Chromatic Dispersion Compensation Methods Research Articles

Distributed Chromatic Dispersion Compensation Method Based on Mismatch Factor for High Resolution OFDR

Distributed Chromatic Dispersion Compensation Method Based on Mismatch Factor for High Resolution OFDR

Advanced Chromatic Dispersion Compensation in Optical Fiber FBMC-OQAM Systems

We report on several methods for the chromatic dispersion (CD) compensation in optical fiber offset-QAM-based filterbank multicarrier (FBMC-OQAM) systems. We show that several equalization structures, initially proposed for wireless FBMC-OQAM systems, can also be applied to optical FBMC-OQAM systems to enhance the CD tolerance. The different CD compensation algorithms are numerically validated and compared to the conventional one tap equalizer in a 30-Gbaud optical FBMC system, in terms of performance and complexity. Considering a 1-dB optical signal-to-noise ratio penalty at a bit error rate of $3.8\times 10^{-3}$ and 256 subcarriers, the results show that the maximum CD tolerance of the frequency spreading method can be enhanced by a factor 10 and 30 for 4-OQAM and 16-OQAM modulations, respectively, compared to that of the conventional one-tap equalizer, at the cost of higher complexity. Even though the other CD compensation methods provide a reduced CD tolerance compared to the frequency spreading method, they require less complexity and hence can be good alternatives.

Comparison of Chromatic Dispersion Compensation Method Efficiency for 10 Gbit/S RZ-OOK and NRZ-OOK Wdm-Pon Transmission Systems

Abstract In the paper, the authors compare efficiency of two physical dispersion compensation methods for single channel and 8-channel WDM fibre-optical transmission systems using return-to-zero (RZ) and non-return-to-zero (NRZ) line codes for operation within optical C-band frequencies by means of computer simulations. As one of the most important destructive effects in fibre optical transmission systems (FOTS) is chromatic dispersion (CD), it is very important to reduce its negative effect on a transmitted signal. Dispersion compensation methods that were implemented in the research were dispersion compensating fibre (DCF) and fibre Bragg grating (FBG). The main goal of the paper was to find out which dispersion compensation method (DCF or FBG) provided the highest performance increase for fibre-optical transmission system and provided the longest transmission distance after dispersion compensation was implemented at different locations in the fibre-optical line while RZ or NRZ line codes were used. In the paper the reference point of signal quality for all measurements, which were obtained at the receiver, was BER<10−12.

Impact of Chromatic Dispersion Compensation in Single Carrier Two-Dimensional Stokes Vector Direct Detection System

We experimentally demonstrate, aided with mathematical analysis, two methods for chromatic dispersion (CD) compensation for two-dimensional Stokes vector direct detection (2D-SV-DD) system. Results show that the better CD compensation method is dependent on transmission distance and operating symbol rate relative to the digital-to-analog converter (DAC) sampling rate. When 84 GBd 16 QAM signal is generated using an 84 GSps DAC, the bit error rate (BER) after 640 km propagation is $\sim1.67\times 10^{-2}$ and $\sim2\times 10^{-2}$ using CD post- and precompensation, respectively. When 64 GBd 16 QAM signal is generated at the same DAC sampling rate, the BER at 960 km is $\sim1.61\times 10^{-2}$ and $\sim9.8\times 10^{-3}$ using CD post- and precompensation, respectively. In addition, our findings reveal that CD precompensation allows for transmission distances greater than 1000 km at which CD postcompensation is no longer viable due to the required training. Finally, enabled by CD precompensation, we report the highest capacity-times-distance products of 591 360 (Gb/s) $\cdot$ km and 614 400 (Gb/s) $\cdot$ km in 2D-SV-DD system using QPSK modulation format and symbol rates of 84 and 64 GBd, respectively. Also, we can achieve 300G transmission for distances below 320 km using 84 GBd 16 QAM signal with BER below hard decision forward error correcting threshold of $\sim3.8\times 10^{-3}$ .

Efficient Chromatic Dispersion Compensation and Carrier Phase Tracking for Optical Fiber FBMC/OQAM Systems

Offset quadratic-amplitude modulation (QAM) based filterbank multicarrier (FBMC/OQAM) is an attractive candidate to improve the spectral containment of optical fiber communication systems, especially when considering a sufficiently high number of subcarriers. As for other multicarrier modulations, the chromatic dispersion (CD) compensation is simplified in FBMC/OQAM systems since it is performed in the frequency domain. Unfortunately, FBMC/OQAM systems are sensitive to the laser phase noise (PN). The PN becomes difficult to mitigate when the number of subcarriers increases due to the increased symbol period. It results in intercarrier interference and intersymbol interference due to the loss of OQAM orthogonality. In this paper, we consider the use of moderate numbers of subcarriers to allow for simpler PN tracking. Consequently, more advanced CD compensation methods are required and a trade-off between CD and PN compensations needs to be studied. In this paper, the frequency sampling equalizer is used for the CD compensation, whereas an innovative adaptive maximum likelihood estimator is used for the PN compensation. A methodology is then presented to analyze this performance trade-off between CD and PN compensations, and design the desirable system parameters such as the number of subcarriers and the equalizer length. This is illustrated in the case of a terrestrial long-haul FBMC/OQAM transmission system, with 400-kHz laser linewidth and a 1000-km optical link.

Analysis of chromatic dispersion compensation and carrier phase recovery in long-haul optical transmission system influenced by equalization enhanced phase noise

The performance of long-haul coherent optical fiber transmission system is significantly affected by the equalization enhanced phase noise (EEPN), due to the interaction between the electronic dispersion compensation (EDC) and the laser phase noise. In this paper, we present a comprehensive study on different chromatic dispersion (CD) compensation and carrier phase recovery (CPR) approaches, in the n-level phase shift keying (n-PSK) and the n-level quadrature amplitude modulation (n-QAM) coherent optical transmission systems, considering the impacts of EEPN. Four CD compensation methods are considered: the time-domain equalization (TDE), the frequency-domain equalization (FDE), the least mean square (LMS) adaptive equalization are applied for EDC, and the dispersion compensating fiber (DCF) is employed for optical dispersion compensation (ODC). Meanwhile, three carrier phase recovery methods are also involved: a one-tap normalized least mean square (NLMS) algorithm, a block-wise average (BWA) algorithm, and a Viterbi-Viterbi (VV) algorithm. Numerical simulations have been carried out in a 28-Gbaud dual-polarization quadrature phase shift keying (DP-QPSK) coherent transmission system, and the results indicate that the origin of EEPN depends on the choice of chromatic dispersion compensation methods, and the effects of EEPN also behave moderately different in accordance to different carrier phase recovery scenarios.

Optimal Least-Squares FIR Digital Filters for Compensation of Chromatic Dispersion in Digital Coherent Optical Receivers

This paper proposes optimal finite-length impulse response (FIR) digital filters, in the least-squares (LS) sense, for compensation of chromatic dispersion (CD) in digital coherent optical receivers. The proposed filters are based on the convex minimization of the energy of the complex error between the frequency responses of the actual CD compensation filter and the ideal CD compensation filter. The paper utilizes the fact that pulse shaping filters limit the effective bandwidth of the signal. Then, the filter design for CD compensation needs to be performed over a smaller frequency range, as compared to the whole frequency band in the existing CD compensation methods. By means of design examples, we show that our proposed optimal LS FIR CD compensation filters outperform the existing filters in terms of performance, implementation complexity, and delay.

Realization of Combined Chromatic Dispersion Compensation Methods in High Speed WDM Optical Transmission Systems

Chromatic dispersion (CD) has a significant impact on a quality of transmitted optical signal in high-speed fiber optic communication systems with data rates up to 10 Gbit/s, and as a result CD limits the maximum length of transmission distance. In order to operate fiber optic communication system with a sufficiently low bit error ratio (BER) and minimize the performance degradation caused by pulse distortion and broadening, dispersion compensation is needed. In this work using OptSim simulation software we realize an experimental high-speed WDM fiber optic communication system model with a new combined dispersion compensation mechanism where a conventional dispersion-compensating fiber (DCF), fiber Bragg grating (FBG) or optical phase conjugator (OPC) are used together. The best results were obtained by using FBG-OPC dispersion compensation scheme which showed the lowest BER value. Basis of the results we recommend avoiding the use of DCF for CD compensation where it is possible and use FBG instead. Ill. 15, bibl. 9 (in English; abstracts in English and Lithuanian).http://dx.doi.org/10.5755/j01.eee.116.10.875

Realization of Combined Chromatic Dispersion Compensation Methods in High Speed WDM Optical Transmission Systems

Chromatic dispersion (CD) has a significant impact on a quality of transmitted optical signal in high-speed fiber optic communication systems with data rates up to 10 Gbit/s, and as a result CD limits the maximum length of transmission distance. In order to operate fiber optic communication system with a sufficiently low bit error ratio (BER) and minimize the performance degradation caused by pulse distortion and broadening, dispersion compensation is needed. In this work using OptSim simulation software we realize an experimental high-speed WDM fiber optic communication system model with a new combined dispersion compensation mechanism where a conventional dispersion-compensating fiber (DCF), fiber Bragg grating (FBG) or optical phase conjugator (OPC) are used together. The best results were obtained by using FBG-OPC dispersion compensation scheme which showed the lowest BER value. Basis of the results we recommend avoiding the use of DCF for CD compensation where it is possible and use FBG instead. Ill. 15, bibl. 9 (in English; abstracts in English and Lithuanian).http://dx.doi.org/10.5755/j01.eee.113.7.622

Automatic Chromatic Dispersion Compensation Method Based on Spectrum Change of Transmission Signal

Because of increase of communication bandwidth demand, upgrading the speed of optical fiber networks is a future issue. However, in the case of high speed transmission at wavelength of 1.5 μm band on the existing single mode fiber, transmission distance is limited due to chromatic dispersion. Thus, in addition to chromatic dispersion compensation devices, automatic optimization methods of the compensation value are important especially in the case of photonic networks, on which transmission distances often change dynamically. But problems remain such that signal quality measuring instruments are expensive under existing automatic chromatic dispersion compensation methods.In this report, focusing on spectrum profile change by long transmission of optical signals, a simple automatic control method of chromatic dispersion compensation is proposed. And some results of basic experiments are described. By doing feedback control for optimizing the chromatic dispersion compensation value, an error-free state of a 10 Gbps optical signal is demonstrated even if the dispersion value of the transmission line is rapidly changed.