Directly modulated active distributed reflector distributed feedback lasers over wide temperature range operation(-40 to 85℃)

We experimentally demonstrated that the distributed feedback(DFB) lasers with the active distributed reflector achieved a 25.8 Gb/s operation over a wide temperature range of -40 to 85℃. The DFB lasers can achieve additional feedback from an active distributed reflector with accurately controlled phase, and single-mode yields are not related to the position of cleave. The threshold currents of the fabricated laser are 6 mA and 20 mA at -40℃ and 85℃, respectively. The side mode suppression ratio of the fabricated laser is above 50 dB at all temperatures. Transmissions of 25.8 Gb/s after 10 km single-mode fibers with clear eye openings and less than 0.8 dB power penalty over a wide temperature range have been demonstrated as well.     

Zero-Dispersion Slow Light with Wide Bandwidth in Photonic Crystal Coupled Waveguides

By introducing an adjustment waveguide besides the incident waveguide, zero-dispersion slow light with wide bandwidth can be realized due to anticrossing of the incident waveguide mode and the adjustment waveguide mode. The width of the adjustment waveguide （W2） and the hole radii of the coupling region （r＇） will change the dispersion of incident waveguide mode. Theoretical investigation reveals that zero dispersion at various low group velocity vg in incident waveguide can be achieved. In particular, proper W2 and r＇ can lead to the lowest vg of 0.0085c at 1550 nm with wide bandwidth of 202 GHz for zero dispersion.     

2-nm narrow band pass filter in standard configuration evaporate coating machine

High sophisticated optical monitoring systems like the OMS 5000 from Leyboldoptics are commonly used in vacuum coating system to improve the capabilities and reliability of production processes concerning optical performance and repeatability optics. This letter describes a method to perform high end optical filters with additional backside blocking over a wide spectral range. The direct monitoring with intermittent measurement on a large area rotating substrate holder is used to facilitate a narrow band pass filter of 2-nm half bandwidth at 532 nm and high transmittance together with a complex blocking filter to retard disturbing radiation from the ultraviolet （UV） range to the near infrared range. The machine is an ARES 1350 coating system with basically standard configuration.     

Experimental study on electrical resistivity measurement of a specimen at high temperature

A new technique is developed to measure the electrical resistivity of conductor with a nonuniform tem- perature profile. The calculation method is derived from the temperature dependence of the electrical resistivity. The apparatus consists mainly of a high temperature environmental chamber, a power circuit of heating, a twenty-wavelength pyrometer, and a scanning pyrometer. After getting the resistance from the voltage drop of the specimen, the electrical resistivity in a wide temperature range of the specimen can be obtained by our calculation model. Preliminary results of the electrical resistivity of SRM 8424 over a wide temperature range （1000-3000 K） are presented. The perfect consistency between the measurement results and the nominal values justifies the validity of this technique.     

Transmission Bandwidth Tunability of a Liquid-Filled Photonic Bandgap Fiber

A temperature tunable photonie bandgap fiber （PBGF） is demonstrated by an index-guiding photonic crystal fiber filled with high-index liquid. The temperature tunable characteristics of the fiber are experimentally and numerically investigated. Compression of transmission bandwidth of the PBGF is demonstrated by changing the temperature of part of the fiber. The tunable transmission bandwidth with a range of 250nm is achieved by changing the temperature from 30℃ to 90℃.     

基于银膜孔阵列超强透射效应的相敏表面等离子体共振传感器的仿真研究

A high spatial resolution, phase-sensitive Surface Plasmon Resonance（SPR） sensor based on Extraordinary Optical Transmission （EOT） is proposed to monitor the binding of organic and biological molecules to the silver surface. The 2D nanohole-array configuration is well suited ~br dense integration in a sensor chip. The optical geomeWy is collinear, which simplifies the alignment with respect to the traditional Kretschmann arrangement for SPR sensing. Various design parameters of the device have been studied by simulation. The heterodyne technique is used to improve the sensitivity. The optimization results indicate that the sensor has the advantages of achieving high resolution and a wide dynamic range simuhaneously.     

Hopping Conductivity in a Single-Walled Carbon Nanotube Network

We investigate the resistance and magnetoresistance （MR） of an entangled single-walled carbon nanotube （SWNT） network. The temperature dependence of conductance is fitted by formula G（T） = Go exp[-（To/T）^1/2] with To = 15.8 K at a wide temperature range from 4 K to 300K. The MR defined by [R（T, H） - R（T, 0）]/ R（T, 0） as a function of temperature and magnetic field perpendicular to the tube axis is negative at low temperatures. The MR amplitude increases as the temperature decreases at relative high temperature, but becomes decrease when temperature below 4 K. The results are explained in terms of the coherent hopping of carriers in the presence of a Coulomb gap at low temperature.     

Switching response of dual-output Mach–Zehnder modulator in channel-interleaved photonic analog-to-digital converter

This Letter theoretically and experimentally studies the response of photonic switching in a channel-interleaved photonic analog-to-digital converter(PADC) with high sampling rate and wide input frequency range. A figure of merit(FoM) is introduced to evaluate the switching response of the PADC when a dual-output Mach–Zehnder modulator(MZM) serves as the photonic switch to parallelize the sampled pulse train into two channels. After the optimization of the FoM and utilization of the channel-mismatch compensation algorithm,the system bandwidth of PADC is expanded and the signal-to-distortion ratio is enhanced.     

Pressure dissociation of dense hydrogen

The self-consistent fluid variational model （SFVM） has been used to describe the pressure dissociation of dense hydrogen at high temperatures. This paper focuses on a mixture of hydrogen atoms and molecules and is devoted to the study of the phenomenon of pressure dissociation at finite temperatures. The equation of state and dissociation degree have been calculated from the free energy functions in the range of temperature 2000-10,000K and density 0.02-1.0g/cm^3, which can be compared with other approaches and experiments. The pressure dissociation is found to occur in higher density range, while temperature dissociation is a more gradual effect.     

Measurement of thermal expansion coefficient of nonuniform temperature specimen

A new technique is developed to measure the longitudinal thermal expansion coefficient of C/C composite material at high temperature.The measuring principle and components of the apparatus are described in detail.The calculation method is derived from the temperature dependence of the therinal expansion coefficient.The apparatus mainly consists of a high temperature environmental chamber,a power circuit of heating,two high-speed pyrometers,and a laser scanning system.A long solid specimen is resistively heated to a steady high-temperature state by a steady electrical current.The temperature profile of the specimen surface is not uniform because of the thermal conduction and radiation.The temperature profile and the total expansion are measured with a high-speed scanning pyrometer and a laser slit scanning measuring system,respectively.The thermal expansion coefficient in a wide temperature range(1000-3800 K)of the specimen can therefore be obtained.The perfect consistency between the present and previous results justifies the validity of this technique.     

Linear Analysis of Folded Double-Ridged Waveguide Slow-Wave Structure for Millimeter Wave Traveling Wave Tube

A novel slow-wave structure （SWS）, the folded double-ridged waveguide structure, is presented and its linear gain properties are investigated. The perturbed dispersion equation is derived and the small signal growth rate is caleulated for dimensions of the ridge-loaded region and the parameters of the electron beam. The novel structure has potential applications in the production of high power and broad band radiation. For a cold beam, the linear theory predicts a gain of 1.1-1.27dB/period and a 3-dB small-signal gain bandwidth of 30% in W-band. A comparison between the folded double-ridged waveguide SWS and folded waveguide SWS （FWSWS） shows that with the same physical parameters, the novel SWS has an advantage over the FWSWS on the bandwidth and electron efficiency.     

Tunable circularly-polarized turnstile-junction mode converter for high-power microwave applications

Frequency tunability has become a subject of concern in the field of high-power microwave(HPM) source research.However, little information about the corresponding mode converter is available. A tunable circularly-polarized turnstilejunction mode converter(TCTMC) for high-power microwave applications is presented in this paper. The input coaxial TEM mode is transformed into TE_(10) mode with different phase delays in four rectangular waveguides and then converted into a circularly-polarized TE_(11) circular waveguide mode. Besides, the rods are added to reduce or even eliminate the reflection. The innovations in this study are as follows. The tunning mechanism is added to the mode converter, which can change the effective length of rectangular waveguide and the distance between the rods installed upstream and the closest edge of the rectangular waveguide, thus improving the conversion efficiency and bandwidth. The conversion efficiency of TCTMC can reach above 98% over the frequency range of 1.42 GHz–2.29 GHz, and the frequency tunning bandwidth is about 47%. Significantly, TCTMC can obtain continuous high conversion efficiency of different frequency points with the change of tuning mechanism.     

First-Principle Calculations for Transition Phase and Elastic Properties of SrS

The transition phase and elastic properties of SrS from NaCl structure （B1） to CsCl structure （B2） are investigated by ab initio plane-wave pseudopotential density functional theory method and by the quasi-harmonic Debye model. The transition pressure varies non-linearly with temperature, and the pressure of the mechanical instability increases linearly with increasing temperature. It is shown that the B1 structure SrS is a most elastically anisotropic minerat any pressure. The Debye temperature, the heat capacity, thermal expansion and Gruneisen parameter over a wide range of pressures and temperatures are also obtained.     

Effects of Dislocation on High Temperature Transport Characteristics of Unintentionally Doped GaN

High temperature transport characteristics of unintentionally doped GaN have been investigated by means of high temperature Hall measurements from room temperature to 500^o C. The increment of electron concentration from room temperature to 500^o C is found to vary largely for different samples. The dispersion of temperature dependence of electron concentration is found to be directly proportional to the density of dislocations in GaN layers calculated by fitting the FWHM of the rocking curves in x-ray diffraction measurements （XRD）. The buildup levels in persistent photoconductivity （PPC） are also shown to be directly proportionM to the density of dislocations. The correlation of XRD, Hall and PPC results indicate that the high temperature dependence of electron density in unintentional doped GaN is directly dislocation related.     

A Thermodynamic Cavitation Model for Cavitating Flow Simulation in a Wide Range of Water Temperatures

A thermodynamic cavitation model is developed to simulate the cavitating water flow in a wide temperature range. The thermal effect on bubble growth during cavitation is introduced in the developed model by considering both pressure difference and heat transfer between the vapor and liquid phase. The cavitating turbulent flow over a NACA0015 hydrofoil has been simulated at various temperatures from room temperature to 150°C by using the present cavitation model, which has been validated by the experimental data. It is seen that the thermodynamic effects of cavitation, vapor depression and temperature depression are much more predominant in high temperature water compared with those in room temperature water. These results indicate that the proposed thermodynamic cavitation model is reasonably applicable to the cavitating water flow in a wide temperature range.     

Magnetism and magnetic entropy change in LaFe11Al2Cx compounds around room temperature

Magnetism and magnetic entropy changes in LaFe11A12Cx(x=0.0, 0.2 and 0.5) compounds have been investigated.The Curie temperature TC is conveniently controlled from 200K to room temperature by varying the carbon concentration.Large magnetic entropy change is obtained over a wide temperature range due to the high magnetization and the drastic decrease in the magnetization around TC.The large magnetic entropy change in wide temperature range,low cost and the convenience of controlling TC suggest that the LaFe11Al2Cx compounds are promising candidates for magnetic refrigerants in the corresponding temperature range.     

First-principles calculations on the elastic and thermodynamic properties of NbN

<正>The elastic and thermodynamic properties of NbN at high pressures and high temperatures are investigated by the plane-wave pseudopotential density functional theory（DFT）.The generalized gradient approximation（GGA） with the Perdew-Burke-Ernzerhof（PBE） method is used to describe the exchange-correlation energy in the present work.The calculated equilibrium lattice constant a₀,bulk modulus B₀,and the pressure derivative of bulk modulus B₀’ of NbN with rocksalt structure are in good agreement with numerous experimental and theoretical data.The elastic properties over a range of pressures from 0 to 80.4 GPa are obtained.Isotropic wave velocities and anisotropic elasticity of NbN are studied in detail.It is indicated that NbN is highly anisotropic in both longitudinal and shear-wave velocities. According to the quasi-harmonic Debye model,in which the phononic effect is considered,the relations of（V-V₀）/V₀ to the temperature and the pressure,and the relations of the heat capacity C_V and the thermal expansion coefficientαto temperature are discussed in a pressure range from 0 to 80.4 GPa and a temperature range from 0 to 2500 K.At low temperature,C_V is proportional to T³ and tends to the Dulong-Petit limit at higher temperature.We predict that the thermal expansion coefficientαof NbN is about 4.20×10^-6/K at 300 K and 0 GPa.     

Ultra broadband flat dispersion tailoring on reversed-rib chalcogenide glass waveguide

In this paper,we introduce a horizontal slot in the reversed-rib chalcogenide glass waveguide to tailor its dispersion characteristics.The waveguide exhibits a flat and low dispersion over a wavelength range of 1080 nm,in which the dispersion fluctuates between-10.6 ps·nm~(-1)·km~(-1) and +11.14 ps·nm~(-1)·km~(-1).The dispersion tailoring effect is due to the mode field transfer from the reversed-rib waveguide to the slot with the increase of wavelength,which results in the extension of the low dispersion band.Moreover,the nonlinear coefficient and the phase-matching condition of the fourwave mixing process in this waveguide are studied,showing that the waveguide has great potential in nonlinear optical applications over a wide wavelength range.     

Temperature-insensitive fiber cantilever vibration sensor based on a fiber-to-fiber structure

A simple optical fiber cantilever vibration sensor consisting of two opposite aligned bare optical fibers sealed in a quartz capillary is presented.The fiber with the longer bare section is suspended in air and acts as a cantilever.By detecting the transmission power of the sensor directly,the environmental vibrational frequencies and amplitudes may be obtained.By adjusting the cantilever's natural deflection angle,the sensor can achieve high sensitivity,good response linearity,and a wide dynamic range.Coupling conditions are optimized to minimize temperature effects by simply setting an appropriate air gap between the bare fibers.     

Waveguide structure optimization of arrayed waveguide gratings concatenation in cascaded optical add/drop multiplexers

The dimensions of input waveguide and output waveguide of arrayed waveguide gratings (AWGs) determine the crosstalk, insertion loss and 1-dB bandwidth. In cascaded optical add/drop multiplexers (OADMs), the value of these parameters will largely affect the power penalty of system. The power penalty of cascaded OADMs is calculated with different waveguide dimensions of AWGs in this paper. Considering of wavelength misalignment, an optimization design of AWGs is obtained.