Multiple-quantum-well Mach-Zehnder modulators: comparison of calculated and measured results for modulator properties and system performance

A measurement-based model of a /spl pi/ phase-shift multiple-quantum-well Mach-Zehnder modulator with asymmetric Y-branch waveguides is presented. Using this model, calculated and measured results for the transmission contours, /spl alpha/-parameter, intensity modulation, and time-resolved chirp are compared. The suitability of the model for system performance evaluation is demonstrated by examining the implications of the modulator chirp on 10-Gb/s transmission over nondispersion shifted fiber, and the combined effect of the modulator chirp and group delay ripple of a dispersion compensating fiber Bragg grating on 10-Gb/s dispersion compensated transmission. Calculated and measured results for the system performance are compared.     

Optical Signal Processing by Phase Modulation and Subsequent Spectral Filtering Aiming at Applications to Ultrafast Optical Communication Systems

This paper describes optical signal processing based on optical phase modulation and subsequent optical filtering, which is applicable to 160-Gb/s optical time-division multiplexed (OTDM) subsystems. Ultrafast phase modulation of an optical signal is done by self-phase modulation (SPM) and cross-phase modulation (XPM) when an optical pulse passes through a nonlinear optical fiber. Such phase modulation induces the spectral shift of the optical signal. Various types of optical signal processing are realized simply by filtering out the spectral-shifted component. Using SPM-based pulse reshaping in a 500-m-long silica-based highly nonlinear fiber (HNLF), we demonstrate highly stable generation of a 10-GHz 2-ps optical pulse train tunable over the entire C band. A phase-locked loop (PLL) can suppress the slow phase drift of the output pulse train induced by fluctuations of the nonlinear fiber length, enabling the application of the pulse generator to a 160-Gb/s OTDM transmitter. Based on XPM in a 2-m-long photonic crystal fiber, optical time-division demultiplexing of 160-Gb/s optical signals is demonstrated. The long-term stability is drastically improved as compared with the device composed of a conventional silica-based HNLF, because the short fiber length reduces the phase fluctuation between the signal and control pulses. Instead of nonlinear fibers, an electrooptic modulator such as a (LN) modulator also performs the phase modulation in a more practical manner. We propose and demonstrate an optoelectronic time-division demultiplexing scheme for a 160-Gb/s OTDM signal, which consists of an LN phase modulator driven by a 40-GHz electrical clock and an optical bandpass filter (BPF). We also demonstrate base-clock recovery from a 160-Gb/s optical signal with an optoelectronic PLL. The phase comparator is simply composed of an LN phase modulator and an optical BPF, ensuring the stable and reliable operation in the 160-Gb/s receiver.     

On the use of electrical precompensation of dispersion in optical single-sideband transmission systems

The use of electrical predistortion in optical single-sideband (OSSB) transmission systems is proposed to extend the tolerance to fiber dispersion impairment. Due to the spectral properties of OSSB signals, a simple electrical dispersive line can be used to mitigate the fiber dispersion, reducing the complexity of electrical predistortion methods proposed recently for optical modulations other than OSSB. Carrier-suppressed and carrier-unsuppressed optical modulations can be compensated by such technique, extending the range compared to previously reported works on fiber dispersion mitigation after direct detection using OSSB signals, where only carrier-unsuppressed modulations can be effectively compensated. The use of electrical precompensation is investigated for three signaling formats: Nonreturn to zero, return to zero, and alternate mark inversion (AMI). Due to distortion occurring in the sideband suppression process, signaling formats with reduced duty cycles present improved performance as a consequence of enhanced tolerance to intersymbol interference. Using such formats with electrical predistortion, the reach limitation arises not from fiber dispersion but from nonlinear impairments and optical noise accumulation. Using AMI and ideal electrical predistortion, distances greater than 1200 km of standard single mode fiber are achieved at 10 Gb/s with bit error ratio (BER) lower than 10/sup -12/, without using optical dispersion compensation. Introducing accurate models for the electrical dispersive lines, the transmission distance is reduced to 720 km for BER lower than 10/sup -12/.     

分布式光纤温度传感检测技术及其应用

分布式光纤温度传感是一种用于实时测量空间温度场分布的新技术，对光纤沿线地点的温度进行分布连续检测，光纤本身就是温度传感器，由于光纤传感器的本征特点，该技术特别适合应用电气设备的温度检测，并能和消防报警系统配合使用，在发电厂，变电站的电气设备状态检测中有广阔的应用前景。     

Demonstration of negative dispersion fibers for DWDM metropolitanarea networks

We present a detailed experimental and theoretical study, showing that a novel nonzero dispersion-shifted fiber with negative dispersion enhances the capabilities of metropolitan area optical systems, while at the same time, reducing the system cost by eliminating the need of dispersion compensation. The performance of this dispersion-optimized fiber was studied using different types of optical transmitters for both 1310- and 1550-nm wavelength windows and for both 2.5-and 10-Gb/s bit rates. It is shown that this new fiber extends the nonregenerated distance up to 300 km when directly modulated distributed feedback (DFB) laser transmitters at 2.5 Gb/s are used. The negative dispersion characteristics of the fiber also enhance the transmission performance in metropolitan area networks with transmitters that use electroabsorption (EA) modulator integrated distributed feedback (DFB) lasers, which are biased for positive chirp. In the case of 10 Gb/s, externally modulated signals (using either EA-DFBs or external modulated lasers using Mach-Zehnder modulators), we predict that the maximum reach that can be accomplished without dispersion compensation is more than 200 km for both 100- and 200-GHz channel spacing. To our knowledge, this is the first demonstration of the capabilities of a nonzero dispersion-shifted fiber with negative dispersion for metropolitan applications     

Dispersion compensation using only fiber Bragg gratings

Efficient and low cost dispersion compensation is necessary to achieve useful transmission distances in optical communication systems at bit rates above 10 Gb/s. In the paper, we present a novel method for dispersion compensation that uses three fiber gratings in series. This method eliminates the requirement for an optical circulator, commonly used in grating-based dispersion compensators. As a result, our device is inexpensive to fabricate and have a low insertion loss. We present a theoretical model that predicts how the efficiency of the device can be maximized. We also present experimental results showing complete dispersion compensation for 30-ps pulses, broadened to 67 ps by propagating through 10 km of standard, singlemode fiber     

在线检测电力设备局部放电信号传输系统的研究

在研制的用于电力设备局部放电在线检测装置的信号传输系统中,考虑到检测装置微机系统和控制室的安全,并加强抗干扰性能,采用光纤系统来传输信号。并选择频分复用和时分复用的方式,分别传送多路局部放电信号和控制信号,从而简化了系统并降低了费用。叙述了电子传输系统各个部件的设计和工作原理。该系统已用于局部放电的在线检测装置中,并成功地进行了多次现场电力设备局部放电的在线检测试验。     

基于Optisystem的光电色散补偿技术的性能分析

为了实现光信号的有效传输,减少光纤中色散和非线性效应对通信系统的影响,提出一种基于光纤布拉格光栅(fiber bragg grating,FBG)中间补偿的光电色散补偿技术,即在传输链路上采用FBG中间补偿方式,在接收端采用电色散补偿技术,分别实现了对40 Gbit/s,归零(RZ)码信号的单信道和多信道系统的色散补偿.通过与全光色散补偿技术作对比,可以得到在入射功率较高的条件下,光电色散补偿技术的补偿性能明显优于全光色散补偿技术,同时能够保持较高的Q值,为系统以后的升级、扩容做铺垫.     

OPPC在电网中的应用研究与实验技术

OPPC是将光纤单元复合在架空相线中的光缆,具有电能传输和光通信信号传输的双重功能。OPPC技术是OPGW和ADSS等技术的有益补充,可以填补不能适用OPGW和ADSS的应用空白,方便地将电力特种光缆的应用从输电网络延伸到配电网络,增大了光纤通信的覆盖面,提高了电力系统通信的安全性、可靠性。OPPC的应用在国内属于起步阶段,市场发展前景广阔。文章提出了OPPC在电网中应用的关键技术和研究进展,对OPPC产品进行了试验分析,最后给出结论。     

Experimental studies of optical Raman amplifiers for 1.3‐µm wavelength band and its application to 20 Gbit/s × 2 WDM transmission

Configurations of a Raman amplifier suitable for a 1.3‐µm wavelength band are discussed and their properties are experimentally investigated. Pump light with a wavelength of 1.23 µm that is necessary for the Raman amplification in the 1.3‐µm wavelength band is obtained using a 1.06‐µm fiber laser and Raman laser technique. Concerning the Raman laser, wavelength conversion from 1.06 µm to 1.23 µm is effectively achieved using a cavity configuration including fiber Bragg gratings and a dispersion‐shifted fiber. On the other hand, a conventional dispersion compensation fiber which has an essential property of high nonlinearity is applied in order to obtain large gain at 1.3 µm. Net gain of 35 dB and output power of 15 dBm are achieved. To confirm the applicability of the Raman amplifiers to high‐speed optical transmissions, experiments of 20 Gbit/s × 2 WDM repeaterless transmission through a 80‐km conventional single‐mode fiber are carried out. The 1.3‐µm signal should be degraded due to the dispersion caused by the dispersion compensation fiber in the Raman amplifier; However, bit error rate of less than 10 to 12 is obtained at both wavelengths, which is sufficient performance for practical uses. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 143(1): 58–65, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10137     

Tuning range extension by active mode-locking of external cavity laser including a linearly chirped fiber Bragg grating

We demonstrate electrical wavelength tuning by mode locking of an external cavity laser (ECL) with linearly chirped fiber Bragg grating (LCFBG). The configuration consists of a laser chip providing the gain coupled to an LCFBG with a large chip rate of 10 or 55 nm/cm providing the counter-reaction for laser oscillation. The laser chirp is electrically modulated by a sinusoidal signal in such a way that the ECL is mode locked. By changing the modulation frequency, a wavelength tuning range of 27 nm is achieved with the 10 nm/cm LCFBG, and a partial tuning range over 41 nm is demonstrated with the 55-nm/cm LCFBG. The output pulse stream at a specific mode-locking frequency and a corresponding wavelength is obtained for both positively and negatively chirped grating. A time bandwidth product reduction is measured in the case of negatively chirp grating when compared with positively chirp grating. A simple general law between the laser parameters is given (locking frequency, tuning range, and FBG chirp value). The parameters for a 40-nm tunable source modulated at 10 GHz are given. This simple tuning mechanism is very well adapted for a structure that requires accurate wavelength monitoring.     

Optimization of transmission performance of 10-Gb/s optical vestigial sideband signals using electrical dispersion compensation by numerical simulation

We analyze the transmission performance of vestigial sideband (VSB) signals with electrical dispersion compensator (EDC) by numerical simulations. Optimizing the dispersion and bandwidth of EDC, and the extinction ratio and chirp of the modulator, we can improve the dispersion tolerance of VSB signals. VSB signals with negative chirp have better transmission performance while VSB signals with positive chirp are advantageous to the implementation of EDC due to low optimum dispersion in EDC. VSB transmission with EDC can be a very cost-effective solution for 10-Gb/s single-channel systems with the maximum transmission distance of 320 km.     

Silicon-Based Microring Resonator Modulators for Intensity Modulation

We numerically analyze the characteristics of silicon-based microring modulators consisting of a single-ring resonator. Performance of the devices as digital intensity modulators is examined in terms of extinction ratio, pulsewidth, frequency chirp, spectral broadening, and signal quality. Three types of the modulators built in single-waveguide under-/overcoupling and dual-waveguide configurations are discussed. We show that cavity dynamics significantly affect the modulation properties. Data transmission performance over single-mode fibers is also presented. A silicon microring modulator with negative chirp could achieve 0.8 dB power penalty in 80-km fiber transmission without dispersion compensation.      

光纤色散脉冲展宽分析仪的研制

光纤色散特性会引起传输信号的畸变,限制通信容量.对光纤色散参数,光信号在长距离传输后脉冲展宽程度进行准确测量,可以为工程人员在设计高速光通信系统设计时提供可靠设计数据来源,在实际的工程应用中有着重要意义.本文理论上分析了光脉冲在光纤中传播的展宽现象,重点介绍了光纤色散分析仪的设计方案,最后,自行研制了一套用于色散测量的脉冲展宽设备,对标准多模光纤进行了脉冲展宽的测试,测量结果和出厂测试结果相吻合.     

一种新型的高精度Sigma_Delta调制器结构

为实现低失真高动态范围的模数转换,提出了一种新型高精度Sigma_Delta调制器系统。首先,设计了一种新型的二阶单环一位量化结构,结构中增加两支前馈路径,并调整了核心积分器和信号加算模块的逻辑关系。同时,为实现量化噪声的二阶整形以及输入信号的无延迟传输,进一步适配和改进了积分器的传输函数。最终,所提出的调制器实现了更高的信噪比和更宽的动态输出范围。基于Matlab 的系统级仿真结果表明,在信号带宽1KHz、采样信号频率1024KHz的条件下,所提出调制器的信噪比为106.6dB,有效位数为17.41bit,二次谐波失真为-82.7dB,动态范围为104.76dB,整体指标性能良好,为高阶MASH结构Sigma Delta调制器的研发提供了新方向。     

Tunable compensation of channel degrading effects using nonlinearlychirped passive fiber Bragg gratings

Several channel-degrading effects are present in nonstatic and dynamically reconfigurable wavelength-division-multiplexed systems and networks due to various types of dispersion in the optical transmission fiber. These effects must be addressed by tunable methods so that data signals do not fade with time. The relevant effects for which we demonstrate tunable compensation include: chromatic dispersion accumulated in a single channel and in multiple channels, polarization mode dispersion, and periodic RF power fading. We utilize a nonlinearly chirped fiber Bragg grating that provides a dispersive function that can be varied continuously by tuning a single mechanical stretching element     

基于光纤光栅传感器的智能电器温度场监测

介绍了布拉格光纤光栅传感器工作原理,针对光纤光栅传感器检测智能电器温度场的关键技术,提出一种基于分布式光纤温度传感原理的智能电器在线监测系统的技术架构,并做了相应的分析.该技术可提高智能电器设备的可靠性.     

Nonlinear Phase Noise Reduction of DQPSK Signals by a Phase-Preserving Amplitude Limiter Using Four-Wave Mixing in Fiber

It is experimentally shown that phase-preserving amplitude regeneration by an all-optical amplitude limiter using saturation of four-wave mixing in a highly nonlinear fiber can enhance differential quadrature phase-shift keying (DQPSK) transmission performance. The limiter suppresses amplitude fluctuations of the signal, by which the nonlinear phase variance caused by self-phase modulation in the transmission fiber is reduced. The 10-GSymbol/s short-pulse DQPSK transmission experiment over densely dispersion-managed fiber shows that the amplitude limitation after an imperfect transmitter increases maximum transmitted signal power by 5 dB.     

Wavelength tunable 10-GHz 3-ps pulse source using a dispersion decreasing fiber-based nonlinear optical loop mirror

We experimentally demonstrate the use of a dispersion decreasing fiber (DDF)-based nonlinear optical loop mirror (NOLM) for the generation of wavelength tunable soliton-like pulses at a repetition rate of 10 GHz. We compress /spl sim/12-ps Gaussian pulses from an electro-absorption modulator (EAM) (followed by 125 m of DCF for preliminary linear dispersion compensation) into 3-ps pedestal-free pulses using both high-order soliton compression and nonlinear switching effects within an 8.5-km DDF-based loop mirror. The output pulses from the DDF-based NOLM show considerable pedestal reduction compared to those obtained by directly compressing the EAM seed pulses via a single passage through the DDF. Wavelength tuning of the compressed pulses over a /spl sim/15-nm bandwidth (from 1541 to 1556 nm) is demonstrated without a significant increase in pulse duration or degradation in pulse quality.     

光纤拉曼放大器在云南电力通信网的运用

损耗、色散、非线性等是限制光信号长距离传输的主要问题,光纤拉曼放大器正是补偿损耗实现光长距离传输的有效方法。文章阐述了光纤拉曼放大器的原理及特点,提出了解决光纤长距离传输相应的技术对策。采用光纤拉曼放大器对传输光纤在损耗、色散、非线性及偏振模等方面进行优化,可以满足长距离、大容量传输系统的要求。分析了实际运用中的参数算法和相关指标要求,介绍了测试方法和结果,实现了光信号超长距离的传输。同时节约了工程建设投资,降低了通信运行维护费用,为光通信系统建设提供了参考。