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1.
A simple analytical solution is derived from coupled-mode theory to describe the evolution of polarization mode dispersion (PMD) in spun fibers. For practical fibers with a beat length greater than a few meters, the solution is valid for a whole category of periodic spin profiles. We find that the PMD change factor is independent of the intrinsic birefringence of the fiber and the fiber PMD scales linearly with the fiber length in the short length regime. This solution allows us to determine phase-matching conditions for spun fibers, in which the PMD evolves periodically along the fiber. An example of determining the phase-matching conditions of sinusoidal-type spin profiles is given. 相似文献
2.
The scaling properties of polarization mode dispersion (PMD) in spun fibers are studied. Simple equations have been obtained to describe the scaling properties of spun fibers as a function of intrinsic fiber birefringence, spin parameters, and mode-coupling length under both optimal and nonoptimal spin conditions. In particular, a counterintuitive result is found for fibers with perfect spin optimization, in which case the fiber PMD increases as the mode-coupling length is shortened. The results are verified with direct numerical modeling. 相似文献
3.
The spin profile of a fiber is usually optimized to reduce transmission impairments caused by polarization-mode dispersion (PMD). In this paper, we show that fiber-optic-based plug-and-play quantum-key distribution systems using polarization modulation and fibers with a spin profile optimal for PMD may suffer from a large Faraday rotation induced by the geomagnetic field. We show that, for periodic spin patterns of small periods, the Faraday rotation is minimum when no spin is applied to the fiber. 相似文献
4.
A. S. Abramov I. O. Zolotovskii D. I. Sementsov D. A. Stolyarov 《Optics and Spectroscopy》2014,117(5):792-798
Specific features of the formation of frequency-modulated pulses with large peak powers in amplifier-modulator-compressor cascade schemes based on length-inhomogeneous optic fibers are considered. Optimum profiles of fiber parameters ensuring the most effective amplification and modulation of pico- and subpicosecond frequency-modulated pulses are proposed. It is established that the use of a cascade consisting of active (gain) and passive (modulating) fibers with optimized profiles of the normal group-velocity dispersion and mode area can ensure the formation of pico- and subpicosecond pulses with energies higher than 100 nJ and peak powers above 100 kW. 相似文献
5.
Potentials of mean force (PMF) are calculated for two model ion pairs in two non-aqueous solvents. Standard non-polarizable molecular dynamics simulation (NPMD) and approximate polarizable simulation (PMD) are implemented and compared as tools for monitoring PMF profiles. For the polar solvent (dimethylsulfoxide, DMSO) the PMF generated in terms of the NPMD reproduces fairly well the refined PMD–PMF profile. For the non-polar solvent (benzene) the conventional NPMD computation proves to be deficient. The validity of the correction found in terms of the approximate PMD approach is verified by its comparison with the result of the explicit PMD computation in benzene. The shapes of the PMF profiles in DMSO and in benzene are quite different. In DMSO, owing to dielectric screening, the PMF presents a flat plot with a shallow minimum positioned in the vicinity of the van der Waals contact of the ion pair. For the benzene case, the observed minimum proves to be unexpectedly deep, which manifests the formation of a tightly-binded contact ion pair. This remarkable effect arises owing to the strong electrostatic interaction that is incompletely screened by a non-polar medium. The PMFs for the binary benzene/DMSO mixtures display intermediate behaviour depending on the DMSO content. 相似文献
6.
Although fiber spinning is known to reduce polarization mode dispersion (PMD) effects in optical fibers, relatively few studies
have been performed of the dependence of the reduction factor on the strength of random birefringence fluctuations. In this
paper, we apply a general mathematical model of random fiber birefringence to sinusoidally spun fibers. We find that while
even in the presence of random birefringence perturbations the maximum reduction of PMD is still obtained when the phase matching
condition is satisfied, the degree of PMD reduction and the probability distribution function of the DGD both vary with the
random birefringence profiles. 相似文献
7.
A. V. Zhukov I. O. Zolotovskii O. G. Okhotnikov D. I. Sementsov A. A. Sysolyatin I. O. Yavtushenko 《Optics and Spectroscopy》2012,113(1):75-80
Conditions of the formation and amplification of frequency-modulated soliton-like pulses in longitudinally inhomogeneous active optical waveguides with anomalous dispersion of group velocities are studied. Group velocity dispersion profiles that are necessary for existence and amplification for active and passive optical waveguides are determined, and the dependences on the distance passed along the waveguide, duration, and chirp of the pulse are established. 相似文献
8.
《Journal of Magnetic Resonance, Series A》1993,101(3):257-264
Slice-selective amplitude-modulated and adiabatic frequency-modulated π pulses are obtained by optimizing a small number of significant pulse parameters by unconstrained optimization of a suitable function. The method is also used to optimize the slice profile of AM pulses taking into account the RF inhomogeneity in the selection direction and to reduce the specific absorption rate and peak power. Experimental slice profiles are presented to verify the performance of the optimized pulses. 相似文献
9.
This paper presents an analysis of the performance of frequency-modulated pulses and of pulses modulated simultaneously in amplitude and frequency in the pure nuclear quadrupolar resonance (NQR) spectroscopy of spin 3/2 nuclei. Computer simulations are given of the offset compensation efficiency of such pulses as applied to single crystals. Spin evolution equations were solved numerically. Experimental measurements, using FM pulses, of the35Cl NQR of sodium chlorate (NaClO3) single crystal and of mercuric chloride (HgCl2) powder are reported. The results suggest that frequency modulated pulses are alternative pulses to composite pulses in NQR. 相似文献
10.
Gapped pulses for frequency-swept MRI 总被引:1,自引:0,他引:1
Idiyatullin D Corum C Moeller S Garwood M 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2008,193(2):267-273
A recently introduced method called SWIFT (SWeep Imaging with Fourier Transform) is a fundamentally different approach to MRI which is particularly well suited to imaging objects with extremely fast spin–spin relaxation rates. The method exploits a frequency-swept excitation pulse and virtually simultaneous signal acquisition in a time-shared mode. Correlation of the spin system response with the excitation pulse function is used to extract the signals of interest. With SWIFT, image quality is highly dependent on producing uniform and broadband spin excitation. These requirements are satisfied by using frequency-modulated pulses belonging to the hyperbolic secant family (HSn pulses). This article describes the experimental steps needed to properly implement HSn pulses in SWIFT. In addition, properties of HSn pulses in the rapid passage, linear region are investigated, followed by an analysis of the pulses after inserting the “gaps” needed for time-shared excitation and acquisition. Finally, compact expressions are presented to estimate the amplitude and flip angle of the HSn pulses, as well as the relative energy deposited by the SWIFT sequence. 相似文献
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12.
John Cameron 《Fiber and Integrated Optics》1999,18(1):49-59
Polarization mode dispersion (PMD) measurements are presented for a sample of installed optical fibers. High PMD values are fairly common, with 9 of the 71 fibers having PMD coefficients above 0.3 ps km1 2. The results are analyzed in terms of the age of the fibers and the type of cabling. Measurements are presented for a number of concatenated fiber links, and the results show that the PMD value of the link is approximately equal to the square root of the sum of the squares of the PMD values of the individual fibers. 相似文献
13.
In this paper, the statistical distributing and magnitude of the first and the second-order PMD (polarization mode dispersion)
vectors are evaluated and the filters control PMD effects also are analyzed on DMS (dispersion-managed soliton) links. Firstly,
the so-called coarse-step approach is applied to the DMS links. The PMD statistical characteristics of the first and the second-order
are simulated and the evolutions of energy and mean square of time displacement of DMS two polarization modes are gotten.
Secondly, The DMS transmission of filter control with the conventional model of PMD is analyzed by Varitional method, from
which the evolving rules of characteristically DMS parameters are obtained and the stability of filter control the DMS transmission
are investigated. The results are not only very useful to simplify the measurement of the second-order PMD and instructively
reveal degree of PMD effects in DMS systems, but also give that condition of stability of filter control PMD in DMS systems. 相似文献
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15.
研究了无损光纤的密勒矩阵,进而得出了偏振模色散矢量的解析表达式、主偏振态对应的斯托克斯矢量的解析表达式,以及高阶偏振模色散矢量的解析表达式.这些解析表达式是由光纤参数决定的.讨论了局部偏振模色散矢量与整体偏振模色散矢量的关系,讨论了利用偏振模色散矢量进行偏振模色散补偿的原理.引入了偏振模色散补偿元件的偏振模色散补偿矢量C,具体计算了正规的非圆光波导类的补偿元件的C.从理论上证明了仅仅利用一个正规的非圆光波导类的补偿元件,例如一根保偏光纤或是一个双折射晶体,是不能实现偏振模色散补偿
关键词:
偏振模色散
密勒矩阵
色散补偿
主偏振态斯托克斯矢量 相似文献
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通过建立一个简单的模型推导了偏振模色散与偏振度椭球的关系式,可以直接从偏振度椭球的长轴和短轴得到偏振模色散的大小.将得到的一阶偏振模色散大小与理论上从琼斯矩阵中计算的结果进行比较,发现在差分群时延小于20 ps时,模拟结果与理论计算值较好相符.分析了如何从偏振度椭球的长轴判断偏振模色散矢量的方向.因此,从得到的偏振模色散矢量的大小和方向信息可以为一阶偏振模色散补偿提供前馈信息. 相似文献
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We report the observation of spin segregation, i.e., time-dependent separation of the spin density profiles of two spin states, in a trapped, coherently prepared Fermi gas of 6Li with a magnetically tunable scattering length a12 close to zero. For |a12| approximately = 5 bohr, as the cloud profiles evolve, the measured difference in the densities at the cloud center increases in 200 ms from 0 to approximately = 60% of the initial mean density and changes sign with a12. The data are in disagreement in both amplitude and temporal evolution with a spin-wave theory for a Fermi gas. In contrast, for a Bose gas, an analogous theory has successfully described previous observations of spin segregation. The observed segregated atomic density profiles are far from equilibrium, yet they persist for approximately = 5 s, long compared to the axial trapping period of 6.9 ms. We find the zero crossing in a12=0, where spin segregation ceases, at 527.5+/-0.2 G. 相似文献