Polarization Mode Dispersion Values Research Articles

Machine Learning-Based Optical Performance Monitoring for Super-Channel Optical Networks

In this paper, and for the first time in literature, optical performance monitoring (OPM) of super-channel optical networks is considered. In particular, we propose a novel machine learning OPM technique based on the use of transformed in-phase quadrature histogram (IQH) features and support vector regressor (SVR) to estimate different optical parameters such as optical signal-to-noise ratio (OSNR) and chromatic dispersion (CD). Two transformation methods, the two-dimensional (2D) discrete Fourier transform (DFT) and 2D discrete cosine transform (DCT), are applied to the IQH to extract features with a considerably reduced dimensionality. For the purpose of simulation, the OPM of a 7 × 20 Gbaud dual-polarization–quadrature phase shift keying (DP-QPSK) is considered. Simulations reveal that it can accurately estimate the various optical parameters (i.e., OSNR and CD) with a coefficient of determination value greater than 0.98. In addition, the effectiveness of proposed OPM scheme is examined under different values of polarization mode dispersion and frequency offset, as well as the utilization of different higher order modulation formats. Moreover, proof-of-concept experiments are performed for validation. The results show an excellent matching between the simulation and experimental findings.

Birefringence and Polarization Mode Dispersion Phenomena of Commercial Optical Fiber in Telecommunication Networks

The development of optical fibers from attenuation and absorption of fiber material for efficiency and quality has produced several positive results. However, several natural negative factors and environmental errors cause problems such as birefringence and dispersion mode variations. This article therefore proposed a simulation of birefringence and polarization mode dispersion (PMD) to investigate the emergence of interference and efforts towards finding a solution to the problem of optical fiber. Moreover, a single-mode fiber was investigated at the core refractive index and cladded with a core radius and fixed sample for a wavelength of infrared regimes. The performance of fibers was also evaluated through the determination of the PMD value of the fibers. The simulation results showed the difference observed in birefringence produced the power affecting the output. Meanwhile, the PMD also produced the light waves discovered to be experiencing widening pulses in the cladding.

Separability of Histogram Based Features for Optical Performance Monitoring: An Investigation Using t-SNE Technique

In this paper, we study the separability of the commonly used features to monitor the performance of optical signal in coherent optical systems. Specifically, our study focuses on the histogram-based features; the asynchronous amplitude histogram (AAH) and the two-dimensional extension of AAH, which we call IQ histogram (IQH). We investigate the conditions under which the optical channel impairments can be monitored. This study utilizes a dimensionality reduction technique, known as the t-distribution stochastic neighbor embedding (t-SNE). Using t-SNE, we show that under certain conditions the histogram-based features cannot be used to distinguish between the high and low impairment effects, rendering these features useless for certain cases, regardless of the type or complexity of the implemented impairments’ estimator/classifier. Extensive simulations results have been conducted to investigate single and multiple impairments conditions and the performance of histogram-based features in each case. The results show that both AAH and IQH can be used for monitoring all types of single Impairment except phase noise in case of AAH. Moreover, under multiple impairments conditions, polarization mode dispersion values can be monitored to some extent, while it is difficult to monitor optical signal-to-noise ratio and chromatic dispersion values especially in the case of concurrent presence of more than two impairments. The results of these investigations are validated by providing a quantitative measure that ties their usefulness to the actual monitoring performance through the estimation of channel impairments under different conditions using linear support vector machine (SVM) regression. It has been found that there is a match to a great extent between the separability investigation using t-SNE and estimation results obtained using SVM.

Adaptation of transmitting signals over joint aged optical fiber and free space optical network under harsh environments

Over the last two decades, a large amount of optical fiber (OF) cables has been deployed as part of the global communication networks. Both the aging of OFs as well as the need to increase transmission data rates, particularly in the backbone, have become hot topics. We present the study of the aged OF deployment in various optical networks including free space optics (FSO) link as a part of modern optical communication networks. Here, we show extended results obtained using a dedicated OF testbed focusing on the long-term monitoring of polarization mode dispersion (PMD) because of its time-varying nature. The adaptation of polarization multiplexed radio over fiber (RoF) and radio over FSO (RoFSO) systems as well as 10Gbps on-off-keying (OOK) non-return-to-zero (NRZ) intensity modulation with the direct detection system, which is common cost-effective transmission system in passive networks, are demonstrated. Moreover, simulation of 100 and 200Gbps return-to-zero (RZ) differential quadrature phase shift keying (DQPSK) with direct detection is outlined to verify the impact of aged OF network connected with FSO under turbulence conditions. Results reveal more than 6dB of power penalty with the aged OF route for 100Gbps systems. In addition, there is a 0.8dB power penalty due to the strong seasonal induced PMD fluctuations. The influence of scintillations in terms of Rytov variance for the FSO link is also investigated for weak to moderate turbulence. Finally, we derive an expression for the long-term mean PMD value determined over one-month measured frequency response.

Long-Term Polarization Mode Dispersion Evolution and Accelerated Aging in Old Optical Cables

Today’s optical networks are composed of thousands of kilometers of aging optical cables. Many of these cables are located in harsh environments, which contribute to induced birefringence of the fibers and a corresponding increase of polarization mode dispersion (PMD). This letter introduces derived statistics from the longest-known running evaluation of a PMD measuring campaign and an investigation into how higher optical power affects these aging systems. Results indicate strong seasonal dependence of PMD on temperature for an optical cable test bed exposed to atmospheric changes, leading to a 16% increase of a mean PMD value in summer. This fluctuation causes bit error rate limits to be exceeded for 10 and 40 Gbps non-return-to-zero signals, which is a critical issue for applications where high reliability is required. Moreover, due to the high optical power load within old optical infrastructures, a more than 0.15 dB increase of relative loss per year in tested routes, compared with reference routes, has been observed.

Insight into PMD Regimes: An Analysis on Buried Optical Fibres

Polarization mode dispersion (PMD) field measurements on deployed buried fibres showed that the PMD variation over the 1520 to 1570 nm wavelength was stochastic. The PMD variation over the 98-hour period for each wavelength was directional and limited; they are due to the presence of random mode coupling along the fibre length and limited influence from extrinsic perturbations over time, respectively. PMD variation in the wavelength domain showed that the mean first-order PMD (FO-PMD) value is independent of whether the FO-PMD statistics of a fibre link approaches the Maxwellian theoretical distribution; the key factor is sufficient random mode coupling. The accompanying second-order PMD (SO-PMD) statistics, with FO-PMD statistics approaching Maxwellian, followed the PDF given by Foschini et al. (1999). The FO- and SO-PMD statistics at a given wavelength gave nonstochastic PMD distributions with time.

Simultaneous optical signal-to-noise ratio and differential group delay monitoring based on degree of polarization measurements in optical communications systems

We present a simultaneous optical signal-to-noise ratio (OSNR) and differential group delay (DGD) monitoring method based on degree of polarization (DOP) measurements in optical communications systems. For the first time in the literature (to our best knowledge), the proposed scheme is demonstrated to be able to independently and simultaneously extract OSNR and DGD values from the DOP measurements. This is possible because the OSNR is related to maximum DOP, while DGD is related to the ratio between the maximum and minimum values of DOP. We experimentally measured OSNR and DGD in the ranges from 10 to 30 dB and 0 to 90 ps for a 10 Gb/s non-return-to-zero signal. A theoretical analysis of DOP accuracy needed to measure low values of DGD and high OSNRs is carried out, showing that current polarimeter technology is capable of yielding an OSNR measurement within 1 dB accuracy, for OSNR values up to 34 dB, while DGD error is limited to 1.5% for DGD values above 10 ps. For the first time to our knowledge, the technique was demonstrated to accurately measure first-order polarization mode dispersion (PMD) in the presence of a high value of second-order PMD (as high as 2071 ps(2)).

SOP and PMD monitoring on deployed aerial optical fibres

State of polarization (SOP) and polarization mode dispersion (PMD) are stochastic in nature due to changes in the properties of the optical fibres and its positions because of both intrinsic and extrinsic perturbations. With 184 PMD values obtained by use of the FTB-5700 single-ended dispersion analyzer, the predicted theoretical Gaussian fit was obtained with a mean of 0.47ps and standard deviation of 0.08ps. This small standard deviation was justification for its accuracy in measuring PMD of aerial optical fibres. A comparison is also made on the accuracy of the GINTY and the FTB-5700 on measurement of PMD of aerial optical fibres with results showing that the latter is more accurate compared to the former. The time scale over which to compensate PMD in aerial optical fibres was determined and it is slightly higher than 400s; the decorrelation time obtained for SOPs on a particular windy and hot day. This is because the changes of the PMD vector are known to be slower than SOP changes.

A Wavelength-Diversity Method for Complete Spatial Polarization Profiling in Optical Fibers

Fully distributed optical-fiber sensing (FDOFS) systems are developing rapidly and offering significant advantages for measurement functions in a variety of industrial applications. Polarization techniques are well established in FDOFS and the analysis of polarization-mode dispersion (PMD) for optical-fiber telecommunications. However, a major problem has been of determining, from one end of the fiber, the complete spatial distribution of the full polarization properties of a monomode optical fiber, along its length, with some specified spatial resolution (~1 m). This paper will present the theoretical framework for provision of this full polarization-profile information and thus for measuring the spatial distribution of any parameter, external to the fiber, which can modify its polarization behavior, such as strain. The techniques comprise a wavelength-diverse extension of polarization-optical time-domain reflectometry and necessitate on-line processing. Details of the physical principles and the polarimetry will be presented. The practical techniques can be extended, importantly for the oil and gas industries, to the distributed measurement of fluid pressure. Extensions also are possible to electric and magnetic field distributions. Finally, it is possible fully to characterize the PMD profile of a telecommunications fiber and, in particular, to identify any sections with anomalously large values of PMD.

PMD Design for High-Speed WDM Backbone Network Systems Based on Field PMD Measurements

We propose a polarization mode dispersion (PMD) design for high-speed wavelength-division multiplexing (WDM) backbone network systems based on field PMD measurements on installed optical fibers for long-term commercial use. Implementing a high-speed network system on an installed fiber requires measuring PMD, because the PMD characteristics of most installed fibers are unknown. For enhanced practicality, we must be able to precisely evaluate PMD characteristics precisely with just one measurement. To understand the statistical properties of measured PMD values, we use the Jones Matrix Eigenanalysis (JME) method to conduct long-term (12 months) PMD measurements on installed fibers. We statistically analyze the measurement results and confirm that the measured values match the theory that considers the accuracy of the measurement instrument. This enables a PMD design of desired outage probability based on PMD measurements of installed fibers. We also carry out a 43-Gb/s return-to-zero differential quadrature phase shift keying (RZ-DQPSK) signal transmission with high PMD fibers in order to confirm the effectiveness of our PMD design. The PMD values of the in-line amplifier transmission line are settled so as to meet the worst value of the design. We confirm that 43-Gb/s RZ-DQPSK signals are stably transmitted at the design value.

Dynamic PMD compensator for 40 Gb/s PM-DQPSK system

The adaptive polarization mode dispersion (PMD) compensation in high-speed transmission system has become more and more necessary for the link PMD causing strong signal distortions. A dynamic adaptive PMD compensator in 40 Gb/s polar-multiplex differential quadrature phase shift keying (PM-DQPSK) system is reported. Experimental results show that the PMD compensator can track the average polarization state variation at 65 rad/s without any lost of the optimum tracking. The 1st-order PMD compensation is demonstrated experimentally, and the compensator can increase the maximal tolerable PMD value by 26 ps from 17 ps to 43 ps in an optical transmission system.

In-service light path PMD (polarization mode dispersion) monitoring by PMD compensation

We describe a novel method of measuring PMD (polarization mode dispersion) of an in-service DWDM system by PMD compensation. We successfully demonstrate the method in a 1500-km ultra-long haul DWDM test bed. We further verify the feasibility of the method for in-service light path PMD monitoring in a field trial in a revenue-generating route in Verizon Network, and obtain an accurate PMD value without impacting live network traffic. The discrepancy between the measured and expected PMD values is less than 6% for all cases tested.

Low birefringence depressed cladding photosensitive fiber

The highly Ge-doped photosensitive fiber (PSF) has been widely used in the fabrication of fiber Bragg gratings (FBGs). Its birefringence and cladding mode coupling characteristics greatly influence FBG's transmission feature in communication application areas. In this work, a new concept of the PSF is introduced which, along with an optimized birefringence design, a precisely controlled fabrication process, and a cladding mode depressed design, results in a written FBG with -25-dB clad mode-depressed ratio and a polarization mode dispersion value less than 0.045 ps.

Impairments Due to Polarization-Mode Dispersion in Chaos-Encrypted Communication Systems

In this letter, we present a numerical investigation of impairments due to polarization-mode dispersion (PMD) in chaos-encrypted communication systems. We show that PMD could affect master-slave synchronization, hence degrading system performance at typical PMD values of deployed fiber plants. We also analyze the effectiveness of a first-order compensation.

Polarization mode dispersion emulation using polarization maintaining fibers: Fixed root-mean-square differential group delay but varying second-order polarization mode dispersion

We report on a polarization mode dispersion (PMD) emulator with a fixed root-mean-square differential group delay (RMS-DGD) but varying second-order PMD (SO-PMD) using only a combination of polarization maintaining fibers and a polarization controller. The SO-PMD control mechanism is not completely in real time. Besides controlling the mean PMD values of the emulator, simultaneous adjustments in the maximum and minimum values of PMD statistics can be performed. We therefore illustrate irregular fluctuations that occur around the RMS-DGD due to SO-PMD. This novel design can be used to further show the impact of a high first-order PMD segment on the DGD and SO-PMD statistical distributions that might occur in an optical network system.

Polarization-mode dispersion effect of an acousto-optic tunable filter

The effect of the polarization-mode dispersion (PMD) of an acousto-optic tunable filter (AOTF) is studied both theoretically and experimentally. A coupled-mode method derived from Maxwell's equations is proposed to study the evolution of the polarization of light and hence the deterministic dynamics of the PMD inside an AOTF. It is found that the PMD value of a typical AOTF is around several picoseconds and is adjustable by tuning the strength of the applied sound signal. A set of experimental data acquired by the wavelength scanning method is employed to check the validity of the proposed method. A high degree of similarity is observed between the experimental and the theoretical data.

Polarization-dependent gain and gain fluctuations in a fiber Raman amplifier

We report a new vector model of a fiber Raman amplifier with a randomly varying birefringence. We find that the analysis of gain fluctuations and polarization-dependent gain can be used for measurements of beat and birefringence correlation lengths and the polarization mode dispersion value on a long single-mode fiber. Results are consistent with a standard technique based on differential group delay measurements.

On the Pulsewidth Analysis in the Presence of PMD and PDL in Optical Fibers Using Neural Network Algorithm

In long haul networks, the random birefringence induced in the optical fiber leads to a considerable Polarization Mode Dispersion (PMD). Polarization Dependent Loss (PDL) mainly occurs in optical components and depends on the state of polarization of optical signals. The presence of PMD and PDL causes pulsewidth narrowing and the pulsewidth reduction depends on states of polarization at which the input light launched and also the input pulsewidth. A system comprising of a PDL element sandwiched between two PMD elements was considered. This system was characterized using neural network approach. Back propagation algorithm was applied to train the network with four input vectors namely PMD, PDL, input pulsewidth and the angle describing the input states of polarization and one output vector indicating effective squared pulsewidth difference. On analysis, it was found that the pulsewidth reduction was higher for a PMD of 30ps, a PDL of 3.5 and input pulsewidth of 100ps at various (Linear and Circular) input states of polarization with the angle describing the input state of polarization to be |π/4|. Similarly, for a given value of PMD, PDL, input pulsewidth and a specific pulsewidth reduction, the input state of polarization at which the light was to be launched can also be determined using neural network approach.

Adaptive, online polarization mode dispersion monitoring technique using acousto-optic tunable filters

We propose an online, wide-band, adaptive, and no data-traffic interruption polarization mode dispersion (PMD) monitoring system using acousto-optic tunable filters (AOTFs). With the nonsignal carrying amplified spontaneous emission (ASE) noise as the reference signal, without interrupting the signal-carrying data traffic, multiple cascaded AOTFs are used at the optic receiver side to scan the spectrum of the ASE noise. Using the fixed-analyzer method, PMDs of different wavelength bands, which ranges from 1200–1700 nm of an optic-fiber communication system, can be found by adaptively changing the radio frequency of AOTFs. The monitoring range of the PMD value can be up to several hundred ps by properly increasing the cascading number of AOTFs.

PMD variations from factory to field in OPGW cabled fibers

Factory measurements of polarization-mode dispersion (PMD) on optical ground wire cabled fibers are compared with field measurements of the installed span links. Analysis of the expected PMD values calculated from the factory measurements and the as-built reports reveals a systematic overestimation of the PMD in installed links, mitigated by correction of the limited sensitivity of commercial equipments. Unexpectedly high PMD values are observed, indicating that important changes on the PMD characteristics of the fibers may occur during cable installation.