Showing papers on "Polarization mode dispersion published in 1995"

Dispersion effects in optical millimeter-wave systems using self-heterodyne method for transport and generation

Abstract: This paper describes the detrimental effects of chromatic and polarization mode dispersion (PMD) on systems using single-laser-based optical self-heterodyning for generation and transport of millimeter (mm)-wave signals. The decrease of the generated mm-wave power due to chromatic dispersion in conjunction with nonnegligible laser phase noise is calculated and experimentally verified. Considering statistical properties of the PMD an analytical expression for the cumulative probability distribution of the power penalty is found and used to determine the required system margin for a given system outage rate. Furthermore, two system experiments using ASK and DPSK modulation scheme, respectively, are presented showing no limitation due to the dispersion effects. >

Intermodal dispersion in two-core optical fibers.

Abstract: The switching characteristics of a two-core optical fiber can be described by the beating of the even and odd modes of the composite two-core structure. It is shown that the group-delay difference between these two modes can be as large as 10 ps/m. This intermodal dispersion sets a limit on the shortest duration of the optical pulse that can be switched effectively in devices that use long lengths of two-core fibers, such as wavelength-division multiplexers, polarization splitters, and nonlinear directional couplers.

A compact device for highly efficient dispersion compensation in fiber transmission

Abstract: We show that the supermodes of two coupled waveguides may exhibit a giant tunable group‐velocity dispersion, which allows for dispersion compensation in long‐haul fiber transmission lines, pulse compression, as well as bright soliton propagation in materials with large normal dispersion.

Limitations imposed by polarization-dependent gain and loss on all-optical ultralong communication systems

Abstract: The performance degradation of an all-optical ultralong system due to polarization dependent loss and polarization dependent gain is analytically analyzed. In particular, both the mean and the standard deviation of the performance are calculated. The analytical predictions are compared against a computer simulator, which includes the effects of nonlinearity and polarization mode dispersion. The result show that polarization dependent gain is the major source of degradation for the mean performance, while both polarization dependent loss and gain affect the standard deviation from the mean performance. Finally, the performance improvement due to polarization scrambling is evaluated. >

Dispersion compensation for optical fiber systems

Abstract: Much of the currently embedded optical fiber was originally designed for light with a wavelength of 1.3 microns. If this fiber is to be used with tomorrow's optically amplified, high-speed, long span-length lightwave system operating at 1.5 microns, the chromatic dispersion in the fiber must be compensated. Dispersion compensation will be required in long-haul l0 Gb/s systems using conventional fiber. Many compensation techniques have been demonstrated and they exhibit a variety of different and often complimentary properties. Transmitter compensation techniques are the most easily implemented but provide a limited amount of compensation. The most commercially advanced technique is negative dispersion fiber. Chirped Bragg gratings are advancing rapidly, but will always be hampered by their narrow bandwidth. The adoption of any particular technique for use in a high-speed network will depend on the constraints imposed by the, as yet, undefined network architecture. >

Polarization scattering by soliton-soliton collisions.

Abstract: We have discovered experimentally that soliton–soliton collisions in wavelength division multiplexing significantly alter the polarization states of the colliding solitons. Analysis shows that the change in polarization is according to the cross product of the Stokes vectors of the colliding solitons. Birefringence of the fiber spans can turn this polarization scattering into a significant source of timing jitter.

by Polarization-Dependent Gain and Loss on All-Optical Ultralong Communication Systems

Abstract: The performance degradation of an all-optical ultra- long system due to polarization dependent loss and polarization dependent gain is analytically analyzed. In particular, both the mean and the standard deviation of the performance are calcu- lated. The analytical predictions are compared against a com- puter simulator, which includes the effects of nonlinearity and polarization mode dispersion. The results show that polarization dependent gain is the major source of degradation for the mean performance, while both polarization dependent loss and gain af- fect the standard deviation from the mean performance. Finally, the performance improvement due to polarization scrambling is evaluated. IGHTWAVE systems with optical amplifiers are vul- L nerable to performance degradation due to polarization dependent loss (PDL) and polarization dependent gain (PDG) 111-141. PDL may be caused by optical components such as directional couplers and isolators, while PDG is caused by polarization hole burning (PHB) in optical amplifiers 1.51. Due to PDL and PDG, a polarized signal may be attenuated or amplified differently than the unpolarized noise, and the signal-to-noise ratio (SNR) is modified accordingly. The SNR modifications lead to performance degradation. Furthermore, since the state of polarization (SOP) of the transmitted light is randomly changed in time, PDL and PDG may cause the system performance to vary in a random manner as a function of time. In a previous work, we derived analytic expressions for the mean system performance degradation due to PDL and PDG 131. In order to complete the analysis, it is also necessary to calculate the time variations of the system performance. In this paper, we expand our previous analysis to look further at the system performance degradation. In particular, we analyze the statistics of the signal and the noise as they propagate in a system which exhibits PDL and PDG. The analysis enables us to derive analytic expressions for both the mean and the standard deviation of the system performance as determined by PDL and PDG. In order to verify the results of the analytical analysis, which was based on few simplified assumptions, we compared its predictions to the predictions of computer simulator. The

Polarization mode dispersion minimization in fiber-wound piezoelectric cylinders.

Abstract: We describe a technique for minimizing polarization mode dispersion (PMD) in broadband interferometry for use with phase modulators of the type formed by coiling nominally circular-core single-mode optical fiber onto piezoelectric cylinders. The technique involves using two piezoelectric elements, arranged to be optically orthogonal. We show that in the general case the two cylinders give rise to four distinct interferograms, but by careful alignment of the elements we reduce these to two coincident interferograms. Hence the large PMD of a single-element modulator is reduced to a negligible level.

Theoretical analysis of birefringence and form‐induced polarization mode dispersion in birefringent optical fibers: A full‐vectorial approach

Abstract: A new numerical method for analyzing birefringence and dispersion characteristics of birefringent optical fibers is presented. A major advantage of the method, based on the solution of full‐vectorial Maxwell equations, is its high accuracy no matter how great the geometrical anisotropy of the optical fiber. To verify the reliability of our numerical procedure, the modal birefringence and the form‐induced polarization mode dispersion in elliptical core fibers with different eccentricities are investigated and their values compared with some theoretical and experimental results.

Increased capacity optical waveguide

Abstract: An compound core optical waveguide fiber designed for high data rate or single channel or WDM systems which may include optical amplifiers. The waveguide is characterized by a core having two or three regions wherein the refractive index can be varied. The relative size of the regions may also be varied. By adjusting these variables, the desired mode field diameter, zero dispersion wavelength, dispersion slope and cut off wavelength were obtained. The optical properties are chosen to limit non-linear effects while maintaining low attenuation and acceptable bend performance. In addition, the residual stress within the waveguide is maintained at a low level to limit stress induced birefringence. The low residual stress in the uncoated waveguide, together with a dual coating system having selected moduli and glass transition temperatures results in low polarization mode dispersion.

Controlled dispersion optical waveguide

Abstract: A single mode optical waveguide fiber having low, non-zero dispersion over a pre-selected wavelength range is disclosed. The refractive index profile of the core is characterized in that the core includes a plurality of distinct regions, each having an index profile, and a radius or width. By adjusting the index profile sizes and shapes of the plurality of core regions, a waveguide fiber may be made having a set of properties tailored for a high performance telecommunication system. In particular, dispersion slope can be maintained less than 0.05 ps/nm2 -km and absolute magnitude of total dispersion maintained in the range of 0.5 to 3.5 ps/nm-km over a pre-selected wavelength range. The zero dispersion wavelength is outside the pre-selected wavelength range and the cut off wavelength and mode field diameter are controlled to target values.

Optical isolator with low polarization mode dispersion

Abstract: The present invention provides for a compensating element in the form of a birefringent plate in an optical isolator which uses a first GRIN lens to collimate the light signal from an input optical fiber, a first birefringent polarizer wedge, an optical Faraday rotator, a second birefringent polarizer wedge, and a second GRIN lens to recollimate the light signal to an output optical fiber. Polarization mode dispersion through said optical isolator is substantially reduced by arranging the fast optical axis of the plate to be perpendicular to the fast optical axis of the polarizer on the same side of the Faraday rotator as the plate and selecting the thickness of the plate in a predetermined manner. The present invention also allows for minimization of "walk-off", which also contributes to some polarization mode dispersion through the isolator.

Compensation of polarization mode dispersion by means of the Kerr effect for nonreturn-to-zero signals.

Abstract: We demonstrate numerically that a compensation of the polarization mode dispersion can be observed for nonreturn-to-zero signals as a result of a trapping effect, in analogy to the well-known soliton behavior. Conditions for such compensation are shown, and a comparison with the soliton case is reported.

Apparatus for compensating chromatic and polarization dispersion and frequency chirp in fiber optics and for pulse compression in laser systems

Abstract: Chromatic and polarization dispersion and transmitter frequency chirp are the dominant data rate limiting factors for high-speed, long distance communication systems. To overcome such limitations, a chromatic and polarization dispersion and frequency chirp compensator is utilized. The applicants provide a compensator by combining a wavelength to polarization transformer with a polarization to delay converter having a dispersion characteristic of substantially equivalent in magnitude, and opposite in sign, to the desired amount of dispersion and frequency chirp to be compensated. Optical gain may be incorporated in any of the elements of the compensator which makes the present invention a lightwave amplifier as well as a dispersion compensator. The present invention is also applicable as an optical pulse time compressor that compresses a relatively long width optical pulse to a short width pulse.

Definition of polarization mode dispersion and first results of the COST 241 round-robin measurements

Abstract: Two definitions and three measurement schemes for polarization mode dispersion are presented. Their relations, advantages and drawbacks are discussed. A connection with the dynamical equation for the principal polarization states is made. First results from the COST 241 interlaboratory measurement campaign are also presented.

Dispersion compensator and optical amplifier

Abstract: A dispersion compensator of the present invention includes a dispersion compensation fiber and a polarization conversion mirror. The dispersion compensation fiber has color dispersion of a sign opposite to the sign of the color dispersion of the optical fiber transmission line, and the length thereof is set so as to conform to the value of the color dispersion of the optical fiber transmission line. Light propagating in the optical fiber transmission line then propagates in the dispersion compensation fiber from a first end toward a second end of it and is supplied to the polarization conversion mirror. The light supplied to the polarization conversion mirror is converted into light of a polarization condition orthogonal and time-reversed to the polarization condition of the light supplied to the polarization conversion mirror, and propagates in the dispersion compensation fiber from the second end toward the first end of it. This enables compensation not only for color dispersion but also for polarization mode dispersion.

Polarization state changing apparatus and polarization degree measuring apparatus using the same

Abstract: A polarization state changing apparatus which can change the polarization state of an incident polarized light entering to an optical fiber to any direction and can output is provided. This polarization state changing apparatus, in an embodiment, comprises three polarization plane maintaining optical fibers 10, 20 and 300 which are serially connected at two polarization plane changing parts 30 and 30'. Those three polarization plane maintaining optical fibers are connected at the polarization plane changing parts 30 and 30'so that the optical axes X and Y of the adjacent optical fibers are mutually rotated at an angle of 45 degrees in terms of the fiber axis. Stress application parts for applying stress to each of the polarization plane maintaining optical fibers are provided. In a specific example, each optical fiber is wound around each piezoelectric element cylinder and predetermined stress is applied to each optical fiber by driving those piezoelectric element cylinders by power supplies each of which oscillating frequency and generated voltage are both variable. Also, a polarization degree measuring apparatus using the polarization state changing apparatus is provided to measure degree of polarization accurately and quickly.

Optical communication transmission system

Abstract: An optical communication transmission system including an optical amplifier lumped repeater system of the present invention includes, for the purpose of preventing degradation of the transmission characteristic arising from wavelength dispersion of optical fibers due to raised power of the optical signal, transmission optical fibers provided for all or most of the repeating sections and having wavelength dispersion values set to different values from zero, and optical fibers provided for the individual sections to compensate for the sum of wavelength dispersion of the sections so as to reduce the total wavelength dispersion to zero. The optical fiber for compensation for each section may be replaced by a substitutive compensation element. Alternatively, very small wavelength dispersion which remains due to failure in compensating to zero dispersion may be compensated for using a dispersion equalizer of an electric system in the reception section.

Dispersion compensation using a variable group-delay dispersion equaliser

Abstract: The effectiveness of a variable group-delay dispersion equaliser in compensating for the dispersions of various lengths of fibre is explained The variable dispersion equaliser has a lattice-form programmable optical filter configuration and its dispersion can be varied from -681 to 786 ps/nm The dispersion of three different fibres has been compensated for with a single equaliser

Dispersion-shifted single-mode fiber for high-bit-rate and multiwavelength systems

Abstract: Dispersion-shifted single-mode fibers operating in the 1550-nm window have been available commercially since 1985.1 With the advances in high-speed optical-communication technology and, in particular, with the introduction of high-power erbium-doped fiber amplifiers (EDFAs), fiber systems have evolved very rapidly. For terrestrial systems, bit rates as high as 10–40 Gbit/s and unrepeatered system lengths as long as a few hundred kilometers have been contemplated. Under such conditions, in addition to chromatic dispersion, polarization mode dispersion (PMD) is a consideration. These systems operate with high-power EDFAs to compensate for the fiber loss. In addition, multiwavelength systems with only 1-or 2-nm channel spacings are being considered for increasing the fiber capacity and making use of the wide spectral range in the 1550-nm window. A combination of these factors makes the nonlinear effects in these systems very critical.2 Single-mode fibers need to be tuned to optimize their performance in such systems. Also, the dispersion-zero and slope requirements for terrestrial and submarine systems can be different. Because of the rapid changes in technology, such designs need to be flexible in their optical characteristics in order to meet future dispersion requirements of both high-bit-rate and WDM systems. In this paper we present theoretical-model and experimental results on a dispersion-shifted single-mode fiber optimized to take into account many of these factors.

All-fiber dispersive transmission filters based on fiber grating reflectors.

Abstract: A novel, low-insertion-loss transmission filter with the implementation of linearly chirped fiber Bragg grating reflectors and polarization-splitting fiber fusion couplers is reported. Pulse chirping, chromatic dispersion compensation, and pulse compression are demonstrated. Cascading of dispersive filters, including application to a low-loss pulse stretcher/recompressor of femtosecond pulses, is also demonstrated.

Anisotropic diffusion of the state of polarization in optical fibers with randomly varying birefringence.

Abstract: Polarization diffusion in communication fibers is studied Diffusion of the states of polarization in an optical fiber is found to be anisotropic on the surface of the Poincare sphere The predicted anisotropy has significant implications for nonlinear evolution in long-distance communication systems

Method and apparatus for high resolution measurement of very low levels of polarization mode dispersion (PMD) in single mode optical fibers and for calibration of PMD measuring instruments

Abstract: A method and apparatus for measuring Polarization Mode Dispersion (PMD) of a single mode optic fiber by providing a PMD measuring instrument with a light source. Light is transmitted serially through the optic fiber being tested and an artefact with a known, stable PMD value. The artefact biases the total PMD measured by the instrument away from zero. The PMD of the optic fiber may then be determined by data reduction of the total measured PMD. The method may also be used to calibrate a PMD instrument.

Dual stage optical device with low polarization mode dispersion and wavelength insensitivity

Abstract: The present invention provides for a two-stage optical isolator with reduced polarization mode dispersion. Each stage has two birefringent polarizers separated by a Faraday rotator. The polarizers in each stage are oriented with respect to each other to operate conventionally as an optical isolator for light in a backward direction. However, the polarizers in each stage are oriented with respect to the polarizers in the other stage so that a polarization mode along one direction, say, the ordinary direction, of light in the first stage travelling toward the second stage is aligned along the opposite, extraordinary, direction in the second stage and vice versa. In this manner the component of any polarization travels the same optical distance through the optical isolator to substantially reduce polarization mode dispersion. The birefringent polarizers and Faraday rotators of multiple stages can also be fitted into a single magnet to substantially reduce the sensitivity of the optical isolator to changes in wavelength.

Performace Evaluation of ASK and DPSK Optical Coherent Systems affected by Chromatic Dispersion and Polarization Mode Dispersion

Abstract: We present theoretical estimates on performances of ASK and DPSK coherent systems employing optical fibers affected by both chromatic dispersion and polarization mode dispersion. Results of simulations in terms of error probability show that, at the same bit rate, repeaterless ASK systems are intrinsically less sensitive than DPSK systems to dispersion effects.

Numerical and analytical modeling of polarization-dependent gain in erbium-doped fiber amplifiers

Abstract: We present a rate-equation model that accounts for polarization hole burning in erbium-doped fiber amplifiers. This model yields analytical expressions for the polarization sensitivity of the amplifier for arbitrary signal polarization states. We investigate the influence of the birefringence properties of the fiber and calculate the average polarization properties of an amplifier chain.

Full characterization of polarization-mode dispersion with random-mode coupling in single-mode optical fibers

Abstract: Theoretical expression has been derived for polarization-mode dispersion with random-mode coupling in optical fiber by simple means. The square-root dependence of polarization-mode dispersion not only on a fiber length but on a mean-coupling length has been experimentally verified for the first time. This characterization became possible only by the use of highly birefringent polarization-maintaining fiber and introduction of fusion splices with desired coupling lengths. >

Light depolarization owing to amplified spontaneous emission and Kerr nonlinearity in long-haul fiber links close to zero dispersion.

Abstract: The interplay between amplified spontaneous emission noise and Kerr nonlinearity is shown to produce significant depolarization of light in long-haul transmission links operating close to zero dispersion. If polarization mode dispersion is neglected, a simple analytical theory predicts the length scale over which depolarization occurs. The analytical theory is compared with computer simulations, which also permit analysis of the case in which polarization mode dispersion is included.

Impact of polarisation mode dispersion on 10 Gbit/s terrestrial systems over non-dispersion-shifted fibre

Abstract: Depending on the launched state of polarisation, 10 Gbit/s system impairments are investigated experimentally in the presence of chromatic dispersion and variable differential group delay caused by polarisation mode dispersion. In addition, an actual fibre cable, not an optical simulator, was used to bring polarisation mode dispersion.

Polarization characteristics, control, and modulation of vertical-cavity surface emitting lasers

Abstract: The gain-dependent polarization properties of vertical-cavity surface emitting lasers and methods for polarization control and modulation are discussed. The partitioning of power between the two orthogonal eigen polarizations is shown to depend upon the relative spectral alignment of the nondegenerate polarization cavity resonances with the laser gain spectrum. A dominant polarization can thus be maintained by employing a blue-shifted offset of the peak laser gain relative to the cavity resonance wavelength. Alternatively, the polarization can be controlled through use of anisotropic transverse cavity geometries. The orthogonal eigen polarizations are also shown to enable polarization modulation. By exploiting polarization switching transitions in cruciform lasers, polarization modulation of the fundamental mode up to 50 MHz is demonstrated. At lower modulation frequencies, complementary digital polarized output or frequency doubling of the polarized output is obtained. Control and manipulation of vertical-cavity laser polarization may prove valuable for present and future applications.