Performance investigation on harmonic distortion and inter-modulation distortion induced degradation for a single- and two-tone IM-DD SCM optical link

Subcarrier multiplexing (SCM) has been utilized for data transmission in high performance broadband in access networks which requires high transport capacity and throughput with guaranteed quality of service. In a transmitter employing SCM technique in an Intensity Modulation Direct Detection (IM-DD) system, laser source nonlinearity is an important issue of concern. This work investigates the sensitivity of resulting harmonic distortion (HD) and inter-modulation distortion (IMD) to changes in subcarrier amplitude, laser bias current operational parameters and laser quantum efficiency, laser active layer volume and laser carrier life time design parameters. Results show that IMD impairment mechanism is more dominant than HD mechanism. The spectrum analyser shows distinct difference in the frequency domain display of HD and IMD dominated systems. HD and IMD mechanisms show high sensitivity to carrier amplitude and active layer volume with a positively increasing slope gradient and high sensitivity to bias current and carrier life time with negatively decreasing slope gradients. Also these impairments are moderately sensitive to laser quantum efficiency. The investigations will help in identification of the most influencing operational and design parameters and their suitable values to be used to effectively reduce the influence of the source nonlinearity of SCM links.     

IM－DD SCM光波系统的非线性分析

本文在简要分析了激光器非线性机理的基础上,采用计算机模拟及数学归纳的方法,着重分析了IM-DDSCM光纤通信系统中各种非线性失真项的数目、幅度及其抑制方法,归纳出了落入各个信道中的各种非线性失真项的数目的数学表达式,推导出了非线性失真项的功率之和的计算公式;通过对计算结果的比较得知,激光器P-I曲线的非线性是影响系统非线性失真的主要因素,指出了利用预失真的方法补偿激光器P-I曲线非线性的影响。     

基于Volterra滤波器的参量阵扬声器互调失真补偿研究

针对单边带调制方法预处理的参量阵扬声器系统在复杂信号输入情况下存在明显互调失真的问题,引入Volterra滤波器模型和简化的一维Volterra滤波器模拟了其互调失真。设计了相应的逆滤波器,并对其抑制系统互调失真的性能进行了实验对比。结果表明,所设计的逆滤波器都能有效降低系统的互调失真,而后者具有较低的计算复杂度。     

Nonlinear Distortion Analyses in IM-DD SCM Lightwave Systems

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Time-domain simulation of channel crosstalk and inter-modulation distortion in gain-clamped semiconductor optical amplifiers

A time-domain model is implemented for gain-clamped semiconductor optical amplifiers (GC-SOAs) based on a combination of the separated traveling-wave equations and effective Bloch equations. The key feature of this model lies in its capability of handling the lasing-signal, signal-signal, and signal-noise interactions over a broad wavelength band. Therefore, various nonlinear phenomena such as the cross-gain saturation (XGS) and nondegenerate four-wave mixing (ND-FWM) can readily be captured. After being implemented and validated, this model is applied to the simulation of GC-SOA dynamic behaviors such as the channel crosstalk and intermodulation distortion (IMD). Simulation results show that the third-order IMD can be effectively suppressed by a gain-clamping lasing mode in GC-SOAs in comparison with that in conventional SOAs. The channel crosstalk can also be suppressed to some extent in GC-SOAs, but not as effectively. Other than a homogeneous reduction, the gain-clamping in GC-SOAs does not change the dependence of the channel crosstalk and IMD on the input signal power and channel spacing. It is also shown that the channel crosstalk, unlike the IMD, cannot be efficiently reduced by enlarging the channel spacing even in GC-SOAs.     

Simulation of Third-Order Intermodulation Distortion Suppression Incorporating Dual-Parallel Mach–Zehnder Modulator in a CR-SSB Modulation

A novel scheme is proposed to enlarge the spurious free dynamic range (SFDR) of microwave photonic (MWP) link by using dual-parallel Mach–Zehnder modulator, which modifies the single sideband signal and replaces the optical carrier with an unmodulated one to remove the optical main sources of third-order intermodulation distortion (IMD3). Simulation results show that the IMD3 and fifth-order intermodulation distortion can be suppressed greatly even when the modulation depth increases to a high value, and the link is limited by seventh-order intermodulation distortion and the SFDR is improved by 34.2 dB Hz in a 1-Hz bandwidth. The error vector magnitude of the MWP link with the proposed scheme is improved significantly for the transmitted 1-Gbit/s 16- quadrature amplitude modulation (QAM) signal.     

Amphiphilic polysilane-methacrylate block copolymers — Formation and interesting properties —

Several polysilane block copolymers have been prepared by the newly developed method, anionic polymerization of masked disilenes. Especially amphiphilic block copolymers of poly(1,1-dimethyl-2,2-dihexyldisilene) and poly methacrylate are focused. Poly(1,1-dimethyl-2,2-dihexyldisilene)-b-poly(2-hydroxyethyl methacrylate) (PMHS-b-PHEMA) is the first example of the amphiphilic polysilane copolymer that can form micelles in polar solvents. Poly(1,1-dimethyl-2,2-dihexyldisilene)-b-poly(methacrylic acid) (PMHS-b-PMAA) is more polar than (PMHS-b-PHEMA), soluble in water to form micelles. The cross-linking reaction of (PMHS-b-PMAA) with 1,10-diaza-4,7-dioxadecane and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride afforded the first shell cross-linked micelles (SCM) of polysilane. In addition to interesting properties, SCM is indicated to be able to form hollow sphere particles (hollow shell cross-linked micelles, HSCM) by a photochemical process. Reversible encapsulation of guest molecules by SCM and HSCM is demonstrated. Finally, SCM can be used as the template for the synthesis of metal nanoparticles, which may be used as catalysts.     

Impact of 2OD and 3OD on SRS- and XPM-induced crosstalk in SCM-WDM optical transmission link

In this paper, the impact of second-order dispersion (2OD), third-order dispersion (3OD) and modulation frequency over stimulated Raman scattering (SRS)- and cross-phase modulation (XPM)-induced crosstalk in sub-carrier-multiplexed (SCM) wavelength division multiplexed (WDM) transmission link has been analyzed. It has been observed that there is significant effect of 2OD, 3OD and modulation frequency on the SRS- and XPM-induced crosstalk in a SCM-WDM transmission link. Here the results for SRS- and XPM-induced crosstalk have been reported with independent and combined higher-order dispersion. It has been observed that XPM-induced crosstalk lies between [−52.8 to −45.3] and [−94.7 to −78.6] dB in the presence of 2OD and 3OD respectively for modulation frequencies varied from 500 MHz to 2.0 GHz, while it is in the range of [−94.4 to −84] and [−128.5 to −117] dB when both SRS and XPM are taken into consideration.     

Balanced differential phase-shift keying detector performance: an analytical study

A simple explanation of the observed approximately 3 dB advantage of differential phase-shift keying (DPSK) balanced detection over the intensity-modulated directly detected (IM-DD) type detection that can be easily used for system engineering purposes is presented. A Gaussian approximation is used to describe the tails of the detected noisy random signals leading to an analytical explanation of the observed approximately 3 dB advantage of DPSK balanced detection over the IM-DD type detection.     

Simulative investigation for third order-IM terms in multi-tone RoF system

A multi-tone radio over fiber (RoF) system design for three RF signals has been investigated for different modulation techniques like direct and external modulation with EDFA and SOA amplification techniques. Frequency response has been studied including the effects of third order intermodulation terms. Frequency separation between the modulating tones has been varied to study its impact on received carrier power. The performance in terms of electrical RF power of three receiving channels at different frequency separations using different amplification techniques have been measured and compared. An improvement in the received RF power and IM suppression has been observed by using an external modulation based system with EDFA amplifier.     

Theory of electrically controlled exhibition of circular Bragg phenomenon by an obliquely excited structurally chiral material – Part 2: Arbitrary dc electric field

Numerical examination of the solution of the boundary-value problem of the reflection and transmission of a plane wave due to a slab of an electro-optic structurally chiral material (SCM) indicates that the exhibition of the circular Bragg phenomenon by the SCM can be controlled not only by the sign and the magnitude of a dc electric field but also by its orientation in relation to axis of helicoidal non-homogeneity of the SCM. Thereby, the possibility of electrical control of circular-polarization filters has been extended.     

Intermodulation distortion characteristics of a semiconductor laser amplifier in subcarrier multiplexing

The intermodulation distortion (IMD) characteristics of a subcarrier multiplexed signal in semiconductor laser amplifiers have been calculated. The minimum value of the carrier to the second-order IMD with detuning decreases 3 dB for the amplifier under consideration when the facet reflectivity changes from 10^-4 to 10^-3. In the case of third-order IMD the minimum value of the carrier to IMD ratio with detuning decreases 10 dB for the same change of reflectivity.     

太阳辐照绝对辐射计及其在航天器上的太阳辐照度测量

介绍了我国自主研制的太阳辐照绝对辐射计(SIARs)的原理和结构,该辐射计主要有两个创新点,即把电加热导线埋入锥腔壁以提高光电等效性和用无源热电温度传感器代替有源电阻温度传感器。SIARs参加了第九届和第十届国际日射（强度）计比对（IPC IV和IPC X）, 同世界辐射基准（WRR）在02％以内符合。 置于世界辐射中心(WRC)的用于保存和传递WRR的世界标准（辐射计）组（WSG）上的两台SIARs已同WSG仪器进行了6年的比对测量,性能稳定,不确定度在0.2％以内。“神舟三号”飞船应用SIARs构成的太阳常数监测器进行了5个月的在轨测量,与同期国外星上测量数据在0.2％以内吻合。采用3台SIARs构成的“风云三号”卫星太阳辐射监测仪从2008年6月起也已经开始了长期的在轨测量。     

Scanning capacitance microscopy and spectroscopy applied to local charge modifications and characterization of nitride-oxide-silicon heterostructures

We have combined a home-built capacitance sensor with a commercial scanning force microscope to obtain a Scanning Capacitance Microscope (SCM). The SCM has been used to study Nitride-Oxide-Silicon (NOS) heterostructures which offer potential applications in charge storage technology. Charge writing and reading on a submicrometer scale is demonstrated with our SCM setup. In addition, SCM appears to be very useful for the characterization of subsurface defects in semiconductor devices which are inaccessible by most of the other scanning probe microscopies. Finally, we introduce a novel spectroscopic mode of SCM operation which offers combined voltage-dependent and spatially resolved information about inhomogeneous charge distributions in semiconductor devices.     

Nonlinearity of traveling-wave electroabsorption modulator according to microwave characteristics

In this paper, we introduce a model to analyze the linearity of multiple-quantum-well (MQW) traveling-wave electroabsorption modulator (TW-EAM). The device length, microwave loss (ML), velocity mismatch (VM) between lightwaves and the microwaves, and internal reflection (IR) due to impedance mismatch have effect on the linearity of a TW-EAM. ML has little effect on the intermodulation distortions (IMDs). VM also has little influence on IMD3 (third-order IMD), but severely affect IMD2 (second-order IMD), which become as high as 30 dB for the input frequency of 100 GHz, the device length of 0.8 mm, and VM of 20%. IR has different nonlinear characteristics according to the wavelength of the input frequency and the device length. As a result, it is known that IMDs improve when the device length equal to a quarter of the wavelength of the input signal and that the device length of 0.4 mm is appropriate for the analog fiber-optic communication with the frequency range of 50 GHz.     

Bidirectional WDM-PON architecture using a reflective filter and cyclic AWG

We proposed and demonstrated a bidirectional SCM-WDM PON using a reflective filter and cyclic AWG where up/downlink data could be provided using a single optical source. In the proposed scheme, the signal for downstream was modulated by a single CW laser diode and remodulated in the optical network unit as an upstream, the proposed WDM-PON scheme can offer the SCM signal for broadcasting service. In this paper, 1 Gb/s signals both for up- and downstream were demonstrated in 10 km bidirectional optical fiber link.     

Fluorimetric Analysis of the Structural-Dynamic State of Alkaline Phosphatase of Escherichia coli

By the methods of tryptophan fluorescence and phosphorescence at room temperature, the action on the conformational state and intramolecular dynamics (IMD) of alkaline phosphatase of Escherichia coli of the competitive inhibitor sodium pyrophosphate (1–10 mM) has been investigated. On the basis of the results of the fluorimetric investigations, it has been concluded that pyrophosphate is capable of changing the conformation and IMD of enzymatic protein towards an increase in the fast and slow mobility of the globule structural elements. The most probable cause of the shifts of the alkaline phosphatase structural-dynamic state observed by fluorimetric methods is the replacement of phosphate in the active center of one of the protein subunits by pyrophosphate.     

An extension of implicit Monte Carlo diffusion: Multigroup and the difference formulation

Implicit Monte Carlo (IMC) and Implicit Monte Carlo Diffusion (IMD) are approaches to the numerical solution of the equations of radiative transfer. IMD was previously derived and numerically tested on grey, or frequency-integrated problems [1]. In this research, we extend Implicit Monte Carlo Diffusion (IMD) to account for frequency dependence, and we implement the difference formulation [2] as a source manipulation variance reduction technique. We derive the relevant probability distributions and present the frequency dependent IMD algorithm, with and without the difference formulation. The IMD code with and without the difference formulation was tested using both grey and frequency dependent benchmark problems. The Su and Olson semi-analytic Marshak wave benchmark was used to demonstrate the validity of the code for grey problems [3]. The Su and Olson semi-analytic picket fence benchmark was used for the frequency dependent problems [4]. The frequency dependent IMD algorithm reproduces the results of both Su and Olson benchmark problems. Frequency group refinement studies indicate that the computational cost of refining the group structure is likely less than that of group refinement in deterministic solutions of the radiation diffusion methods. Our results show that applying the difference formulation to the IMD algorithm can result in an overall increase in the figure of merit for frequency dependent problems. However, the creation of negatively weighted particles from the difference formulation can cause significant numerical instabilities in regions of the problem with sharp spatial gradients in the solution. An adaptive implementation of the difference formulation may be necessary to focus its use in regions that are at or near thermal equilibrium.     

Channel length effect in a MOSFET structure by scanning capacitance microscopy

Depth dependent carrier density and trapped charges in a metal-oxide-semiconductor field effect transistor (MOSFET) like structure have been studied using scanning capacitance microscopy (SCM). For a MOSFET structure, since minority carrier can be provided by the source and drain diffusions, its response time is shorter than that of metal-oxide-semiconductor (MOS) system. So the high frequency C-V relation is slightly different from that of MOS capacitor and shows the characteristics dependent on the channel length. Bias dependent SCM images which represent the depth dependent carrier density and detrapping time constant of trapped charges in the oxide layer were observed to see the channel effect in a MOSFET structure.     

An improved recommendation algorithm via weakening indirect linkage effect

We propose an indirect-link-weakened mass diffusion method(IMD), by considering the indirect linkage and the source object heterogeneity effect in the mass diffusion(MD) recommendation method. Experimental results on the MovieLens, Netflix, and RYM datasets show that, the IMD method greatly improves both the recommendation accuracy and diversity, compared with a heterogeneity-weakened MD method(HMD), which only considers the source object heterogeneity. Moreover, the recommendation accuracy of the cold objects is also better elevated in the IMD than the HMD method. It suggests that eliminating the redundancy induced by the indirect linkages could have a prominent effect on the recommendation efficiency in the MD method.