First-order Polarization Mode Dispersion Compensation Research Articles

First-order polarization mode dispersion compensator using two independent feedback signals enabling separation of principal states of polarization and differential group delay controls

We propose and demonstrate a novel first-order polarization mode dispersion (PMD) compensator separating principal-states-of-polarization (PSP) control from differential-group-delay (DGD) control by using two independent feedback monitoring signals. To verify the proposed operating principle, we fabricated an automatically adaptive module-type 40-Gb/s PMD compensator on printed circuit boards. The results show that unlike previous typical compensation method of controlling alternately PSP and DGD, the proposed scheme provides independent continuous PSP tracking regardless of DGD control by delay line under rapidly varying PSP condition, thus resulting in stable compensated signal with reduction in compensation time.

PMD Effect on the Clock-based Optimum Dispersion Compensation Monitoring Technique

We investigate the effect of polarization-mode dispersion (PMD) on the optimum dispersion compensation (ODC) monitoring and nonlinear penalty in optical transmission systems. We report that PMD may reduce the fiber nonlinearity. We also report that the monitoring error of the clock-based ODC monitoring technique decreases after the first-order PMD compensation. A simple explanation of this phenomenon is shown.

Analysis of Degree of Polarization as a Control Signal in PMD Compensation Systems Aided by Polarization Scrambling

The performance of degree of polarization (DOP) is investigated as a control signal in polarization-mode dispersion (PMD) compensation systems aided by polarization scrambling. The relation between the input and output polarization states of a signal propagating through a polarization scrambler and a PMD-induced optical fiber is described by a 3 times 3 Stokes transfer matrix. The average DOP of the output signal over a period of polarization scrambling is derived as an alternative to the conventional DOP-based control signal, i.e., minimum DOP. In the presence of first- and all-order PMDs, the performance of the average and minimum DOPs in monitoring of differential group delay (DGD) for different data formats (i.e., RZ and NRZ) is evaluated. The performance of the two control signals are further investigated by calculating the outage probability of a feedforward first-order PMD compensation system. The results show that the average DOP outperforms the minimum DOP and also gives a wider DGD monitoring range.

First-order PMD compensation using optical FIR filter

We present a synthesis algorithm to design an optical finite impulse response (FIR) filter for compensating a first-order polarization mode dispersion (PMD) by minimizing the differential group delay (DGD). The desired frequency response was approximated using two widely used methods in designing digital FIR filters: the Fourier series expansion method and the frequency sampling method. A numerical simulation was performed for an eighth-order filter to demonstrate the difference between the two methods. The simulation results produced a sharper cutoff for the Fourier series expansion and higher stopband attenuation for the frequency sampling method. The Fourier series method produced better results in reducing the DGD.

Tracking and separation of time-varying principal states of polarization in optical fiber link for first-order PMD compensation and its filter-dependent performance

We propose a simple method for tracking and separating time-varying principal states of polarization (PSP) occurring in a fiber-optic transmission link with polarization mode dispersion (PMD) for use in PMD compensation. The proposed method uses as a feedback monitoring signal the bandpass-filtered RF power at bit-rate frequency for NRZ signal format. We demonstrated the operating principle of the method through theoretical simulation and experiment using an automatically adaptive PMD compensator employing a single polarization beam splitter (PBS). The effects of electrical filtering on the PSP tracking performance were also investigated by using three types of filters, i.e., a low-pass filter (LPF), a band-pass filter (BPF), and a high-pass filter (HPF). The simulation results showed that only a BPF centered at bit-rate frequency was found to allow for tracing and separation of two PSPs via PBS. The proposed method, when applied to a conventional PMD compensator that alternately controls a polarization controller and a delay line, enables separation of PSP control from differential-group-delay (DGD) control, thus allowing fast tracking of rapidly changing PSP in a PMD-impaired optical fiber link and reducing compensation time.

Comments on "Compact first-order polarization mode dispersion compensator based on birefringent crystals"

In 2004, with the title quoted above, Yang Chang-Xi, Li Shi-Guang, Miao Hou-Xun, Tian Yu, Zhang Er-Yao, and Jin Guo-Fang published an article in Chinese Physics Letters (CPL), vol.21 p.326 (2004). Regrettably, the technical contents of this paper are substantially the same as those of a paper published in the Journal of Lightwave Technology (JLT) in 2003 (Yan et al., vol.21, no.7, p.1676) and an OFC postdeadline paper, which was presented and published in 2002. However, the authors (Yang et al.) did not reference any of the earlier publications. Yao and Yan compares the journal papers in this commentary.

Editorial Preface: Notice of Violation of IEEE Publication Principles

This Notice is an Editorial Preface for the Note authored by X. Steve Yao and Lianshan Yan entitled "Comments on 'Compact first-order polarization mode dispersion compensator based on birefringent crystals,' by Yang Chang-Xi et al., in Chinese Physics Letters, vol. 21, no. 2, pp. 326-328, 2004." After careful and considered review of the content and authorship of the paper by Yang Chang-Xi et al., by a duly constituted committee, this paper has been found to be in violation IEEE's Publication Principles. This paper contains essentially a duplication of the results from a paper [L. Yan, C. Yeh, G. Yang, L. Lin, Z. Chen, Y.Q. Shi, A.E. Willner, and X.S. Yao, "Programmable group delay module using binary polarization switching," J. Lightw. Technol., vol. 21, no. 7, pp. 1676-1684, Jul. 2003]. There was no reference by the offending paper to the earlier work published in JLT, and the device described in this paper was described as new. In this paper, the only apparent descriptive difference from the device published in JLT was considered not technically crucial; the six crystal stages are in a length-decreasing arrangement with respect to the light versus the length-increasing arrangement published in JLT. The Note by Yao and Yan in this issue comprehensively identifies a number of instances in the offending paper where the device concepts and construction are identical to those in the JLT article. Due to the nature of this violation, all reasonable effort should be made to reference not the offending paper, but to the work of L. Yan, et al., as the source of the original journal description of the device concepts, implementation, and results.

Pulse broadening due to polarization mode dispersion with first-order compensation

We give the exact analytical expression for the autocorrelation function of the polarization mode dispersion (PMD) vector of a fiber link in which first-order PMD is compensated for at the output. We use the result to obtain the mean-square width of a Gaussian pulse in the presence of a first-order PMD compensator.

Comparison of different feedback signals for one-stage polarization-mode dispersion compensators

The performance of a one-stage polarization-mode dispersion (PMD) compensator with different feedback signals is studied and compared with that of a pure first-order PMD compensator. We show that the performance of the one-stage PMD compensator has a strong dependence on feedback signals, and that the efficiency of some feedback signals depends on modulation formats. With proper choice of feedback signals, the one-stage PMD compensator can achieve better performance than the first-order PMD compensator.

Optimal Choice of Compensation PMD Vector in Feedforward-Type Second-Order PMD Compensation

In this paper, the formula of an optimal compensation vector, which is defined as an input polarization-mode dispersion (PMD) vector of the compensator, for second-order PMD compensation has been derived from the minimization of the root-mean-square (rms) pulse-broadening factor. The derived optimal compensation vector is a linear combination of frequency-averaged PMD vectors and output states of polarization, which shows a similar trend to the previously reported optimal first-order PMD compensation. The rms pulse-broadening factor after optimal second-order PMD compensation has been semianalytically calculated and compared with the previously reported simulation result. They are in good agreement. The formula of the optimal second-order compensation vector derived in this paper provides indispensable information for feedforward second-order PMD compensation.

Performance evaluation of systems using a novel adjustable first-order PMD compensator and forward error correction

In this paper, we numerically evaluate the performance of 10 Gbit/s systems with a novel adjustable first-order polarization mode dispersion (PMD) compensator and forward error correction (FEC). The scheme of PMD compensation employs sampled fiber Bragg gratings (FBG) written into a high-birefringence fiber using uniform phase masks. And the technique of FEC is based on the concatenated Reed–Solomon codes of RS(247,239) + RS(255,247), which is also called enhanced FEC (EFEC). The numerical simulation results show that the combined use of PMD compensation and EFEC can increase system PMD tolerance to one bit period of average PMD when keeping the sensitivity penalty (@BER=10 −10) below 1 dB.

Effects of nonlinear crosstalk in optical PMD compensation

We report on the effects of nonlinear crosstalk on the optical polarization-mode dispersion (PMD) compensation in wavelength-division-multiplexing (WDM) systems. An analytical model is presented to describe the effect of nonlinear crosstalk on the first-order PMD compensation. We also experimentally show that the performance of WDM systems could be degraded by nonlinear birefringence, even when the first-order PMD is completely compensated.

PMD—Induced Pulse Broadening in Optical Fibers

In this paper, by means of analytical expressions we compare the expected pulse broadening in a fiber-optic transmission system suffering from both first- and higher order Polarization Mode Dispersion (PMD). The results are compared for compensated fiber with uncompensated fiber. Compensation could be achieved both before the transmission or after the transmission, accordingly it is classified as Pre-Transmission Compensation or Post-Compensation techniques. We discuss the influence of both the PMD Compensation schemes. Firstly, we analyze the First-Order PMD Compensation and subsequently the Principal State of Polarization (PSP) Transmission Compensation scheme.

Simple all-fiber-optic component for first-order polarization mode dispersion compensation

A simple and reliable all-fiber-optic component for a first-order polarization mode dispersion compensator is presented and tested in a 10-Gbit/s transmission system. The proposed component incorporates tunable differential group delay (DGD) provided by several pieces of polarization maintaining (PM) fibers of different DGD that were spliced together with short lengths of single-mode fibers between them. The total DGD of the compensator is determined by the alignment of fast and slow axes of the PM fiber sections. Applying this component as a first-order polarization mode dispersion (PMD) compensator, we demonstrate that a component with seven pieces of PM fiber segments could possibly compensate the first-order PMD up to 63.5 ps with 1-ps steps and a switching time of 300 ms. We also optimize the number of PM fiber sections in this component for a first-order PMD compensation in a 10Gbit/s system based on experimental results.

Compensation of higher order polarization-mode dispersion using phase modulation and polarization control in the transmitter

We demonstrate a higher order polarization-mode dispersion (PMD) compensation scheme using a polarization controller and a phase modulator in the transmitter, as well as a traditional first-order compensator in the receiver. The effectiveness of this approach is experimentally demonstrated for a 10-Gb/s nonreturn-to-zero (NRZ) transmission over a link with an average PMD of 50 ps. Under this large PMD condition, the system power penalty can be reduced from /spl sim/4 dB that is achieved with a first-order compensator to 1 dB using the proposed technique. According to a reasonable outage criterion, simulation results show that the tolerance to average PMD for the 40-Gb/s NRZ system is improved to /spl sim/10 ps, as compared to the 7-ps value using only first-order PMD compensation. Such improvement may double the PMD-limited transmission distance.

Impacts of polarization mode dispersion on the pulse-width with considering initial pulse chirp and fiber GVD

The impacts of polarization mode dispersion (PMD) on the pulse-width in linear systems have been investigated. The analytical solutions, including the effects of initial frequency chirp and group velocity dispersion (GVD), are derived. Analyses show that the pulse broadening effects induced by the second-order PMD depend on GVD and chirp parameter, which are different from those induced by the first-order PMD. An initially chirped Gaussian pulse is taken as an example, upon which analytical solutions of rms pulse-width are derived before and after the first-order PMD compensation. The first-order PMD compensator is also evaluated based on these solutions. The results show that the pulse broadening effects will be resisted efficiently by choosing appropriate GVD and chirp parameter; in general, the post-transmission compensation method will be less efficient than the PSP-transmission method.

Comparison of soliton robustness with respect to polarization-mode dispersion with first-order polarization-mode dispersion–compensated linear systems

Soliton robustness to polarization-mode dispersion (PMD) is compared, both analytically and numerically, with that of linear pulses that use first-order PMD compensation. It is found that soliton robustness to PMD is comparable with first-order PMD compensation and in some cases is even better. The effects of soliton control methods on soliton robustness to PMD were also investigated, and it was found that soliton control methods can significantly improve the soliton's robustness to PMD, particularly for long-distance systems.

Statistics of PMD-induced power fading for intensity-modulated double-sideband and single-sideband microwave and millimeter-wave signals

Polarization-mode dispersion (PMD) can severely degrade the performance of millimeter-wave fiber-optic links by inducing a power fading penalty of the received signal that is dependent on the subcarrier frequency and accumulated PMD along the fiber. We experimentally investigate the statistics of PMD-induced power fading as a function of the differential group delay (DGD) for intensity-modulated double- and single-sideband subcarrier-multiplexed signals in the absence of chromatic dispersion. We find a similar susceptibility to PMD-induced power fading for both modulation formats with a subcarrier frequency of 7 GHz using a PMD emulator with a Maxwellian distribution of DGD (average DGD /spl sim/40 ps). A significant improvement in the worst case power fading penalty (/spl sim/20 dB) is achieved by using an electronically controlled polarization controller in combination with a single section of polarization maintaining fiber in a dynamic first-order PMD compensator. Furthermore, the results of numerical Monte Carlo simulations support the measured data and show the scalability of PMD-induced power fading for subcarrier-multiplexed signals in the microwave and millimeter-wave region.

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.

Optical all-pass filters for polarization mode dispersion compensation

Polarization mode dispersion (PMD) compensation is addressed by decomposition of a fiber's Jones matrix into amplitude and phase responses, which are then compensated for separately. Cubic and higher-order phase compensation substantially reduce the cumulative probability at a given system penalty over first-order PMD compensation, as demonstrated for a 40-Gbit/s non-return-to-zero signal and a fiber PMD with a differential group delay of 20 ps (rms). Single-stage all-pass filters provide tunable compensation that is comparable to that obtained with a variable-delay line, and multistage all-pass filters are well suited for higher-order phase compensation.