Showing papers on "Polarization mode dispersion published in 2001"

Designing the properties of dispersion-flattened photonic crystal fibers

Abstract: We present a systematic study of group-velocity-dispersion properties in photonic crystal fibers (PCF’s). This analysis includes a thorough description of the dependence of the fiber geometrical dispersion on the structural parameters of a PCF. The interplay between material dispersion and geometrical dispersion allows us to established a well-defined procedure to design specific predetermined dispersion profiles. We focus on flattened, or even ultraflattened, dispersion behaviors both in the telecommunication window (around 1.55 µm) and in the Ti-Za laser wavelength range (around 0.8 µm). We show the different possibilities of obtaining normal, anomalous, and zero dispersion curves in the above frequency domains and discuss the limits for the existence of the above dispersion profiles.

Analysis of signal degree of polarization degradation used as control signal for optical polarization mode dispersion compensation

Abstract: The basic property of degree of polarization (DOP) degradation of optical signal induced by polarization mode dispersion (PMD) in high-speed optical fiber transmission is investigated in detail. The DOP of the optical signal reflects the degree of waveform degradation caused by PMD, therefore, it is proposed to be used as the control signal judging the best compensation point for the optical adaptive PMD compensation techniques. However, the signal DOP is not only affected by PMD, but also by various factors, such as the modulation format, modulator chirp, fiber nonlinearity, amplified spontaneous emission (ASE), and so on. We use numerical simulations and experiments to explore the basic DOP property to detect PMD with these factors. We also show that using the signal DOP as control signal is especially useful for the optical duo-binary modulation because of its high sensitivity and wide PMD detection range.

Time and frequency domain characteristics of polarization-mode dispersion emulators

Abstract: We investigate both experimentally and theoretically a new technique to realistically emulate polarization-mode dispersion (PMD). We propose and demonstrate a PMD emulator using rotatable connectors between sections of polarization-maintaining fibers that generates an ensemble of high PMD fiber realizations by randomly rotating the connectors. It is shown that: (1) the DGD of this emulator is Maxwellian-distributed over an ensemble of fiber realizations at any fixed optical frequency; and (2) the frequency autocorrelation function of the PMD emulator resembles that in a real fiber when averaged over an ensemble of fiber realizations. A realistic autocorrelation function is required for proper emulation of higher order PMD and indicates the feasibility of using this emulator for wavelength-division-multiplexing (WDM) systems.

All-fiber grating-based higher order mode dispersion compensator for broad-band compensation and 1000-km transmission at 40 Gb/s

Abstract: We use a novel fiber-grating device to demonstrate the first polarization-insensitive all-fiber higher order mode dispersion compensator for broad-band dispersion compensation. Its low loss and high effective area have enabled transmission through 1000 km (10/spl times/100 km) of nonzero dispersion-shifted fiber (NZDSF) at 40 Gb/s.

Comparison of polarization mode dispersion emulators

Abstract: We analyze polarization mode dispersion (PMD) emulators comprised of a small number of sections of polarization-maintaining fibers with polarization scattering at the beginning of each section. Unlike previously studied devices, these emulators allow the emulation of a whole ensemble of fibers. We derive an analytical expressions and determine two main criteria that characterize the quality of PMD emulation. The experimental results are in good agreement with the theoretical predictions.

Measurement of the spatial distribution of birefringence in optical fibers

Abstract: We describe a technique for the measurement of the birefringence spatial distribution in a single-mode optical fiber with a resolution of 1 m. This technique is based on a polarization optical time-domain reflectometer using a rotary linear polarizer. We report results performed on different types of fibers: standard step-index and dispersion shifted fibers.

Higher order polarization mode dispersion compensation using a fixed time delay followed by a variable time delay

Abstract: We propose and analyze a higher order polarization mode dispersion (PMD) compensator using a fixed differential group delay (DGD) section followed by a variable section. The performance limits of various PMD compensators are quantified and compared using dynamic PMD tracking. Compared with existing compensators with a single fixed DGD, the proposed compensator improves an nonreturn-to-zero 10-Gb/s link tolerance to average PMD from 28 to 44 ps. Alternatively, the tolerance increases to only 36 ps using a compensator with two fixed-DGD sections.

Automatic PMD compensation at 40 Gbit/s and 80 Gbit/s using a 3-dimensional DOP evaluation for feedback

Abstract: We demonstrate that polarization scrambling combined with degree of polarization (DOP) evaluation enables polarization mode dispersion (PMD) compensation without feedback fading due to varying input polarization. PMD of an installed fiber as well as PMD of an emulator was successfully compensated.

Optimized spinning design for low PMD fibers: an analytical approach

Abstract: It is known that the differential group delay (DGD) due to polarization mode dispersion (PMD) can be effectively reduced by spinning the fiber during drawing. In this paper, we propose an analytical approach that allows optimization of the spinning design. The fundamental idea is that, in the absence of polarization coupling, an optimized spinning profile can balance the effects of the intrinsic linear birefringence so that the differential group delay can be forced to be periodic and, consequently, have a limited amplitude as a function of distance. Our approach Is independent of the spin profile. In other words, with a fixed set of parameters that characterize a particular spin function, we are able to find analytically the values corresponding to a periodic DGD in a deterministic regime. Numerical results based on waveplate model confirm the analytical prediction and show that PMD can be reduced by about two orders of magnitude with respect to the same fiber without spinning, even after the introduction of random polarization coupling.

Methods and systems for polarization control and polarization mode dispersion compensation for wideband optical signals

Abstract: An optical processing method includes: receiving an optical signal from an optical system, wherein the optical signal is distorted by frequency-dependent polarization effects in the optical system; spatially dispersing frequency components of the distorted optical signal on a spatial light modulator (SLM); and independently adjusting the polarization transfer matrix of multiple regions of the SLM to reduce the distortion of the optical signal. A related optical processing method includes: providing a precompensation signal indicative of frequency-dependent polarization effects in a downstream optical system; spatially dispersing frequency components of an optical signal on a spatial light modulator (SLM); and independently adjusting the polarization transfer matrix of multiple regions of the SLM to at least partially precompensate the optical signal for distortions caused by the frequency-dependent polarization effects in the downstream optical system. Another related optical processing method includes: providing a model of the frequency-dependent polarization effects; spatially dispersing frequency components of the optical signal on a spatial light modulator (SLM); and independently adjusting the polarization transfer matrix of multiple regions of the SLM based on the model to emulate the optical signal transmission.

Measurement of birefringence correlation length in long, single-mode fibers

Abstract: Measurements of birefringence correlation length performed on long single-mode telecommunication fibers are reported. The proposed technique relies on the statistical properties of the backscattered-field polarization, which was measured by means of a polarization-sensitive optical time-domain reflectometer. Experimental results are reported that show good agreement with the underlying theory based on stochastic differential equations.

Polarization-mode dispersion compensation in WDM systems

Abstract: We demonstrate, both experimentally and numerically, polarization-mode dispersion (PMD) compensation in wavelength-division-multiplexing (WDM) systems without wavelength demultiplexing. Our technique improves the overall system performance by reducing the fading probability for the worst-performing channel at any given time. The effectiveness of our approach is based on the fact that, for moderate PMD, the probability that all channels are severely degraded at the same time is extremely small. A single-section PMD compensator reduces the 2% worst-case power penalty for a four-channel 10-Gb/s WDM system with /spl sim/42 ps average differential group delay from 9.6 to 5.3 dB.

Compensation of chromatic dispersion and dispersion slope using a virtually imaged phased array

Abstract: Chromatic dispersion produced by the virtually imaged phased array (VIPA) is discussed. A newly designed 3-dimensional mirror produces uniform dispersion for each WDM channel with a wide variable dispersion range. The VIPA with the mirror also produces dispersion slope by including a diffraction grating.

Statistics of second-order PMD depolarization

Abstract: The second-order polarization mode dispersion (PMD) components associated with depolarization of the principal states can cause significant system impairments. We discuss the probability densities of these components and find excellent agreement between extensive measurements, simulations, and theoretical predictions.

Calculation of penalties due to polarization effects in a long-haul WDM system using a Stokes parameter model

Abstract: We derive a Stokes parameter model to calculate the penalties due to the combination of polarization mode dispersion (PMD), polarization dependent loss (PDL), and polarization dependent gain (PDG) in long-haul, dense wavelength division multiplexed (WDM) systems. In this model, we follow the Stokes parameters for the signal and the noise in each channel instead of following the full time domain behavior of each channel. This approach allows us to determine the statistical distribution of penalties with up to 10/sup 5/ fiber realizations and 40 channels. We validate this model to the extent possible by comparison to full numerical simulations. Using this model, we find that the interaction of PMD and PDL is the major source of penalties and that the effect of PDG is negligible in WDM systems with more than ten channels.

Exact evaluation of the Jones matrix of a fiber in the presence of polarization mode dispersion of any order

Abstract: Describes how to evaluate exactly in a recursive manner the Jones transfer matrix of a fiber for any order of polarization mode dispersion (PMD) and derives for it a second-order accurate analytical approximation. The second-order approximation is then compared against the exact result as well as with other models found in the literature.

Compensating polarization mode dispersion in fiber optic transmission systems

Abstract: A real-time optical compensating apparatus reduces the PMD in an optical fiber by determining the principal states of polarization of the optical fiber and delaying one principal state of polarization with respect to the other.

Dispersion tailoring in optical fibres

Abstract: An optical fibre is provided with dispersion tuning holes (510) arranged in the wings of the modal field distribution (512). These dispersion tuning holes can be used in a holey or conventional fibre geometry to tune the fibre dispersion independently from the other modal properties, such as the mode shape, to generate birefringence and for other dispersion tuning applications. These holes contrast from the usual 'holey fibre' holes in that they are generally carefully placed laterally offset from the geometrical axis of the optical fibre by a distance of the same order as the mode field radius. The placement and size of the proposed 'dispersion tuning holes' ensures that they affect the dispersion of the mode in a desired manner.

Method and system for compensating chromatic dispersion

Abstract: Disclosed herein are a method and system for compensating chromatic dispersion. The method includes the steps of generating WDM signal light by wavelength division multiplexing a plurality of optical signals having different wavelengths, transmitting the WDM signal light by an optical fiber transmission line, and receiving the WDM signal light transmitted by the optical fiber transmission line. The receiving step includes the steps of detecting chromatic dispersion related to at least one of the plural optical signals, and providing a variable dispersion compensator whose chromatic dispersion and dispersion slope are controlled so that the detected chromatic dispersion is reduced. According to this method, waveform degradation due to dispersion can be compensated with high accuracy in consideration of dispersion and dispersion slope.

Recent progress in fiber dispersion compensators

Abstract: This paper reviews the progress in fiber dispersion compensators. Different dispersion compensation technologies including dispersion compensation fibers, fiber Bragg gratings, virtual image phased array and planar waveguide-based devices are discussed with the focus on new developments in dispersion and dispersion slope compensation fibers.

Method and system for controlling polarization mode dispersion

Abstract: In an optical data communications link, a modulated optical signal is emitted from an optical transmitter. Coupled into one end of an optical fiber, and received by an optical receiver at the opposite end of the fiber (reference numeral 1000). The present invention relates to reducing the polarization-mode dispersion (PMD) of the modulated optical signal caused by the birefringence of the fiber, which tends to limit the usable bandwidth of the fiber. A polarization controller (reference numeral 1090) is applied to the modulated optical signal substantially near the transmitter. The receiver measures the quality of the received signal and issues commands to the polarization controller to improve the received signal quality (reference numeral 1090). In various embodiments, the signal quality measurement may be based on observed bit-error-rate (BER), estimated best attainable BER, or estimates of Plum affecting the received signal. Such measurements may be performed in the receiver by altering the threshold level and sampling timing of a bit detector in the receiver and monitoring the resulting changes in BER. Polarization control from the receiver are preferably coupled to the polarization controller through the same optical fiber carrying the modulated optical signal.

A new method for measurement of group velocity dispersion of optical fibers by using a frequency-shifted feedback fiber laser

Abstract: A new method for the measurement of the group velocity dispersion (GVD) in optical fibers, based on optical frequency domain reflectometry (OFDR), is proposed and demonstrated Frequency chirped light is used as a light source, which allows the dispersion to be determined from changes in the frequency chirp rate Accurate measurement of the average dispersion, at a single terminal, in fibers up to several tens of kilometers, is accomplished using a frequency-shifted feedback fiber laser as a light source

Dispersion compensation method, dispersion compensating device and optical transmission system

Abstract: PROBLEM TO BE SOLVED: To provide a dispersion compensation method which can easily and automatically compensate waveform deterioration due to the dispersion characteristics of an optical transmission line and to provide a small and low- cost dispersion compensating device and optical transmission system. SOLUTION: The dispersion compensation device 1 is provided with a variable dispersion compensation 10 for compensating the dispersion of an optical signal input via the optical transmission line, a code error information monitor circuit 12 generating code error information of a reception signal output from the variable dispersion compensator 10 via a light-receiving circuit 11 and a control circuit 13 which optimally controls the waveform dispersion value of the variable dispersion compensator 10, based on code error information from the code error information monitor circuit 12.

Dispersion compensating method, dispersion compensating apparatus and optical transmission system

Abstract: The present invention aims at realizing a dispersion compensating method capable of readily conducting automatic compensation of waveform degradation caused by dispersion characteristics of an optical transmission path, and at providing a dispersion compensating apparatus and an optical transmission system, of a smaller size at a reduced cost. To this end, the dispersion compensating apparatus of the present invention comprises: a variable dispersion compensator for compensating for the dispersion of optical signal input via an optical transmission path; a bit error information monitoring circuit for generating bit error information of a received signal output from the variable dispersion compensator via an optical receiving circuit; and a controlling circuit for optimally controlling a wavelength dispersion value of the variable dispersion compensator based on the bit error information from the bit error information monitoring circuit.

Methods and apparatus for compensating chromatic and polarization mode dispersion

Abstract: Integrated and stand-alone methods and apparatus for adaptively compensating for DGD, SOPMD, and CD in optical communication networks are provided. One apparatus includes at least three optical compensators that are optically coupled together in series and a feedback controller. Each compensator includes a variable optical controller that is optically coupled in series to a birefringent element. An optical communication network is also provided that at least includes an optical transmission line, at least two network terminals, and at least one static compensation module. At least one terminal includes an optical demultiplexer that is coupled to that element, a plurality of λ-compensators, and, optionally, a static optical dispersion compensation element.

Polarization mode dispersion and polarization dependent loss for a pulse in single-mode fibers

Abstract: Polarization mode dispersion (PMD) and polarization dependent loss (PDL) for a pulse in optical fibers are calculated with a model of two concatenated fibers. Each of the two fibers has both elliptical birefringence and PDL. The results show that the PMD and PDL for a short pulse can be very different from those for a narrow-band pulse in optical fibers. Two anomalous results are reported: (1) the effective PDL for a pulse can be smaller than the PDL difference of the two fibers and (2) the effective PMD for a pulse can be either larger than the sum of the differential group delays (DGDs) of the two fibers or less than the DGD difference of the two fibers, depending on the input pulsewidth. The pulse distortions when the pulses are launched into the two principal states of polarization (PSPs) are discussed.

Crosstalk detection schemes for polarization division multiplex transmission

Abstract: Polarization division multiplex (PolDM) is a bandwidth-efficient and sensitive modulation format suitable for upgrading bandwidth-limited trunk lines. We show how control signals for polarization demultiplex can be obtained efficiently. For interleaved return-to-zero (RZ) signals, incoherent crosstalk has to be detected and minimized. In other cases, in particular for non-return-to-zero (NRZ) signals, coherent crosstalk senses penalties much better and should be detected instead. NRZ transmission experiments with either scheme are presented at a data rate of 2/spl times/10 Gb/s, with endless polarization tracking. Polarization mode dispersion (PMD) tolerance is also assessed.

Fast adaptive control for electronic equalization of PMD

Abstract: We propose an adaptive control scheme, based on the least mean squares algorithm, for electronic equalization of polarization mode dispersion. Fast adaptation is demonstrated by numerical simulations and experiments at 10 Gb/s.

Compensation and control of both first-order and higher-order polarization-mode dispersion

Abstract: Techniques and devices for controlling or compensating for both the first-order and high-order PMD effects in an optical signal by processing the signal in a fixed DGD stage and a variable DGD stage in sequence.

Method for PMD vector monitoring in picosecond pulse transmission systems

Abstract: A method and a device are proposed that allow measurement of the polarization mode dispersion (PMD) in a transmission line without data traffic interruption. The PMD vector information is extracted from the optical data signal spectrum. The method is experimentally verified by measuring of first-order PMD.