Showing papers on "Polarization mode dispersion published in 2002"

Polarization-Mode Dispersion

Abstract: Publisher Summary Polarization mode dispersion (PMD) is a linear effect that can be compensated in principle. In an ideal circularly symmetric fiber, the two orthogonally polarized modes have the same group delay. However, in reality, fibers exhibit a certain amount of birefringence because of imperfections in the manufacturing process or mechanical stress on the fiber after manufacture. It is noted that fluctuations in the polarization mode and fiber birefringence produced by the environment lead to dispersion that varies statistically with time and frequency. PMD causes different delays for different polarizations and when the difference in the delays approaches a significant fraction of the bit period, it leads to pulse distortion and system penalties. Environmental changes— including temperature and stress—cause the fiber PMD to vary stochastically in time. PMD, illustrating the basic concepts, the measurement techniques, the PMD measurement, the PMD statistics for first- and higher orders, the PMD simulation and emulation, the system impairments, and the mitigation methods has been summarized in the chapter. Both the optical and the electrical PMD compensations are considered.

Subcarrier multiplexing for high-speed optical transmission

Abstract: The performance of high-speed digital fiber-optic transmission using subcarrier multiplexing (SCM) is investigated both analytically and numerically. In order to reduce the impact of fiber chromatic dispersion and increase bandwidth efficiency, optical single-sideband (OSSB) modulation was used. Because frequency spacing between adjacent subcarriers can be much narrower than in a conventional DWDM system, nonlinear crosstalk must be considered. Although chromatic dispersion is not a limiting factor in SCM systems because the data rate at each subcarrier is low, polarization mode dispersion (PMD) has a big impact on the system performance if radiofrequency (RE) phase detection is used in the receiver. In order to optimize the system performance, tradeoffs must be made between data rate per subcarrier, levels of modulation, channel spacing between subcarriers, optical power, and modulation indexes. A 10-Gb/s SCM test bed has been set up in which 4 /spl times/ 2.5 Gb/s data streams are combined into one wavelength that occupies a 20-GHz optical bandwidth. OSSB modulation is used in the experiment. The measured results agree well with the analytical prediction.

A comparison between different PMD compensation techniques

Abstract: We quantify the benefits of using different techniques for compensation of polarization mode dispersion (PMD) in fiber-optic communication systems by means of numerical simulations. This is done both with respect to PMD-induced pulse broadening and in terms of system outage probability for different data formats [nonreturn-to-zero (NRZ) and return-to-zero (RZ)]. Attention is focused on simple and relevant single- and double-stage post-transmission compensators with a few degrees of freedom (DOF). It is generally believed that a PMD compensator with a polarization controller and a variable delay line can only compensate the PMD to the first order. We show, from analytical results, the counterintuitive fact that this scheme can also partially compensate for higher order PMD. We also investigate the benefit of using a polarizer as compensation element where the optical average power can be used as a feedback signal.

10 Gb/s optical differential quadrature phase shift key (DQPSK) transmission using GaAs/AlGaAs integration

Abstract: We demonstrate the first integrated realization of a new modulation format-optical DQPSK. Transmission experiments using an integrated encoder demonstrate tolerance to chromatic dispersion, polarization mode dispersion, self phase modulation and low OSNR.

Polarization-mode dispersion in high-speed fiber-optic transmission systems

Abstract: We review recent research related to polarization mode dispersion (PMD) in fiber-optic transmission systems operating at 40 Gb/s and above. We investigate the benefits of using different passive techniques for mitigating the effects of PMD, including more advantageous data formats compared to the conventional nonreturn-to-zero (NRZ) format, soliton transmission, and forward error correction (FEC). We also compare a number of active pre- and posttransmission compensators.

Chromatic dispersion monitoring technique using sideband optical filtering and clock phase-shift detection

Abstract: We propose and demonstrate a novel technique for 40- and 10-Gb/s chromatic dispersion monitoring that uses an optical filter to select the upper and lower vestigial-sideband (VSB) signals in the transmitted optical data and determine the relative clock phase shift caused by dispersion. Without modification of transmitters, this technique provides low cost chromatic dispersion monitoring for WDM systems, <3 ps/nm dispersion resolution for 40-Gb/s data, and greatly reduced sensitivity to the influence of polarization mode dispersion.

Wavelength switching components for future photonic networks

Abstract: This article provides a review of integrated laser and semiconductor optical amplifier components that have been configured to provide a variety of all-optical functions such as wavelength conversion, routing, signal regeneration, and add-drop multiplexing. The components have been devised so that they can be reliably and simply used within a multiwavelength network. The article introduces the components by outlining the current leading techniques for wavelength conversion using SOAs, namely by way of cross-gain modulation, cross-phase modulation, and four-wave mixing. The integrated SOA distributed feedback laser is then shown to provide excellent regeneration properties, not only overcoming fiber dispersion limitations but also polarization mode dispersion. Finally, the devices are shown to make possible a regenerative wavelength switching node where routing is achieved using a tunable laser to provide regenerative wavelength conversion followed by an arrayed waveguide router. This switch shows promise for use in future photonic packet switching architectures.

Importance sampling for polarization-mode dispersion

Abstract: We describe the application of importance sampling to Monte-Carlo simulations of polarization-mode dispersion (PMD) in optical fibers. The method allows rare differential group delay (DGD) events to be simulated much more efficiently than with standard Monte-Carlo methods and, thus, it can be used to assess PMD-induced system outage probabilities at realistic bit-error rates. We demonstrate the technique by accurately calculating the tails of the DGD probability distribution with a relatively small number of Monte-Carlo trials.

Electronic equalization of transmission impairments

Abstract: We have reviewed experimental and numerical results on electrical signal processing for the reduction of penalty induced in the optical domain. Since a few years integrated electronic equalizer circuits are available for 10 Gb/s operation. Penalty reduction of signal distorted by chromatic dispersion, PMD, and self-phase modulation has experimentally been demonstrated. First studies on equalization of DWDM typical crosstalk have already been conducted. Nevertheless, as compared to the decade long experience with dynamic equalization of thermal noise limited signal, for amplified optical signal limited by the optical signal-to-noise-ratio (OSNR) the residual penalty after equalization roughly doubles and the fast responding LMS adaptation leads to a sub-optimum setting of the equalizer failing the optimum by up to 0.8 dB which can be avoided by the slower steepest-descend scheme which optimising Q-factor related criteria at equalizer output.

Perturbation analysis of dispersion properties in photonic crystal fibers through the finite element method

Abstract: Perturbations to the ideal cross section of photonic crystal fibers (PCFs) are introduced in order to investigate their performance as a function of the structural fluctuations which may occur during fabrication. The effects of the cross-section geometry perturbations on dispersion characteristics like dispersion parameter and differential group delay are presented and discussed. The analysis has been performed through the finite element method which assures high flexibility and high solution accuracy.

Dispersion compensation with optical materials for compression of intense sub-100-fs mid-infrared pulses

Abstract: We report on the generation of essentially transform-limited mid-infrared pulses as short as 75 fs centered at 5 µm with 6 µJ of energy. Infrared materials with group-velocity dispersion values of opposite sign are used in combination to null second-order dispersion and compress the mid-infrared pulses.

Elimination of polarization degeneracy in round waveguides.

Abstract: We show how to design a round optical fiber so that it is effectively single moded, with no polarization degeneracy. Such fibers would be free from the consequences of polarization degeneracy or near degeneracy – phenomena such as polarization fading in interferometry, and polarization mode dispersion – and so may offer an alternative to polarization maintaining fibers for the avoidance of these phenomena. The design presented builds on an earlier observation of polarization selective refection in Bragg fibers.

Measure of twist-induced circular birefringence in long single-mode fibers: theory and experiments

Abstract: Production defects and external perturbations cause standard telecommunication fibers to be randomly birefringent. Fiber birefringence is the origin of the well-known polarization mode dispersion (PMD), which degrades system performances. The knowledge of birefringence properties may be crucial, especially when problems like development of low-PMD fibers or PMD interaction with optical nonlinearities in very high-capacity systems are faced. Some techniques are known to measure birefringence, and useful results have been obtained for both installed and wound-on-drum fibers. However, measurement of the circular component of birefringence still presents difficulties. In this paper, a new method for circular birefringence measurement is proposed that applies to long single-mode twisted fibers. The technique is based on polarization-sensitive optical time-domain reflectometry. Experimental results are in good agreement with the theoretical analysis.

Measurement of residual chromatic dispersion of a 40-Gb/s RZ signal via spectral broadening

Abstract: In this letter, we examine the spectrum of a 40-Gb/s return-to-zero (RZ) data stream, which has been broadened by self-phase modulation in a nonlinear fiber. Spectra were recorded as the residual chromatic dispersion at the input of the nonlinear fiber was varied using a tunable dispersion element. We show that spectral broadening can provide a useful measure of the residual chromatic dispersion of the data stream.

Dispersion of birefringence and differential group delay in polarization-maintaining fiber

Abstract: We present an interferometric technique for measurement of the dispersion of birefringence in polarization-maintaining fibers. The approach yields measurements over a broad spectral range from analysis of single interferograms obtained in a tandem inteferometer. The technique is demonstrated to measure first-, second-, and third-order dispersion of the differential propagation constant, corresponding to differential group delay (DGD) and its dispersion to second order; measurements are immune to asymmetry in the interferomgram that is being processed. The technique is further applied to measurement of the temperature dependence of DGD and its first-order dispersion.

Numerical comparison between distributed and discrete amplification in a point-to-point 40-Gb/s 40-WDM-Based transmission system with three different modulation formats

Abstract: We describe a detailed numerical investigation on the relative merits of gain flattened distributed Raman amplification (DRA) and discrete gain flattened amplifiers. We simulate a system with forty 40-Gb/s channels spaced at 100 GHz and compare the performance of three different modulation formats nonreturn-to-zero (NRZ), return-to-zero (RZ) and carrier-suppressed RZ (CS-RZ). Three types of amplifiers, multifrequency backward- and forward-pumped DRAs, and an idealized discrete gain flattened amplifier are examined for various signal powers and transmission distances. For the backward-pumped DRA, we also describe calculated tolerance limits imposed by incomplete dispersion slope compensation and polarization mode dispersion (PMD) level.

Multichannel tunable dispersion compensation using all-pass multicavity etalons

Abstract: We have proposed and demonstrated a novel approach to multi-channel tunable dispersion compensation using all-pass multi-cavity etalon filters for 10 Gb/s applications.

Multiple importance sampling for first- and second-order polarization-mode dispersion

Abstract: A simulation method that targets all possible combinations of first- and second-order polarization-mode dispersion (PMD) is described. Use of this method in importance-sampled Monte Carlo simulations yields a more comprehensive determination of PMD-induced system penalties than first-order biasing alone and significantly speeds up the calculation of outage probabilities, particularly when PMD compensation is employed. The technique is demonstrated by using it to calculate the probability distribution function (pdf) of second-order PMD and the joint pdf of the magnitude of first- and second-order PMD.

Dispersion shifted optical waveguide fiber

Abstract: A single mode optical waveguide fiber designed for high data rate, or WDM systems or systems incorporating optical amplifiers. The optical waveguide has a compound core having a central region and at least one annular region surrounding the central region. A distinguishing feature of the waveguide core is that the minimum refractive index of the central core region is less than the minimum index of the adjacent annular region. A relatively simple profile design has the characteristics of ease in manufacturing together with, flexibility in tailoring D w to yield a preselected zero dispersion wavelength, dispersion magnitude over a target wavelength range, and dispersion slope. The simplicity of profile gives reduced polarization mode dispersion.

Method for compensating polarization mode dispersion occurring in optical transmission fiber and apparatus therefor

Abstract: Method for compensating polarization mode dispersion, The method includes: transforming states and directions of polarization components of an optical signal received from the optical transmission line, rotating the polarization components of the optical signal output from the polarization controller, separating two orthogonal polarization components of the output from the polarization rotator so that a first polarization component is transmitted to an output path and a second polarization component is transmitted to a monitoring path, controlling the PC using a feedback control to minimize an electrical power filtered at a specified frequency so that the two orthogonal polarization components of the optical input signal to the polarization beam splitter are aligned to two axes of the PBS, and controlling the polarization rotator by comparing an optical power of the first polarization component transmitted to the output path with an optical power of the second polarization component transmitted to the monitoring path.

All fiber polarization mode dispersion compensator

Abstract: A polarization mode dispersion compensator corrects polarization mode dispersion in an optical signal having a fast polarization mode component, a slow polarization mode component and a time differential between the components. The compensator includes a phase shifter and a variable delay section. An input of the phase shifter is coupled to an optical device that provides an optical signal that exhibits polarization mode dispersion. The phase shifter functions to rotate the optical signal principal states of polarization to a desired orientation. The variable delay section includes an input, an output and at least one optical fiber delay line. The input of the variable delay section is coupled to the output of the phase shifter and the desired orientation of the optical signal principal states of polarization are substantially rotated to be in alignment with one of a fast axis and a slow axis of each of the one or more fiber delay lines. In this manner, the variable delay section functions to delay the principal states of polarization of the optical signal with respect to one another as a function of whether the principal states of polarization traverse said one of a fast axis and a slow axis of the at least one optical fiber delay line, thus reducing the time differential between the components.

Demonstration of a feed-forward PMD compensation technique

Abstract: We demonstrate a feed-forward technique, which characterizes first-order polarization-mode dispersion (PMD) and aligns it to a compensator. With appropriate components, the system could perform real-time compensation of first-order PMD with rapidly varying principal states of polarizations.

Adaptive dispersion slope equalizer using a nonlinearly chirped fiber Bragg grating pair with a novel dispersion detection technique

Abstract: We realized the first adaptive-dispersion equalizer that equalizes dispersion over a wide wavelength range (6 nm) in the zero-dispersion wavelength region of a dispersion-shifted fiber (DSF). The equalizer is based on a pair of nonlinearly chirped fiber Bragg gratings, which are designed to equalize exactly the dispersion profile of a DSF. The dispersion changes were tracked using a technique that employs opposite dispersion fibers to identify the sign of the dispersion change. Unlike previous approaches, no additional sources or changes in the source wavelength are required. We demonstrate the adaptive equalization of the dispersion changes in an 83-km DSF, induced by temperature changes between -10/spl deg/C and 60/spl deg/C.

Fixed and Tunable Management of Fiber Chromatic Dispersion

Abstract: Publisher Summary It is noted that the essence of chromatic dispersion lies in the fact that in any medium other than a vacuum and in any waveguide structure, different electromagnetic frequencies propagate at different speeds. Chromatic dispersion in optical fibers is therefore, because of the frequency–dependent nature of the propagation characteristics, for both the material and the waveguide structure. Chromatic dispersion, essentially, is a linear effect that can be compensated by adding the complementary dispersion before any significant nonlinearities intervene. It is noted that nonlinearities do intervene in many of the systems and the periodic dispersion mapping is required for managing them. The issues surrounding the compensation of chromatic dispersion in high-performance optical systems have been addressed in the chapter. The chapter also describes the effects of dispersion, the various fixed compensation techniques, the need for tunable compensation and its potential solutions, and also the techniques for monitoring accumulated dispersion. Chromatic dispersion phenomenon exhibits profound implications for opticalfiber communications systems.

Experimental demonstration of the system performance degradation due to the combined effect of polarization-dependent loss with polarization-mode dispersion

Abstract: The combined effect of polarization-mode dispersion (PMD) and polarization-dependent loss (PDL) is investigated experimentally using a recirculating fiber-loop testbed for 10-Gb/s nonreturn-to-zero transmissions over an 800-km fiber link. We find that the PDL of inline components combined with the link PMD will increase the penalty distribution. As the average link PDL varies from 1.0 to 2.1 dB with an average PMD of 18 ps, the system penalty distribution tail at 2% probability increases from 2.5 to 4.3 dB.

Polarization mode dispersion characterization apparatus and method

Abstract: The invention relates to an entangled-photon apparatus capable of measuring particular characteristics of an optical element, device or channel. Specifically, the apparatus and a method of using said apparatus to measure polarization mode dispersion in an optical communications fiber is disclosed. The apparatus includes a source of entangled photons, which are injected into the device under test, and a quantum interference device for determining the state of entanglement of said photons after they pass through the device. The quantum interference device includes a variable, polarization-specific delay element that is incremented to null out polarization mode dispersion in the device under test, and a wavelength demultiplexer/array detector that permits simultaneous measurements across a wide wavelength band. A second preferred embodiment of the invention and method is suitable for characterizing PMD in-situ that is, PMD measurements can be made while an optical fiber is in use for optical communications.

Impact of polarization-mode dispersion on the design of wavelength-routed networks

Abstract: In this letter, we address the impact of polarization-mode dispersion on the design of wavelength-routed optical networks. A mathematical formulation of the problem is provided which optimizes the cost of the network comprising the total number of regenerators and additional installed fiber for a given traffic forecast. The hill-climbing search algorithm is employed with random restarts. Numerical examples show the efficiency of the heuristic, especially in networks with nonhomogeneous fiber quality.

Statistical characterization of the Jones matrix of long fibers affected by polarization mode dispersion (PMD)

Abstract: The unitary transfer matrix of a fiber affected by polarization mode dispersion (PMD) is analyzed using the Stokes representation of its eigenmodes and its retardation angle, or equivalently through its Pauli coordinates. We develop a statistical theory applied to these parameters and relate it to the extensive existing literature on the statistics of the PMD vector Dynamical equations are established for the Pauli coordinates. Assuming a standard "white Gaussian" model for the local birefringence, and using the tools of stochastic calculus, we derive the distributions of the eigenmodes, the retardation angle, the Pauli coordinates, and of the frequency derivatives of all these parameters. The evolution in space of the Pauli coordinates is also characterized as a standard Brownian motion on the unit sphere in /spl Rfr//sup 4/. An expression for the frequency autocorrelation function of the Pauli coordinates, the eigenmodes and the retardation angle is derived and their coherence bandwidth is compared to that of the PMD vector. All theoretical results are supported by simulation over an ensemble of 10000 fibers, using the standard retarder plate model.

Calculation of the mean differential group delay of periodically spun, randomly birefringent fibers.

Abstract: Spinning is one of the most effective and well-known ways to reduce polarization mode dispersion of optical fibers. In spite of the popularity of spinning, a detailed theory of spin effects is still lacking. We report an analytical expression for the mean differential group delay of a randomly birefringent spun fiber. The result holds for any periodic spin function with a period shorter than the fiber's beat length.