Flexible broadcasting and multicasting in 4λ × 10 Gb/s AOPR TWDM PON system

In this letter, we propose a new architecture of Time Wavelength Division Multiplexing Passive Optical Network (TWDM PON) system to support dynamic multi wavelength allocation (DMWA) in both upstream and downstream directions using an integrated semiconductor optical amplifier (SOA) and arrayed waveguide grating (AWG) with multi wavelength select continuous wave (CW) pump probe signal module. The significance of this architecture is the flexible routing function with the capability of multicasting and broadcasting between multiple optical line terminal (OLT) PON port with multiple optical distribution network (ODN) link using a new wavelength tuning free (WTF) OLT transmitter module to eliminate wavelength tuning delay in downstream signal utilizing multicasting Cross Gain Modulation (XGM) wavelength conversion. The experimental results show that 4λ × 10-Gb/s TWDM PON system can be used to connect 4096 users with the conventional fixed wavelength OLT transceivers with 36 dB link loss.     

Spectroscopy of AlO: Combined analysis of the AΠi → XΣ and BΣ → XΣ transitions

A combined analysis of the A²Π_i → X²Σ⁺ and B²Σ⁺ → X²Σ⁺ band systems of AlO, involving 21,500 line assignments, has been performed. The analysis indicates that the previously reported γ values of the B²Σ⁺ state are questionable. The present analysis shows that γ(B²Σ⁺) ≈ 0.014 cm⁻¹, essentially independent of the vibrational level. The positive sign is consistent with second order interaction with the higher-lying C²Π_r and lower-lying A²Π_i states. It also appears that many of the previously reported γ and γ_D values of X²Σ⁺ (v > 0) are doubtful. In fact, γ(X²Σ⁺) is observed to become increasingly negative for v″ > 1, due to second order interaction with the low-lying A²Π_i state. The present results are based on models where the hyperfine structure of the ²Σ⁺ states has been taken into account explicitly. Intensity patterns of the branches of the B²Σ⁺ → X²Σ⁺ system have been shown to be influenced by the case bβ_S coupling in the ground state v = 0,1 levels. This gives rise to intensity differences of around 10 percent in the R₁/R₂ and P₁/P₂ doublet components. The synthesized intensity patterns are fully in accord with the F₁/F₂ assignments of the present work.     

Segregation of H, C and B to Σ = 5 (0 1 3) α-Fe grain boundary: A theoretical study

The ASED-MO theory is used to study the effects of H and the HC and HB pairs in the electronic structure of a Fe grain boundary (GB). The results obtained for H in a GB model are consistent with its behavior as a chemical embrittler. The total energies calculated for FeH, FeC and FeB clusters indicate that all interstitials segregate to the GB. C has the lowest energy, followed by B, and could compete with other impurities for the site location on the GB.The results obtained for FeCH and FeBH are consistent with the observed behavior of C and B as cohesion enhancers. A strong repulsive interaction between C and H and B and H atoms is developed if they occupy the nearest interstitial site on the GB. When C or B are present, the total energies are similar to that obtained for the FeH cluster. This indicates that H is displaced from the capped trigonal prism (CTP). Also, we do not detect any CH or BH interaction.Density of states (DOS) and crystal orbital overlap population (COOP) curves are used to shed more light on the interstitial-Fe GB interaction. The existence of strong metal-metalloid bonds is shown, which are primarily due to Fe 3d, 4s and C (or B) 2s, 2p interactions.     

Stability, oxygen permeability and chemical expansion of Sr(Fe,Al)O3 − δ- and Sr(Co,Fe)O3 − δ-based membranes

Perovskite-type SrFe_0.7Al_0.3O_3 − δ and SrCo_0.8Fe_0.2O_3 − δ, and two related dual-phase composites with nominal compositions (SrFeO_3 − δ)_0.7(SrAl₂O₄)_0.3 and (SrCo_0.8Fe_0.2O_3 − δ)_0.7(SrAl₂O₄)_0.3, were comparatively studied employing controlled-atmosphere dilatometry, thermogravimetry, Mössbauer spectroscopy, and measurements of steady-state oxygen permeation fluxes through dense ceramic membranes. The composite materials display lower thermal and chemical expansion compared to the parent single-phase perovskites. The thermal expansion coefficients at 1023-1223 K are however still high, (20-23) × 10^− 6 K^− 1 at atmospheric oxygen pressure and (17-18) × 10^− 6 K^− 1 at p(O₂) = 10 Pa, thus limiting the range of possible membrane reactor configurations. Sr(Co,Fe)O_3 − δ-based materials exhibit extensive vacancy-ordering processes in inert atmospheres, resulting in a slow relaxation of the oxygen nonstoichiometry, chemical expansion and oxygen permeation fluxes. In comparison to Sr(Fe,Al)O_3 − δ, the stability of cobalt-containing ceramics in CO₂ is also poor, which leads to a partial blocking of the membrane surface by decomposition products and degradation of the oxygen transport. Thermogravimetric analysis showed that the interaction with carbon dioxide occurs even at elevated temperatures, up to 1223 K. Under high oxygen chemical potential gradients such as air/(H₂-H₂O), the composite membranes showed kinetically stable operation without bulk decomposition at 1073 K. The kinetic stabilization associated with surface-limited oxygen permeation was confirmed by the conversion-electron Mössbauer spectroscopy analysis of one (SrFeO_3 − δ)_0.7(SrAl₂O₄)_0.3 membrane exposed to dry CH₄ at 1173 K, where no traces of Fe²⁺ and metallic iron were detected in the reduced surface layer.     

High-temperature magnetic properties of noninteracting randomly oriented single-domain Fe3 − δO4 nanoparticles

Magnetic measurements have been performed on 40-nm sphere-like Fe_3 − δO₄ (δ=0.043) nanoparticles using a Quantum Design vibrating sample magnetometer. Coating Fe_3 − δO₄ nanoparticles with SiO₂ effectively eliminates magnetic interparticle interactions so that the coercive field HC in the high-temperature range between 300 K and the Curie temperature (855 K) can be well fitted by an expression for noninteracting randomly oriented single-domain particles. From the fitting parameters, the effective anisotropy constant K is found to be (1.38±0.11)×¹⁰⁵ erg/cm³, which is very close to the bulk magnetocrystalline anisotropy constant of 1.35×¹⁰⁵ erg/cm³. Moreover, the inferred mean particle diameter from the fitting parameters is in quantitative agreement with that determined from transmission electron microscope. Such a quantitative agreement between data and theory suggests that the ensemble of our SiO₂-coated sphere-like Fe_3 − δO₄ nanoparticles represents a good system of noninteracting randomly-oriented single-domain particles.     

Antiferroelectric phase transition in pyrochlore-like (Dy1− xCax)2Ti2O7 − δ (x = 0, 0.1) high temperature conductors

Low-temperature ordering transitions in polycrystalline high temperature conductors (Dy_1 − xCa_x)₂Ti₂O_7 − δ (x = 0, 0.1) prepared using co-precipitation, mechanical activation and solid-state reactions at 1400 or 1600 °C have been studied by impedance spectroscopy at low frequencies and thermal mechanical analysis (TMA). The dielectric permittivity and loss tangent of the ceramics obtained have been measured as a function of temperature at low frequencies (0.5−500 Hz). The results provide evidence for the relaxation of point defects, most likely oxygen vacancies, at 500−600 °C and an antiferroelectric low-temperature phase transition of the second order, associated with re-arrangement process in the oxygen sublattice of pyrochlore structure. The temperature of the antiferroelectric transition is 700 to 800 °C, depending on the synthesis procedure and ceramic composition. Calcium doping of Dy₂Ti₂O₇ leads to the formation of additional oxygen vacancies and, in the case of the samples prepared via co-precipitation, increases the peaks in permittivity due to the relaxation process and ordering transition by three or six times, respectively.     

Defect structure and oxide ion transport in Sr- and Cr-doped LaCoO3 − δ

The results of oxygen nonstoichiometry, δ, measured by means of coulometric technique as a function of oxygen partial pressure, p_o2, in temperature range 1223 ≤ T, K ≤ 1323 are presented for the perovskite-type doped with chromium solely LaCo_0.7Cr_0.3O_3 − δ and simultaneously doped both with strontium and chromium La_0.7Sr_0.3Co_0.7Cr_0.3O_3 − δ cobaltites. The limit stability of the latter was found to exceed that of undoped cobaltite LaCoO_3 − δ on six orders of magnitude of p_o2 at a given temperature. The modeling of the defect structure of these perovskites was carried out and its adequate model was found. Chemical and self-diffusion coefficients of oxygen vacancies and oxygen ionic conductivity and ionic transport numbers were measured for the first time for La_0.7Sr_0.3Co_0.7Cr_0.3O_3 − δ as a function of oxygen partial pressure p_o2and temperature in the ranges − 4 ≤ log(p_o2, atm) ≤ 0 and 1223 ≤ T, K ≤ 1323, respectively. The additional substitution of Sr for La in LaCo_0.7Cr_0.3O_3 − δ was shown to lead to noticeable increase of ionic conductivity and oxygen chemical diffusion coefficient at given values of oxygen partial pressure and temperature as compared to lanthanum cobaltite doped with chromium solely. Self-diffusion coefficient of oxygen vacancies and their mobility in La_0.7Sr_0.3Co_0.7Cr_0.3O_3 − δ were found to be dependent on oxygen partial pressure and nonstoichiometry unlike undoped and doped with chromium lanthanum cobaltites.     

Characterization of YSr2Fe3O8 − δ as electrode materials for SOFC

YSr₂Fe₃O_8 − δ was prepared by traditional solid state reaction method and characterized by X-ray diffraction, ac impedance, dc conductivity, dilatometry and thermogravimetric analysis for possible use in solid oxide fuel cells (SOFCs). YSr₂Fe₃O_8 − δ crystallizes with tetragonal symmetry in the space group P4/mmm and found to be stable at high temperatures under H₂ and air. Four probe dc electrical conductivity measurements show that the conductivity increases up to 745 K and then decreases with temperature; the highest conductivity σ_745K = 43.5 S cm^− 1. The n-type conductivity at low oxygen partial pressure (pO₂) changes to p-type at high pO₂. Polarization behavior was investigated measuring the ac impedance response in symmetrical cell arrangements in air with YSZ and GDC electrolytes. Cathodic area specific resistance (ASR) varies with firing temperature. The lowest area specific resistance was observed with a GDC electrolyte fired at 1000 °C. In case of YSZ, ASR increases and in case of GDC, ASR decreases in air when electrode firing temperature decreases. At 800 °C ASRs are 0.20 Ω cm² and 0.65 Ω cm² with GDC and YSZ electrolytes, respectively, in air. Fuel cell measurements with symmetrical electrodes were performed using a thin YSZ electrolyte under H₂ at anode and air at cathode, show that the power density is about 0.035 W/cm² at 900 °C.     

Oxygen nonstoichiometry, thermo-chemical stability and lattice expansion of La0.6Sr0.4FeO3 − δ

The oxygen nonstoichiometry of La_0.6Sr_0.4FeO_3 − δ was measured at intermediate temperatures (773 to 1173 K) between 1 bar and the decomposition oxygen partial pressure by thermogravimetry and coulometric titration. The decomposition of the ABO₃ perovskite phase was found to occur at low oxygen partial pressures (below 10^− 20 bar). Using an atmosphere-controlled high-temperature XRD setup, the rhombohedral lattice parameters were obtained between 10^− 4 and 1 bar at 773 to 1173 K. A phase transition from rhombohedral to cubic might be expected to occur at high temperatures and for δ near the plateau at δ = [Sr] / 2. The lattice expansion was separated into “pure” thermal and chemically induced expansion by combining the lattice parameters with the oxygen nonstoichiometry data. The linear thermal expansion was formulated with a “pure” thermal expansion coefficient of α_th = 11.052 · 10^− 6 K^− 1 and a chemical expansion coefficient of α_chem = 1.994 · 10^− 2.The results were compared with previous data obtained for La_0.6Sr_0.4Co_1 − yFe_yO_3 − δ with y = 0.2-0.8. La_0.6Sr_0.4FeO_3 − δ was confirmed to show the highest thermo-chemical stability. While the chemical expansion of La_0.6Sr_0.4Co_1 − yFe_yO_3 − δ seems little affected by the iron content, the thermal expansion coefficient was the lowest for La_0.6Sr_0.4FeO_3 − δ.     

Oxygen nonstoichiometry, defect structure and electrical properties of LaFe0.7Ni0.3O3 − δ

Oxygen nonstoichiometry (δ), total conductivity (σ) and thermoelectric power (S) of the LaFe_0.7Ni_0.3O_3 − δ sample have been studied as functions of temperature and oxygen partial pressure. Based on the results of the direct reduction of the sample in hydrogen flow at 1100 °C the absolute oxygen content (3 − δ) has been found to vary from 2.999 to 2.974 in the range of 1273-1373 K and 10^− 3-0.21 atm. The point defect equilibrium models have been proposed and fitted to the set of experimental data in the form of log p(O₂) = f(δ)_T dependences. The values of standard thermodynamic quantities of defect formation reactions have been assessed. The joint analysis of oxygen nonstoichiometry, total conductivity and thermoelectric power has been performed using a small-polaron approach. The values of partial conductivity, partial thermopower and mobilities of electronic charge carriers have been calculated. The p-type semiconducting behavior of LaFe_0.7Ni_0.3O_3 − δ has been explained by the higher mobility values of electron holes than those of electrons in the whole range of thermodynamic parameters studied.     

Structural and optical properties of Ga2(1−x)In2xO3 films prepared on α-Al2O3 (0 0 0 1) by MOCVD

Ga_2(1−x)In_2xO₃ thin films with different indium content x [In/(Ga + In) atomic ratio] were prepared on α-Al₂O₃ (0 0 0 1) substrates by the metal organic chemical vapor deposition (MOCVD). The structural and optical properties of the Ga_2(1−x)In_2xO₃ films were investigated in detail. Microstructure analysis revealed that the film deposited with composition x = 0.2 was polycrystalline structure and the sample prepared with x up to 0.8 exhibited single crystalline structure of In₂O₃. The optical band gap of the films varied with increasing Ga content from 3.72 to 4.58 eV. The average transmittance for the films in the visible range was over 90%.     

Fabrication, sintering and electrical properties of cobalt oxide doped Gd0.1Ce0.9O2 − δ

Ceria-based electrolytes have been widely researched in intermediate-temperature solid oxide fuel cell (SOFC), which might be operated at 500~600 °C. Gd0.1Ce0.9O1.95(GDC10) powders were prepared by a modified chemical co-precipitation process with Gd(NO3)3 and Ce(NO3)3 as precursors, and ammonia and hydrogen peroxide as precipitants. The precursors of GDC10 were fired at 350 °C for 2 h, then the fluorite structure cerias were identified by X-ray diffraction. The powders are well crystallized, with the size about 5 nm and surface area of 148.3 m2/g. Loading 1mol% cobalt oxide as additive, the GDC10 were succeeded to densify at 950 °C by liquid phase sintering mechanism. The grain size of 1CoGDC10 is small, about 100 nm. The electrical conductivity of samples sintered at 950 °C is about 0.01S/cm at 600 °C. The existence of cobalt oxide and smaller grain size of 1CoGDC10 don't affect the electrical conductivity.     

Synthesis and characterization of (h 0 h)-oriented silicalite-1 films on α-Al2O3 substrates

A simple and well-designed synthesis procedure is proposed to fabricate silicalite-1 films on porous α-Al₂O₃ substrates on purpose of preventing the aluminum leaching. The continuous and 2 μm thick seed layer of silicalite-1 crystals is fabricated by using a spin coater. The first-time seeded growth is performed to synthesize a thin layer of intergrown ZSM-5 crystals on the silicalite-1 seed layer, where the use of low alkalinity and short synthesis time is to reduce the aluminum leaching. The intergrown layer of ZSM-5 crystals serves as a barrier to block the aluminum leaching from porous α-Al₂O₃ substrates in the second-time seeded growth, leading to the formation of ca. 11 μm thick intergrown and oriented silicalite-1 films with an extremely high Si/Al ratio. According to SEM images and XRD measurements, the as-synthesized silicalite-1 film is dense, continuous, and (1 0 1)-oriented. The electron probe microanalysis (EPMA) of the resulting film demonstrates that there is no aluminum leaching in the second-time seeded growth. The leaking tests confirm that non-zeolitic pores in the silicalite-1 film are negligible.     

Adsorption and decomposition of γ-butyrolactone on Pd(1 1 1) and Pt(1 1 1)

The adsorption and thermal chemistry of γ-butyrolactone (GBL) on the (1 1 1) surface of Pd and Pt has been investigated using a combination of high resolution electron energy loss spectroscopy (HREELS) and temperature programmed desorption (TPD). HREELS results indicate that GBL adsorbs at 160 K on both surfaces through its oxygenate functionality. On Pd(1 1 1), adsorbed GBL undergoes ring-opening and decarbonylation by 273 K to produce adsorbed CO and surface hydrocarbon species. On Pt(1 1 1), very little dissociation is observed using HREELS, with almost all of the GBL simply desorbing. TPD results are consistent with decarbonylation and subsequent dehydrogenation reactions on Pd(1 1 1), although small amounts of CO₂ are also detected. TPD results from Pt(1 1 1) indicate that a small proportion of adsorbed GBL (perhaps on defect sites) does undergo ring-opening to produce CO, CO₂, and H₂. These results suggest that the primary dissociation pathway for GBL on Pd(1 1 1) is through O-C scission at the carbonyl position. Through comparisons with previously published studies of cyclic oxygenates, these results also demonstrate how ring strain and functionality affect the ring-opening rate and mechanism.     

Vertically emitting, dye-doped polymer laser in the green (λ ∼ 536 nm) with a second order distributed feedback grating fabricated by replica molding

Lasing in the green from a distributed feedback (DFB) structure, based upon a second order grating fabricated by replica molding in a dye-doped UV curable polymer, has been demonstrated. For a Bragg grating having a periodicity and depth of 360 ± 2 nm and 78 ± 5 nm, respectively, a coumarin 540-polymer laser operates at 535.6 nm, which is in agreement with calculations of the photonic band diagram for the structure. The fabricated laser exhibits a linewidth of 0.15 nm, a threshold pump fluence of ∼0.7 mJ cm⁻² at 355 nm, and a slope efficiency of ∼14%. Incorporation of the dye gain medium into a one- (or two-) dimensional photonic crystal and fabrication of the grating by replica molding at room temperature provides an inexpensive approach to fabricating polymer-based DFB lasers on flexible substrates of large area.     

Oxygen deficiency, vacancy clustering and ionic transport in (La,Sr)CoO3 − δ

The equilibrium p(O₂)-T-δ diagrams of perovskite-type La_1 − xSr_xCoO_3 − δ (x = 0.3-0.7), collected at 873-1223 K in the oxygen partial pressure range 10^− 5-1 atm by coulometric titration and thermogravimetric analysis, were analyzed in order to appraise the effects of the point-defect interactions. The nonstoichiometry variations were adequately described combining the rigid-band approach for delocalized holes and the pair-cluster formation reaction involving oxygen vacancies and Co²⁺ cations, whilst coulombic repulsion between the positively charged vacancies can be neglected. The resultant relationships between the oxygen chemical potential and mobile vacancy concentration were used for numerical regression analysis of the steady-state oxygen permeation through dense La_1 − xSr_xCoO_3 − δ membranes, affected by the surface exchange kinetics when Sr²⁺ content is higher than 40-50%. The calculated ionic conductivity is strongly influenced by the defect association processes, and decreases with decreasing concentration of the mobile vacancies as clustering starts to prevail on reduction. The Mössbauer spectroscopy studies of La_1 − xSr_xCoO_3 − δ, doped with 1 mol% ⁵⁷Fe isotope and moderately reduced at p(O₂) ≈ 10⁻⁵ atm, show no long-range vacancy ordering at x ≤ 0.5.