Solitons in optical communications

In this paper we have calculated the effects of loss on the propagation of soliton solutions of the nonlinear Schrodinger equation. Since we are interested in the application of these results to optical communications, it is necessary to go beyond perturbative results. This is due to the fact that propagation distances in optical fibers are significantly greater than the decay length of the energy in the pulses. Some conclusions are drawn about the application of solitons in long-distance communications.     

Mode dependence of splice loss in graded-index optical fibers

Various measurements of the mode dependence of loss in fusion splices are presented. Both laser diodes and light-emitting diodes are employed as sources and measurements are made using both the cutback method and the backscattering technique. Empirical relations, quantifying the form of the mode dependent loss function, are derived and discussed.     

Germanium-dopant effect on hydroxyl loss increase in optical fibers

The germanium-dopant effect on hydroxyl loss increase in optical fibers is studied experimentally. The distribution profile of hydroxyl absorption which is caused by hydrogen diffusion is measured for GeO2-doped silica glasses. From the experiment, it is found that the distribution profile of induced hydroxyl absorption is similar to the GeO2concentration profile. Moreover, the absorption loss increases due to hydrogen diffusion are measured for GeO2-doped silica fibers. From the experiment, it is concluded that the induced molecular hydrogen loss as well as the induced hydroxyl loss increases with an increase in the GeO2concentration.     

Practical microbending loss formula for single-mode optical fibers

Microbending loss in a step-index single-mode fiber is formulated in an expression which provides an explicit dependence on wavelength λ and relative index difference Δ. For the permissible mean bending radiusRdaggercorresponding to a given loss,Delta^{3/2}Rdagger/lambdais the functionfof only a normalized frequency υ. This property resembles that for the uniform-bending loss. However,fin the microbending loss depends less critically on υ than in the uniform-bending loss.     

Absorption loss at high temperatures in aluminum- and copper-coated optical fibers

Thermally induced variations in the optical loss of optical fibers with metal (copper and aluminum) coatings are studied. It is demonstrated that an increase in the loss related to the OH groups depends on the medium in which the annealing takes place (an increase in the loss related to the OH groups in argon is greater than the increase in air) and on the dopant (an increase in the loss in the core doped with GeO₂ + P₂O₅ is greater than the increase in GeO₂).     

Infrared loss increase phenomenon of coated optical fibers at high temperatures

The loss increase phenomenon of coated optical fibers at high temperature has been studied. The wavelength dependent loss increase, observed for plastic-coated fibers at 200°C, is found to be irreversible. During heating, the absorption peak of second overtone of Ge-OH preferentially appeared. The dependence of the loss increase on temperature, heating time, and dopant is also examined. The loss increase level is strongly dependent on phosphorous concentration. The experimental results indicate that the loss increase is caused by chemical reactions between fiber constituent materials and hydrogen generated from coating materials. It is also confirmed that the heating test of secondary coated fiber is a practical, useful method to evaluate the hydroxyl loss increase of optical fibers.     

Evaluation of extrinsic scattering loss due to crystallization influoride optical fibers

Extrinsic scattering loss caused by crystallization in current fluoride optical fibers is evaluated in order to investigate the possibility of realizing long-length low-loss fibers. In the current fabrication process, which consists of melting, casting, and drawing, crystallization occurs mainly in the latter two heat processes. Crystal initiation and growth are simulated based on the thermal history during these processes. Scattering loss is calculated from the crystal distribution obtained. When the preform diameter is increased, scattering loss increases rapidly. A low scattering loss is essentially expected only for the fibers drawn from small diameter preforms, although drawing has a relatively large effect on crystallization     

Sensing with suspended-core optical fibers

The development of optical fibers with suspended cores has enabled the demonstration of a range of powerful new techniques for chemical and biological sensing. Here the fabrication, design and application of this new class of fibers are reviewed. The performance and potential of sensors based on these fibers is evaluated, including dip sensors for sensing small sample volumes, exposed-core fibers for real-time and distributed measurements, and surface functionalized fibers for the specific detection of chemicals and biomolecules.     

Soliton stability in optical fibers with polarization-modedispersion

This letter presents a detailed investigation of how solitons broaden in the presence of polarization-mode dispersion. For a given amount of polarization-mode dispersion and pulsewidth there exists an optimal choice of group-velocity dispersion, for which solitons are most resistant to the effect of polarization-mode dispersion. We also optimize the soliton power enhancement factor and find that solitons can propagate roughly twice the distance compared to linear pulses in the absence of group-velocity dispersion     

Engineering modes in optical fibers with metamaterial

In this paper, we report a preliminary theoret-ical study on optical fibers with fine material inclusions whose geometrical inhomogeneity is almost indistinguish-able by the operating wavelength. We refer to such fibers as metamaterial optical fibers, which can conceptually be considered as an extension from the previously much publicized microstructured optical fibers. Metamaterials can have optical properties not obtainable in naturally existing materials, including artificial anisotropy as well as graded material properties. Therefore, incorporation of metamaterial in optical fiber designs can produce a new range of fiber properties. With a particular example, we will show how mode discrimination can be achieved in a multimode Bragg fiber with the help of metamaterial. We also look into the mean field theory as well as Maxwell-Garner theory for homogenizing a fine metamaterial structure to a homogeneous one. The accuracies of the two homogenization approaches are compared with full-structure calculation.     

Polarization in optical fibers

Recent research on fibers with very small or very large birefringence for polarization-dependent applications is reviewed. The nature of random coupling between normal modes of polarization is analyzed and discussed in connection with various applications.     

光学格点中玻色-爱因斯坦凝聚的自旋孤子

得到了一个有关光学格点中的玻色-爱因斯坦凝聚的改进的非线性薛定谔方程,并且通过仔细考察自旋概率幅方程的高阶非线性项,求得了一个改进孤子解.并求出了孤子的宽度、峰值和能量.     

Bend loss in single-mode fibers

In this paper, we present the results of extensive single-radius bend loss measurements for two different fibers over wide ranges of wavelength (800-1600 nm) and curvature radius (13.5-27.5 mm). A new bend loss formula is also derived, allowing a good fit of experimental data over the whole range of both parameters. Using an equivalent step-index (ESI) approach we obtain a good agreement between estimated and real parameters: e.g., cutoff wavelengths are within 1%     

Soliton switching in twin-core fibers with gain and loss

Soliton propagation and switching in twin-core nonlinear fibers with gain and loss have been investigated based on a pair of coupled nonlinear Schrödinger equations. We have found the fiber with equal amount of gain in both cores has the minimum ascending energy Δ? of 1.5K, while the fiber with a certain amount of gain in one core and the same amount of loss in the other core has the minimum switching threshold? _th of 2.05K. A new vector field is defined and its potential function is derived, which explains the switching behavior of the minimum? _th switch satisfactorily.     

Soliton propagation in long fibers with periodically compensated loss

With computer simulation, we study soliton propagation in an all-optical, long-distance communications system where fiber loss is periodically compensated by Raman gain. We find that distortion of the transmitted pulses from true solitons shows a peak nearz_{0} = L/8whereLand z0are the amplification and soliton periods, respectively. We also describe optimal system design based on the exceptional pulse stability and low soliton powers obtained in the regionz_{0} gg L/8. Typical amplification periods are in the range 30-50 km, pump powers are less than 100 mW, and for bit rates in the 10 GHz range, time average signal powers are at most a few milliwatts. The single-channel rate-length product for error rate less than 10^-9issim29 000GHz Km. Finally, we show that in the gain-compensated system with wavelength multiplexing, soliton-soliton collisions produce random modulation of individual pulse velocities. Nevertheless, multiplexing can yield rate-length products greater than 300 000 GHz km.     

Infrared optical fibers with vapor-deposited cladding layer

Core-cladding structures constructed for KRS-5 polycrystalline and As₂S₃ glass infrared fibers by means of vapor deposition are discussed. In order to obtain high-numerical-aperture fibers, KRS-6 and AsS₃, respectively, have been used as cladding materials. A CO₂ laser beam of 15-20 W has been successfully transmitted through the KRS-5 fiber. For the As₂S₃ fiber an absorption loss due to Teflon coating has been reduced, and a loss of 0.13 dB/m has been achieved     

Bending effects in optical fibers

Mode coupling at bends in optical fibers supporting one or only a few guided modes is analyzed by considering the local normal modes for the corresponding straight waveguide. Matrix elements giving the strength of coupling between guided modes at a corner bend, and for coupling between guided modes and radiation modes, are calculated as a function of guiding strength for this "geometrical" effect. The correction to these matrix elements due to the longitudinal strain in a bent fiber is also determined. The increase in propagation constant for the fundamental mode of a fiber wrapped in a coil of constant radius is calculated from information on the coupling strengths and mode propagation constants. The phase shift and attenuation of the fundamental mode caused by a spatially periodic microbending of the fiber axis are also considered. Finally, potential applications of these effects in fiber-optic devices such as mode converters, phase shifters, switches, and sensors are discussed.     

Polarization-maintaining optical fibers with hollow circular pits

This paper gives a detailed investigation on the polarization-maintaining optical fibers with one hollow circular pit across the core-clad interface (single circular-pit fiber (SCF)), and two hollow circular pits across the core-clad interface (double circular-pit fiber (DCF)). The field problems are analyzed by the improved point matching method. Waveguide parameters of SCF and DCF which provide the largest modal birefringence, are investigated. It was found from numerical analysis that 1) the maximum modal birefringence Bmaxfor DCF is larger than that for SCF and 2) the value ofB_{max} = 4.49 times 10^{-4}has been attained for DCF when the refractive-index difference is 0.5 percent. Zero-polarization-mode dispersion can be realized atV=V_{max}, but cannot be realized just atV = V_{max}, whereVis normalized frequency and Vmaxis the value ofVfor Bmax. These results are quite reliable because a) the relative error of the modal birefringence computed by our method is less than 10^-4and b) this new method never produces ghost solutions.     

Guided optical waves in fibers with negative dielectric constant

We classify and discuss all optical guided modes able to propagate in ideal metallic-dielectric structures having the symmetry of a step index fiber. The cases of a metallic core with a dielectric cladding and a dielectric core with a metallic cladding are considered. In each case, the intensity profile of the allowed guided modes is shown. The geometric and frequency dispersion of the effective index of the modes is discussed as a function of the optogeometrical parameters of the fibers