resulting structure. We show that continuous star-formation can lead to the build-up of an NSC with properties similar to those of the Milky-way NSC. We also find that the general structure of the old stellar population in the NSC with in-situ star-formation could be very similar to the steady-state Bahcall-Wolf cuspy structure. However, its younger stellar population does not yet achieve a steady state. In particular, formed/evolved NSCs with in-situ star-formation contain differential age-segregated stellar populations which are not yet fully mixed. Younger stellar populations formed in the outer regions of the NSC have a cuspy structure towards the NSC outskirts, while showing a core-like distribution inwards; with younger populations having larger core sizes.

Metallic attenuated total reflection infrared hollow fibers for robust optical transmission systems

A durable metallic attenuated total reflection (ATR) hollow fiber (bore size: 1.45 mm, wall thickness: 50 μm) was designed and fabricated based on a nickel capillary tube and hexagonal germanium dioxide (GeO2). The anomalous dispersion of the hexagonal GeO2 layer grown inside a nickel tube achieves low-loss light transmission at two peak-power wavelengths for CO2 laser devices (10.2 and 10.6 μm). An 11–28 W, 10.2 or 10.6 μm CO2 laser power was steadily delivered via a fiber elastically bent from 0° to 90° (radius: 45 cm) for over 40 min (transmission loss: 0.22 to 4.2 dB/m). Theoretically fitting the measured temperatures showed that front-end clipping caused greater thermal loading than the distributed mode absorption. The maximum external temperature of a nickel ATR fiber is much lower than that of a silica glass ATR fiber owing to their different heat dissipation abilities. The HE11 mode purity of the output beam profiles decreased from 90.3% to 44.7% as the bending angle increased from 0° to 90°. Large core sizes and wall roughnesses (scattering loss 0.04 dB/m) contributed to mode mixing and excess losses that were above the value predicted by the classical Marcatili and Schmeltzer equation (0.024–0.037 dB/m).

Ytterbium-doped large-mode-area silica fiber fabricated by using chelate precursor doping technique.

We reported on a highly effective chelate precursor doping technique for Yb-doped large-mode-area (LMA) fiber manufacture. By accurately controlling the evaporation temperature and flow rate of carrier gas, the chelate precursor doping technique is capable of making Yb-doped LMA silica fiber with good uniformity free of center dip, low numerical aperture of ~0.056, large preform core size of 4.46 mm, and appropriate cladding absorption of 1.17 dB/m at 976.4 nm. Based on a single-end-pump all-fiber oscillator laser setup, the laser output at 1080 nm reached 700 W with slope efficiency of 54.2%.

Multimode interference refractive index sensor based on coreless fiber

A multimode interference refractive index (RI) sensor based on the coreless fiber was numerically and experimentally demonstrated. Two identical single mode fibers (SMF) are spliced at both ends of a section of the coreless fiber which can be considered as the equivalent weakly guiding multimode fiber (MMF) with a step-index profile when the surrounding refractive index (SRI) is lower than that of the coreless fiber. Thus, it becomes the conventional single-mode multimode single-mode (SMS) fiber structure but with a larger core size. The output spectra will shift along with the changes in the SRI owing to the direct exposure of the coreless fiber. The output spectra under different SRIs were numerically studied, as well as the sensitivities with different lengths and diameters of the coreless fiber. The predication and calculation showed the good agreement with the experimental results. The proposed RI sensor proved to be feasible by verification experiments, and the relative error was merely 0.1% which occupied preferable sensing performance and practicability.

Competition between Icosahedral Motifs in AgCu, AgNi, and AgCo Nanoalloys: A Combined Atomistic–DFT Study

The structures of AgCu, AgNi, and AgCo nanoalloys with icosahedral geometry have been computationally studied by a combination of atomistic and density-functional theory (DFT) calculations, for sizes up to about 1400 atoms. These nanoalloys preferentially assume core–shell chemical ordering, with Ag in the shell. These core–shell nanoparticles can have either centered or off-center cores; they can have an atomic vacancy in their central site or present different arrangements of the Ag shell. Here we compare these different icosahedral motifs and determine the factors influencing their stability by means of a local strain analysis. The calculations find that off-center cores are favorable for sufficiently large core sizes and that the central vacancy is favorable in pure Ag clusters but not in binary clusters with cores of small size. A quite good agreement between atomistic and DFT calculations is found in most cases, with some discrepancy only for pentakis-dodecahedral structures. Our results support the accuracy of the atomistic model. Spin structure and charge transfer in the nanoparticles are also analyzed.

Hollow-core photonic crystal fibre for high power laser beam delivery

AbstractWe review the use of hollow-core photonic crystal fibre (HC-PCF) for high power laser beam delivery. A comparison of bandgap HC-PCF with Kagome-lattice HC-PCF on the geometry, guidance mechanism, and optical properties shows that the Kagome-type HC-PCF is an ideal host for high power laser beam transportation because of its large core size, low attenuation, broadband transmission, single-mode guidance, low dispersion and the ultra-low optical overlap between the core-guided modes and the silica core-surround. The power handling capability of Kagome-type HC-PCF is further experimentally demonstrated by millijoule nanosecond laser spark ignition and ${\sim }100~\mathrm{\mu} \mathrm{J} $ sub-picosecond laser pulse transportation and compression.

Size Distribution and Magnetization Optimization of Single-Core Iron Oxide Nanoparticles by Exploiting Design of Experiment Methodology

The synthesis of single-core superparamagnetic iron oxide nanoparticles (SPIONs) via high temperature decomposition of the self-synthesized Fe(III)-oleate was studied by exploiting factorial design of experiment methodology to investigate the influence of Fe(III)-oleate concentration, reaction temperature and time, and heating rate on the particle core and hydrodynamic size distributions and magnetization. This approach enabled us to establish a reliable and reproducible protocol for the synthesis of monodisperse SPIONs with high magnetic performance. The structural and magnetic properties of SPIONs were characterized utilizing a variety of methods. By applying a multiple linear regression model, a simple and robust empirical growth model was found for the particle hydrodynamic diameter, presenting its dependencies on reaction temperature and time, and Fe(III)-oleate concentration. Having studied the thermal decomposition behavior of Fe(III)-oleate, the synthesis of highly monodisperse particles with a core size of ~ 12-14 nm and suitable magnetic properties was attributed to burst nucleation which is followed by a rapidly terminating growth. In contrast, the particles with a large primary core size of ~ 22-24 nm, crystallized via a gradual and low temperature nucleation accompanied by a slow growth and Ostwald ripening, show a broader or multi-modal size distribution with relatively poor magnetic performance.

Core Percolation on Complex Networks

We analytically solve the core percolation problem for complex networks with arbitrary degree distributions. We find that purely scale-free networks have no core for any degree exponents. We show that for undirected networks if core percolation occurs then it is continuous while for directed networks it is discontinuous (and hybrid) if the in- and out-degree distributions differ. We also find that core percolations on undirected and directed networks have completely different critical exponents associated with their critical singularities.

Design, fabrication, and characterization of Si-based ARROW photonic crystal bend waveguides and power splitters

Silicon-based (Si-based) photonic crystal waveguide based on antiresonant reflecting optical waveguide (ARROW PCW) structures consisting of 60° bends and Y-branch power splitters were designed and first efficiently fabricated and characterized. The ARROW structure has a relatively large core size suitable for efficient coupling with a single-mode fiber. Simple capsule-shaped topography defects at 60° photonic crystal (PC) bend corners and Y-branch PC power splitters were used for increasing the broadband light transmission. In the preliminary measurements, the propagation losses of the ARROW PC straight waveguides lower than 2 dB/mm with a long length of 1500 μm were achieved. The average bend loss of 60° PC bend waveguides was lower than 3 dB/bend. For the Y-branch PC power splitters, the average power imbalance was lower than 0.6 dB. The results show that our fabricated Si-based ARROW PCWs with 60° bends and Y-branch structures can provide good light transmission and power-splitting ability.

Design and fabrication of hollow-core photonic crystal fibers for high-power ultrashort pulse transportation and pulse compression

We report on the recent design and fabrication of kagome-type hollow-core photonic crystal fibers for the purpose of high-power ultrashort pulse transportation. The fabricated seven-cell three-ring hypocycloid-shaped large core fiber exhibits an up-to-date lowest attenuation (among all kagome fibers) of 40 dB/km over a broadband transmission centered at 1500 nm. We show that the large core size, low attenuation, broadband transmission, single-mode guidance, and low dispersion make it an ideal host for high-power laser beam transportation. By filling the fiber with helium gas, a 74 μJ, 850 fs, and 40 kHz repetition rate ultrashort pulse at 1550 nm has been faithfully delivered at the fiber output with little propagation pulse distortion. Compression of a 105 μJ laser pulse from 850 fs down to 300 fs has been achieved by operating the fiber in ambient air.

Colloidal synthesis of gold semishells.

This work describes a novel and scalable colloid chemistry strategy to fabricate gold semishells based on the selective growth of gold on Janus silica particles (500 nm in diameter) partly functionalized with amino groups. The modulation of the geometry of the Janus silica particles allows us to tune the final morphology of the gold semishells. This method also provides a route to fabricating hollow gold semishells through etching of the silica cores with hydrofluoric acid. The optical properties were characterized by visible near-infrared (vis-NIR) spectroscopy and compared with simulations performed using the boundary element method (BEM). These revealed that the main optical features are located beyond the NIR region because of the large core size.

Exchange bias in magnetic nanoparticle capped with amorphous magnetic shell

An extensive Monte Carlo (MC) simulation is performed to investigate exchange bias in a novel model of a nanoparticle consisting of a ferromagnetic (FM) core and an amorphous magnetic (AM) shell. The magnetic glassy ordering of the AM shell governed by random magnetic anisotropy (RMA) is shown to be responsible for the unidirectional anisotropy to the FM core. Our MC results show that, while the bias field and coercivity exhibit a strong dependence on RMA strength, which looks like that on the antiferromagnetic (AFM) thickness in traditional FM/AFM bilayers, they are independent of AM thickness. However, the bias field and coercivity abruptly change with increasing small core size and get saturated for a large enough core size. The cooling field and temperature dependencies show the peculiar sign inversion of the bias field. Our study supports the argument that the exchange bias observed in some magnetic nanoparticles or nanocrystallined alloys is not necessarily due to the presence of an AFM phase.

Near-diffraction-limited output from confined-doped ytterbium fibre with 41 µm core diameter

A confined-doped ytterbium fibre with a 41 µm core diameter has been fabricated by direct nanoparticle deposition process. Near-diffraction-limited beam quality (M2∼1.3) was experimentally demonstrated from an amplified spontaneous emission source setup. Owing to the large core size and the confined Yb doping, the mode area is significantly enlarged while good beam quality is maintained. Such fibres have great potential for mitigating the detrimental nonlinear effects and for power scaling of fibre lasers and amplifiers.

Nanoparticle targeting using multivalent ligands: computer modeling

Using Monte Carlo simulations, we analyze the efficiency in targeting mobile receptors on cell surfaces by nanoparticles carrying multivalent (divalent, tetravalent) ligands. We show that in most cases the nanoparticles with multivalent ligands exhibit very minor or no advantage in cell surface targeting compared to nanoparticles functionalized with monovalent ligands with the same density of functional groups, as in both cases nanoparticles can interact with a receptor surface in a multivalent manner. We identify a few cases when using multivalent ligands in nanoparticle targeting can be beneficial, especially for a high binding energy of ligand–receptor interactions and large receptor densities. We demonstrate that for nanoparticles with longer tether length or larger core size, where the entropic loss for stretching tethers carrying ligands is significant, the possibility to deliver the same number of functional groups to a cell surface by using a smaller number of ligated tethers, as in the case of using multivalent ligands, becomes favorable. We also show that multivalent ligands can enhance the selectivity of nanoparticle targeting by increasing the nanoparticle affinity to cells with a high density of mobile receptors. The obtained results provide guidance for the experimental development of targeted nanoparticles with multivalent ligands for imaging and therapeutic applications.

Polyaspartic acid coated manganese oxide nanoparticles for efficient liver MRI

We report in this communication a simple, facile surface modification strategy to transfer hydrophobic manganese oxide nanoparticles (MONPs) into water by using polyaspartic acid (PASP). We systematically investigated the effect of the size of PASP-MONPs on MRI of normal liver and found that the particles with a core size of 10 nm exhibited greater enhancement than those with larger core sizes.

10 x 112Gb/s PDM-QPSK transmission over 5032 km in few-mode fibers

Few-mode fibers (FMFs) are used for the first time to transmit over 5000 km. Ten WDM channels with 50GHz channel spacing at 112 Gb/s per channel using PDM-QPSK are launched into the fundamental mode of the FMFs by splicing single-mode fibers directly to the FMFs. Even though few-mode fibers can support an additional spatial mode LP(11) at 1550 nm, the signal remains in the fundamental mode and does not experience mode coupling throughout fiber transmission. After each span the signal is collected by a second single-mode fiber which is also spliced to the FMF. Span loss is compensated by single-mode EDFAs before it is launched to the next FMF span. The lack of mode coupling ensures that the signal does not suffer any impairments that may result from differential mode delay or excess loss. Therefore the FMFs used in this "single-mode operation" have the same bandwidth as single-mode fibers. Experimental results verified that FMFs have the significant advantage of large core size which reduces the nonlinear impairments suffered by the signal. It is shown that FMFs with an effective area of 130 μm(2), have an optimum launch power 2 dB higher compared to standard single-mode fibers and as a result a 1.1 dB improvement in the Q-factor is obtained after 3000 km.

A breathing rate sensor with plastic optical fiber

A breathing rate sensor has been developed using plastic optical fiber and the test results are presented in this letter. The principle of coupling loss was used in designing this sensor to take advantage of the large core size of plastic optic fiber. The sensor was placed near the nostril to determine the rate of breathing as air was exhaled. The results demonstrated the ability to quantify the breathing rate and monitor different breathing patterns up to a resolution of 1 breath/s (1 Hz).

Nanoparticle design optimization for enhanced targeting: Monte Carlo simulations.

Using computer simulations, we systematically studied the influence of different design parameters of a spherical nanoparticle tethered with monovalent ligands on its efficiency of targeting planar cell surfaces containing mobile receptors. We investigate how the nanoparticle affinity can be affected by changing the binding energy, the percent of functionalization by ligands, tether length, grafting density, and nanoparticle core size. In general, using a longer tether length or increasing the number of tethered chains without increasing the number of ligands increases the conformational penalty for tether stretching/compression near the cell surface and leads to a decrease in targeting efficiency. At the same time, using longer tethers or a larger core size allows ligands to interact with receptors over a larger cell surface area, which can enhance the nanoparticle affinity toward the cell surface. We also discuss the selectivity of nanoparticle targeting of cells with a high receptor density. Based on the obtained results, we provide recommendations for improving the nanoparticle binding affinity and selectivity, which can guide future nanoparticle development for diagnostic and therapeutic purposes.

Quantitative evaluation of protein expression as a function of tissue microarray core diameter: is a large (1.5 mm) core better than a small (0.6 mm) core?

Abstract Context.—Tissue microarrays (TMAs) have emerged as a high-throughput technology for protein evaluation in large cohorts. This technique allows maximization of tissue resources by analysis of sections from 0.6-mm to 1.5-mm core “biopsies” of standard formalin-fixed, paraffin-embedded tissue blocks and by the processing of hundreds of cases arrayed on a single recipient block in an identical manner. Objective.—To assess the expression of a series of biomarkers as a function of core size. Although pathologists frequently feel better if larger core sizes are used, there is no evidence in the literature showing that large cores are better (or worse) than small cores for assessment of TMAs. Design.—Estrogen receptor, HER2/neu, epidermal growth factor receptor, STAT3, mTOR, and phospho-p70 S6 kinase were measured by immunofluorescence with automated quantitative analysis. One random 0.6-mm field (one 0.6-mm spot) was compared to 6 to 12 fields per spot, representing 1-mm and 1.5-mm cores, for 3 differen...