Measurement of ultralow Gordon-Haus timing jitter in dispersion-managed soliton systems

We measure, for the first time, the growth of the Gordon-Haus timing jitter in dispersion-managed soliton communication systems without inline soliton control. After 650-km transmission with a relatively high average dispersion of 0.87 ps/nm/km and a pulsewidth of 14 ps, compatible with 20 Gb/s, we measure a very low timing jitter of 45 fs. Hence, medium range dispersion-managed soliton transmission systems have, in general, a good margin toward Gordon-Haus timing jitter.     

Gordon-Haus timing jitter reduction in dispersion-managed solitoncommunications

An analytic theory is presented which demonstrates that the noise induced Gordon-Haus timing jitter in arbitrary dispersion-managed transmission systems is reduced by the power-enhancement factor required to support a dispersion-managed solitons provided the path-average soliton period is much greater than the dispersion-map period. The analysis further predicts the behaviour of the amplitude, width, and quadratic chirp fluctuations due to the amplified spontaneous emission (ASE) noise     

Reduction of Gordon-Haus jitter in soliton transmission systems byoptical phase conjugation

The effect of optical phase conjugation on Gordon-Haus jitter in long-distance soliton communication systems is considered. In-line optical phase conjugation at an optimal point two-thirds of the way down the system reduces the rms jitter by a factor of three. A post-transmission-line compensation scheme based on optical phase conjugation and soliton-supported dispersion compensation reduces the rms jitter by a factor of two     

Analysis of power jitter induced by interchannel interactions indispersion-managed optical soliton transmission systems

Collision-induced power jitter is theoretically and numerically examined in dispersion-managed wavelength-division multiplexed optical soliton transmission systems. The variational method is mainly used to develop a time efficient jitter calculation approach. The power jitter causes a serious problem for a singly periodic dispersion managed line having almost zero average dispersion, which can be reduced by applying doubly periodic dispersion management     

40 Gb/s single-channel soliton transmission over transoceanicdistances by reducing Gordon-Haus timing jitter and soliton-solitoninteraction

Forty Gb/s single-channel soliton transmission experiments using periodic dispersion compensation were conducted. The impact of the dispersion map on the transmission performance was experimentally investigated. The transmission performance was significantly varied with the dispersion map. The improvement of the transmission performance by the polarization division multiplexing, which reduced soliton-soliton interaction furthermore, was also confirmed. By using the polarization division multiplexing in the optimum dispersion map, 40 Gb/s single-channel transmission over 10200 km has been successfully demonstrated without any active inline transmission control     

Experimental evidence of pseudoperiodical soliton propagation indispersion-managed links

A new technique for measuring chirp evolution of Gaussian-like pulses transmitted on single-mode fiber is presented. It is used in a recirculation loop experiment to characterize propagation in anomalous-dispersion regime over megametrical distances. In-quadrature periodical variations of the two characteristic parameters of pulses (i.e., spectral width and chirp) are measured versus distance for different values of prechirp and in-line power. This constitutes the first experimental evidence of pseudoperiodical soliton propagation in dispersion-managed links. It also demonstrates that the prechirp is a key element for the control of nonlinearity as predicted by the theory     

Effect of amplifier spacing on four-wave mixing in multichannel coherent communications

The buildup of four-wave mixing (FWM) is studied for the case of a multichannel coherent system using cascaded optical fibre amplifiers. It is shown, both analytically and numerically, that FW interactions can be either reduced or resonantly enhanced depending on the choice of the amplifier spacing. An example is given of a three channel phase modulated system with a channel separation of 12.5 GHz transmitted over 1000 km. For this example, resonance of FWM occurred at an amplifier spacing of 53 km.<>     

Collision-induced timing jitter reduction by periodic dispersionmanagement in soliton WDM transmission

The authors propose to use dispersion management to reduce collision-induced timing jitter in soliton WDM transmission. The performance of dispersion-managed fibres is compared numerically to dispersion-decreasing and uniform dispersion fibres with up to eight channels, and it is shown that dispersion management can provide the best performance     

Effect of distributed Raman amplification on timing jitter indispersion-managed lightwave systems

It is shown that the timing jitter of dispersion-managed soliton systems can be reduced by up to 40% by using a hybrid amplification scheme in which fiber losses are compensated by using erbium-doped fiber amplifiers in combination with backward pumped Raman gain. The jitter is smallest in the case of 100% Raman amplification, but considerable reduction occurs even for partial distributed amplification     

Experimental investigation of soliton optical phase jitter

The soliton optical phase stability versus amplified spontaneous noise is investigated in a recirculation loop experiment in the presence of in-line filters. The behavior of phase fluctuations is shown to be in good agreement with numerical simulations. The phase standard deviation is kept below 0.15×π for distances up to 8000 km. We, therefore, demonstrate the feasibility of phase-shift keying on solitons for long-haul transmission systems     

Effect of soliton interaction on timing jitter in communicationsystems

Timing jitter in soliton communication systems is studied, taking into account both soliton interaction and amplifier noise. Deviations from Gordon-Haus jitter for closely spaced solitons are observed. A new analytical model for the timing jitter is proposed. The model presented considers interaction in a random sequence of solitons and the effect of the amplified spontaneous emission noise added in each amplification stage. We obtain a good agreement between the new analytical model and simulation results for practical communication systems     

Dynamically optimum lookup-table spacing for power amplifier predistortion linearization

The lookup-table-based digital adaptive predistortion (DAPD-LUT) approaches are low cost and effective for power amplifier (PA) linearization in wireless applications. However, most existing DAPD-LUT schemes are sub-optimum because they adopt uniformly spaced LUTs regardless of the system state information (SSI), i.e., the PA characteristics and the input signal statistics. Other existing DAPD-LUT schemes assume either full or partial knowledge of the SSI to optimize and then to freeze the LUT spacing. Without prior knowledge of the SSI, we propose an SSI-learning low-complexity procedure to optimize the LUT spacing for a DAPD-LUT scheme. The proposed procedure is capable of online adapting the LUT spacing for PAs with various nonlinear characteristics, for input signals with various statistics, and for wireless environments with various time-varying properties.     

1.8 GHz class E power amplifier for wireless communications

The authors present a 1.8 GHz class E power amplifier for wireless communications. A fully integrated class E power amplifier module was designed, fabricated and tested. The circuit was implemented in a self-aligned-gate, depletion mode 0.8 μm GaAs MESFET process. The amplifier delivers 23 dBm of power to the 50Ω load, with a power added efficiency of 57% at a supply voltage of 2.4 V     

A cascode modulated class-E power amplifier for wireless communications

A cascode modulated CMOS class-E power amplifier (PA) is presented in this paper. It is shown that by applying a modulated signal to the gate of the cascode transistor the output power is modulated. The main advantage of the proposed technique is a high 35 dB output power dynamic range. The peak power added efficiency (PAE) is 35%. The concept of the cascode power control of class-E RF PA operating at 2.2 GHz with 18 dBm output power was implemented in a CMOS technology and the performance has been verified by measurements. The prototype CMOS PA is tested by single tone excitation and by enhanced data rates for GSM evolution (EDGE) modulated signal. Digital predistortion is used to linearize the transfer characteristic. The EDGE spectrum mask is met and the rms error vector magnitude (EVM) is less than 4° in the entire output power range.     

低抖动准分子激光放大器光源的研究

为了获得低抖动的准分子激光放大器光源,设计了一种以氢闸流管作为高压开关的低抖动准分子激光放大器系统。利用抖动小于4 ns的闸流管触发电路来触发导通氢闸流管,从外部触发信号到准分子光信号之间有一定的延时时间。研究了以氢闸流管作为高压开关的准分子激光放电回路,外部控制信号发生电路产生外部充电信号和出光信号,转换电路将外部充电信号和出光信号转换成固定脉宽的光信号,在实现低抖动出光前,准分子激光放大器系统热平衡过程中会有一定的出光延时漂移现象。讨论了激光运行重复率、激光运行电压和气体状态在热平衡过程中对稳定延迟时间大小的影响。实验表明,在相同运行电压下,稳定延迟时间随着激光运行重复频率的提高而增大;运行电压越高,稳定延迟时间上升的幅度越大。气体恶化后,光脉冲稳定延迟时间变小。激光运行电压和重复频率越高,延时漂移时间越大。在温漂一定时间后,准分子激光放大器内部系统达到热平衡,以外部触发信号为基准,准分子光脉冲信号实现在5、10、15 Hz重复频率下的5 ns内低抖动出光。     

光孤子在分布式光纤放大器中传输特性的研究

光纤放大器用于补偿光信号在光纤中的传输损耗,是全光通信网中的核心器件。建立了光孤子在分布式光纤放大器中传输的物理模型,采用分步傅里叶变换法数值模拟了光孤子的传输放大特性,讨论了增益色散对光孤子形状和频谱的影响。结果表明：在放大器的反常色散区,随着光孤子的放大,会不断地产生啁啾孤子,孤子频谱会加宽并且产生振荡结构。放大介质的增益色散将会使光孤子幅度下降,宽度展宽,频谱窄化。因此,光纤放大器的色散、非线性效应和增益色散均会对光孤子的传输特性产生影响。     

放大器噪声对色散管理光孤子传输的影响

采用变分法讨论了放大器噪声对色散管理光孤子脉冲参数的影响。讨论了ASE噪声对脉冲相位、脉冲中心时间和中心频率的影响，并且对比讨论了采用密集色散管理系统和降低平均色散值后，ASE噪声对脉冲的影响，结果表明：密集色散管理孤子系统和平均色散接近于零的色散管理系统更有利于降低放大器噪声对脉冲的扰动。     

Effects of fiber nonlinearities and amplifier spacing on ultra-longdistance transmission

It is shown that it should be possible to send error-free signals at a 2.5-Gb rate (or higher) over distances of at least 9000 km using an amplitude shift keying (ASK) soliton modulation system. To accomplish this, the amplifiers must be kept close enough that their power gain is less than 10 dB. (It is noted that timing jitter and other noise effects measured in recent soliton transmission experiments carried out at low D and with amplifier spacing of 25 km are in close accord with predictions of this work). Frequency division multiplexing of several channels over the same fiber should also be possible, as solitons of different frequencies interact very weakly, provided the distance over which they pass through one another is large compared to the amplifier spacing     

Calculation of timing and amplitude jitter in dispersion-managedoptical fiber communications using linearization

An approach based on linearization that allows us to calculate the timing and amplitude jitter for arbitrary pulse shapes in dispersion-managed fibers is developed. We apply this approach to calculate the jitter for dispersion-managed soliton, return-to-zero (RZ), and nonreturn-to-zero (NRZ) transmission formats. We then estimate the bit error rates. The approach described here yields more precise results than Monte Carlo simulations at a fraction of the computational cost     

Timing jitter due to carrier linewidth of laser-diode pulse sourcesin ultra-high speed soliton transmission

We theoretically analyze the timing jitter due to both the carrier phase noise of laser-diode (LD) pulse sources and the Gordon-Haus effect in soliton transmission. A formula is derived for the timing jitter in terms of the carrier linewidth, one of the measurable parameters common to all types of LD pulse sources. The transmission distance restricted by the timing jitter is analyzed, and the carrier linewidths required for ultra-long distance and ultra-high speed soliton transmission are estimated as well. Recirculating loop experiments at 10 Gb/s are demonstrated using two pulse sources; a gain-switched DFB-LD and a sinusoidally driven monolithically integrated MQW-DFB-LD/MQW-EA modulator, which have different carrier linewidths due to their different pulse formation processes. The difference in the carrier linewidths of the two pulse sources is measured by the proposed technique which is based on the optical heterodyne method. The observed difference between the two pulse sources in terms of timing jitter accumulation and timing jitter reduction with optical bandpass filters for the two pulse sources well support the theoretical predictions