Analytical evaluation of transmission penalty due to group velocitydispersion, self-phase modulation, and amplifier noise in opticalheterodyne CPFSK systems

An analytical bit error rate evaluation of an optical heterodyne continuous-phase frequency shift keying (CPFSK) transmission system affected by group-velocity dispersion (GVD), self-phase modulation (SPM), and erbium-doped fiber amplifier (EDFA) amplifier spontaneous emission noise (ASE) in a nonlinear fiber medium is carried out following a perturbative and a transfer matrix approach. The utility of both approaches has been exemplified by applying them to different dispersion compensation schemes in optical and electronic domains. The theoretical penalty estimates are found to have good agreement with both the reported experimental results and those obtained by the Q-value simulation     

Polarization independent demultiplexing in a polarization diversity nonlinear optical loop mirror

We present a novel technique to achieve polarization insensitive all-optical demultiplexing using standard dispersion shifted fibers in a nonlinear optical loop mirror. A polarization dependence of /spl plusmn/0.2 dB is reported with no power penalty due to change in polarization.     

通过恒包络调制提高相干光OFDM系统的光纤非线性容限

相干光正交频分复用(CO-OFDM)对光纤链路中 的色度色散(CD)和偏振模色散(PMD)具有较强的容忍性,但 是OFDM信号高峰均功率比(PAPR)的特点使其对光纤非线性效应 非常敏感,严重影响了系统传输性能。 本文提出了基于恒包络(CE)调制的方法使得系统中光信号PAPR降低为0dB,从而提高了CO-OFDM系统的非 线性传输性能。仿真结果表明,子载波采用16QAM调制的40Gbit/s单信道CE调制CO -OFDM系统,在经800km无色散补偿、欠色散补偿和周期全色散补偿 标准单模光纤(SSMF)链 路传输后,虽然较传统CO-OFDM存在约1.8dB的代价,但是系统最大 发射光功率分别提高 了6.2、9.3dB。并且,将本文方案应 用 到CO-OFDM和10Gbit/s NRZ-OOK混合传输WDM系统中,信道最大发 射光功率仍获得了5.2dB的提高。因此,本文提出的CE调制方法能有 效地提高CO-OFDM系统在不同传输环境中的光纤非线性容限。     

Enhancement of system performance in directly modulated metro-WDMsystems by a spectral filtering method

A numerical demonstration is presented of the reduction of both the chirp-induced dispersion penalty and the extinction ratio penalty in directly modulated metro-wavelength-division multiplexed transmission systems by a spectral filtering method. The pre-filtering method suppresses nonlinear effects and gives better performance     

Dispersion penalty analysis for VSR-1 optical links

This paper presents an approach to calculate dispersion penalty for VSR-1 optical links. Based on parameters of a specific VSR-1 link, dispersion penalties are computed for various modal dispersion bandwidths respectively. The worst-case eye closure is expressed numerically by using the signal waveform at time 0, and the signal waveform is obtained in frequency domain through FFT algorithm. By this approach,the dispersion penalty is determined by the shape of transfer functions of the various components in the links. To simplify the derivation of multimode fiber link transfer function,a Gaussian form of normalized impulse response is used. This calculation approach can be used to estimate the worst-case dispersion penalty of VSR-1 links in the link budget analysis.     

Mean Field Method with Different Dispersion Maps for WDM Systems

Using mean field method proposed in Ref. [4], the 40 Gb/s multi--channel WDM optical fiber transmission systems with different dispersion maps are simulated. By this method, the computation time can be greatly reduced since following only the full time evolution of a limited number of channels while treating the other ehannels as continuous wave. But since dispersion plays an important role in the process of FWM and XPM,different dispersion maps will affect the application of the method. The dependence of the method on dispersion maps is investigated. The results not only confirm the mean field method,but also give useful approach for system design.     

Application of the Manakov-PMD equation to studies of signalpropagation in optical fibers with randomly varying birefringence

We report on our investigations of the Manakov-polarization mode dispersion (PMD) equation which can be used to model both nonreturn-to-zero (NRZ) and soliton signal propagation in optical fibers with randomly varying birefringence. We review the derivation of the Manakov-PMD equation from the coupled nonlinear Schrodinger equation, and we discuss the physical meaning of its terms. We discuss our numerical approach for solving this equation, and we apply this approach to both NRZ and soliton propagation, We show by comparison with the coupled nonlinear Schrodinger equation, integrated with steps that are short enough to follow the detailed polarization evolution, that our approach is orders of magnitude faster with no loss of accuracy. Finally, we compare our approach to the widely used coarse-step method and demonstrate that the coarse-step method is both efficient and valid     

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.     

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     

Broad-band dynamic dispersion compensation in nonlinear fiber-based device

In this paper we report on the design, numerical simulation and experimental testing of a novel dynamic dispersion compensation device based on self-phase modulation (SPM) in nonlinear fiber. The proposed all-fiber device is inherently simple and presents several unique advantages, most notably the potential for a broad-band operation covering all wave-length division multiplexing (WDM) channels of a system and the ability to address variable amounts of residual dispersion in each individual channel. Dynamic compensation ranges of up to 140 ps/nm for a single-stage and 240 ps/nm for a two-stage device are demonstrated with 40 Gb/s CS-RZ signal. It is shown that the device can operate with a minimum channel spacing of 200 GHz. For a two-stage device with inter-stage spectral filtering, simultaneous dynamic dispersion compensation (130 ps/nm for 1 dB penalty) and 2R regeneration (2 dB receiver sensitivity improvement) are demonstrated.     

The RP method: a new tool for the iterative solution of the nonlinear Schrodinger equation

An original approach to the solution of the nonlinear Schrodinger equation (NLSE) is pursued in this paper, following the regular perturbation (RP) method. Such an iterative method provides a closed-form approximation of the received field and is thus appealing for devising nonlinear equalization/compensation techniques for optical transmission systems operating in the nonlinear regime. It is shown that, when the nonlinearity is due to the Kerr effect alone, the order n RP solution coincides with the order 2n + 1 Volterra series solution proposed by Brandt-Pearce and co-workers. The RP method thus provides a computationally efficient way of evaluating the Volterra kernels, with a complexity comparable to that of the split-step Fourier method (SSFM). Numerical results on 10 Gb/s single-channel terrestrial transmission systems employing common dispersion maps show that the simplest third-order Volterra series solution is applicable only in the weakly nonlinear propagation regime, for peak transmitted power well below 5 dBm. However, the insight in the nonlinear propagation phenomenon provided by the RP method suggests an enhanced regular perturbation (ERP) method, which allows the first order ERP solution to be fairly accurate for terrestrial dispersion mapped systems up to launched peak powers of 10 dBm.     

A New Phase Acquisition Method of Address Code Utilizing the Combination of Logistic Map and BP Network

A novel phase acquisition method of code division multiple access (CDMA) address code is proposed in this paper. Based on the combination of chaotic nonlinear maps and backpropagation neural networks, this new approach can be applied to realize the phase acquisition of a CDMA address code, which plays an important role in wireless mobile communications. Both the theoretical analysis and computer simulation results show that it can increase the detection probability of the received signals compared with the conventional series acquisition method, which can improve the performance of the CDMA receiving system significantly.     

Reduction of fiber chromatic dispersion effects in fiber-wireless and photonic time-stretching system using polymer modulators

We have investigated the general characteristics of the power penalty due to the fiber chromatic dispersion effects in both fiber-wireless and photonic time-stretching systems. Two different modulation schemes have been demonstrated to reduce this penalty using our novel polymer modulators incorporating a multimode interference (MMI) structure. A single-sideband (SSB) modulator configuration has almost completely eliminated this penalty without a bandwidth limit. A double-sideband (DSB) modulator configuration with an appropriate quadrature bias has also shown significant improvement in bandwidth limitations for a given fiber link length.     

Three-level modulation scheme on standard fibers to extend thedispersion limit

Numerical simulations show that the impact of the pulse shape on the power penalty in intensity modulated systems with standard, nonlinear fibers is decisive. This can be used to define a three-level modulation scheme that makes use of the interaction between fiber dispersion and fiber nonlinearities. By adjusting the pulse shape and peak power in a three-level modulation scheme, the standard dispersion limit of 65 km at 10 Gb/s can be extended to 170 km. The control of the pulse shape can be accomplished in the electrical domain, and therefore the effects of fiber dispersion can be compensated electrically. This is very advantageous compared with dispersion compensation schemes in the optical domain     

Degree-of-polarization and eye-closure penalty associated with optical signals with orthogonal polarizations

We perform a systematic measurement of the degree-of-polarization (DOP) and eye-closure penalty for optical signals with orthogonal polarizations. We find that the symmetry of DOP is maintained for the orthogonal polarizations under both first and higher order polarization-mode dispersion (PMD), whereas the symmetry of eye-closure penalty is broken under second-order PMD. An orthogonal polarization pair can have large disparity of eye-closure penalty despite an identical DOP. We also demonstrate a novel approach to estimate the maximum eye-closure penalty asymmetry with three orthogonal polarizations on the Poincare/spl acute/ sphere.     

Parametric-gain approach to the analysis of single-channel DPSK/DQPSK systems with nonlinear phase noise

This paper presents a novel method based on a parametric gain (PG) approach to study the impact of nonlinear phase noise in single-channel dispersion-managed differentially phase-modulated systems. This paper first shows through Monte Carlo simulations that the received amplified spontaneous emission (ASE) noise statistics, before photodetection, can be reasonably assumed to be Gaussian, provided a sufficiently large chromatic dispersion is present in the transmission fiber. This paper then evaluates in a closed form the ASE power spectral density by linearizing the interaction between a signal and a noise in the limit of a distributed system. Even if the received ASE is nonstationary in time due to pulse shape and modulation, this paper shows that it can be approximated by an equivalent stationary process, as if the signal were continuous wave (CW). This paper then applies the CW-equivalent ASE model to bit-error-rate evaluation by using an extension of a known Karhunen-Loe/spl acute/ve method for quadratic detectors in colored Gaussian noise. Such a method avoids calculation of the nonlinear phase statistics and accounts for intersymbol interference due to a nonlinear waveform distortion and optical and electrical postdetection filtering. This paper compares binary and quaternary schemes with both nonreturn- and return-to-zero (RZ) pulses for various values of nonlinear phases and bit rates. The results confirm that PG deeply affects the system performance, especially with RZ pulses and with quaternary schemes. This paper also compares ON-OFF keying (OOK) differential phase-shifted keying (DPSK) systems, showing that the initial 3-dB advantage of DPSK is lost for increasing nonlinear phases because DPSK is less robust to PG than OOK.     

Suppression of intrachannel nonlinear effects using pseudoternary constrained codes

In this paper, a novel approach for suppressing the intrachannel nonlinear effects using pseudoternary constrained codes is proposed. A significant Q-factor improvement of up to 9.75 dB is obtained. The eye opening penalty (EOP) is also significantly improved by more than 10.24 dB.     

Optimization of Key Parameters in 622-Mb/s Amplitude Shift Keying Labeled 40-Gb/s Return to Zero Differential Phase Shift Keying Optical Switching Network

Optimized are the label extinction ratio and dispersion compensation of an optical label switching transmission system, which employs 40-Gb/s return to zero differential phase shift keying（RZ-DPSK） payload labeled with 622-Mb/s amplitude shift keying（ASK） control data. In our scheme, the receiver sensitivities of payload and label achieves -27.8 dBm and -33.5 dBm, respectively. After transmitted over 40 km, 60 km and 80 km single mode fiber（SMF）（with dispersion compensation） respectively, the payload can be recovered with no power penalty, while the label can be recovered with less than 2 dB penalty.     

Random Walk Guided Decap Embedding for Power/Ground Network Optimization

The reliability of power/ground networks is becoming significantly important in modern integrated circuits, while decap insertion is a main approach to enhance the power grid safety. In this brief, we propose a fast and efficient decap allocation algorithm, and adequately consider the leakage effect of decap. This approach borrows the idea of random walks to perform circuit partitioning and does subsequent decap insertion based on locality property of partitioned area, which avoids solving a large nonlinear programming problem in traditional decap optimization process. The optimization flow also integrates a refined leakage current model for decaps which makes it more practical. Experimental results show that our proposed method can achieve approximate 15 X speed up over the optimal budget method within the acceptable error tolerance. Also this algorithm only causes a few penalty area to compensate the leakage effect.     

Elimination of acoustic sensitivity in nonlinear optical loopmirrors

Acoustic disturbance is known to give rise to bit error rate (BER) floor when using the nonlinear optical loop mirror as a switch. Here, the acoustically induced penalty is investigated and >30 dB improvement in the acceptable acoustic sound pressure (50 Hz-5 kHz) is achieved by rewinding the loop fiber symmetrically. Only 1.5 dB sensitivity penalty was observed at a sound pressure of 110 dBA when using a nonlinear optical loop mirror (NOLM) containing 3.9 km of dispersion shifted fiber