Polymer-silica hybrid 1 × 2 thermooptic switch with low crosstalk

A new polymer-silica hybrid 1 × 2 thermooptic switch with significantly low crosstalk is demonstrated. The top cladding and the core layers are composed of polymer, while the bottom cladding layer is made of silica. Since polymer and silica have algebraic signs of their thermooptic coefficients that are opposite to each other, the refractive index of the core changes in the opposite direction to that of the bottom cladding as the temperature is increased. Thus, switching operation is initially done through adiabatic mode evolution in the Y-branch, and then a heated waveguide arm in the Y-branch can enter into the optical cut-off region if the temperature is sufficiently high. Using this phenomenon, low crosstalk performance is achieved. The proposed device has a crosstalk of −35 dB, while most integrated-optic switches with a single stage have a relatively high crosstalk in the region of −20 dB. The switching power of the proposed device is about 70 mW.     

1 × N add-drop filter structures using one dense wavelength division multiplexing thin-film filter

This paper proposes 1 × N add-drop filter structures in which only one thin-film filter (TF) is used. Our key idea is based on a combination of an angle-multiplexing concept and the flexibility of the optical fiber to allow a multiwavelength optical beam hit the TF several times, each time at a different angle but same position. Due to the TF angle sensitivity, the desired wavelength optical beam corresponding to the incident angle is therefore spatially isolated from the main optical beam. Our first TF-based 1 × N add-drop filter structure is arranged in a reflective design in which N wavelength optical beams can be dropped out from the main channel. For our transmissive architecture, N − 2 channels are directed to their associated output terminals while the remaining λ_N−1 and λ_N wavelength optical beams are sent out at the same port. Experimental proof of concept for our reflective TF-based 1 × 3 add-drop filter using one off-the-shelf TF, a triple fiber-optic collimator, and an optical circulator separates two wavelength optical beams with their channel spacing of 0.8 nm from the main channel. In this case, measured optical losses of 0.67 dB, 1.66 dB, and 2.59 dB are obtained for the first, the second, and the remaining dropped wavelength optical beams, respectively. Optical crosstalk and polarization dependent loss of <−18 dB and <0.08 dB are also investigated, respectively.     

Performance evaluation of SCM-WDM communication in the presence of SRS induced crosstalk for different types of fiber

In this paper, the SRS-induced crosstalk has been evaluated in a SCM-WDM communication link at different modulation frequencies for various type of fibers. Results show that SRS-induced crosstalk dominates at low frequency. As the dispersion and effective area of fiber (A_eff) decreases, initially the crosstalk remains high and then it decreases with increase in modulation frequency. The present work shows that out of five different types of fibers, Standard Single Mode Fiber (SMF) has minimum crosstalk (−53 to −64 dB) and True Wave fiber (TW) has maximum crosstalk (−47 to −48 dB).     

Modify SRS-induced crosstalk with variety of fiber in SCM–WDM transmission links

In this paper, the SRS-induced crosstalk has been evaluated in a SCM–WDM communication links at different modulation frequencies and transmission lengths for variety of fiber. Results show that SRS-induced crosstalk dominates at low frequency. As the dispersion and effective area of fiber (A_eff) decreases, initially the crosstalk remains high and then it decreases with increase in modulation frequency. The present work shows that out of five different types of fiber, standard single mode fiber (SMF) has minimum crosstalk (−78 to −38) dB, (−55 to −33) dB and (−46 to −34) dB at modulation frequencies, transmission lengths and optical powers. Dispersion compensation fiber (DCF) has maximum crosstalk (−60 to −12) dB, (−37 to −12) dB and (−27 to −12) dB at modulation frequencies and transmission lengths.     

Orbital angular momentum crosstalk of single photons propagation in a slant non-Kolmogorov turbulence channel

We analyze the orbital angular momentum (OAM) crosstalk of single photons propagation through low-order atmospheric turbulence. The probability models of the orbital angular momentum crosstalk for single photons propagation in the channel with the non-Kolmogorov turbulence tilt, coma, and astigmatism and defocus aberration have been established. It is found, for α = 11/3, that the turbulent tilt is the dominant aberration which causes the orbital angular momentum crosstalk, the coma is second and the astigmatism is third, but the defocus aberration has no impact on OAM. The results also indicate that the regularities of orbital angular momentum crosstalk caused by the tilt, the coma and the astigmatism are almost the same, respectively. The crosstalk probability of the orbital angular momentum increases as the azimuth mode index p of Laguerre-Gaussian (LG) beam increases, the turbulent strength C_n² enhances, the orbital angular momentum quantum number rises, the diameter of circular sampling aperture D and the channel zenith angle θ increase.     

Cardinality enhancement of spectral/spatial modified double weight code optical code division multi-access system by PIIN suppression

A new two-dimensional (2-D) optical code division multiple access (OCDMA) scheme to increase the achievable system capacity is proposed. The code exhibits good cross-correlation property time and wavelength shift. Performances are analyzed on code size and correlation properties affecting two important system parameters, bit error rate (BER) as a function of cardinality generated and optical power transmission requirement. The proposed system can effectively suppress phase-induced intensity noise (PIIN) and has multi-access interference (MAI) cancellation property. Results in a good agreement indicate that 2-D modified double weight (MDW) offers 163.7% and 336.2% larger cardinality compare to 2-D perfect difference code (PDC) and 2-D modified quadratic congruence (MQC) code. By increasing spatial code (N) and keeps similar code length system performance can be further optimized. 2-D MDW (M = 45, N = 18) accommodates 252.2% and 18.3% cardinality increment and low effective transmitted power (P_sr) at −17.9 dBm, compare to 2-D MDW (M = 247, N = 3) and (M = 84, N = 9) at 10⁻⁹ BER error floor. The architecture of the spectral/spatial MDW OCDMA system with property of MAI cancellation is presented.     

Effective biaxial modulus and strain energy density of ideally (h k l)-fiber-textured cubic polycrystalline films

The effective biaxial modulus (M_eff) and strain energy density (W) of cubic polycrystalline films with ideally (h k l) fiber textures are estimated using Vook-Witt (VW) grain interaction model and the data are compared with those derived from Voigt, Reuss and Voigt-Reuss-Hill (VRH) models. Numerical results show that the VW average of M_eff for ideally (1 0 0)- or (1 1 1)-fiber-textured films is identical to the VRH average of M_eff. For (1 1 0) and (1 1 2) planes, however, the VW average of M_eff for (1 1 0)-fiber-textured film is larger than that of (1 1 2)-fiber-textured film when the Zener anisotropic factor (A_R) is not equal to 1. Furthermore, M_eff and W exhibit incremental tendencies with the increase of the orientation factor (Γ_h k l) for the [h k l] axis when A_R > 1, implying that M_eff and W have the minimums on the (1 0 0) plane. Reversely, M_eff and W decrease with the increasing Γ_h k l when A_R < 1. This means that M_eff and W on (1 1 1) plane have the minimums.     

Magnetic relaxation near a fishtail peak of isothermal magnetization in B1 NbCy encapsulated in multiwall carbon nanocages

Isothermal magnetization near a fishtail peak in nanocrystalline B1 NbC_y encapsulated in multiwall carbon nanocages is studied within the time window of 100 < t < 4000 s. The current density J exhibits a linear logarithmic time decay. The effective activation energy U_eff increases linearly with temperature T and is independent of applied magnetic field H. The results of J(t) and U_eff (T, H) are consistent with the Anderson–Kim flux–creep model for thermally activated motion of uncorrelated vortices or vortex bundles over a net potential barrier U_eff. U_eff at a fishtail peak field H_fp evolves quickly above a fishtail peak temperature T_fp, but slowly below that temperature. The result suggests that a decrease of flux viscosity coefficient above T_fp at H_fp is the origin of the fishtail peak in nanocrystalline B1 NbC_y encapsulated in multiwall carbon nanocages.     

Influence of grain growth on the high-frequency behaviour of ferromagnetic Fe-Co-(M)-N (M=Ta, Hf) nanocomposite films

The CMOS compatible ferromagnetic Fe-Co-(M)-N (M=Ta, Hf) films were investigated with regard to their grain size-dependent frequency behaviour. Predominantly Fe₃₃Co₄₀Ta₁₀N₁₇ films were deposited by reactive r.f. magnetron sputtering. These films were compared to Fe₃₆Co₄₄Hf₉N₁₁ films. In order to induce an in-plane uniaxial anisotropy H_u as well as to investigate the grain growth behaviour, the films were annealed in a static magnetic field. The in-plane uniaxial anisotropy field of around 4 mT as well as a good soft magnetic behaviour with a saturation polarisation of approximately 1.2-1.4 T could be observed after heat treatment. Ferromagnetic resonance frequencies (FMR) of approximately up to 2.4 GHz could be achieved according to the Kittel theory. Depending on the heat treatment, high-frequency losses through energy dissipation was made conspicuous by means of the full-width at half-maximum (FWHM) Δf_eff of the imaginary part of the frequency-dependent permeability which was between 0.4 and 1 GHz. This FWHM was basically discussed in terms of two-magnon scattering theories, in combination with the Herzer random anisotropy model. In order to correlate the resonance line broadening with a phenomenological damping parameter α_eff, which ranged from about 0.0125 to 0.028, the modified Landau-Lifschitz-Gilbert equation was used to fit and describe the permeability spectra of the ferromagnetic films.     

Photoluminescence of Si from Si nanocrystal-doped SiO2/Si multilayered sample

A multilayered Si nanocrystal-doped SiO₂/Si (or Si-nc:SiO₂/Si) sample structure is studied to acquire strong photoluminescence (PL) emission of Si via modulating excess Si concentration. The Si-nc:SiO₂ results from SiO thin film after thermal annealing. The total thickness of SiO layer remains 150 nm, and is partitioned equally into a number of sublayers (N = 3, 5, 10, or 30) by Si interlayers. For each N-layered sample, a maximal PL intensity of Si can be obtained via optimizing the thickness of Si interlayer (or d_Si). This maximal PL intensity varies with N, but the ratio of Si to O is nearly a constant. The brightest sample is found to be that of N = 10 and d_Si = 1 nm, whose PL intensity is ∼5 times that of N = 1 without additional Si doping, and ∼2.5 times that of Si-nc:SiO₂ prepared by co-evaporating of SiO and Si at the same optimized ratio of Si to O. Discussions are made based on PL, TEM, EDX and reflectance measurements.     

Analysis of polymer electro-optic microring resonator switches

The structure and the principle for the polymer electro-optic microring resonator (MRR) switch are proposed as well as the transfer functions. The structural parameters are optimized; the transmission characteristics are analyzed including the output power, switching time, switching voltage, insertion loss, and crosstalk. When the operation voltage is 0 V, the insertion loss and crosstalk are ∼1.2 and −20.2 dB, respectively; when the operation voltage is 10.0 V, those are ∼0.35 and −20.0 dB, respectively. Furthermore, a novel method is presented for analyzing time-domain response of the device and the switching time is determined to be ∼10.71 ps. These results indicate the favorable switching functions of the designed device.     

Optimized design of a new three branch optical waveguide

A new type of 1 × 3 Y-branch optical waveguide structure with a cone transitional section is introduced in this paper. The symmetrical branch ratio of the 1 × 3 Y branch optical waveguide is obtained by changing the width of this waveguide. The loss and the uniformity are obtained by using the finite difference beam propagation methods, and their values are 0.2 dB and 0.05 dB, respectively. Therefore, it provides some experimental basis for production of three branch optical waveguide.     

Antiferromagnetic ordering in magnetic ionic liquid Emim[FeCl4]

The magnetic ionic liquids (MILs) are considered to open up a wide range of applications because of their magnetic and electrochromic switching. Until recently almost all magnetic ionic liquids containing tetrachloroferrate ion FeCl₄⁻ evidenced a paramagnetic temperature dependence of the magnetic susceptibility, with only small deviations from the Curie law at low temperatures. However, 1-ethyl-3-methylimidazolium tetrachloroferrate, Emim[FeCl₄], clearly exhibits a long-range antiferromagnetic ordering below the Neel temperature T_N≈3.8 K. In addition, the shape of the magnetic ordering depends on the cooling speed, indicating that the magnetic coupling could be modified.     

N incorporation and electronic structure in N-doped TiO2(1 1 0) rutile

We describe the growth and properties of well-defined epitaxial TiO_2−xN_x rutile for the first time. A mixed beam of atomic N and O radicals was prepared in an electron cyclotron resonance plasma source and Ti was supplied from a high-temperature effusion cell or an electron beam evaporator, depending on the required flux. A very high degree of structural quality is generally observed for films grown under optimized anion-rich conditions. N substitutes for O in the lattice, but only at the ∼1 at.% level, and is present as N³⁻. Epitaxial growth of TiO₂ and TiO_2−xN_x rutile prepared under anion-rich conditions is accompanied by Ti indiffusion, leading to interstitial Ti (Ti_i), which is a shallow donor in rutile. Our data strongly suggest that Ti_i donor electrons compensate holes associated with substitutional N²⁻ (i.e., Ti(III) + N²⁻ → Ti(IV) + N³⁻), leading to highly resistive or weakly n-type, but not p-type material. Ti 2p core-level line shape analysis reveals hybridization of N and Ti, as expected for substitutional N. Ti-N hybridized states fall in the gap just above the VBM, and extend the optical absorption well into the visible.     

Antiferromagnetic resonance study of sodalite loaded with sodium by multi-frequency ESR

We have carried out electron spin resonance (ESR) measurements on powder samples of sodalite loaded with Na at several frequencies between 9.7 and 35 GHz and at temperatures between 1.5 and 60 K. The ESR absorption spectrum below a Néel temperature T_N turns into an asymmetric spectrum with a long tail at low fields from a symmetric one above T_N. The line shape of the spectra below T_N is analyzed by a powder pattern simulation of the antiferromagnetic resonance spectra with easy-plane anisotropy. The calculated line shape reproduces the experimental one considerably well by assuming a Gaussian distribution of the zero-field energy gap. We have evaluated a small anisotropy field of about 2×10⁻⁴ T by using the exchange coupling constant calculated from the Weiss and the Néel temperatures. This result indicates that the sodalite loaded with Na is quite an ideal Heisenberg antiferromagnet as expected from the s-electron character of Na clusters and the cubic arrangement of nano-spaces in the sodalite.     

Rovibrational spectrum and potential energy surface of the N2-N2O van der Waals complex

The rovibrational spectrum of the N₂-N₂O van der Waals complex has been recorded in the N₂O ν₁ region (∼1285 cm⁻¹) using a tunable diode laser spectrometer to probe a pulsed supersonic slit jet. The observed transitions together with the data observed previously in the N₂O ν₃ region are analyzed using a Watson S-reduced asymmetric rotor Hamiltonian. The rotational and centrifugal distortion constants for the ground and excited vibrational states are accurately determined. The band-origin of the spectrum is determined to be 1285.73964(14) cm⁻¹. A restricted two-dimensional intermolecular potential energy surface for a planar structure of N₂-N₂O has been calculated at the CCSD(T) level of theory with the aug-cc-pVDZ basis sets and a set of mid-bond functions. With the intermolecular distance fixed at the ground state value R = 3.6926 Å, the potential has a global minimum with a well depth of 326.64 cm⁻¹ at θ_N2 = 11.0° and θ_N2O = 84.3° and has a saddle point with a barrier height of 204.61 cm⁻¹ at θ_N2 = 97.4° and θ_N2O = 92.2°, where θ_N2(θ_N2O) is the enclosed angle between the N-N axis (N-N-O axis) and the intermolecular axis.     

What does Finite Volume-based implicit filtering really resolve in Large-Eddy Simulations?

The study illustrated in this paper completes the topics initially investigated in Ref. [42], the aim being here to analyze the role of the integral-based Finite Volume (FV) discretizations in Large Eddy Simulations that exploit the implicit filtering approach. Specifically, a theoretical study on the effective shape and length of three-dimensional filters induced by some FV-based flux reconstructions is the object of this paper. For any integral-based flux reconstruction, one gets always an approximation of the top-hat filter kernel. This is not the case of the filters induced by the differential-based Finite Difference operators, such as those reported and analyzed in Refs.  and . Considering the sub-filter resolution parameter Q = Δ_eff/h, being Δ_eff the effective filter width and h the computational grid size, allows us discerning the effective measure of the approximate built-in top-hat filter. The induced shape and width is analyzed by means of a modified wavenumber-like analysis that is developed in the 3D Fourier space. Several evaluation criteria applied on different schemes are considered and the differences in terms of either velocity or flux interpolations on staggered or non-staggered grids are analyzed. Conclusions are reported that, depending on the using of either the integral or the differential form of the filtered equations, the induced numerical filter is or is not a congruent approximation of the exact top-hat transfer function for some value Q. The need of a suitable estimation of the sub-filter parameter Q is assessed from several real LES computations, that make use of the new integral-based version of the eddy-viscosity dynamic modeling presented in Ref. [42]. In fact, it is shown that the test-filtering length has to be carefully chosen as a function of the FV-based induced filter.     

Design of wide-spectrum polymer Mach-Zehnder interferometer electro-optic switches using two symmetric N-th order phase-generating couplers

To enlarge the output spectrum, a novel reasonable structure of one kind of Mach-Zehnder interferometer (MZI) electro-optic (EO) switches containing two symmetric N-th order phase generating couplers (PGCs) is presented, and thorough model, analysis and design technique are proposed. A non-linear least square method is investigated for optimizing the PGC structure to eliminate the phase difference error caused by the wavelength variation. Under the central wavelength of 1550 nm, optimization and simulation are performed on three MZI EO switches using two first, second and third order PGCs, respectively. The switches exhibit a low switching voltage of 1.156 V with an active region length of 4 mm. The output spectrums covering the whole S-C-L bands are as wide as 320, 390 and more than 435 nm, respectively, the insertion loss are less than 5.57, 5.98 and 7.90 dB, respectively, and the crosstalk is less than −30 dB over the wide wavelength ranges, for the three designed switches. The design technique is supported to be feasible by the comparison with beam propagation method (BPM).     

Simulation and optimization of a polymer 2×2 multimode interference-Mach Zehnder interferometer electro-optic switch with push-pull electrodes

Structural model and design technique are proposed for a polymer 2×2 multimode interference-Mach Zehnder interferometer electro-optic (MMI-MZI EO) switch with push-pull electrodes. The electric field distribution is analyzed by the conformal transforming method and image method. To get the minimum mode loss and half-wave voltage, the parameters of the waveguide and electrodes are optimized, such as the core width, core thickness, buffer layer thickness, size of the MMI couplers and the modulating region, electrode thickness, electrode width, and electrode gap. Switching characteristics are analyzed, including the output power, crosstalk, and wavelength shift. Simulation results show that the half-wave voltage is 0.74 V, the optical 3 dB bandwidth is 12.66 GHz, and the crosstalk is less than −30 dB for the designed device.     

Formation of p-type ZnMgO thin films by In-N codoping method

In-N codoped ZnMgO films have been prepared on glass substrates by direct current reactive magnetron sputtering. The p-type conduction could be obtained in ZnMgO films by adjusting the N₂O partial pressures. The lowest resistivity was found to be 4.6 Ω cm for the p-type ZnMgO film deposited under an optimized N₂O partial pressure of 2.3 mTorr, with a Hall mobility of 1.4 cm²/V s and a hole concentration of 9.6 × 10¹⁷ cm⁻³ at room temperature. The films were of good crystal quality with a high c-axis orientation of wurtzite ZnO structure. The presence of In-N bonds was identified by X-ray photoelectron spectroscopy, which may enhance the nitrogen incorporation and respond for the realization of good p-type behavior in In-N codoped ZnMgO films. Furthermore, the ZnMgO-based p-n homojunction was fabricated by deposition of an In-doped n-type ZnMgO layer on an In-N codoped p-type ZnMgO layer. The p-n homostructural diode exhibits electrical rectification behavior of a typical p-n junction.