基于重构等效啁啾制作光纤光栅编解码器的光码分多址系统实现

在光码分多址(OCDMA)系统中，光纤布拉格光栅(FBG)编解码器是极具竞争力的核心器件，满足光接入网低成本、高性能的要求. 将重构等效啁啾 (REC) 技术制作的FBG作为编解码器运用于OCDMA系统. 实验采用一对511个码片、编码速率为6.4×10⁹/s的FBG编解码器，在编码匹配的情况下能恢复出输入信号，与编码非匹配的情况相比获得了8 dB的功率增益.这为REC技术制作的编解码光栅在OCDMA系统中的应用提供了实验依据. 关键词： 光纤布拉格光栅 光码分多址 重构等效啁啾 编解码器     

基于色散效应的光纤光栅高速高精度解调方法研究

利用普通单模光纤(SMF)与色散补偿光纤(DCF)分别具有正色散和负色散系数特性,实现光纤光栅阵列的高速高精度解调.系统采用全光纤结构,仅需发出单一高速光脉冲,即可根据反射光脉冲时延差同时获取各个光栅的波长与位置信息,大幅提高了光纤光栅解调速度;通过建立DCF-SMF双通道和色散差矫正模型,削弱了温度变化及色散值误差对系统解调精度的影响.实验表明,本方法解调速率可达1 MHz,解调过程受传感网络光纤及双通道温变影响较小,具有良好稳定性及高精度;5—75?C温度扰动实验中,传感网络传输光纤温变时系统解调均方差16.8 pm,DCF-SMF双通道受温度扰动时系统解调均方差为11.9 pm,恒温下系统长时间解调时均方差为6.4 pm;应力实验中,解调线性度可达0.9998,解调精度约为8.5 pm.     

Power-independent technique to extract the dispersion parameters of an optical fiber using four wave mixing

Conventional methods which extract dispersion parameters of an optical fiber using four wave mixing rely on the measurement of optical power in the generated wavelengths, and hence are prone to measurement errors. We propose and demonstrate a power-independent method to extract the dispersion curve of a fiber using four wave mixing (FWM). The analytical equations that have been traditionally used to estimate the phase mismatch in FWM are modified to cater to low-dispersion fibers, and are verified. Experiments to obtain the dispersion curve of a low-dispersion and highly nonlinear fiber are discussed and the results are analyzed. Limitations of any FWM-based method to extract the dispersion curve of a fiber are presented for the first time.     

Modeling and simulation of long reach high speed inter-satellite link (ISL)

A hybrid OFDM–IsOWC system incorporating diverse modulation schemes like optical double side band (ODSB), optical tandem side band (OTSB) and optical single side band (OSSB) is carried out to optimize a long reach high speed inter-satellite link (ISL) with acceptable SNR and BER. The proposed system is also reported under the influence of antenna efficiency and pointing error at varied values of power levels. Simulations point toward that the proposed hybrid OFDM–OSSB–IsOWC transmission system promises significantly enhanced ISL link compared to conventional IsOWC systems.     

Measurement of optical fiber parameters by the backscattering method (Review)

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 48, No. 3, pp. 359–372, March, 1988.     

The influence of fiber dispersion on the code form of the optical mm-wave signal generated by single sideband intensity-modulation

We have theoretically investigated the transmission performance of the optical mm-wave generation by using an external modulator based on single sideband (SSB) intensity modulation. Though the SSB millimeter (mm)-wave can immune the fading effect, the baseband signals with a high bit rate are degraded greatly after transmission along fiber. The main reason is that the fiber dispersion causes the time shift of the code edges; therefore the maximum transmission distance of the baseband signals is limited. The experimental and simulation results agree well with our theoretical analysis. We also propose a novel scheme to extend the transmission distance. In this novel scheme, the data signals are modulated only onto one of the two optical carriers; hence the shift of the code edges in the down-converted signals after transmission is eliminated.     

Distribution of millimeter waves over a fiber link with high frequency stability(Invited Paper)

We present a theoretical analysis, systematic simulation, and experimental measurements for the phase noise,timing jitter, and frequency stability in the frequency distribution of millimeter waves over distant optical fiber links. The conception that the dissemination of a higher frequency reference instead of a lower one can achieve a better frequency stability is discussed and verified. We find that the system's noise floor, including thermal noise,shot noise, and any other noise from electronic components, is considered to be a fundamental limitation for a frequency reference transmission system. Benefiting from the high-precision time delay variation discrimination and accurate locking control operation, a highly stabilized reference is distributed to a remote end over a 60 km spooled fiber, achieving a frequency stability of 4 × 10~(-17) at an average time 1000 s, corresponding to 23 fs of RMS timing jitter(0.01 Hz~(–1) MHz).     

光纤偏振模色散对信号偏振度的影响

采用一种简化的线路传输模型，详细讨论了在高速光纤通信系统中，线路偏振模色散（PMD ），尤其是二阶PMD、输入信号偏振态等对信号偏振度（DOP）的影响，并指出以信号DOP做 反馈控制信号适合于一阶PMD优化补偿系统，但在较大二阶PMD的影响下，将增加控制算法的 复杂性，使系统可能陷入局部最优解. 关键词： 信号偏振度 偏振模色散 信号偏振态     

Implications of constraints on mass parameters in the Higgs sector of the nonlinear supersymmetric SU(5) model

By using the non-relativistic effective Lagrangian approach to bound states, a complete expression for the isospin-breaking corrections to the energy levels and the decay widths of kaonic hydrogen is obtained up-to-and-including in QCD. It is demonstrated that, although the leading-order corrections at emerging due to the unitarity cusp are huge, they can be expressed solely in terms of the KN S-wave scattering lengths. Consequently, at leading order, it is possible to derive parameter-free modified Deser-type relations, which can be used to extract the scattering lengths from the hadronic atom data.A. Rusetsky: On leave of absence from HEPI, Tbilisi State University, University st. 9, 380086 Tbilisi, Georgia     

An analysis on the effect of the equalizer parameters in a direct-modulation optical communication system employing an all-pass filter to combat chirp and dispersion

We consider the effect of the equalizer parameters in the performance of a direct modulated high-bit-rate communication system where the degrading combination of fibre dispersion and source chip is compensated using an all-pass optical filter.     

The optical properties of high quality ZnO/ZnMgO quantum wells on Si(111) substrates

The ZnO/Zn_0.85Mg_0.15O multiple quantum wells (MQWs) were fabricated on Si(111) substrates by plasma-assisted molecular beam epitaxy (P-MBE) using ZnMgO as buffer layers. The RHEED images indicated that the MQWs were of high quality. The free exciton (FE) emission line originated from the well region and its phonon replicas (FE-1LO, FE-2LO and FE-3LO) were observed in the 86 K photoluminescence (PL) spectrum. Blueshift of the FE line in the MQW sample as compared to that in the ZnO bulk was found at temperatures as high as room temperature. Time-resolved PL study on the FE line showed a fast lifetime of 140 ps. The high quality of the MQW structure was revealed by the observation of the quantum-confinement-induced blueshift and shortened lifetime of the FE emission.     

Influence of porous morphology on optical dispersion properties of template free mesoporous titanium dioxide (TiO2) films

This paper focuses the influence of porous morphology on the microstructure and optical properties of TiO₂ films prepared by different sol concentration and calcination temperatures. Mesoporous TiO₂ thin films were prepared on the glass substrates by sol-gel dip coating technique using titanium (IV) isopropoxide. Porous morphology of the films can be regulated by chemical kinetics and is studied by scanning electron microscopy. The optical dispersion parameters such as refractive index (n), oscillator energy (E_d), and particle co-ordination number (N_c) of the mesoporous TiO₂ films were studied using Swanepoel and Wemple-DiDomenico single oscillator models. The higher precursor concentration (0.06 M), films exhibit high porosity and refractive index, which are modified under calcination treatment. Calcinated films of low metal precursor concentration (0.03 M) possess higher particle co-ordination number (N_c = 5.05) than that of 0.06 M films (N_c = 4.90) due to calcination at 400 °C. The lattice dielectric constant (E_∞) of mesoporous TiO₂ films was determined by using Spintzer model. Urbach energy of the mesoporous films has been estimated for both concentration and the analysis revealed the strong dependence of Urbach energy on porous morphology. The influence of porous morphology on the optical dispersion properties also has been explained briefly in this paper.     

Spectral efficient hybrid wireless optical broadband access network (WOBAN) based on transmission of wireless MIMO OFDM signals over WDM PON

In this paper, a spectral efficient hybrid wireless optical broadband access network (WOBAN) is proposed and demonstrated based on the transmission of wireless multi-input multi-output orthogonal frequency division multiplexing (MIMO OFDM) signals over wavelength division multiplexing passive optical network (WDM PON). By using radio over fiber (ROF) techniques, the optical fiber is well adapted to propagate multiple wireless services having different carrier frequencies. It is a known fact that multiple wireless signals having the same carrier frequency cannot propagate over a single optical fiber at the same time, such as MIMO signals feeding multiple antennas in fiber wireless (FiWi) system. A novel optical single-sideband frequency translation technique is designed and simulated to solve this problem. This technique allows four pairs of wireless MIMO OFDM signals with the same carrier frequency for each pair to be transmitted over a single optical fiber by using one optical source per wavelength. The crosstalk between the different MIMO channels with the same frequency is eliminated, since each channel is upconverted on specified wavelength with enough channel spacing between them. Also the maximum crosstalk level between the different MIMO channels with different frequencies is very low around ?76 dB. The physical layer performance of the proposed WOBAN is analyzed in terms of the bit error rate (BER), error vector magnitude (EVM), and signal-to-noise ratio (SNR). The proposed WOBAN achieves 7.68 Gb/s data rate for 20 km for the optical back-end and 240 Mb/s for the outdoor wireless front-end.     

Clustering of chemisorbed H(D) atoms on the graphite (0001) surface due to preferential sticking

We present scanning tunneling microscopy experiments and density functional theory calculations which reveal a unique mechanism for the formation of hydrogen adsorbate clusters on graphite surfaces. Our results show that diffusion of hydrogen atoms is largely inactive and that clustering is a consequence of preferential sticking into specific adsorbate structures. These surprising findings are caused by reduced or even vanishing adsorption barriers for hydrogen in the vicinity of already adsorbed H atoms on the surface and point to a possible novel route to interstellar H2 formation.     

A novel video opto-mechanical (VOM) device for studying the effect of stretching speed on the optical and structural properties of fibers

Using a novel video opto-mechanical (VOM) device, the effect of stretching speed on the optical and structural properties of polypropylene (PP) fibers during the dynamic stretching process is studied. The objective of the present study is to correlate the optical and mechanical properties of PP fibers with the speed of stretching using the multiple-beam Fizeau fringes system. The skeletonization of the multiple-beam Fizeau fringes are determined automatically by using one-dimension Fourier transform method. The stepper motor is adjusted in order to stretch the fibers continuously with constant and uniform speed until breaking of the fiber. The refractive indices, birefringence, transverse sectional area and the orientation function of PP fibers are studied as a function of the draw ratio at different speeds of stretching. An empirical formula is given to correlate the birefringence of PP fiber and both the draw ratio and the speed of stretching. Stretching process of PP with low speed (slow stretching) is recommended to overcome the necking deformation along the fiber. The VOM device could be used to measure the yield strain. The draw ratio-stretching speed superposition is discussed with some details. Microinterferograms are given for illustration.     

Enhancement of high PT hadrons due to collapsing Z(3) walls in heavy-ion collisions

We discuss enhancement of multiplicities of hadrons at high transverse momentum due to multiple reflections of quarks from collapsing Z(3) interfaces in the QGP produced in relativistic heavy-ion collisions. By modeling the dependence of effective mass of the quarks on the Polyakov loop order parameter, we evaluate the reflection coefficient of quarks from collapsing Z(3) interfaces. We use the effective potential proposed by Pisarski for the Polyakov loop to determine the profile of the Z(3) interfaces and calculate the reflection probability for quarks. We discuss the formation of a network of these Z(3) walls in relativistic heavy-ion collisions, in the QGP phase. We do a numerical simulation to calculate the modifications in the thermal transverse momentum spectra of the quarks/anti-quarks that results from a collapsing wall. We then use the recombination model to calculate the transverse momentum spectrum of final hadrons. Our results show enhancement of high P _T hadrons, with the enhancement being stronger for heavier quarks. Further, we find that due to larger reflection coefficient for heavier quarks, the density of strange and charm quarks/anti-quarks increases inside the collapsing walls. This implies enhancement in the multiplicities of multi-strange and multi-charmed hadrons.