Accurate Receiver Model for Optical Fiber Systems with Polarization Induced Performance Degradation

PMD mitigation through interleaving LDPC codes with polarization scramblers

At present, optical fiber communication systems are developing in the direction of large capacity, high speed, long distance, etc., making nonlinear effects and polarization mode dispersion (PMD) and other optical fiber performance defects that were negligible for low-rate systems become the main factors limiting system upgrades and transmission distances. Polarization mode dispersion is an important factor affecting the performance of optical fiber communication systems, and it has become one of the main obstacles to the development of high-speed and long-distance optical fiber communication systems. It can cause pulse widening in the digital transmission system, thereby limiting the transmission rate of the system. Therefore, the influence of polarization mode dispersion on the transmission system and the compensation method are analyzed in this paper.

Polarization effects such as polarization mode dispersion (PMD) and polarization dependent loss (PDL) have become the critical limiting factors for long haul high bit rate optical fiber transmission. This paper use waveplate models to simulate the statistical performance of optical link with PMD and PDL in 40Gbit/s optical system. Three DPSK modulation formats are compared each other for their tolerance against PMD and PDL. The 33% RZ-DPSK is superior to the other two DPSK formats, the 50% RZ-DPSK and the CSRZ-DPSK whose duty cycle is 67% when only PMD is considered. And in case of PDL, the outages for three DPSK formats do not show obvious changes with the increasing of PDL. Furthermore, the performance of two RZ-DPSK formats, whose duty cycles are 33% and 50% respectively, is superior to that of CSRZ-DPSK. This shows that modulation format with narrower pulse width owns more high tolerance against PMD and PDL, therefore the CSRZ-DPSK format shows poorer performance when it is compared with the other two DPSK formats.

As human society to the information in the process of moving and growing demand for bandwidth communications capacity, the optical of new modulation formats increasingly attention and quickly play an important role in optical communications. How can the system bit error rate within a certain degree of stability while still maintaining high-speed long-distance dispersal system, has been a popular issue is the optical communications industry. Starting from the optical modulation format herein, the generation process of the system introduced various optical signal modulation format, the optical signal through the optical fiber was studied and the performance of the simulation, on the basis of the design of advanced optical modulation formats in an optical fiber communication system .

Polarization mode dispersion (PMD) is one of the major obstacles in high-speed (above 100 Gbits rate) and long-haul optical communication system. In order to meet the requirements of high-sped optical communication quality, some PMD compensation and mitigation schemes had been developed. Forward error correction (FEC) is useful to increasing the system margin. The combination of distributed fast polarization scrambler (D-FPS) and FEC is an effective method to improving the optical system’s PMD tolerance. The fundamental reason is that D-FPS can accelerate the redistribution of the link PMD to enable FEC to be more effective during the periods that would otherwise have PMD outages. Another advantage of this scheme is that it can mitigate the influence of PMD in multichannel system without feedback control and compensation based on each channel. The principle and performance of scrambling is introduced in this paper and the fundamental idea of improving PMD mitigation by using D-FPS combined with FEC is proposed. Some key factors such as scrambling speed and the number of scrambler which affecting the performance of this scheme are also introduced. Finally, proposing an assumption that the impact for system performance caused by the style of FPSs is distributed along the fiber link, and the mathematical estimation model is established. The combination of D-FPS and FEC would be a promising approach for performance improvement in ultra-high-speed optical communication system.

The paper analyses the effects of intra-channel four-wave mixing (IFWM) on the high-speed optical fiber communication system. A new code format is developed with double 0 and double π phase separating 1 code; it can decrease the transmission penalty from fiber nonlinearity by counteracting the perturbation terms of IFWM. From the simulation of transmission of two classic code data “11011” and “11100”, we find that our proposed code format has a better suppression effect than the alternative modulation inversion (AMI) or the normal RZ format and supports a wider pulse mode. In a 40 Gbps system, the AMI format is 2 dB less than the RZ format, and our proposed format is 1 dB less than the AMI format when a 1 dB eye open penalty is taken as a metewand. Moreover, it can be realized as easily as the AMI format.

We investigate polarization mode dispersion (PMD) and polarization dependent loss (PDL) impairments in polarization division multiplexing (PDM) signals with optical polarization demultiplexing and direct detection. We find that the time alignment between the bits in the two polarizations has a significant impact on the PMD impairments, and PMD impairments also depend on the bandwidth of PDM signals, whereas PDL impairments have little dependence on the relative time alignment between the two polarizations and the signal bandwidth. We show that with a proper configuration of the polarization demultiplexing, the PDL-induced crosstalk between the two polarizations can be completely eliminated. The combined effects of PMD and PDL are also studied, and we find that, in the presence of concatenated PMD and PDL, the impairment from one effect does not enhance that from the other.

Combined effect of PMD and PDL on four-wave-mixing-induced crosstalk in WDM system

Polarization dependent loss complications on polarization mode dispersion emulation

We report on an exact analytic method to evaluate the optical eye diagram due to polarization-mode dispersion (PMD), polarization-dependent loss (PDL), and chromatic dispersion (CD) in dynamic fiber links for any given optical pulse sequence. With this method we consider all orders of PMD and PDL, and we obtain the time-dependent average output light intensity as well as its corresponding variations. With this method we can obtain accurate impairment evaluations for communication systems due to given PMD, PDL, and CD. Time jitter caused by the PMD and PDL polarization direction correlation is also discussed.

High-speed transmission limitations due to Polarization Mode Dispersion

Polarization mode dispersion (PMD), polarization dependent loss (PDL) and chromatic dispersion (CD) of fiber optic components and fiber transmission links are key issues in fiber optical communication. Of interest are the respective static values as well as their variations in time which might be due to environmental changes or due to rerouting. Basic aspects will be briefly addressed, a variety of standard and state-of-the-art characterization and monitoring techniques will be reviewed and recent experimental results will be presented.

We study a novel configuration and synthesis algorithm for equalization of polarization-mode dispersion (PMD) alone and combined with polarization-dependent loss (PDL) using a nonunitary optical lattice filter (NU-OLF). The NU-OLF is a generalization of a previously studied unitary lattice filter (U-OLF) for PMD equalization. Comparison of the improvement in the noise loaded PMD/PDL-induced eye closure, for typical optical signal-to-noise ratio values, shows that a NU-OLF is always superior to a U-OLF of the same order and it offers a significant advantage over a U-OLF with the same number of degrees of freedom in the equalization of PMD in the presence of PDL.

A novel differential-group-delay (DGD) monitoring scheme that can provide feedforward information to facilitate the compensation of polarization mode dispersion (PMD) is demonstrated. Using a polarization scrambler at the beginning of the link, the instantaneous DGD can be monitored at the end of the link by using a second polarization scrambler followed by a fixed 0.8-dB polarization dependent loss (PDL) element or a polarizer. As the PMD value along the link increases, the instantaneous degree-of-polarization will decrease, thereby resulting in a decrease in the measured RMS power fluctuation value through the PDL element. The authors show instantaneous DGD monitoring of up to /spl sim/70 ps for both nonreturn-to-zero (NRZ) and return-to-zero data formats, and they demonstrate PMD compensation of a 10-Gb/s NRZ channel using the monitor output as part of the control feedforward signal.

The long-span and high-speed optical transmission networks require high-quality optical cables and components to reduce the detrimental effects of polarization-mode dispersion (PMD) and polarization-dependent loss (PDL) on system performance. In addition, many high-accuracy fiber-optic sensing networks also require low polarization-dependent components. As a result, polarization-insensitive transmission fibers and components have been pursued recently. A well-established technique to produce low-PMD and PDL fibers is to spin the fiber during the fiber drawing process, known as spun fibers. As key optical components, fiber Bragg gratings (FBGs) play important roles in optical fiber communications and fiber sensors. However, FBGs written into traditional single-mode fibers exhibit relatively high polarization dependence due to the birefringence introduced by side UV exposure in FBG fabrication process. In this paper, we report for the first time the characteristics of FBGs written into spun fibers that were formed by spinning fibers with certain intrinsic birefringence. Distinct properties of FBGs in spun fibers are found in the experiments, compared to those in traditional single-mode fibers. Based on Jones matrix method, the FBG spectra are simulated and compared with the measured ones. Preliminary experimental results indicate that the spun fiber gratings suffer lower PMD under the same fabrication conditions. Moreover, our theoretical analysis shows that the PMD and PDL characteristics of spun fiber gratings can be further improved by optimizing the structures of spun fibers.