Showing papers on "Polarization mode dispersion published in 1990"

Ultrashort-pulse propagation in optical fibers

Abstract: A more exact model is suggested for the description of nonlinear light propagation in fibers. In addition to the previously discussed self-phase modulation, parametric, dispersion, self-steepening, and Raman self-scattering effects, this model also takes into account the Stokes losses associated with the material excitation, the dependence of nonlinear effects on the light frequency, and the frequency dependence of the fiber mode area. The self-steepening effect is taken into account more correctly in comparison with previous models. The effects influence considerably the femtosecond soliton propagation. The model is generalized for the case of various fiber dispersion properties along the fiber length. The possibility of obtaining high-quality pulses of less than 15-fsec duration by compression of fundamental solitons with approximately 100-fsec duration in fibers with slowly decreasing dispersion is shown.

Stimulated four-photon mixing with crossed pump dividing in an optical fiber.

Abstract: An experimental study of stimulated four-photon mixing with crossed pump dividing in a birefringent optical fiber is described. The interactive four photons are all in the same mode but with different polarizations. The pump wave is distributed in two orthogonal linear polarizations, and the polarizations of Stokes and anti-Stokes waves are also orthogonal. It is shown that the Stokes shift of this stimulated four-photon mixing process is related not only to the material dispersion but also to the waveguide dispersion and is directly proportional to the birefringence.

of the Evolution of the Principal States of Polarization in Single-Mode Fibers

Abstract: A simple expression is given for the evolution of the prin- cipal states of polarization (PSP's) and their differential group delay in fiber links. A statistical treatment for the differential group delay in long fiber is also given using a model based on the Brownian motion. This theory has been verified experimentally on an optical cable con- taining 12 single-mode dispersion-shifted fibers 2.2 km long. I. INTRODUCTION HE study of the polarization mode dispersion is im- T portant to determine the maximum bit rate that can be used in the optical communication systems. A tool, which proved to be very important in this study, is pro- vided by the principal states of polarization (PSP's) ( 11. The PSP's and their differential group delay (DGD) allow us to characterize in a simple way, at least over a limited wavelength range, a fiber affected by random birefrin- gence and coupling. The above theory has also allowed us to carry out new experimental measurements of DGD on low-birefringence long-fiber cable (2)-(4). An important problem regarding the DGD is its depen- dence on length. A statistical treatment, based on the PSP's, has already been given (5) using the coupled-mode theory under the assumption of weak coupling. A still lacking part of the theory is the evolution and the expres- sion of the PSP's in a long fiber under the most general assumptions regarding the birefringence and coupling. In this paper we have found a simple relationship among the PSP's of a long fiber link and the PSP's of the ele- mentary composing fibers; a simple relationship is also given for the DGD of the whole fiber. Furthermore, the evolution of the DGD is studied from a statistical point of view since this evolution is similar to a Brownian motion. The study of the DGD has also been investigated from an experimental point of view, over an optical cable in- corporating 12 single-mode dispersion-shifted fibers and using a color center laser, in the wavelength interval be- tween 1530 and 1560 nm. The experimental results are in agreement with the theory and show that DGD grows like the square root of the length, and for each fiber, consid-

Waveform degradation due to dispersion effects in an optical CPFSK system

Abstract: Waveform degradation due to polarization and chromatic dispersion in a single-mode fiber is calculated for a coherent continuous-phase frequency-shift-keying (CPFSK) signal. Both kinds of dispersion distort the amplitude of the baseband signal and can limit transmission distance and capacity. For instance, polarization dispersion of 5 ps will restrict a bit rate by approximately 60 Gb/s when chromatic dispersion is fully reduced using a dispersion-shifted fiber or applying electrical equalization. >

Fading in lightwave systems due to polarization-mode dispersion

Abstract: System fading caused by polarization-mode dispersion is investigated at 1.7 Gb/s using highly-birefringent, dispersion-shifted fiber at 1.55 mu m. The observed fading, which is manifested by random fluctuations of the bit error rate for a fixed receiver power, is observed to depend on the environmental conditions of the fiber, with the time constant for fading varying from minutes to hours depending on the rate of change of the ambient temperature. The mean dispersion penalty inferred from the observed fluctuations in the bit error rate is consistent with a square-law dependence on the polarization-mode dispersion for small penalties. >

Simple method for polarization dispersion measurements in long single-mode fibres

Abstract: A novel method of polarization dispersion measurements using an interferometric loop is presented. It can be carried out using a particularly simple set-up and provides a representation of the probability distribution of the polarization dispersion

Analysis of chromatic dispersion properties of triple-clad fibers by coupling-mode theory.

Abstract: A model based on coupling-mode theory, for the quantitative analysis of chromatic dispersion characteristics of triple-clad single-mode fibers, is proposed. The strong wavelength dependence of the coupling between a core mode and a ring mode supported by the high-index second cladding of the waveguide structure is shown to be responsible for the dispersion-flattened characteristics of the fiber. Cutoff properties of this type of fiber are also analyzed according to the proposed model.

Material dispersion of graded-index fibers from numerical aperture measurements.

Abstract: The material dispersion of a parabolic graded-index fiber can be completely characterized through numerical aperture measurements. The relation between the dispersion slope and wavelength of zero dispersion is discussed for single-mode fibers, and the corresponding relation for material dispersion in multimode fibers is presented. Then the effective wavelength of zero material dispersion in a multimode fiber is expressed in terms of a quantity that resembles a numerical aperture. Formulas relating that quantity to measured numerical apertures are derived in the Appendix. Starting with just numerical aperture measurements, therefore, one may determine the effective wavelength of zero material dispersion and effective material dispersion slope for a multimode fiber.

Random coupling theory of single-mode optical fibers

Abstract: A random coupling theory is developed for analyzing the propagation characteristics of the polarization state of light in single-mode optical fibers (including conventional and polarization maintaining fibers) under random disturbances. The basic idea is that the disturbances that a fiber suffers in practice continuously change with time and space, so time-varying coupling will occur along the fiber between two linearly polarized modes HE/sub 11/ that may propagate in the fiber. A coupled-mode equation of single-mode fibers under random disturbances is derived and solved rigorously with few assumptions. A random coupled-mode equation is derived considering time and space variation. Analytic solutions are obtained and used for analyzing the effect of random birefringence, polarization dispersion, polarization fluctuation, and evolution of the degree of polarization in single-mode fibers and for characterizing fiber properties. >

Interferometric Measurements Of Birefringence In Single Mode Fibers And Devices

Abstract: A simple method for interferometric measurements of chromatic and polarization mode dispersion os single mode fibres and devices is presented. Accuracy of the method and resolution limits are discussed.

Chromatic and polarization dispersion measurements of single-mode fibers with a Mach-Zehnder interferometer

Abstract: Chromatic dispersion is one of the relevant parameters which describes optical transmission systems by defining their bandwidth. It can be measured by determining the spectral group delay tG(λ) or τG - the group delay normalized with respect to the fiber length L. The measuring results are presented in an analytic form by a polynominal, the coefficients of which will be calculated by the method of the least square fit. The chromatic dispersion is the differential quotient dγG(λ)/dX. The group delay is not measured as an absolute value.

Stress and temperature effects on the performance of polarization-maintaining fibers

Abstract: Three stress effects on the state of polarization in high birefringent polarization-maintaining fibers are reviewed. The stresses induced in PM fibers by the different thermal expansion coefficients between the stress-applying parts and the surrounding glass make stress-induced-birefringent fibers very sensitive to temperature variations. Mechanical perturbations can change the polarization state of PM fibers. Temperature changes can enhance any random microbends in wound optical fiber and cause mode coupling. The effect of periodic bends, small-radius bends, and twist and fiber individual crossing in the presence of transverse pressures on the degradation of the state of polarization rotation is investigated. A procedure for evaluating the performance of wound PM fibers in low temperature environments is also discussed.

Femtosecond Raman Scattering In Birefringent Fibers

Abstract: Summary The effect of stimulated Raman scattering on the propagation of ultrashort optical pulses in silica fibers has been recently studied by means of the Schriidinger equation with a delayed contribution to the nonlinearity.1 In this work we extend the analysis to deal with pulses of arbitrary polarization which propagate in the two orthogonal polarization modes of a birefringent fiber. This has important implications for femtosecond pulse compression experiments, where intensity-dependent polarization rotation may be used to eliminate the wings of a compressed pulse, and for all-optical switching devices employing the two polarization modes of a fiber.293 Figure 1 shows examples of computed pulse envelopes emerging from the slow (1 a) and the fast (lb) axis of a birefringent fiber of length z = 0.25 (in soliton units1**), respectively, whenever the input pulse is slightly misaligned with the slow axis. As can be seen, considerable polarization rotation occurs near the edges of the weak pulse component. Moreover, a temporal asymmetry is introduced by the nonistantaneous Raman contribution, in close agreement with recent pulse shaping measurements.4 A similar asymmetry also results in the spectral distributions. By simulating the passage of these pulses through a grating with anomalous dispersion, we have studied the effect of Raman-induced asymmetries on the choice of parameters for optimal pulse compression. Figure 2 illustrates the coupling between linear polarization modes which is predicted to occur in the anomalous dispersion regime for femtosecond solitons in a periodically twisted fiber filter.* The distance is given in terms of the linear coupling length of the polarization coupler. The input pulse is launched on the fast axis (fig. 2(a)): as can be seen, the pulse slowing down due to soliton self-frequency shift competes with the differential group delay and the linear coupling between the modes. The results of the calculations permit an optimal design of femtosecond soliton switching and wavelength demultiplexing experiments with birefringent fibers and filters, in the presence of selfstimulated Raman scattering.

Screening dispersion-shifted fibers for polarization-mode dispersion due to core ellipticity

Abstract: An attempt to relate polarization dispersion directly to some physical property and then use this as a means by which to characterize polarization-mode dispersion (PMD) is reported. A new diagnostic procedure has been developed and tested for screening dispersion-shifted (DS) fibers with PMD due to core ellipticity. Measurements of far-field radiation profiles across major and minor core axes are used to characterize polarization-mode dispersion. This technique is a relatively simple and quick method of screening dispersion-shifted fibers for polarization-mode dispersion greater than 5 ps/km. Differences in these far-field pattern widths were then correlated with direct core ovality measurements performed using the near-field refraction technique. The authors outline the test procedure in detail, analyze sources of error, and discuss detection limitations. >