Characterization Of Polarization Mode Dispersion Research Articles

Impact of Wind Gust on High-Speed Characteristics of Polarization Mode Dispersion in Optical Power Ground Wire Cables.

Polarization mode dispersion is recognized as a key factor limiting optical transmission systems, particularly those fiber links that run at bit rates beyond 10 Gbps. In-line test and characterization of polarization mode dispersion are thus of critical importance to evaluate the quality of installed optical fibers that are in use for high-speed signal traffics. However, polarization-based effects in optical fibers are stochastic and quite sensitive to a range of environmental changes, including optical cable movements. This, in turn, gives rise to undesired variations in light polarization that adversely impair the quality of the signal transmission in the link. In this work, we elaborate on experimental testing and theoretical analysis to asses changes of polarization mode dispersion in optical fibers that are caused by environmental variations, here wind gusts in particular. The study was performed on commercially harnessed optical fibers installed within optical power ground wire cables, taking into account different weather conditions. More specifically, we showed that changes caused by wind gusts significantly influence the differential group delay and the principal state of polarization in those optical fibers. For this, we experimentally measured a number of parameters to characterize light polarization properties. Measurements were carried out on C-band operated fiber-optic link formed by 111-km-long power ground wire cables and 88 spectral channels, with a test time step of 1 min during 12 consecutive days. Variations in differential group delay allowed for sensitive testing of environmental changes with measured maxims up to 10 ps under the worst wind conditions. Moreover, measured parameters were used in a numerical model to assess the quality of transmitted high-bit-rate optical signals as a function of wind conditions. The analysis revealed a negligible impact of wind on a 10 Gbps transmission, while substantial influence was noticed for higher bit rates up to 100 Gbps. These results show promises for efficient sensing of environmental changes and subsequent monitoring of the quality of recently used fiber-optic link infrastructures.

PMD Characterization of a Dispersion Managed Link up to the Second-order with High Accuracy

We report an algorithm on the characterization up to second-order polarization mode dispersion (PMD). Our algorithm is able to characterize very short link with low PMD coefficient (less than 0.04 ps/ \(\sqrt{km}\)). The link includes dispersion compensating fiber modules and loss compensating optical amplifiers. The estimation for first- and second-order PMD is successfully performed for dispersion-managed links of 85 and 265 km using the Jones matrix eigen-analysis (JME). The algorithm was developed to detect the evolution of the principal state of polarization (PSP) and subsequent calculation of second-order PMD components such as polarization-dependence, chromatic dispersion (PDCD) and depolarization.

Design and fabrication techniques for polarization gratings for polarization mode dispersion measurements

To determine the polarization mode dispersion (PMD) in an optical device, a tunable light source and a polarimeter are used to measure the Jones or the Mueller matrix at different wavelengths. We show that a complete real-time PMD characterization can be performed using a broadband source and three polarization gratings. A polarization grating performs a periodic spatial change of the state of polarization of an incident beam. The diffraction pattern of these devices is composed of higher-order waves with a fixed polarization state that is independent of the incident one. Following a general mathematical model, we show that it is possible to design PGs to measure all the Stokes parameters. Since different wavelengths are diffracted under different angles, focusing the output of a PG on an array of photodetector, it is possible to measure simultaneously the Stokes parameters at different frequencies. Various fabrication techniques for continuous and pixillated PGs are described and the corresponding efficiencies and degrees of freedom outlined.

Real-time first- and second-order PMD characterization using averaged state-of-polarization of filtered signal and polarization scrambling

A real-time estimation technique for first- and second-order polarization-mode dispersion (PMD) is presented. It makes use of the spectrum of telecommunication signals. At the output of the transmission fiber, the signal is tapped and filtered. Three filters are used: a high-pass filter, a low-pass filter, and a narrow-band filter. The averaged states of polarization (SOPs) of the filtered signals are then measured using a polarimeter. We repeat the measurement for several different input SOPs using a polarization scrambler at the input of the fiber. From these measurements, we deduce the first-order PMD and, subsequently, the second-order PMD.

Single-end polarization mode dispersion measurement using backreflected spectra through a linear polarizer

Routine characterization of polarization mode dispersion of single-mode fibers in installed cables requires simple and fast techniques. All standardized techniques use both fiber ends, one connected to the optical source and the other one for signal detection. Clearly, this causes several drawbacks in field tests because the two fiber ends are usually far from each other. Among standardized techniques, the fixed-polarizer method (also called wavelength scanning method) is one of the simplest to implement. In this work we present a new single-end measurement scheme based on the fixed polarizer method applied to the signal backreflected by the fiber far-end. We report analytical equations and numerical solutions that permit to calculate the mean value of the differential group delay measuring the crossings and/or extreme densities of the spectrum transmitted through a linear polarizer. We also show that the mean value of the differential group delay can be calculated using the Fourier transform of the detected signal. Finally, experimental results on cascades of single-mode step-index fibers confirm the robustness and easiness of our proposal for polarization mode dispersion measurements.

Polarization mode dispersion characterization of single-mode optical fiber using backscattering technique

This paper presents a completely new method able to characterize polarization mode dispersion (PMD) properties of randomly birefringent single-mode fibers, using polarization sensitive backscattering technique. We show analytical relationships between evolution of polarization state of backscattered signal with respect to state of polarization of forward one. Our technique allows one to measure differential group delay, beat length, and correlation length at the same time over long single-mode fibers using only one fiber end. Experimental data fit very well with numerical results, confirming the capability of our technique for fast routine characterization of PMD during cabling, before and after installation.