In-line performance monitoring for RZ-DPSK signals using asynchronous amplitude histogram evaluation

The asynchronous amplitude histogram evaluation technique has been applied to in-line performance monitoring for return-to-zero differential phase-shift keying (RZ-DPSK) signals. The principle of operation was studied by simulation and experiment. It has been demonstrated that residual dispersion and signal optical signal-to-noise ratio can be obtained by Gaussian curve fitting of only one peak in the amplitude histogram of the RZ-DPSK signal.     

基于异步幅度抽样的高速光信号色散监测方法

针对目前异步幅度统计直方图（AAH）对色散监测范围小、灵敏度低的缺点,提出一种基于异步幅度抽样（AAS）的色散监测方法,定义无量纲色散监测参数G,将色散与其他损伤因子分离开。使用 OptiSystem9.0 软件搭建了200Gbps DP-16QAM 监测系统,在不同信噪比和占空比下进行色散监测仿真实验,探讨了信噪比和占空比对该方法的监测精度的影响,并对色散监测误差进行了分析。仿真结果表明基于该参数的色散监测方法受噪声因子影响小、精确度高,能实现在0~600 ps/nm 全范围内对色散的有效监测,为在更高阶调制信号的光纤通信系统中进行色散监测管理提供一定的参考。     

NRZ-DPSK and RZ-DPSK Signals Signed Chromatic Dispersion Monitoring Using Asynchronous Delay-Tap Sampling

In this paper, we demonstrated a signed chromatic dispersion (CD) monitoring method of 10 GHz nonreturn-to-zero differential phase-shift keying (NRZ-DPSK) and return-to-zero differential phase-shift keying (RZ-DPSK) signals by using asynchronous delay-tap sampling and an imperfect tuned delay interferometer. This method could monitor not only the value but also the polarity of residual CD. The demodulated signals show amplitude shoulders on the rising edge or the trailing edge with CD accumulation. Delay-tap sampling scatter plots could reflect this signal distortion by a unique characteristic and realize the signed CD monitoring. The monitoring range can be up to plusmn400 and plusmn720 ps/nm for NRZ-DPSK and RZ-DPSK signals, respectively. Simulation and experimental results are also proposed.     

Experimental demonstration of the maximum likelihood-based chromatic dispersion estimator for coherent receivers

We perform an experimental investigation of a maximum likelihood-based (ML-based) algorithm for bulk chromatic dispersion estimation for digital coherent receivers operating in uncompensated optical networks. We demonstrate the robustness of the method at low optical signal-to-noise ratio (OSNR) and against differential group delay (DGD) in an experiment involving 112 Gbit/s polarization-division multiplexed (PDM) 16-ary quadrature amplitude modulation (16 QAM) and quaternary phase-shift keying (QPSK).     

Experimental Investigation of Delay-Tap Sampling Technique for Online Monitoring of RZ-DQPSK Signals

We experimentally demonstrate optical performance monitoring of 20-Gb/s return-to-zero differential quadrature phase-shift keying signals using an asynchronous delay-tap sampling technique. This method allows online monitoring of accumulated chromatic dispersion in the range from $-$600 to $+$600 ps/nm. We also show evaluation of optical signal-to-noise ratio at a level of 6.7 dB and monitor operation at input power of $-$ 16 dBm.      

All-Optical Chromatic Dispersion Monitoring for Phase-Modulated Signals Utilizing Cross-Phase Modulation in a Highly Nonlinear Fiber

We propose and experimentally demonstrate an all-optical chromatic dispersion (CD) monitoring technique for phase-modulated signals utilizing the cross-phase-modulation effect between the input signal and the inserted continuous-wave probe. The probe's optical spectrum changes with the accumulated CD on the input signal, indicating that the optical power variations can be measured for monitoring. The experimental results show that this technique can monitor up to 120 ps/nm of CD for a 40-Gb/s return-to-zero differential phase-shift keying (RZ-DPSK) transmission system, with the maximum measured optical power increment of 16.5 dB. The applicability of this monitoring technique to higher bit-rate phase-modulated signals, such as 80-Gb/s RZ differential quadrature phase-shift keying and 80-Gb/s polarization-multiplexed RZ-DPSK, is also investigated via simulation.      

OSNR Monitoring Technique for DPSK/DQPSK Signals Based on Self-Heterodyne Detection

We describe a new method for monitoring the “in-band” optical signal-to-noise ratio (OSNR) of differential phase-shift-keying (DPSK) and differential quadrature phase-shift-keying (DQPSK) signals. This technique estimates the OSNR by analyzing the radio frequency spectrum obtained by the self-heterodyne detection. The results show that the performance of the proposed technique is not sensitive to the effects of chromatic dispersion and polarization-mode dispersion. In addition, this technique can be used for monitoring the polarization-scrambled signals. For a demonstration, we measure the OSNR of the polarization-scrambled 10-Gb/s DPSK and 20-Gb/s DQPSK signals in a 640-km-long transmission link.      

Optical Signal-to-Noise Ratio Estimation Using Reference Asynchronous Histograms

This paper presents and experimentally demonstrates a novel method for the estimation of optical signal-to-noise ratio (OSNR) based on the comparison of an asynchronous histogram of the signal under analysis with a reference asynchronous histogram. The latter is acquired from the signal under analysis at a calibration stage. The proposed method allows the use of optical amplification to increase the sensitivity of the optical monitoring system (OMS) by a factor 20 dB, when using an erbium doped fiber preamplifier. In addition, the use of a semiconductor optical preamplifier, initially designed for nonlinear operation at 2.5 Gb/s is used in the OMS to preamplify 40-Gb/s signals, achieving a sensitivity gain of 10 dB. It will be experimentally demonstrated that the proposed method is applicable to 40-Gb/s nonreturn to zero (NRZ) signals arbitrarily degraded by group velocity dispersion (GVD). Furthermore, accurate monitoring of the OSNR of return-to-zero (RZ) signals will also be possible using a simple RZ-to-NRZ converter based on narrow-band optical filtering within the OMS. The proposed method also allows estimating of the GVD-induced OSNR penalty between the signal under analysis and the signal at the calibration stage.     

Chromatic dispersion dependence of asynchronous amplitude histogram evaluation of NRZ signal

This paper presents the chromatic dispersion dependence of the averaged Q-factor method based on an evaluation of an asynchronous amplitude histogram. We analyze nonreturn-to-zero optical signals using a numerical simulation based on several parameters for signal quality monitoring. The results are compared with the optical signal-to-noise ratio dependence of the method and the possibility of distinguishing the origins of the bit-error-rate distortion is discussed.     

OSNR Monitoring Method for OOK and DPSK Based on Optical Delay Interferometer

We describe a simple method to measure the optical signal-to-noise ratio (OSNR) of on-off-keying (OOK) and differential phase-shift-keying (DPSK) signals by using an optical delay interferometer (ODI) having a sinusoidal and tunable passband. This OSNR monitoring method is independent of chromatic dispersion, polarization-mode dispersion, and noise polarization. We show experimentally that accurate OSNR measurements are made for a 10-Gb/s OOK signal by using a 1-bit ODI and a 40-Gb/s DPSK signal by using a partial-bit ODI with the OSNR ranging from 5 to 25 dB.     

Joint Effect of MLSE and Receiver Filters Optimization on Dispersion Robustness of IMDD, DPSK, DQPSK, and Duobinary Modulation

We analyze the effectiveness of a 32-state maximum-likelihood sequence-estimation (MLSE) receiver on chromatic dispersion robustness of optical transmission based on several binary modulation formats: intensity modulation direct detection, differential phase-shift keying, and duobinary line coding. Multilevel differential quadrature phase-shift keying modulation is also analyzed using a four-state 2-bit/symbol joint MLSE processor. For all modulation formats, receiver filters are optimized together with the use of the MLSE technique.     

Simultaneous Demodulation and Clock-Recovery of 40-Gb/s NRZ-DPSK Signals Using a Multiwavelength Gaussian Filter

We demonstrate a novel optical circuit that has the potential of simultaneous demodulation and all-optical clock-recovery of 40-Gb/s wavelength-division-multiplexing nonreturn-to-zero differential phase-shift keying (NRZ-DPSK) signals. A key device of the circuit is an ad hoc periodic fiber Bragg grating filter that simultaneously demodulates the input signals and seeds a series of clock recovery circuits. We report the complete characterization of the proposed scheme in the whole-band using a tunable transmitter. The DPSK demodulated signals show enhanced resilience to chromatic dispersion with respect to the usual NRZ _ON-OFF keying format. On the other hand, the recovered clock signals are very stable and have around 200-fs root-mean-square time jitter.     

Chromatic dispersion monitoring technique using optical asynchronous sampling and double sideband filtering

This paper introduces a new chromatic dispersion monitoring technique using optical asynchronous sampling and double sideband filtering. We present simulation results that relate chromatic dispersion with the ratio between the maximum amplitude of the signal and the average optical output power, yielding in a method which is power transparent. We also show theoretical investigation and theoretical results that prove the approach used in this paper.     

100Gb/s RZ-ODQPSK实现方法性能比较

光差分正交移相键控(0DQPSK)调制格式在高速光纤通信系统中有着巨大的应用潜力.文章给出了高速0DQPSK调制格式的三种实现方式(串联调制、并联调制和双驱动单调制器调制),在建立仿真模型的基础上,对光信噪比(0SNR)、色散、偏振模色散(PMD)以及光纤非线性四个方面的容纳能力进行了对比、分析和研究.     

A novel chromatic dispersion monitoring technique for 16/64-QAM system based on asynchronous amplitude histogram

A novel chromatic dispersion (CD) monitoring technique based on asynchronous amplitude histogram (AAH) for higher order modulation formats is proposed in this paper. Without demodulating the signal, in the monitoring scheme, the received signal is sampled asynchronously, and thus clock information and high-speed sampling units are unnecessary, resulting in low cost and high reliability. Simulations of CD monitoring technique for non-return-to-zero/return-to-zero (NRZ/RZ) 16- and 64-quadrature amplitude modulation (QAM) systems with different optical signal-to-noise ratios (OSNRs) and duty cycles are investigated, and the tolerance of the scheme is also discussed. Simulation results show that the presented CD monitoring technique with high sensitivity can be applied to monitor the residual CD of a transmission link in the next-generation optical networks.     

用偏振模色散模拟器加偏振片实现带内光信噪比检测

提出了一种基于偏振模色散(PMD)模 拟器加偏振片的带内检测光信噪比(OSNR)的方法,理论分析了检测方 法的工作原理,证明了方法不受光纤链路色散和PMD的影响,并且与信号偏振态 、调制格式及传输 速率无关。测试结果表明:在9dB到34dB的测量范围 内,本文检测方 法的测量误差在0.5dB内;在1dB的测量误差范围内,对偏振相关损 耗(PDL)的容忍范围为1dB。     

A novel chromatic dispersion monitoring method for 1 024 QAM fiber-optic system based on asynchronous amplitude sampling

A new chromatic dispersion (CD) monitoring method is proposed, and the CD monitoring is achieved on the whole range of 0—600 ps/nm. A dual-polarization (DP)-1 024 quadrature amplitude modulation (QAM) 400 Gbit/s CD monitoring system is built using OptiSystem14.0 software. With different optical signal to noise ratio (OSNR) values, different filter bandwidths or different duty cycles, the simulations are carried out. The simulation results show that this new CD monitoring method can be less affected by noise and has a high tolerance for different filter bandwidths. At the same time, this method can do effective CD monitoring on the signal with duty cycle greater than 80%. A high sensitivity in 0—200 ps/nm can be achieved using this CD monitoring method. The technique supports a wide range of data traffic and enhances operation flexibility of optical networks. This work has been supported by the National Natural Science Foundation of China (Nos.61274121 and 61574080). E-mail:zhub@njupt.edu.cn      

Combining DPSK and duobinary for the downstream in 40-Gb/s long-reach WDM-PONs

We propose and demonstrate combining differential phase-shift keying (DPSK) and duobinary transmission for the downstream in 40-Gb/s long-reach wavelength division multiplexed-passive optical networks (WDM-PONs) in order to provide robust transmission performance in the backhaul section and simple detection at the ONUs. DPSK is deployed in the trunk span as it provides stronger robustness to fiber nonlinearity. Duobinary is used in the access span where its higher chromatic dispersion tolerance relieves the need for dispersion compensation. All-optical multichannel modulation format conversion from DPSK to duobinary is realized in the local exchange in a single delay interferometer to reduce system cost. Single and multi-channel 80-km long-reach DPSK transmission and up to 5-km duobinary access transmission are experimentally demonstrated at 40 Gb/s. The proposed approach shows great potential for future high data rate optical access networks.     

A Bidirectional WDM/TDM-PON Using DPSK Downstream Signals and a Narrowband AWG

We present an innovative architecture to realize a single feeder bidirectional amplified wavelength-division-multiplexing/time-division-multiplexing passive optical network based on modified nonreturn-to-zero differential phase-shift keying (DPSK) downstream signals at 20 Gb/s and a narrowband arrayed waveguide grating (AWG). The AWG plays at the same time the role of channel distributor, simultaneous demodulator for all DPSK channels, and eliminates the need for chromatic dispersion compensation. A saturated semiconductor optical amplifier (SOA) provides bidirectional amplification to compensate the splitter losses. The remodulated upstream signals are obtained at 1 Gb/s by means of a reflective SOA. Experimental results show error-free operation on both downstream and upstream signal.     

A novel chromatic dispersion monitoring method for 400 Gbit/s 256 QAM fiber-optic system based on asynchronous amplitude sampling

A novel chromatic dispersion (CD) monitoring technique based on asynchronous amplitude sampling (AAS) is proposed for a higher modulation format and higher rate system. The dispersion and other impairment factors can be separated with the definition of monitoring parameter M. A 400 Gbit/s 256 quadrature amplitude modulation (QAM) system is built using Optisystem13.0 beta software. Simulations of CD monitoring technique for different bandwidths of sampling Gaussian filter, optical signal to noise ratios (OSNRs) and duty cycles are investigated, and the tolerance is also discussed. Simulation results show that the method can be less affected by noise, and a higher accuracy of 600 ps/(nm.km) can be achieved. The technique supports a wide range of data traffic and enhances operation flexibility of optical networks.