Performance of MSE configured PLC optical equalizers for chromatic dispersion compensation

In this letter, we propose a mean square error (MSE) strategy to control a planar lightwave circuit (PLC) optical equalizer. We show by simulation that MSE is a suitable criterion to exploit the PLC programmability for realizing an adaptive optical equalizer. When controlled through the MSE criterion, a PLC equalizer for chromatic dispersion compensation performs better than with other control strategies and turns out to be effective even with few component elements.     

Adaptive chromatic dispersion compensation using higher orderpolarization-mode dispersion

The novel adaptive technique for compensating the fiber chromatic dispersion in high-speed optical-fiber transmission by using the higher order polarization-mode dispersion generated when two pieces of polarization-maintaining fibers are connected. Changes in signal wavelength and polarization state are tracked by an automatic polarization controller, which simultaneously adjusts an amount of chromatic dispersion to maximize the eye opening of the received signal. Experiments showed that the dispersion tolerance of a 10-Gb/s nonreturn-to-zero system could be increased about 2.8-fold, from 1000 to 2850 ps/nm     

Design of a transversal equalizer for electronic dispersion compensation in optical communication links

A programmable transversal equalizer for electronic dispersion compensation(EDC) in optical fiber communication systems is developed.Based on the SiGe technology with a cut-off frequency of 80 GHz,the equalizer consists of 6 seriesparallel amplifiers as delay units and 7 Gilbert variable gain amplifiers as taps,which ensure that the equalizer can work at the bit rate of 10 Gb/s.With different tap gains,the forward voltage gain of the transversal equalizer varies,which demonstrates that the equalizer has various filtering characteristics such as low pass filtering,band pass filtering,band reject filtering,and notch filtering,so it can effectively simulate the inverse transfer function of dispersive channels in optical communications,and can be used for compensating the inter-symbol interference and other nonlinear problems caused by dispersion.The equalizer(including pads) occupies an area of 0.40 mm × 1.08 mm,and its total power dissipation is 400 mW with 3.3 V power supply.     

Subband equaliser for chromatic dispersion of optical fibre

An oversampled subband equaliser is designed for chromatic dispersion of singlemode optical fibre. The signal of each subband is equalised individually and delayed to align with other subbands. From simulation, the overall number of equaliser taps is approximately reduced by the upsampling ratio.     

Exact compensation for both chromatic dispersion and Kerr effect ina transmission fiber using optical phase conjugation

We propose a new method to compensate exactly for both chromatic dispersion and self-phase modulation in a transmission fiber, where the light intensity changes due to fiber loss and amplifier gain. This method utilizes optical phase conjugation (OPC). The pulse shape is precompensated before OPC by transmission through a fiber with large dispersion. A computer simulation demonstrates effective compensation for waveform distortion in a 40 Gb/s NRZ intensity-modulated light transmission     

Phased-only sampled fiber Bragg gratings for high-channel-count chromatic dispersion compensation

Binary and multilevel phase-only sampling functions are proposed for the sampled fiber Bragg gratings (FBGs) with high channel count, which require significantly less refractive-index modulation than that does the sampled grating with amplitude sampling. The design using the new simulated quenching optimization with temperature rescaling results in high channel uniformity and minimum energy in the out-of-band channels. The technique can be applied to the sampled FBGs with very high channel count. A five-channel nonlinearly chirped multilevel phase-only sampled FBG for tunable chromatic dispersion compensation is demonstrated.     

基于半导体光放大器色度色散补偿的研究

提出了一种新型的多波长变换方案.该方案包括一个半导体光放大器(SOA)和一个光带通滤波器(OBF).利用SOA的四波混频效应(FWM)和交叉增益调制(XGM)效应,通过调节SOA的偏置电流和信号光及抽运光的强度,可以对进入SOA的光信号实现多波长变换.实验中,实现了10Gb/s的RZ码的多路波长变换.并且对SOA中的双折射及非线性偏振旋转进行了实验研究.     

All-fiber devices for chromatic dispersion compensation based onchirped distributed resonant coupling

We review the principle of operation and characteristics of all-fiber devices for dispersion compensation based on chirped distributed resonant coupling. These devices are the chirped Bragg grating, the chirped intermodal coupler, and the tapered two-dissimilar-core fiber. We discuss the use of a figure of merit to characterize equalizing filters. Based on a specific example, filter responses are computed and their performance is evaluated with a numerical simulation of an optical fiber link. Finally, design constraints are discussed     

Bi-end dispersion compensation for ultralong optical communicationsystem

Bi-end dispersion compensation (DC) for ultralong nonreturn-to-zero (NRZ) optical transmission system is studied. Both the loss and dispersion of the transmission fiber are periodically compensated. Two dispersive elements are placed at the input and output ends of a compensation period, respectively, to compensate for fiber dispersion. The pulse compression owing to self-phase modulation (SPM) can be adjusted by the compensation ratios of the dispersive elements at the two ends of a compensation period. Therefore, the pulse compression can be optimized and the system performance can be improved to compare with the system with either pre- or postdispersion compensation. The rules to design the system are considered. The transmission system of 10-Gb/s bit rate, 9000-km transmission distance, and 100-km compensation period is taken as an example. The second-order fiber dispersion is assumed to be completely compensated. Wave equation is numerically solved to study the system performance which is represented by Q factor. The relations of several system parameters and Q factor are studied. The system parameters include the compensation ratios of the dispersive elements at the two ends of a compensation period, dispersion of transmission fiber, signal power, and the compensation ratios of third-order fiber dispersion. If the third-order fiber dispersion cannot be completely compensated, it is found that one can use a higher signal power to improve the system performance     

基于啁啾光纤光栅色散补偿问题的思考

色散已成为光纤长距离、高速率通信中的巨大障碍.鉴于色散补偿光纤插入损耗大、易引入非线性效应等缺点,文章采用啁啾光纤光栅对系统进行色散补偿,克服了以上不足.通过分析啁啾光纤光栅色散补偿的原理,结合理论分析,提出在多通道波分复用系统中使用啁啾光纤光栅,以实现长距离无中继传输.     

Integrated dispersion slope equalizer of AWG-based optical CDMA for radio-over-fiber transmissions

Chromatic dispersion from optical fiber is the most important problem that produces temporal skews and destroys the rectangular structure of code patterns in the spectra-amplitude-coding optical code-division multiple-access (SAC-OCDMA) system. Thus, the balance detection does not work perfectly and the system performance will be degraded. In order to improve the distortion, we apply cascaded Mach–Zehnder interferometers (MZIs) to design a dispersion slope equalizer for the SAC-OCDMA system integrated with arrayed-waveguide grating (AWG) router coder. The dispersion slopes of a cascaded MZI compensator could be adjusted by the arm length differences of MZIs and be complementary with the fiber links. In this study, we present a set of length differences for 10 km long single-mode fiber (SMF) and verify the compensation scheme by relative delay time slope and signal-to-interference ratio (SIR). The dispersion slope equalizer with perfect complementary slope successfully compensates the dispersion from SMF and the system performance with dispersion slope equalizer is highly improved.     

Improved all optical chromatic dispersion monitoring method for WDM systems

In this paper we propose an improved all optical chromatic dispersion (CD) monitoring method applicable to wavelength division multiplexing (WDM) systems with intensity or phase modulation format. This method can operate over a much larger bandwidth and CD monitoring range and is insensitive to optical signal-to-noise ratio (OSNR) and polarization mode dispersion (PMD). These improvements are achieved by utilizing a wavelength tunable laser as the probe to maintain the appropriate phase-matching condition and a loop-back controlled tunable CD compensator to discriminate CD distortions from PMD and OSNR influences. Numerical simulations show that by this method the operational bandwidth and CD monitoring range can be expanded to cover C + L bands and ±1600 ps/nm, respectively, for different modulation formats and the sensitivity is higher than the other methods proposed before.     

Effects of chromatic dispersion on optical coherent-detection systems

Chromatic dispersion induces to a phase-modulated optical signal a constand phase rotation that was never included in most previous studies. When the constant phase shift is removed by a phase-locked loop, the dispersion tolerance of a coherent-detection system is increased. The dispersion tolerance of phase-shift keying (PSK) signal is compared with differential PSK (DPSK) signals by numerical simulation and experimental measurement. Contrary to conventional belief, PSK signal has larger dispersion tolerance than DPSK signal.     

Compensation of fibre chromatic dispersion in optical heterodynedetection

Compensation of fibre chromatic dispersion in coherent optical fibre transmission is demonstrated. The chromatic dispersion of a 70 km single-mode fibre with 1.3 μm zero dispersion wavelength is compensated for using a microstrip line equaliser in the intermediate frequency band. Amplitude distortion due to fibre chromatic dispersion at 1.55 μm wave-length is reduced to below 2.5 % with the equaliser     

Improved chromatic dispersion tolerance for optical duobinary transmission using coherent detection

The impact of chromatic dispersion on the complex electric field of an optical phase-coded duobinary signal is investigated through numerical simulation. Dispersion causes distortion and rotation of the optical constellation with increasing transmission distance, leading to eye closure of the received signal. When direct detection is employed, rapid eye closure starts after approximately 213 km. Employing coherent detection increases this dispersion limit by 70 km.     

Novel optical line codes tolerant to fiber chromatic dispersion

A novel family of optical line codes to counteract the effects of a dispersive fiber is presented. The performance of the first code in the family, referred to as order-1 code, is analytically evaluated and compared to that of the duobinary and phased amplitude-shift signaling (PASS) codes, which are a modified form of duobinary proposed by Stark et al. (1999). The order-1 line code turns out to be very robust to chromatic dispersion and, for a given penalty, allows the bridging of a distance 1.5 times (or more) greater than duobinary. The novel family of codes was conceived by exploiting the finding that, approximately, a very dispersive fiber turns an input pulse into the form of its Fourier transform seen in the time domain. Higher-order codes allow the bridging of larger distances if combined with appropriate chirping     

Improved phase delays for optical compensation of polarization-mode dispersion

We present numerical simulations of the average frequency dependence of the differential phase delays (DPDs) that are introduced by polarization-mode dispersion (PMD) between the signal components transmitted in the two principal states of polarization of the fiber. Our study confirms that the first-order approximation of frequency-independent DPDs is valid for fibers that normally do not require PMD compensation. However, for fibers with larger mean differential group delays (DGDs), the first-order approximation tends to overestimate the mean DPDs for any given DGD. Based on our numerical results, we derive closed-form approximations for the frequency and group-delay dependence of the mean DPD conditioned on a given DGD and show that these more accurate DPDs may significantly improve the performance of optical PMD compensators.     

光脉冲色散展宽的光纤光栅透射补偿

分析讨论了利用变迹均匀光纤光栅的透射色散对光纤中传输的脉冲色散展宽进行压缩补偿。给出了啁啾高斯脉冲的补偿原理,计算了相关的曲线和光纤光栅的相应参数。通过选择光纤光栅的不同参数,可以使色散展宽的高斯脉冲经光栅后几乎完全恢复原状或受到进一步压缩。     

偏振模色散自适应补偿的设计与实现

分析研究了偏振模色散对系统传输的影响和补偿原理,并设计了以TMS320C6711DSK为核心、通过PAM10偏振计、偏振控制计和可变时延线构成的四自由度二阶PMD补偿器,对高速光纤通信中的偏振模色散进行动态补偿实验.