Effects of precompensation and postcompensation on timing jitter in dispersion-managed systems

We present an analytic theory of timing jitter in dispersion-managed light-wave systems that is based on the moment method and the assumption of a chirped Gaussian pulse. We apply the theory to a soliton system and show that 50% postcompensation of the accumulated dispersion can reduce the jitter by a factor of 2. We also apply the theory to a low-power light-wave system employing the return-to-zero format and find that timing jitter can be minimized along the fiber link for an optimal choice of precompensation and postcompensation.     

Efficient optimisation of per-channel pre-compensation in WDM 20-Gbit/s RZ-DPSK transmission in non-slope matched submarine links

We propose a computationally efficient method to the per-channel dispersion optimisation applied to 50 GHz-spaced N × 20-Gbit/s wavelength division multiplexing return-to-zero differential phase shift keying transmission in non-zero dispersion-shifted fibre based submarine systems.     

Interferometric optical signal-to-noise ratio measurements of telecom signals with degraded extinction ratio

We measure full interferograms of telecom signals impaired by noise and investigate their applicability to in-band optical signal-to-noise ratio (OSNR) monitoring in practical systems. We experimentally establish that the dependence of overall shape of the interferogram on a signal's extinction ratio (ER) is strong but not unique. As the ER is being degraded the interferogram evolves in two distinct ways depending on the modulation conditions. The resulting ambiguity in the interferogram shape prevents OSNR measurements on completely unknown signals and necessitates a calibration for each modulator condition. With appropriate calibration, we experimentally demonstrate reliable OSNR measurements in the 5 to 25 dB range for 42.8 Gb/s nonreturn-to-zero, return-to-zero, and carrier-suppressed return-to-zero on-off-keyed signals.     

40 Gb/s非零色散位移光纤传输系统中四种调制格式的性能比较

介绍了四种调制格式即非归零(NRZ),归零(RZ),载波抑制的RZ(CSRZ)和单边带RZ(SSB-RZ),用计算机仿真方法产生了这四种调制格式的40 Gb/s光信号,比较了其波形和光谱.也对这四种调制格式在非零色散位移光纤(NZDSF)上单信道传输进行了仿真,结果表明:在色散完全补偿情况下,RZ,CSRZ和SSB-RZ抗非线性能力都比NRZ强,其中CSRZ最强, CSRZ能够容忍的入纤光功率比NRZ大10.2 dBm;RZ,CSRZ和SSB-RZ 三种格式抗EDFA噪声能力差不多,但都比NRZ强.     

On the dispersion managed soliton

We review various methods used to study the dispersion managed soliton for nonlinear return-to-zero pulse propagation in optical fibers. A numerical averaging method, the guiding center soliton, the variational method both with a simple and with an extended ansatz, as well as the multiscale theory are discussed and numerically compared, allowing us to show their domains of applicability. Their relative merits and demerits are then exposed. (c) 2000 American Institute of Physics.     

Relation between vestigial-sideband filtering and pi/2 progressive phase shift

We show that a Gaussian-shaped vestigial-sideband (VSB) return-to-zero (RZ) on-off-keying (OOK) optical signal is essentially a RZ OOK signal with pi/2 progressive phase shift. The reduced intersymbol interference of the VSB signal can be explained as a destructive interference effect. We experimentally demonstrate a method for generating an effective 40-Gbit/s VSB signal without relying on the detuning of an optical filter.     

产生暗归零码光标记信号的新方案

在对预编码、调制和编码过程进行改进的基础上,提出了一种利用一个双臂马赫-曾德尔铌酸锂调制器和一个电信号时延器产生可调占空比和消光比的光暗脉冲归零码二进制信号的新方案。实验证明这种信号能用传统的二进制强度调制-直接检测系统的接收机进行检测。实验得到了在调节电信号时延器时速率为2.5 Gbit/s的光暗脉冲归零码二进制信号的频谱变化规律,以及占空比分别为0.25,0.35,0.60和0.80时光暗脉冲归零码二进制信号的误码率和眼图。此外,利用该方案产生的光暗脉冲归零码二进制信号可以作为标记在光标记交换网络中得到应用。     

Generation of DQPSK format and its performance against polarization mode dispersion

We propose a novel transmitter and receiver for differential quadrature phase-shift keying （DQPSK） format. The impact of the first-order polarization mode dispersion （PMD） on systems using DQPSK with 100- Gb/s non-return-to-zero （NRZ） or return-to-zero （RZ） format is investigated. Through computing the eye openings of DQPSK formats under different PMD conditions, it is found that NRZ DQPSK, as compared with RZ DQPSK, incurs smaller eye opening due to PMD. Carrier-suppressed return-to-zero （CSRZ） DQPSK format has better tolerance than RZ DQPSK format to PMD for a given bit rate.     

Multi-Channel NRZ/RZ-DPSK to CSRZ-DPSK Format Conversion Based on Nonlinear Polarization Rotation of SOA

We present an all-optical nonreturn-to-zero/return-to-zero(NRZ/RZ) to carrier-suppressed return-to-zero(CSRZ)format conversion scheme for differential phase-shift ke.ying(DPSK) signals. The conversion is based on nonlinear polarization rotation of a semiconductor optical amplifier(SOA). The 4-channel NRZ-DPSK or RZ-DPSK signals at 10 Gb/s are simultaneously converted to the corresponding CSRZ-DPSK signals, with-0.8 and 1.4 dB average power penalties, respectively. Additionall.y, high quality format conversion performanes are shown with the optical spectra and eye diagrams.     

Analysis of intrachannel impairments in differential phase-shift keying transmission systems

The evolution of the phase in a return-to-zero differential phase-shift keying system is studied by the generalized momentum method. The results show that phase fluctuation in the case of dispersion-managed solitons is much smaller than that in quasi-linear systems for a given launch power.     

Two-stage adaptive PMD compensation experiment for 10-Gb/s optical communication system

We report the adaptive compensation experiment of polarization mode dispersion (PMD) for 10-Gb/s non return-to-zero (NRZ) and return-to-zero (RZ) optical communication systems using a two-stage PMD compensator and the monitoring technique based on degree of polarization (DOP) feedback-signals. The DOP monitor has its advantages of bit-rate independent and modulation format independent. The two-stage compensator has the capacity of compensation for the first- and second-order PMD. The compensated differential group delay (DGD) is up to 80 ps, and compensated principal state of polarization rotation rate is 20 ps. The time used for compensation is less than 1 second.     

Performance Comparison of Long-Haul Direct Detection Optical Transmission Systems Adopting Dispersion Management with Pre-Compensation

Abstract

This article reports a numerical investigation on the performance of return-to-zero intensity-modulated direct detection, return-to-zero differential phase shifting key, and return-to-zero differential quadrature phase shifting key systems operating in G.652 links adopting dispersion management. Also illustrated are the role and benefits of pre-compensation. For such an aim, the influence of the non-linear Kerr impairments on the in-phase and quadrature components of the signal are studied, along with the consequent degradations in terms of the Q-factor for the different modulation formats. Such an investigation is applied to evaluate the maximum propagation distances for 40- and 80-Gb/s capacities.     

Analysis of enhanced-power solitons in dispersion-managed optical fibers

We analyze pulse propagation in an optical fiber employing a periodic dispersion map. Second-order averaging is used to determine a general evolution equation valid for both return-to-zero and non-return-to-zero pulses in dispersion-managed systems. The equation is then applied to the case of solitons, and an analytic expression for the power enhancement arising from the dispersion management is obtained.     

Analysis of modulation format in the 40 Gbit/s optical communication system

Three different modulation formats including nonreturn-to-zero (NRZ), return-to-zero (RZ), carrier-suppressed return-to-zero (CS-RZ) and the differential phase keying (DPSK) modulation format of each code are introduced in the article. A method of their modulated signal generation with computer is described, and a comparison of their spectra and waveforms is made. The 40 Gbps signal transmitted in 200 km G.652 fiber by way of single channel with erbium-doped-fiber-amplifier (EDFA) is simulated for these three formats. The ability of anti-dispersion and anti-PMD is analyzed. It is shown that RZ and CS-RZ formats are more tolerant than NRZ format in the same conditions.     

Preconversion phase modulation of input differential phase-shift-keying signals for wavelength conversion and multicasting applications using phase-modulated pumps

We demonstrate a method to use phase-modulated pumps for multicasting of return-to-zero differential phase-shift keying (RZ-DPSK) signals. The method uses phase modulation of the input signal along with the co-phase-modulated pumps prior to wavelength conversion. Nine copies of a 50?Gbit/s RZ-DPSK data signal are generated via four-wave mixing with an average conversion efficiency of ～0?dB. An average receiver sensitivity penalty of ～1.9?dB is observed at a bit-error rate of 10(-9) with a worst case of 2.3?dB. The effects of synchronization errors and phase-modulation frequencies up to 5?GHz are investigated.     

Reduction of the phase jitter in differential phase-shift-keying soliton transmission systems by in-line Butterworth filters

We examine reduction of phase jitter by use of in-line Butterworth filters in soliton systems in the context of differential phase-shift-keying coding. We also demonstrate numerically that the use of a Butterworth filter in a return-to-zero differential phase-shift-keying system can reduce continuum background radiation.     

Analysis of nonlinear phase noise in single-channel return-to-zero differential phase-shift keying transmission systems

Self-phase modulation and intrachannel cross-phase-modulation- (IXPM) induced nonlinear phase noise is investigated by the variational method. IXPM can cause a considerable increase of phase noise. We show, however, that IXPM leads to a partial correlation between the phase noises of adjacent pulses, which tends to reduce the influence of nonlinear phase noise in return-to-zero differential phase-shift keying transmission. In highly dispersive transmission systems, intrachannel four-wave mixing-induced differential phase fluctuations are typically larger than differential nonlinear phase noise. The analysis is validated by Monte Carlo simulation.     

Use of multicanonical Monte Carlo simulations to obtain accurate bit error rates in optical communications systems

We apply the multicanonical Monte Carlo (MMC) method to compute the probability distribution of the received voltage in a chirped return-to-zero system. When computing the probabilities of very rare events, the MMC technique greatly enhances the efficiency of Monte Carlo simulations by biasing the noise realizations. Our results agree with the covariance matrix method over 20 orders of magnitude. The MMC method can be regarded as iterative importance sampling that automatically converges toward the optimal bias so that it requires less a priori knowledge of the simulated system than importance sampling requires. A second advantage is that the merging of different regions of a probability distribution function to obtain the entire function is not necessary in many cases.     

Nonlinear chirp of dispersion-managed return-to-zero pulses

Applying variational methods, we derive a reduced system of equations from the nonlocal equation that governs the average dynamics in dispersion-managed systems. These equations, which apply for any type of return-to-zero pulse, describe the stroboscopic evolution of the pulse parameters and bypass the fast variations inside each dispersion map. In the limit of large map strength we integrate the equations to obtain explicitly formulas for the parameters of a chirped return-to-zero pulse as well as the amount of post-transmission compensation needed to restore the initial pulse width.     

Pulse-overlapped dispersion-managed data transmission and intrachannel four-wave mixing

We show that strong overlap of adjacent pulses in dispersion-managed return-to-zero transmission reduces pulse-to-pulse interaction and timing jitter. The limiting factors for this pulse-overlapped transmission are the amplitude fluctuations and the ghost pulse generation induced by four-wave mixing between spectral components within a single channel.