Using RLS-TEQ to reduce CP length for 20.48 Gb/s direct-detection optical OFDM transmission over 2400 km of SSMF

This paper uses a Recursive Least Squares-Time Domain Equalizer (RLS-TEQ) to reduce the Cyclic Prefix (CP) length in Direct-Detection Optical Orthogonal Frequency Division Multiplexing (O-OFDM) transmission over 2400 km of Standard Single Mode Fiber (SSMF). The RLS-TEQ can cancel the residual Inter Symbol Interference (ISI) caused by both the Group Velocity Dispersion (GVD) and the CP length being shorter than the Channel Impulse Response (CIR). Using RLS-TEQ reduces size of the CP, and consequently leading to system performance improvement.     

Optical Properties of Gamma Irradiated Soda-Lime Silicate Glasses Exchanged with Copper

The effect of copper ion exchange upon the optical absorption and room temperature gamma colouration of soda lime silicate glasses has been investigated. After ion exchange performed at 720 K, copper ions substitute mainly the alkali ions and do modify the optical absorption spectra of the specimens. It has been shown that gamma irradiation does not induce the formation of colloidal copper. Moreover, the colouration process itself is independent of the presence of copper ions. The generated colour centres are rather related to the presence of sodium and potassium ions. The optical bleaching by the UV light occurs in two stages. First disappear centres related to the Na-type defects and next those related to the K-type defects.     

Interaction Between Pr3☎ Pairs and Excitons in CsCdBr3

CsCdBr₃ consists of linear chains of [CdBr₆]^4- octahedra separated by Cs^? ions. The excited states of the covalently bound [CdBr₆]^4- octahedra form the lowest excitonic states of the crystal lattice. The trivalent Pr ions substitute for the divalent Cd ions. For reasons of charge compensation in the linear Cd^2? chains, pair centers of the form Pr^3?-(Cd vacancy)-Pr^3? are predominantly formed. In CsCdBr₃ the optical band gap is wider than the electronic one. This allows to study the interaction between Pr^3? ions and excitons by means of optical spectroscopy. The interaction leads to quantum up- and down-conversion generating one photon from two lower ones in energy and vice versa. Related experiments are discussed.     

Theory of oxidation/reduction-induced valence transformations of metal ion dopants in oxide crystals mediated by oxide-vacancy diffusion: I. Thermodynamic analysis

We consider theoretically valence transformations of doping metal ions in oxide crystals induced by oxidation and reduction obtained by changes in the ambient oxygen partial pressure. Three types of oxygen vacancies are assumed to mediate transformations: neutral, singly ionized, and doubly ionized. We provide thermodynamic equilibrium analyses, yielding concentration relations among the oxygen vacancy, metal ions, holes and electrons as functions of the ambient oxygen pressure. The results suggest that experimental study of different species concentrations at thermodynamic equilibrium as functions of pressure and temperature should allow assessment of various reversible reaction constants controlling the process. In the Part II companion paper, the kinetic (diffusion) characteristics are considered in detail.     

Facile in situ hydrothermal synthesis of BiVO4/MWCNT nanocomposites as high performance visible-light driven photocatalysts

Visible-light responsive monoclinic BiVO₄/MWCNT nanocomposites were facilely prepared via an in situ hydrothermal method by using sodium dodecyl sulfonate (SDS) as a guiding surfactant. The as-prepared BiVO₄/MWCNT nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, field emission scanning electron microscopy (FE-SEM), the Fourier transform infrared spectroscopy (FTIR) and UV–vis diffuse reflectance spectroscopy. The results showed that the hydrothermal temperature and adding SDS had significant influence on the morphology and size of BiVO₄. The photocatalytic activities of BiVO₄/MWCNT nanocomposites were investigated by degrading methylene blue (MB) under visible-light irradiation. Remarkable enhancement in photodecomposition of MB was observed with BiVO₄/MWCNT composite compared with bare BiVO₄ particles. This improvement of photocatalytic was attributed to the effective charge transfer from BiVO₄ nanocrystals to MWCNT, which promoted the migration efficiency of photogenerated electron–hole. Furthermore, a possible mechanism for the photocatalytic oxidative degradation was also discussed.     

Effect of Co2+ on the growth,optical properties and laser damage threshold of potential nonlinear optical l-alanine single crystal

Good transparent bulk single crystals of pure l-alanine (LA) and cobalt doped LA crystals have been synthesized and successfully grown by slow-cooling method from their aqueous solutions. The concentration of metal dopants in the mother solution with 0.5 mol% for cobalt was carried out individually and crystals were obtained with well defined morphology. The as grown metal doped and pure single crystals were characterized by single crystal XRD studies which confirm that the incorporation of metallic dopants has not changed the basic structure of the parent crystal. The absorption of these crystals was analyzed and the result confirms that they possess low absorption in the range 230–1100 nm. Fourier transform infrared (FTIR) spectroscopy was carried out to investigate the molecular vibrations of these crystals and to confirm the incorporation of the dopants. The thermal properties have been studied by TGA/DTA curves. The EDAX measurement and surface morphology were studied for pure and metal doped LA crystals. The second harmonic generation (SHG) signals were observed using Nd: YAG laser with fundamental wavelength of 1064 nm in pure and metal doped crystals. The laser damage threshold was measured for pure and metal doped LA crystals and also tested by using a Q-switched Nd: YAG laser showed enhanced LDT value for metal (Co²⁺) doped LA crystal compared to pure LA crystal due to the metallic substitutions thus proving their useful candidature for nonlinear optical applications.     

Velocity measurement for moving surfaces using spatial filtering method based on area image sensor

The idea of using spatial filtering method to measure velocity of vehicles for an inertial navigation system is put forward. Corresponding optical system, including a 532 nm solid-state laser as active illumination, is established. A 17.92 mm × 14.34 mm area charge coupled device (CCD) is employed both as detector and as spatial filter. The spatial filtering characteristics are theoretically analyzed using a power spectral density function. The spatial filtering operation of CCD is performed fully by software. Therefore, the parameters of the spatial filter, such as the size and the number of spatial period, are changeable. In addition, the CCD is arranged as two differential spatial filters without any other additional elements. Experiments are carried out to examine the feasibility of CCD as two differential spatial filters and the influence of the number of spatial period on the signal frequency. The results indicate that the more number of spatial period the more accurate measurements can be obtained, and show that the relation between signal frequency and velocity has good linearity. So this velocimeter is suitable to provide velocity information for a vehicle self-contained inertial navigation system.     

Corona discharge in electrospraying

The paper presents investigations of current–voltage and light emission characteristics of electrospraying of various liquids in atmospheric air. The spectroscopic measurements have shown that the onset of corona discharge coincides with the onset of electrospraying, with the voltage increasing. The emission intensity in selected spectral lines during electrospraying depends on spraying mode, discharge power and a kind of liquid. In the specific experimental conditions in air, mainly the N₂ second positive system, which is visible as violet faint light, has been recorded. The emission intensity of other gaseous species, which could be product of electrosprayed molecules decomposition or dissociation, was at very low level for the voltages applied, i.e., for glow or onset streamer discharges. From the measured light emission spectra of discharges from capillary nozzle and liquid jet, the dependence of the amplitude of selected spectral lines on capillary-nozzle voltage has been determined and it was found that this relation can be approximated by a third-degree polynomial function. This approximation has been supported by theoretical considerations. The presented results support the hypothesis that faint electrical discharges (glow, onset streamers) usually occur during and are inherent to electrospraying.     

Analysis of optical re-modulation by multistage modeling of RSOA

The time-resolved multistage reservoir model well-known for semiconductor optical amplifier (SOA) is extended to analyze the behavior of a bulk homogeneous InP-InGaAsP buried heterostructure reflective semiconductor optical amplifier (RSOA). Parameters for simulation have been extracted from the experimental RSOA characteristics. We have employed the model to explain the steady-state and re-modulation dynamics in the RSOA. Electrical modulation bandwidth and intermodulation distortion in the RSOA have been derived from the model and close agreement is obtained with the reported data. It is found out that the ripples in the upstream output from the RSOA for incomplete modulation erase of downstream modulated data follow Gaussian distribution, which simplifies the calculation of upstream SNR and bit error rate. It is explained in detail that amplitude ripples in the upstream data can be reduced by judicious choice of optical and electrical parameters of the RSOA. In particular, for an average low downstream power level (<−20 dBm) a good downstream modulation erase factor about 89% and 23 dB extinction ratio in the upstream modulated signal can be achieved.     

Evaluation of polychromatic image quality of a birefringent lens by means of optical transfer function

Polychromatic or white-light optical transfer function (OTF) is put forward as a criterion to evaluate the performance of a uniaxial birefringent lens sandwiched between two linear polarizers. The optic axis of the birefringent crystal is perpendicular to the lens axis. The results show that the same system may be adapted for both enhanced resolution and apodization just by rotating any of the polarizers included in the system even under broadband illumination. The proposed system may also be exploited for image processing applications under polychromatic input illumination.