光栅参数对折射率剖面非均匀取样光纤光栅的影响

利用传输矩阵法,数值分析了光栅参数对折射率剖面非均匀的均匀光纤光栅及取样光纤光栅的透射谱、偏振关系损耗和偏振模色散的影响。计算结果表明,均匀光纤光栅的光栅条纹可见度及光栅周期对其偏振关系损耗和偏振模色散影响很大;改变取样光纤光栅的取样周期及光栅段长度,透射谐振峰的幅度、偏振关系损耗和偏振模色散的最大值均随取样光纤光栅长度的增加而递增。与靠近中心波长的谐振峰相比,折射率剖面非均匀导致的双折射对取样光纤光栅远离中心波长的谐振峰的影响较小。     

Fibers with low polarization-mode dispersion

Fibers with low polarization-mode dispersion (PMD) enable high-bit-rate time-division-multiplexed optical communication systems. These fibers are becoming increasingly important with the growing implementation of wavelength-division-multiplexing (WDM) transmission with channel bit rates of 40 Gb/s. Important to the realization of low PMD fibers are the fiber's index and stress profiles, polarization-mode coupling, and the evolution of the polarization state with length. This paper reviews recent progress in the understanding of the fabrication and characteristics of these fibers. The paper also discusses the important fiber physical parameters, including the fiber index profile and fiber spinning parameters and their impacts on the realization of low PMD performance.     

Principal Modes in Graded-Index Multimode Fiber in Presence of Spatial- and Polarization-Mode Coupling

Power-coupling models are inherently unable to describe certain mode coupling effects in multimode fiber (MMF) when using coherent sources at high bit rates, such as polarization dependence of the impulse response. We develop a field-coupling model for propagation in graded-index MMF, analogous to the principal-states model for polarization-mode dispersion in single-mode fiber. Our model allows computation of the fiber impulse response, given a launched electric-field profile and polarization. In order to model both spatial- and polarization-mode coupling, we divide a MMF into numerous short sections, each having random curvature and random angular orientation. The model can be described using only a few parameters, including fiber length, number of sections, and curvature variance. For each random realization of a MMF, we compute a propagation matrix, the principal modes (PMs), and corresponding group delays (GDs). When the curvature variance and fiber length are small (low-coupling regime), the GDs are close to their uncoupled values, and scale linearly with fiber length, while the PMs remain highly polarized. In this regime, our model reproduces the polarization dependence of the impulse response that is observed in silica MMF. When the curvature variance and fiber length are sufficiently large (high-coupling regime), the GD spread is reduced, and the GDs scale with the square root of the fiber length, while the PMs become depolarized. In this regime, our model is consistent with the reduced GD spread observed in plastic MMF.     

Fading in lightwave systems due to polarization-mode dispersion

System fading caused by polarization-mode dispersion is investigated at 1.7 Gb/s using highly-birefringent, dispersion-shifted fiber at 1.55 μm. 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     

Soliton robustness to the polarization-mode dispersion in opticalfibers

The influences of chromatic dispersion, coupling length, and soliton energy on the soliton robustness to polarization-mode dispersion (PMD) are investigated numerically. We find that both chromatic dispersion and soliton energy have significant effects on the soliton robustness to PMD, and by optimizing chromatic dispersion and soliton energy, soliton pulse broadening can be depressed to within 10% even when the differential group delay is about twice the input pulse width. In addition, a recent experimental result on soliton robustness is numerically verified     

一种降低相干光OFDM系统非线性效应的方法

相干光正交频分复用(Coherent optical-orthogonal frequency division multiplexing,简称CO-OFDM)可有效降低光纤色散和偏振模色散对系统的影响,是近年来光传输领域研究热点之一.但由于OFDM高的峰均值功率比(PAPR)和较窄的载波间隔(几十兆赫兹),CO-OF...     

Theoretical and experimental study of the dynamics ofpolarization-mode dispersion

The dynamic distribution of the state of polarization (SOP) is studied theoretically and experimentally for aerial fibers with a finite polarization-mode dispersion (PMD). A dynamic mode coupling wave-plate model is proposed to describe the SOP correlation and account for the PMD variations. It is found that the model can closely describe the experimental dynamic correlation of the SOP for an aerial fiber. A new algorithm for PMD emulation is developed     

直接检测光正交频分复用系统噪声分析

针对直接检测光正交频分复用（DDO-OFDM）系统产生的放大器自发辐射（ASE）拍频噪声。通过对系统受ASE噪声影响的数学分析得到噪声影响机理及系统信噪比表达式,根据理论推导提出载波抑制方案,通过数字仿真验证推导结果及方案可行性。理论分析和仿真结果表明,系统受ASE拍频噪声影响严重,合理选择带通滤波器带宽可有效降低噪声...     

Distortion related to polarization-mode dispersion in analoglightwave systems

Analog transmission in single-mode fiber using chirped sources gives rise to nonlinear distortion when polarization-mode dispersion (PMD) is present. We investigate experimentally and theoretically two mechanisms for this distortion: for chirped sources, PMD in the presence of polarization-mode coupling results in second-order distortion that is proportional to the square of the modulation frequency; when polarization-dependent loss is present, an additional second-order distortion term occurs that is independent of modulation frequency. Both mechanisms give rise to distortion that is time varying due to the sensitivity of PMD to ambient temperature changes. Numerical examples indicate that these effects can limit the capacity of analog systems that use directly modulated semiconductor lasers     

Pulsewidth distortion monitoring in a 40-Gb/s optical systemaffected by PMD

A novel technique for monitoring the pulse broadening due to polarization-mode dispersion (PMD) in optical systems is described. The technique is based on the measurement of the Stokes vectors at different frequencies over the spectrum of the received optical pulse find does not require a priori knowledge of the fiber PMD statistics or details of the optical path. The validity of our technique has been demonstrated by both simulation and experimental results     

Characterization of wavelength-selective fiber-optic devices usinga modified phase-shift method

We present a novel measurement setup that can be used for the complete characterization of fiber Bragg gratings and wavelength selective fiber-optic devices. Our setup is based on the phase-shift method (PSM), which we have modified to include the measurement of polarization-induced effects such as polarization-dependant loss (PDL) and polarization-mode dispersion (PMD). We measure the spectral response of devices used in transmission and in reflection, the wavelength dependency of the group delays due to chromatic and polarization-mode dispersion, and the wavelength dependency of the polarization-dependent loss. Experimental results are presented and sources of error are discussed. Comparisons with the Jones matrix eigenanalysis method for the measurement of PDL and differential group delay due to PMD have been carried out     

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

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     

A simple and useful model for Jones matrix to evaluate higher orderpolarization-mode dispersion effects

Starting from the differential equation that relates the Jones matrix of a polarization-mode dispersion (PMD) fiber to its output dispersion vector, the analytical expressions of the matrix coefficients are determined in the case of a dispersion vector rotating on a circumference in the Stokes space. This model, that needs only few parameters with known statistics, is applied to evaluate the performance of an optical system. The results obtained with it and with other models proposed in literature are compared to those evaluated by numerical simulations with all-order PMD effects, showing that our model gives an accurate representation of real system performances     

相干光OFDM系统中的相位估计分析

相干光正交频分复用(Coherent Optical Orthogonal Frequency Division Multiplexing,简称CO-OFDM)可有效降低光纤色散和偏振模色散影响,由于系统采用相干检测,对相位噪声的分析及信道估计尤为重要.文章对CO-OFDM系统数学模型进行了具体分析;OFDM作为一种特...     

Optimum Receiver Filters for Optical Fiber Systems With Polarization Mode Dispersion

We use a semi-analytical receiver model combined with importance sampling applied to first-order polarization-mode dispersion (PMD) to show that the performance of optical fiber systems whose optical and electrical receiver filter bandwidths are optimized for polarization-mode dispersion in practical on-off-keyed systems is equivalent to the performance of the same systems in which the receiver filters are optimized for operation in the absence of PMD. We also observed an increase in the sensitivity of the performance with respect to variations in the receiver filter bandwidths in the return-to-zero format in systems with PMD when compared with PMD-free operation.      

A Model for Temporal Evolution of PMD

We elaborate on a stochastic model of the temporal evolution of polarization-mode dispersion (PMD). The reliability of the model is tested by comparison of theoretical results, obtained in the investigation of the conditional statistics of the PMD vector, with data measured on an installed fiber plant.     

On the performance of electrical equalization in optical fiber transmission systems

A variety of equalizers have been proposed to improve the bit-error rate (BER) of optical fiber communications by reducing the effects of chromatic dispersion (CD), polarization-mode dispersion (PMD), and other fiber impairments. Therefore, it is of interest to establish the ultimate performance of electrical equalizers under different conditions. The results presented here are based on the fact that maximum-likelihood sequence detection (MLSD) obtains the lowest BER of all possible detectors, under mild conditions. Thus, the MLSD performance is a lower bound on the BER of any electrical equalizer. We consider linear channels with PMD (all orders), CD, and the nonlinear effect of the photodetector.     

A tunable multiwavelength fiber ring laser for measuring polarization-mode dispersion in optical fibers

We describe and demonstrate a tunable triple-wavelength erbium-doped fiber ring laser along with a method of measuring polarization-mode dispersion (PMD) in optical fibers based on a broad-band orthogonal-pump four-wave mixing in a semiconductor optical amplifier. The measured PMD results for optical fibers are in good agreement with values measured by means of commercial PMD testing equipment.     

Mitigating PMD in Fiber Optical Parametric Amplifiers With Alternating Fiber Twists

We show by means of analytical calculations and numerical simulations that the impact of polarization-mode dispersion (PMD) on the gain spectrum of fiber optical parametric amplifiers (OPAs) can be reduced by imposing twists along the fiber axis. Alternating twists are used in order to cancel the induced circular birefringence.      

Impact of chirping on polarization-mode dispersion compensated systems

Investigates the effect of chirp, resulting from either the transmitter, chromatic dispersion, or Kerr effect in the fiber, on polarization-mode dispersion (PMD) compensated systems. We demonstrate both experimentally and numerically the deleterious impact of chirping on systems with first-order PMD compensation. We present a way to optimize the PMD compensator performance by minimizing the total chirp of the signal at the receiver side.