Optical Performance Monitoring Using Artificial Neural Network Trained With Asynchronous Amplitude Histograms

Chromatic dispersion (CD) in single-mode optical fibres limits the maximum transmission distance of digital optical transmission systems at 10 and 40 Gb/s. It can be eliminated by a tunable CD compensator, provided that the residual dispersion is detected, including its sign. A low-cost hardware implementation of a signed online CD detection scheme is reported. It is based on synchronous detection of frequency modulation (FM)-induced arrival time modulations in the clock recovery phase locked loop (PLL) of a 2×10 Gb/s return-to-zero differential quadrature phase shift keying (RZ-DQPSK) optical receiver. The RZ-DQPSK transmitter laser is modulated by a synthesised 4.732 MHz sinusoidal signal. This results in ≃1% (rms) intensity modulation and an optical FM with ≃105 MHz (rms) deviation. Low-cost components were used to build a synchronous detector for the arrival time signal that yields the fibre CD, including its sign. The total measurement interval is ≃84 µs. The sign of the CD is detected within a range of ±700 ps/nm. This range is limited by the locking range of the clock recovery PLL. The CD measurement readout is fairly linear over the range ±360 ps/nm.

Cost-effective OSNR monitoring with large chromatic dispersion tolerance using random forest for intermediate nodes

Optical signal-to-noise ratio (OSNR) monitoring is essential to both the operation of reliable and reconfigurable network and the supply of high quality-of-service. Recently, deep learning technique has been proposed for the implementation of OSNR monitoring. However, the potential of deep learning technique for OSNR monitoring has not been fully exploited in terms of the monitoring accuracy and robust operation. Here, we propose an OSNR monitoring scheme with high accuracy and short response time using the long short-term memory neural network (LSTM-NN). The use of LSTM-NN is helpful to identify the relationship between the time-varied data and corresponding OSNR without manual feature extraction. We investigate the optimal number of time steps for the LSTM-NN-based OSNR monitoring and the monitoring accuracy with respect to various modulation formats with variable baud-rates. Finally, we implement an experimental verification for 34.94-GBd polarization division multiplexing-16 quadrature amplitude modulation signal, achieving a mean absolute error of 0.05 dB over the OSNR range from 15 to 25 dB. The advantages of LSTM-NN-based OSNR monitoring include high accuracy and smart response, which is ideal for future agile optical network.

Recently, degree of polarization (DOP) of light has been utilized as a parameter to monitor optical signal-to-noise-ratio (OSNR). However, in the presence of polarization-mode dispersion (PMD), when using DOP to determine OSNR, OSNR is always underestimated due to the depolarization effect induced by PMD. In this paper, we propose and experimentally demonstrate a simple PMD-insensitive OSNR monitoring technique based on DOP measurement. By the assistance of the transmitter-side polarization scrambling, the in-service OSNR parameter can be accurately derived from the measured maximum DOP value within the polarization scrambling period, which is immune to PMD effect. The monitoring performance is experimentally evaluated by statistical method at OSNR of 25 dB. Experimental results show that OSNR monitoring with about 1-dB standard deviation can be achieved in a 10-Gb/s NRZ-OOK system with DGD varying from 0 to 80 ps.

OSNR monitoring technique based on multi-order statistical moment method and correlation function for PM-16QAM in presence of fiber nonlinearities

In this paper, the authors derive the moment generating function (MGF) of the decision variable for a practical optical differential quadrature phase shift keying (DQPSK) receiver affected by phase noise and the amplifier spontaneous emission noise. The effect of the different optical filters, Gaussian, Fabry-Peacuterot (FP), and optical integrator, on the phase noise is examined. Using the saddle point approximation, the authors obtain numerically the bit error rate (BER) for the above system, as a function of the optical-signal-to-noise ratio (OSNR) and the source linewidth. The model is found to agree with previous published simulation results and the Monte Carlo simulations presented in this paper. The authors also calculate the BER floors for DQPSK inflicted by the phase noise and compare its performance with differential phase shift keying (DPSK). Finally, the authors examine the effect of interferometric demodulation on the relative intensity noise (RIN) spectra and the impact on the DQPSK system performance. In particular, the authors examine the influence of system dispersion on the receiver sensitivity

Optical communication transmission systems improvement based on chromatic and polarization Mode dispersion compensation simulation management

This paper depicts a modified return-to-zero differential quadrature phase shift keying (RZ-DQPSK) modulation scheme. A simulative analysis has been performed for an optimization of the proposed scheme. The analysis has also been extended for two different types of commercial fibers; standard single-mode fiber (SSMF) and true wave-reduced slope (TW-RS) fiber to report the similar qualitative performance characteristics. For the sake of better understanding of the proposed modified carving signal RZ-DQPSK scheme, optical spectrum and eye pattern plots are also investigated.

An Optical Performance Monitoring Model Based on RBFANN Trained with Eye-Diagram

We review our recent achievements in the optical performance monitoring techniques such as the optical phasor monitor and optical signal-to-noise ratio (OSNR) monitor developed for differential phase-shift-keyed (DPSK) and quaternary PSK (DQPSK) signals. The optical phasor monitor is a tool that can measure the in-phase and quadrature components of the optical field of the phase-modulated signal and display the measured results on the complex plane as a phasor. We implement such a phasor monitor by using an adjustment-free differential-phase demodulator composed of a 120-degree optical hybrid (which can be realized simply by using a conventional 3x3 optical coupler), and demonstrate its plug-and-play (i.e., phase-adjustment free and wavelength/polarization-independent) operation experimentally. We also show that the proposed phasor monitor is well suited for the use in the diagnosis of DPSK/DQPSK. The OSNR monitoring is another important function to evaluate the signal quality as well as the condition of the transmission link. We have recently proposed a new technique for monitoring the 'in-band' OSNR of DPSK/DQPSK signals. This technique estimates the OSNR by analyzing the radio frequency (RF) spectrum obtained by the self-heterodyne detection. In this paper, we briefly explain its operating principle and show the experimental results. Using this technique, we could accurately monitor the OSNR of the 10-Gb/s DPSK and 20-Gb/s DQPSK signals in a 640-km long transmission link. The results also show that the performance of the proposed technique is not sensitive to the effects of chromatic dispersion and polarization-mode dispersion.

Differential phase-shift keying (DPSK) has been widely implemented and developed in high-speed optical communication systems. The low error rate detection at high access rate is one of the considerable issues in practical engineering application. Balanced detection based on fiber Mach-Zehnder delay interferometer (MZDI) is the typical optical DPSK signal detecting method. It requires that the free spectrum range (FSR) of the MZDI equals the reciprocal of symbol period of the DPSK signal. For the reasons of ambient temperature variation and nonlinear phase noise, a dynamic frequency offset always exists between the FSR and the reciprocal of symbol period. That may introduce some optical signal-to-noise ratio (OSNR) costs and fault detections. Therefore, it is significant to inhibit the frequency offset on DPSK detection. In this paper, firstly, we discuss the effects of frequency offset on DPSK detection, and realize the conclusion that frequency offset is virtually equivalent to an additional phase difference between adjacent symbols. Secondly, through simulation, we analyze the feasibility of DPSK detection in the presence of a definite range of frequency offset, and present the quantitative computation of effective coverage, duty cycle, and optimal sampling time of symbol interference. Some issues which should be considered in practical implementation are also discussed. Finally, according to the relationship among phase difference, temperature and voltage, we propose a phase difference compensation scheme which can automatically adjust the voltage for optimal detections, and dynamically track the changing of ambient temperature and nonlinear phase noise. Furthermore, we ascertain the performance of the voltage requested for implementing the scheme. The scheme can be also developed to quadrature phase-shift keying (QPSK) and differential QPSK (DQPSK) modulation situations.

The reference optical spectrum (ROS) based in-band optical signal-to-noise-ratio (OSNR) monitoring methods are accurate and inherently robust to fiber chromatic dispersion and polarization mode dispersion. They are also very simple and suitable to be deployed ubiquitously in the transmission system. In this paper, a ROS-based in-band OSNR monitoring method is proposed for erbium doped fiber amplifier (EDFA) amplified multispan dense wavelength division multiplexing systems with cascaded filtering effect (CFE) caused by cascaded add-drop filters or wavelength selective switches. In such systems, the optical signal as well as the optical noise may experience significant CFE making the ROS-based methods proposed before ineffective. The new method solves this problem and performs very well for OSNR in the range of 10–30 dB when the fiber nonlinear effect and nonideal filtering effect are present. The OSNR monitor based on the new method is also more convenient to use as only one-time calibration is required when used at different monitoring locations along the optical link.

Optical performance monitoring (OPM) becomes an inviting topic in high speed optical communication networks. In this paper, a novel technique of OPM based on a new elaborated computation approach of singular spectrum analysis (SSA) for time series prediction is presented. Indeed, various optical impairments among chromatic dispersion (CD), polarization mode dispersion (PMD) and amplified spontaneous emission (ASE) noise are a major factors limiting quality of transmission data in the systems with data rates lager than 40 Gbit/s. This technique proposed an independent and simultaneous multi-impairments monitoring, where we used SSA of time series analysis and forecasting. It has proven their usefulness in the temporal analysis of short and noisy time series in several fields, that it is based on the singular value decomposition (SVD). Also, advanced optical modulation formats (100 Gbit/s non-return-to zero dual-polarization quadrature phase shift keying (NRZ-DP-QPSK) and 160 Gbit/s DP-16 quadrature amplitude modulation (DP-16QAM)) offering high spectral efficiencies have been successfully employed by analyzing their asynchronously sampled amplitude. The simulated results proved that our method is efficient on CD, first-order PMD, Q-factor and OSNR monitoring, which enabled large monitoring ranges, the CD in the range of 170-1700 ps/nm.Km and 170-1110 ps/nm.Km for 100 Gbit/s NRZ-DP-QPSK and 160 Gbit/s DP-16QAM respectively, and also the DGD up to 20 ps is monitored. We could accurately monitor the OSNR in the range of 10-40 dB with monitoring error remains less than 1 dB in the presence of large accumulated CD.

Polarization mode dispersion (PMD), polarization dependent loss (PDL) and chromatic dispersion (CD) of fiber optic components and fiber transmission links are key issues in fiber optical communication. Of interest are the respective static values as well as their variations in time which might be due to environmental changes or due to rerouting. Basic aspects will be briefly addressed, a variety of standard and state-of-the-art characterization and monitoring techniques will be reviewed and recent experimental results will be presented.

In this paper, based on the proposed simulation model, the impact of dispersion on the systems performance in 160Gbit/s optical communication systems is detailedly discussed. As chromatic dispersion (CD) and polarization mode dispersion (PMD) are caused by different physical effect, the effects of CD and PMD on systems performance are also analyzed separately in the paper. At first, the CD and CD slope tolerance in 160Gbit/s systems are carefully simulated and analyzed, at the same time, self-phase modulation (SPM) effect is also discussed in this part, and the result shows that for 1dB eye-opening penalty, CD tolerance would be about ±3.1ps/nm and CD slope and SPM also all seriously limit the transmission distance of systems. Furthermore, the impact of PMD on systems property are discussed by virtue of statistical method, and result shows that PMD tolerance of 160Gbit/s is 0.7ps with the outage probability of 10^-5 of 1dB eye-opening penalty and it will increase to 1.8ps for the first-order PMD compensated systems. These results show that CD, CD slope, PMD and SPM all are key challenges in 160Gbit/s systems.