Multichannel wavelength division multiplexing system based on silicon rods of periodic lattice constant of hetero photonic crystal units

Characteristics of two different multichannel wavelength division multiplexing (WDM) systems composed of two-dimensional (2D) hetero photonic crystals (HPCs) are introduced. One utilizes five photonic crystal (PC) units, each fabricated with triangular and rectangular lattice. The other consists of five PC units in rectangular lattice. Both systems have a lattice constant difference of 4 nm between adjacent PC units, and both systems apply silicon rods with a radius of 120 nm. Finite-difference time-domain (FDTD) method and plan wave expansion (PWE) method reveal the ability of wavelength spacing ～8 nm with high quality factor (Q) in a system based on triangular and rectangular lattice; and ～8 nm with almost constant transmission efficiency based on rectangular lattice.     

Universal dynamics behavior in superionic conducting glasses

The inelastic neutron scattering experiment on superionic glass system AgI-AgPO₃ have been performed in the energy and momentum transfer range from ? 5 to 15 meV and 0 to 8 Å^? 1, respectively by using a time of flight MARI instrument at Rutherford Appleton Laboratory, ISIS, UK. The E-dependence of the inelastic data show an excess intensity at low energy around 3 meV, the so-called Boson peak, which increased with the dopant salt. The Q-dependence of the elastic scattering reveals a prepeak at anomalously low Q value around 0.8 Å^? 1, which is not observed in the undoped AgPO₃ glass. The Q-dependence in the energy region from 1 to 3 meV shows clearly an excess intensity at Q ~ 2.2 Å ^? 1compared with the undoped AgPO₃. All these features correlate with the increasing mobility of Ag⁺ ions due to the expansion of the network structure caused by salt doping, which leads to the increase of ionic conductivity. Similar results have also been observed in the corresponding superionic glass system AgI-Ag₂S-AgPO₃ that was observed by both MARI and NEAT instrument at HMI, Berlin. The results show a universal dynamic behavior in silver phosphate glasses.     

Light transmission behaviour as a function of the homogeneity in one dimensional photonic crystals

The average light transmission of one-dimensional photonic media has been studied as a function of the medium homogeneity, quantified by the Shannon–Wiener index. We have found a decrease in the average light transmission by increasing the Shannon–Wiener index up to minimum (corresponding to H′ = 0.9375): from this point, the transmission increases following the Shannon–Wiener index. The behaviour has been confirmed for different pairs of materials forming the photonic structure. Nevertheless, we have observed that the trend slope is proportional to the refractive index ratio between the two materials (n_hi/n_low).     

Microfabrication of solenoid-type RF SMD chip inductors with an Al2O3 core

We investigated micron size, high-performance, and solenoid-type radio-frequency surface-mounted device (SMD) chip inductors with a low-loss Al₂O₃ core for a GHz drive microwave circuit application. Copper coils with a diameter of 27 μm were used and the chip inductors fabricated in this study are 0.86 × 0.46 × 0.45 mm³. The high-frequency characteristics of the inductance (L), quality factor (Q), and impedance (Z) of the developed inductors were measured using a RF impedance/material analyzer (HP4291B with HP16193A test fixture). The developed inductors have a self-resonant frequency of 3.7–5.2 GHz and exhibit L of 15–34 nH. The inductors have Q of 38–49 over the frequency ranges of 900 MHz–1.7 GHz. The calculated data obtained from the equivalent circuit and the derived equation of Q described the high-frequency data of L, Q, and Z of the inductors developed quite well.     

Compact and efficient coupler to interface hybrid dielectric-loaded plasmonic waveguide with silicon photonic slab waveguide

A coupler is proposed to interface a hybrid dielectric-loaded plasmonic waveguide (HDLPW) with a silicon photonic slab waveguide. The HDLPW is firstly designed and optimized to attain the best tradeoff between the mode confinement and the propagation distance. The designed coupler is inspired from the taper configuration and numerically modeled through finite-difference time-domain (FDTD) simulation. The results demonstrate that a high confinement and low loss of the energy is achieved from a silicon photonic slab waveguide into the dielectric slot of area 50×200 nm² in the HDLPW. The transmission attained through the coupler with a compact size of 400 nm is found to be as high as 80% (1 dB). Further, the planar nature of taper configuration makes the coupler easy to fabricate using the state-of-the-art CMOS facilities. The proposed coupler is useful in enabling the integration between photonic and hybrid plasmonic waveguides and thus realizing on-chip hybrid integrated circuits.     

Compact WDM demultiplexer for seven channels in photonic crystal

We demonstrate a new device concept for wavelength division demultiplexing based on planar photonic crystal waveguides. The filtering of wavelength channels is realized by shifting the cutoff frequency of the fundamental photonic bandgap mode in consecutive sections of the waveguide. The shift is realized by modifying the size of the border holes.The proposed demultiplexer has an area equal to (16.5 μm × 6.5 μm) and thus it is verified that this structure is very small and can be integrated easily into optical integrated circuits with nanophotonic technologies. The output wavelengths of designed structure can be tuned for communication applications, around 1550 nm. The wavelengths of demultiplexer channels are λ₁ = 1.590 μm, λ₂ = 1.566 μm, λ₃ = 1.525 μm, λ₄ = 1.510 μm, λ₅ = 1.484 μm, λ₆ = 1.450 μm, λ₇ = 1.400 μm respectively. Designs offering improvement of number of the separate wavelengths (seven), miniaturization of the structure (107.25 μm²) is our aim in this work.In our structure, we consider that the 2D triangular lattice photonic crystal is composed of air holes surrounded by dielectric. Its parameters are: radius of holes (r = 0.130 μm), lattice constant (a = 0.380 μm), and index of membrane (n = 3.181:InP). The numerical model used to simulate the structure of the demultiplexer is based on the finite difference time domain (FDTD).     

GaAs photonic crystal slab nanocavities: Growth,fabrication, and quality factor

In an effort to understand why short wavelength (～1000 nm) GaAs-based photonic crystal slab nanocavities have much lower quality factors (Q) than predicted (and observed in Si), many samples were grown, fabricated into nanocavities, and studied by atomic force, transmission electron, and scanning electron microscopy as well as optical spectroscopy. The top surface of the AlGaAs sacrificial layer can be rough even when the top of the slab is smooth; growth conditions are reported that reduce the AlGaAs roughness by an order of magnitude, but this had little effect on Q. The removal of the sacrificial layer by hydrogen fluoride can leave behind a residue; potassium hydroxide completely removes the residue, resulting in higher Qs.     

Development and characteristics of solenoid-type SMD RF chip inductors

Simple, solenoid-type surface-mounted device (SMD) chip inductors utilizing low-loss Al₂O₃ core materials for a radio-frequency (RF) drive microwave circuit application were developed. The SMD chip inductors were fabricated with five different specifications, namely, 0.86 × 0.46 × 0.45, 1.0 × 0.5 × 0.5, 1.5 × 1.0 × 0.7, 2.1 × 1.5 × 1.0, and 2.4 × 2.0 × 1.4 mm³. Copper coils with diameters in the range of 27–40 μm were used. The frequency characteristics of the inductance (L), quality factor (Q), and impedance of the developed inductors were measured using a RF impedance/material analyzer (HP4291B with HP16193A test fixture). It was observed that the developed inductors with the number of turns of 12 have L of 34–270 nH, exhibit a self-resonant frequency (SRF) of 3.7–0.75 GHz, and have Q of 40–70 over the frequency ranges of 200 MHz–1.2 GHz. The L of inductors increases and the SRF decreases with increasing the size of inductors. From the experimental results, it was concluded that the high-frequency data calculated from the equivalent circuit and the derived equation of Q described quite well the experimental data of the developed inductors.     

Large photonic band gap and strong attenuation of multiconnected Peano network

In this paper, by means of the network equation and generalized eigenfunction method we investigate the optical transmission spectra and attenuation behavior of electromagnetic (EM) waves in multiconnected Peano networks composed of one-dimensional (1D) waveguides. It is found that for some two-segment-connected networks a very large photonic band gap (PBG) can be created in the middle of a frequency period and the width of the large PBG can be controlled by adjusting the matching ratio of waveguide length, d₂ : d₁. When d₂ : d₁ = 2 : 1, the width of the large PBG is bigger than half of frequency period. The influence of generation on the width and attenuation of the large PBG are also studied and the numerical results demonstrate that the first-generation Peano network with d₂ : d₁ = 2 : 1 is a good selectable structure for the designing of optical devices with large PBG and strong attenuation.     

The thermodynamic and kinetic properties of hydrogen dimers on graphene

The thermodynamic and kinetic properties of hydrogen adatoms on graphene are important to the materials and devices based on hydrogenated graphene. Hydrogen dimers on graphene with coverages varying from 0.040 to 0.111 ML (1.0 ML = 3.8 × 10¹⁵cm^? 2) were considered in this report. The thermodynamic and kinetic properties of H, D and T dimers were studied by ab initio simulations. The vibrational zero-point energy corrections were found to be not negligible in kinetics, varying from 0.038 (0.028, 0.017) to 0.257 (0.187, 0.157) eV for H (D, T) dimers. The isotope effect exhibits as that the kinetic mobility of a hydrogen dimer decreases with increasing the hydrogen mass. The simulated thermal desorption spectra with the heating rate α = 1.0 K/s were quite close to experimental measurements. The effect of the interaction between hydrogen dimers on their thermodynamic and kinetic properties was analyzed in detail.     

A new design of low-loss and ultra-flat zero dispersion photonic crystal fiber using hollow ring defect

New hollow ring defect structure is introduced in photonic crystal fiber design for ultra- flat zero dispersion with very low waveguide losses. The hollow ring defect consisted of a central hole surrounded by a doped silica ring provides highly flexible defect engineering capabilities in photonic crystal fibers to achieve precise control of dispersion value and dispersion slope while independently maintaining low waveguide losses, which was not attainable in previous designs. A nearly flat zero dispersion of D=0±0.51 ps/nm km was obtained in the wavelength range of 1.44–1.61 μm with the maximum slope of ?2.7×10^?2 ps/nm² km. The confinement loss was less than 5.75×10^?8 dB/m along with the bending loss of 2.8×10^?6 dB/m for the radius of 10 mm, and splice loss of less than 1.57 dB to conventional single mode fiber at 1.55 μm.     

Performance comparison between 160 Gb/s WDM and TDM systems

The performances of 160 Gb/s time-division multiplexing (TDM) and 4 × 40 Gb/s wavelength-division multiplexing (WDM) signals are comparatively studied in the nonzero-dispersion shifted fibers (NZDSFs). TDM format is superior to WDM, and with the increase of distance, this advantage is enhanced. In the case of adopting the dispersion managed soliton transmission and dispersion flattened fibers (DFFs) technique, the Q values of both formats change little when the channel space varies. So, TDM technique is applicable to the dense and very long haul transmissions. Only by utilizing the conventional loss and dispersion compensation schemes (NZDSFs + DCFs + EDFAs), the available transmission distance of dense WDM signals reaches 1000 km, and for TDM format, it even extends to 2000 km. Both systems have the analogue characteristics: a higher pulse power benefits system's working; ASE noise is the dominant impact factor of system performance; both format's system performances are improved for the case of less channel number; the channel space and duty cycle of return zero pulse have little effect on Q; the impact of duty cycle relates to the filter bandwidths, XPM induced sidebands and pulse broadening effect; the influence of channel space is determined by the walk-off effect.     

Band overlap via chemical pressure control in double perovskite (Sr2−xCax)FeMoO6 (0 ⩽ x ⩽ 2.0) with TMR effect

The chemical pressure control in (Sr_2−xCa_x)FeMoO₆ (0 ⩽ x ⩽ 2.0) with double perovskite structure has been investigated systematically. We have performed first-principles total energy and electronic structure calculations for x = 0 and x = 2.0. The increasing Ca content in (Sr_2−xCa_x)FeMoO₆ samples increases the magnetic moment close to the theoretical value due to reduction of Fe/Mo anti-site disorder. An increasing Ca content results in increasing (Fe²⁺ + Mo⁶⁺)/(Fe³⁺ + Mo⁵⁺) band overlap rather than bandwidth changes. This is explained from simple ionic size arguments and is supported by X-ray absorption near edge structure (XANES) spectra and band structure calculations.     

Luminescence of Eu2+–vc− dipoles and their associates in CsI:Eu crystals

Spectral-kinetics properties of photo-scintillation excited with single light pulses of a nitrogen laser (λ=337.1 nm, t_1/2=5 ns, Q=1 mJ) have been studied in CsI:Eu crystals at temperature within 80–300 K. It is found that the exponential decay of 463 nm emission band has a time constant which grows from 0.85 μs at 78 K to 1.6 μs at 380 K. Such an anomalous temperature behavior of 463 nm emission decay kinetics is discussed in terms of the crystal thermal expansion. It has been proposed that 463 nm emission is caused by a cluster center consisting of three dipoles Eu²⁺v_c^? bounded with each other in a hexagon. Owing to the exchange resonance in the cluster, the energy passes from an excited dipole to a non-excited one and the distance between them gets longer due to thermal expansion of the crystal.     

4D cardiac imaging at clinical 3.0 T provides accurate assessment of murine myocardial function and viability

ObjectivesWe validate a 4D strategy tailored for 3 T clinical systems to simultaneously quantify function and infarct size in wild type mice after ischemia/reperfusion, with improved spatial and temporal resolution by comparison to previous published protocols using clinical field MRI systems.MethodsC57BL/6J mice underwent 60 min ischemia/reperfusion (n = 14) or were controls without surgery (n = 6). Twenty-four hours after surgery mice were imaged with gadolinium injection and sacrificed for post-mortem MRI and histology with serum also taken for Troponin I levels. The double ECG- and respiratory-triggered 3D FLASH (Fast Low Angle Shot) gradient echo (GRE) cine sequence had an acquired isotropic resolution of 344 μm, TR/TE of 7.8/2.9 ms and acquisition time 25–35 min. The conventional 2D FLASH cine sequence had the same in-plane resolution of 344 μm, 1 mm slice thickness and TR/TE 11/5.4 ms for an acquisition time of 20–25 min plus 5 min for planning. Left ventricle (LV) and right ventricle (RV) volumes were measured and functional parameters compared 2D to 3D, left to right and for inter and intra observer reproducibility. MRI infarct volume was compared to histology.ResultsFor the function evaluation, the 3D cine outperformed 2D cine for spatial and temporal resolution. Protocol time for the two methods was equivalent (25–35 min). Flow artifacts were reduced (p = 0.008) and epi/endo-cardial delineation showed good intra and interobserver reproducibility. Paired t-test comparing ejection volume left to right showed no significant difference for 3D (p = 0.37), nor 2D (p = 0.30) and correlation slopes of left to right EV were 1.17 (R² = 0.75) for 2D and 1.05 (R² = 0.50) for 3D.Quantifiable ‘late gadolinium enhancement’ infarct volume was seen only with the 3D cine and correlated to histology (R² = 0.89). Left ejection fraction and MRI-measured infarct volume correlated (R² > 0.3).ConclusionsThe 4D strategy, with contrast injection, was validated in mice for function and infarct quantification from a single scan with minimal slice planning.     

Investigation on two dimensional photonic crystal resonant cavity based bandpass filter

In this paper, different cavities, namely quasi square, tri-quarter square, square, hexagonal, circular, elliptical, diamond and annular ring based photonic crystal bandpass filters (PCBPFs) are proposed and investigated by exploiting coupling between two in-line quasi waveguides and a resonant cavity. The resonant wavelength, output efficiency and bandwidth of designed PCBPFs are studied by varying the size of the cavity. The normalized transmission spectra of PCBPF are observed using 2D finite difference time domain (FDTD) method. The photonic band gap (PBG) is calculated by plane wave expansion (PWE) method. The circular cavity based PCBPF gives better performance than others because of its circular resonating modes. The number of passbands is increased linearly while increasing the size of the cavity. The overall size of the PCBPF chip is about 11.4 μm × 11.4 μm, which is more suitable for photonic integrated circuits (PIC), wavelength division multiplexing (WDM) systems and sensing applications.     

Permeability tensor versus permittivity one in theory of nonreciprocal optical components

We discuss symmetry properties of the combined systems: electromagnetic field (TE and TM modes) + medium (nondiagonal permeability tensor [μ] and nondiagonal permittivity one [?]) in 2D photonic crystals with transverse magnetization. We show that the origin of orthogonality of the pairs (TE mode + [?]) and (TM mode + [μ]) is different parities of the corresponding fields with respect to the horizontal plane of symmetry of the crystal. As a result of this symmetry, a common use only of the permittivity tensor [?] in the electromagnetic theory of nonreciprocal optical components, ignoring the permeability tensor [μ], leads to loss of a significant part of possible solutions related to TE modes.     

Photonic crystal nanocavities in GaAs/AlGaAs with oxidised bottom cladding

We present a solution to the difficult task of removing an oxide-based hard mask from a photonic crystal fabricated in the GaAs/AlGaAs system. We use a polymer backfill technique to seal the AlGaAs layer, thereby making it inaccessible to the wet-etch solution. This allows us to use a GaAs active layer for the photonic crystal placed on an oxidised AlGaAs layer which provides mechanical and thermal support. Using this technique, we fabricated GaAs-based photonic crystal cavities and measured respectable quality factors (Q ≈ 2200) despite the intrinsic asymmetry of the system. The technique presents a viable method for producing electrically injected photonic crystal cavities for operation on a mechanically stable and thermally conducting buffer layer.     

Ultrastructural analysis of the low level laser therapy effects on the lesioned anterior tibial muscle in the Gerbil

Low level laser therapy (LLLT) is known for its positive results but studies on the biological and biomodulator characteristics of the effects produced in the skeletal muscle are still lacking. In this study the effects of two laser dosages, 5 or 10 J/cm², on the lesioned tibial muscle were compared. Gerbils previously lesioned by 100 g load impact were divided into three groups: GI (n = 5) controls, lesion non-irradiated; GII (n = 5), lesion irradiated with 5 J/cm² and GIII (n = 5), lesion irradiated with 10 J/cm², and treated for 7 consecutive days with a laser He–Ne (λ = 633 nm). After intracardiac perfusion, the muscles were dissected and reduced to small fragments, post-fixed in 1% osmium tetroxide, dehydrated in increasing alcohol concentrations, treated with propylene oxide and embedded in Spurr resin at 60 °C. Ultrafine cuts examined on a transmission electron microscope (Jeol 1010) revealed in the control GI group a large number of altered muscle fibers with degenerating mitochondria, intercellular substance containing degenerating cell fragments and budding blood capillaries with underdeveloped endothelial cells. However, groups GII and GIII showed muscle fibers with few altered myofibrils, regularly contoured mitochondria, ample intermembrane spaces and dilated mitochondrial crests. The clean intercellular substance showed numerous collagen fibers and capillaries with multiple abluminal processes, intraluminal protrusions and several pinocytic vesicles in endothelial cells. It was concluded that laser dosages of 5 or 10 J/cm² delivered by laser He–Ne (λ = 633 nm) during 7 consecutive days increase mitochondrial activity in muscular fibers, activate fibroblasts and macrophages and stimulate angiogenesis, thus suggesting effectivity of laser therapy under these experimental conditions.     

Inelastic neutron scattering on iron-based superconductor BaFe2(As,P)2

Inelastic neutron scattering has been performed on powder sample of an iron-based superconductor BaFe₂(As_0.65P_0.35)₂ with superconducting transition temperature (T_c) = 30 K, whose superconducting (SC) order parameter is expected to have line node. In the normal state, constant-E scan of dynamical structure factor, S(Q, E), exhibits a peak structure centered at momentum transfer Q ～ 1.20 Å^?1, corresponding to antiferromagnetic wave vector. Below T_c, the redistribution of the magnetic spectral weight takes place, resulting in the formation of a peak at E ～ 12 meV and a gap below 6 meV. The enhanced magnetic peak structure is ascribed to the spin resonance mode, evidencing sign change in the SC order parameter similar to other iron-based high-T_c superconductors. It suggests that fully-gapped s_± symmetry dominates in this superconductor, which gives rise to high-T_c (=30 K) despite the nodal symmetry.