Over 1000 km FSK heterodyne transmission system experiment usingerbium-doped optical fiber amplifiers and conventional single-modefibers

The influence of spontaneous emission noise on coherent transmission systems using multistage erbium-doped optical fiber amplifiers is experimentally examined. A frequency-shift keying (FSK) heterodyne transmission experiment was successfully performed at 560 Mb/s through 1028 km of fiber using ten cascaded fiber amplifiers and conventional single-mode fibers with a zero dispersion wavelength of around 1.3 μm. In the experiment, no transmission penalty due to accumulated spontaneous emission noise or to fiber chromatic dispersion was observed     

Application of DBR mode-locked lasers in millimeter-wavefiber-radio system

An actively mode-locked laser (MLLD) integrated with a distributed Bragg reflector (DBR) was used as a light source for optical subcarrier transmission. The millimeter (mm)-wave power penalty due to fiber dispersion is suppressed within 4 dB by operating this laser in a symmetric four-mode configuration. The experimental results agree well with the calculation of dispersion-induced penalty for a four-component-lightwave source. Optical subcarrier transmission free from dispersion-induced penalty within experimental error is achieved by further suppression of the end-modes of the DBR-MLLD using a fiber Bragg grating (FBG)     

The Transmission Performance of Non-zero Dispersion Shifted Fiber Communication Systems Using In-line Phase-sensitive Amplifiers

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888nm半导体抽运的60W皮秒激光振荡器模型

为了建立一个基于888nm半导体抽运的高平均功率和高效率皮秒激光振荡器的理论模型,采用模拟计算方法和谐振腔理论、ABCD定律、自洽条件以及连续被动锁模条件,利用激光晶体Nd:YVO4对波长888nm半导体抽运源的吸收特性和元件的相关参量、合适的腔模参量、实现稳定锁模的参量进行了理论分析和计算,并通过以上研究和模拟计算得到了皮秒振荡器模型的相关数据。结果表明,在120W的抽运功率下,激光器可以输出约61.5W的皮秒激光,光光转换效率51.3%。这一理论模型的建立对高平均功率和高效率皮秒激光振荡器的实验研究起着指导作用。     

光纤OFDM系统中的色散补偿技术研究

为了减小光纤的色度色散对光纤正交频分复用（OFDM）系统性能的影响,提出了将无线通信中的信道估计器引入光纤OFDM系统进行信道估计的色散补偿方法。在理论上分析了光纤的色度色散对于传输OFDM信号的影响,并在实验中采用梳状导频的形式,在每个OFDM码元的特定的子载波上插入导频,在接收端通过基于最小平方（LS）原则的LS估计器进行信道估计,得到了OFDM光纤传输的信道幅度响应和相位响应,通过使用LS估计器,直接调制的光OFDM信号在单模光纤中传输200km,误比特率低于10-6 ,功率代价小于2dB。结果表明,高频子载波较低频子载波更容易受到色散的影响,在光纤OFDM系统中引入信道估计器进行信道估计能够有效补偿由色度色散带来的相位偏移和幅度衰减。     

Effects of laser diode parameters on power penalty in 10 Gb/soptical fiber transmission systems

A composite tradeoff study based on the influence of key laser diode parameters on frequency chirp induced power penalty, extinction induced power penalty, the turn-on delay, and the dispersion transmission limit is presented for 10 Gb/s optical fiber transmission systems. The simulated results reveal that an optimum range of differential gain and nonlinear gain coefficient exists, and it is advantageous to set an extinction ratio that minimizes both the total power penalty and the turn-on delay. In addition, it is shown that a reduction of chirp and maximization of the dispersion transmission limit can be realized by designing the laser diode with a linewidth enhancement factor near -0.8     

12300 ps/nm, 2.4 Gb/s nonregenerative optical fiber transmissionexperiment and effect of transmitter phase noise

A nonregenerative optical transmission experiment with a chromatic dispersion of more than 10000 ps/nm is reported. Externally intensity-modulated 2.4 Gb/s optical signals were transmitted over 710 km of nondispersion-shifted optical fiber using ten Er-doped fiber amplifiers with a total net optical gain of 125 dB. Although the total chromatic dispersion amounted to 12300 ps/nm, the power penalty observed was as small as 0.5 dB, and an error floor was not observed. The effect of transmitter phase noise associated with fiber chromatic dispersion was experimentally investigated     

Dispersion penalty reduction using an optical modulator with adjustable chirp

Using a unique Ti:LiNbO/sub 3/ modulator, the value of the modulation chirp parameter that minimizes the transmission power penalty caused by fiber chromatic dispersion was experimentally identified. System experiments at 5 Gb/s using nonreturn-to-zero (NRZ) amplitude-shift-keyed (ASK) transmission with direct detection reception are discussed, and the optimum values of the modulation chirp parameter versus distance for transmission at 1.5 mu m wavelength over fibre having zero dispersion at 1.3 mu m are identified. 5 Gb/s NRZ transmission was achieved through distances of 128, 192, and 256 km of conventional fiber while incurring dispersion penalties of -0.5, 0.1, and 1.1 dB respectively, by operating at the quantum chirp value.<>     

2500 km-10 Gbps RZ transmission system based on dispersion compensation CFBGs without electric regenerator

The characteristics of chirped fiber Bragg gratings (CFBGs) are optimized so that the ripple coefficient of the power reflectivity spectrum and group time delay are less than 1 dB and |± 15| ps, group delay is about 2600 ps/nm, polarization module dispersion is very small, PMD<2 ps, -3 dB bandwidth is about 0.35 nm, and insertion loss is about 4-5 dBm. Using dispersion compensation CFBG, a 2500 km-10 Gbps RZ optical signal transmission system on G.652 fiber was successfully demonstrated without an electric regenerator by optimizing dispersion management and loss management. The RZ optical signal was generated through a two-stage modulation method. At 2081 km, the power penalty of transmission is about 3 dB (conditions: RZ signal, BER = 10-12, PRBS = 1023 - 1); At 2560 km, the power penalty is about 5 dB. It is superior to the system using NRZ under the same conditions.     

Transmission performance of high bit rate spectrum-sliced WDMsystems

We simulate transmission of a spectrum-sliced WDM channel operating at high bit rates (e.g., 622 to 2488 Mb/s). We calculate the bit error rate using the non-Gaussian statistics of thermal light sources that are commonly used in spectrum slicing and account for the effects of fiber dispersion. We evaluate the tradeoff in optical slice linewidth between signal-to-excess optical noise ratio and dispersion penalty in spectrum-sliced WDM systems, and determine the channel slicewidth that minimizes transmission penalty for a given link length and bit rate. We compare our simulations against the measured performance of a 1244 Mb/s channel over 20 km of fiber. The results in this paper provide useful information for the design of spectrum-sliced WDM networks     

光纤传输系统中基于相位预调制的信号整型

利用相位预调制技术解决高速长距离光纤传输系统中面临的接收灵敏度降低和色散容限问题。通过在发射端对非归零(NRZ)的光信号进行比特同步相位预调制,使非归零码在传输过程中得到波形重整,演变为归零(RZ)的波形,从而提高眼图开启度。实验观测了普通非归零码和相位预调制的非归零码在不同相位调制深度和色散下的光谱、眼图和功率代价。10Gb/s的传输结果表明,链路色散绝对值小于1000ps/nm时,施加相位预调制的非归零信号功率代价小于1dB,比普通非归零信号具有更高的接收灵敏度和更低的色散功率代价。因此,基于相位预调制的信号整型技术可减轻系统对光信噪比和色散管理的要求,延长传输距离。     

Evaluation of 4-Gbit/s optical fiber transmission distance with direct and external modulation

Transmission characteristics for a recently modulated measured distributed-feedbacked (DFB) laser and an externally modulated DFB laser using a Ti:LiNbO/sub 3/, Mach-Zehnder modulator at 4 Gb/s are discussed. The transmission characteristics are estimated by an advanced eye-pattern analysis method. The maximum measured fiber dispersion with a directly modulated laser is 100 to 140 ps/nm when the chirp power penalty is 1 dB. However, for external modulation, there is no power penalty after transmission over a 2220-ps/nm dispersive fiber. This confirms that external modulation has superior transmission characteristics. The modulation scheme for 4-Gb/s systems in terms of these results is discussed.<>     

利用啁啾光纤光栅实现10Gb/s WDM系统色散补偿

利用二次曝光法制作的啁啾光纤光栅在国内首次邮１０Ｇｂ／ｓｅ ＷＤＭ系统单路色散补偿,经１８０ｋｍ传输后色散补偿的功率代价为１ｄＢ。     

40Gb/s光纤通信系统中不同码型传输特性的实验研究

在高速光纤通信系统中码型的选择是决定系统传输质量和光谱效率的主要因素。码型的选择和信道速率、信道波长间隔、光放大器的选择、光放大器放置间隔、光纤的类型、色散管理策略等各种因素密切相关。分析了非归零码（NRZ）、归零码（RZ）和载波抑制归零码（CSRZ）码型的产生方式及特点。采用单信道和掺铒光纤放大器（EDFA）放大方式对三种码型进行了40Gb/s的100kmG.652光纤通信传输实验。比较了三种码型的系统传输持性、最佳入纤功率和不同入纤功率下的功率代价：载波抑制归零码最佳入纤功率为9dBm，功率代价小于非归零码和归零码。结果表明，在相同的色散补偿条件下，载波抑制归零码比归零码和非归零码有更优的非线性容忍度。     

Analysis of laser phase noise to intensity noise conversion bychromatic dispersion in intensity modulation and direct detectionoptical-fiber transmission

Laser phase noise conversion to intensity noise due to fiber chromatic dispersion is analyzed by deriving the noise power spectral density. Theory predicts that the phase-modulation-amplitude-modulation conversion noise is a principal limiting factor of the gigabit-per-second nonregenerative transmission using an external modulator when the linewidth of the laser transmitter is above several tens of megahertz and the total chromatic dispersion of fibers exceeds several thousand picoseconds per nanometer. This fact is confirmed by the 2.4-Gb/s transmission experiments using multiple inline Er-doped fiber amplifiers. The system penalty due to this noise in the intensity modulation and direct detection (IM-DD) optical transmission using an external modulator is evaluated     

Evaluation of transmission characteristics of chirped DFB lasers indispersive optical fiber

Experimental and analytical results are presented for pulse distortion and receiver penalty associated with wavelength chirp of 1.5 μm distributed feedback (DFB) lasers in the presence of fiber dispersion. An approximate analytical model for dispersion penalty due to chirp is given and shown to provide reasonable agreement with the experimental results obtained for digital transmission at 1.7 Gb/s. The model captures the important features of chirp that lead to dispersion penalty, such as the maximum wavelength excursion, the chirping time, and the energy content at the leading edge of the pulse during chirp. The utility of the model is that the parameters used in it can be readily obtained from single experimental measurements. The limitations of the model are also discussed     

Dispersion tolerance of coherent WDM

We present the transmission of a 298.2-Gb/s copolarized coherent wavelength-division-multiplexing system over 80 km of standard single-mode fiber, achieving an information spectral density of 1 b/s/Hz with no prefilters at the transmitter. Odd and even tributary channels were encoded with data and delayed-data-bar pseudorandom binary sequence 2/sup 7/-1 patterns. The dispersion tolerance is investigated, and the dispersion penalty of this system is improved through adjustment of the relative phase of adjacent channels. Under optimum conditions, the dispersion penalty could be reduced from over 3 dB to less than 1 dB.     

A 40-Gb/s/ch WDM transmission with SPM/XPM suppression throughprechirping and dispersion management

This paper proposes to combine prechirping with dispersion management scheme in such a way as to suppress the power penalty induced by self-phase modulation (SPM) and cross-phase modulation (XPM) in 40-Gb/s per channel wavelength-division multiplexed (WDM) transmission systems with long-amplifier spacing. First, we show that the optimum total dispersion to minimize SPM depends on prechirping and the local dispersion of the transmission fiber, unlike that for minimizing XPM. Next, it is shown that, by optimizing the combination of prechirping and local dispersion, these two optima can be made to match so as to improve the allowable maximum fiber input power. Finally, the operation of the proposed optimization scheme is confirmed experimentally, and 4×40-Gb/s WDM transmission over 400 km of nonzero dispersion-shifted fiber (NZDSF) is demonstrated successfully with the fiber input power of +10 dBm/ch and 250 GHz channel spacing     

Computationally Efficient Nonlinearity Compensation for Coherent Fiber-Optic Systems

Split-step digital backward propagation (DBP) can be combined with coherent detection to compensate for fiber nonlinear impairments.A large number of DBP steps is usually needed for a long-haul fiber system,and this creates a heavy computational load.In a trade-off between complexity and performance,interchannel nonlinearity can be disregarded in order to simplify the DBP algorithm.The number of steps can also be reduced at the expense of performance.In periodic dispersion-managed long-haul transmission systems,optical waveform distortion is dominated by chromatic dispersion.As a result,the nonlinearity of the optical signal repeats in every dispersion period.Because of this periodic behavior,DBP of many fiber spans can be folded into one span.Using this distance-folded DBP method,the required computation for a transoceanic transmission system with full inline dispersion compensation can be reduced by up to two orders of magnitude with negligible penalty.The folded DBP method can be modified to compensate for nonlinearity in fiber links with non-zero residual dispersion per span.     

445 Mbit/s transmission field experiment at 1.55-µm wavelength region over 80 km using undersea optical-fiber cable

New transmission equipment employing a 1.55-μm distributed feedback laser diode (DFB-LD) to overcome fiber dispersion has been tested at environmental conditions using 1.3-μm zero-dispersion fiber cable on the undersea section of route F-400M. The DFB-LD's dynamic spectrum characteristics, in relation to power penalty, were examined and a suitable laser prebias control level was obtained. Field experimental transmission lines operated error free for a two-month period, and applicability to 1.55-μm 445-Mbit/s systems of over 100 km was shown.