Electronic Dispersion Compensation Research Articles

Compensation of chromatic and polarization mode dispersion in fiber-optic communication lines in microwave signals transmittion.

Methods of dispersion compensation in fiber-optic communication lines. A new proposed method of electronic dispersion compensation in the transmission of microwave signals through fiber-optic lines. Represents is proposed the results of experimental studies of this method.

Equalization Enhanced Phase Noise in Coherent Optical Systems with Digital Pre- and Post-Processing

We present an extensive study of equalization enhanced phase noise (EEPN) in coherent optical system for all practical electronic dispersion compensation configurations. It is shown that there are only eight practicable all-electronic impairment mitigation configurations. The non-linear and time variant analysis reveals that the existence and the cause of EEPN depend on the digital signal processing (DSP) schemes. There are three schemes that in principle do not cause EEPN. Analysis further reveals the statistical equivalence of the remaining five system configurations resulting in EEPN. In three of them, EEPN is due to phase noise of the transmitting laser, while in the remaining two, EEPN is caused by the local oscillator. We provide a simple look-up table for the system designer to make an informative decision regarding practicable configuration choice and design.

Frequency-Domain Volterra-Based Equalization Structures for Efficient Mitigation of Intrachannel Kerr Nonlinearities

Toward reduced-complexity digital implementation, frequency domain Volterra-based nonlinear equalization (VNLE) structures for multistep fiber nonlinearity compensation are proposed. In the cascade structures, nonlinear equalization is performed before (cascade-1) or after (cascade-2) the dispersion compensation in each step. Superior performance with the shorter discrete Fourier transform (DFT) lengths and fewer equalization steps compared to the conventional VNLE with parallel structure is demonstrated in a transmission experiment. The experimental results are obtained for 256 Gb/s single-carrier dual-polarization 16-ary quadrature-amplitude-modulation with root-raised-cosine pulse shaping and a roll-off factor of 0.1. The new cascade structures demonstrate superior robustness to insufficient DFT lengths and/or a limited complexity budget. Compared to the conventional parallel arrangement of linear and nonlinear compensation filters, the cascade-1 structure provides more than 90% complexity reduction without any notable performance penalty. The structure enables the extension of the transmission reach by 1570 km, a 48% increase compared to the linear solution that uses only electronic dispersion compensation.

Comprehensive Study of Equalization-Enhanced Phase Noise in Coherent Optical Systems

A thorough analysis of equalization-enhanced phase noise (EEPN) and its impact on the coherent optical system is presented. We show with a time-domain analysis that EEPN is caused due to the interference of multiple delayed versions of the dispersed signal, generated by intermixing of the received dispersed signal, and the noise side bands of the local oscillator (LO) in the photodetectors. We derive statistical properties such as the mean, variance, and error vector magnitude of the received signal influenced with EEPN. We show that in coherent optical systems utilizing electronic dispersion compensation, this noise corresponds to multipath fading in wireless communication systems. Closed-form expressions of necessary LO linewidth and/or mitigation bandwidth for a general system configuration and specified OSNR penalty are given. The expressions for system design parameters, validated with system simulations, show that higher order modulation formats, such as 16-quadrature amplitude modulation and beyond, put stringent demands on the LO linewidth unless a mitigation technique is used.

Toward Cost-Efficient 100G Metro Networks Using IM/DD, 10-GHz Components, and MLSE Receiver

We demonstrate the generation and transmission of 28-Gb/s data employing inexpensive, off-the-shelf, 10-GHz 3-dB bandwidth optical components, intensity modulation (IM), direct detection (DD), and a digital signal processing-based receiver over uncompensated fiber links. We prove that the proposed technology is an enabler for next-generation 100-G cost-efficient point-to-point dispersion compensation fiber (DCF)-free metro networks up to 80 km, as well as for multispan metro-ring networks up to 400 km, consisting of cascaded erbium-doped fiber amplifiers and DCFs as in real-field implementations. Key techniques to enable transmission are the employment of signal predistortion in the transmitter to compensate for the components’ limited bandwidth, a maximum likelihood sequence estimator (MLSE)-based receiver, and a high-performance sampling phase adjustment algorithm. Furthermore, we show that performance can be optimized, while at the same time the complexity of the electronic dispersion compensation part is significantly reduced by exploiting a simplified variant of MLSE that makes use of a reduced number of states. Results in this paper reveal the potentiality of our proposed scheme for a low-cost transition to 100 Gb/s ( $4 \times 28$ Gb/s) wavelength division multiplexed, point-to-point, metro-core, and multispan metro-ring networks, employing inexpensive optical components and the traditional cost-efficient IM/DD scheme.

Equalization enhanced phase noise in Nyquist-spaced superchannel transmission systems using multi-channel digital back-propagation

Superchannel transmission spaced at the symbol rate, known as Nyquist spacing, has been demonstrated for effectively maximizing the optical communication channel capacity and spectral efficiency. However, the achievable capacity and reach of transmission systems using advanced modulation formats are affected by fibre nonlinearities and equalization enhanced phase noise (EEPN). Fibre nonlinearities can be effectively compensated using digital back-propagation (DBP). However EEPN which arises from the interaction between laser phase noise and dispersion cannot be efficiently mitigated, and can significantly degrade the performance of transmission systems. Here we report the first investigation of the origin and the impact of EEPN in Nyquist-spaced superchannel system, employing electronic dispersion compensation (EDC) and multi-channel DBP (MC-DBP). Analysis was carried out in a Nyquist-spaced 9-channel 32-Gbaud DP-64QAM transmission system. Results confirm that EEPN significantly degrades the performance of all sub-channels of the superchannel system and that the distortions are more severe for the outer sub-channels, both using EDC and MC-DBP. It is also found that the origin of EEPN depends on the relative position between the carrier phase recovery module and the EDC (or MC-DBP) module. Considering EEPN, diverse coding techniques and modulation formats have to be applied for optimizing different sub-channels in superchannel systems.

Impact of local oscillator frequency noise on coherent optical systems with electronic dispersion compensation.

A theoretical investigation of the equalization-enhanced phase noise (EEPN) and its mitigation is presented. We show with a frequency domain analysis that the EEPN results from the non-linear inter-mixing between the sidebands of the dispersed signal and the noise sidebands of the local oscillator. It is further shown and validated with system simulations that the transmission penalty is mainly due to the slow optical frequency fluctuations of the local oscillator. Hence, elimination of the frequency noise below a certain cut-off frequency significantly reduces the transmission penalty, even when frequency noise would otherwise cause an error floor. The required cut-off frequency increases linearly with the white frequency noise level and hence the linewidth of the local oscillator laser, but is virtually independent of the symbol rate and the accumulated dispersion.

A 6 Gb/s Transceiver With a Nonlinear Electronic Dispersion Compensator for Directly Modulated Distributed-Feedback Lasers

This paper presents the design of a 6 Gb/s transceiver with a nonlinear electronic dispersion compensator (EDC) for a directly modulated distributed-feedback (DM-DFB) laser. At the laser output, a DM-DFB laser induces power-dependent frequency chirp, which causes severe chromatic dispersion as well as pattern dependency on the received signal. Such time-varying nature of the dispersion increases the difficulty of compensation using conventional linear methods. The proposed EDC overcomes the chirp-induced dispersion via a nonlinear equalizer at the receiver and a pattern-dependent pre-compensator at the transmitter. The EDC achieves an optical SNR gain of 14.69 dB at a BER of 1 $ \,\times {10^{ - 6}} $ in a 75 km SMF-28 fiber. The test chip is fabricated in a 90 nm CMOS process, and the EDC consumes 68 mW from a 1 V supply at 6 $~$ Gb/s.

Demonstration of a Symmetric 40 Gbit/s TWDM-PON Over 40 km Passive Reach Using 10 G Burst-Mode DML and EDC for Upstream Transmission [Invited

To meet the 2015 timeline, a hybrid time- and wavelength-division multiplexed passive optical network (TWDM-PON) has been selected as the pragmatic path toward the second stage of the next-generation PON (NG-PON2). High-end business users and mobile front-haul/back-haul for next-generation wireless systems that highly rely on symmetrical data rate services are believed to be the main deployment drivers for NG-PON2. In this paper, for the first time to the best of our knowledge, we demonstrate a symmetric 40  Gbit/s TWDM-PON system that fully complies with the up-to-date full service access network/International Telecommunication Union NG-PON2 migration path. There are two distinguishing features from previously reported systems. One is that four symmetric 10  Gbit/s wavelength pairs are supported at the final NG-PON2 wavelength plan [i.e., (C−/L+) band] over 40 km passive reach, and the other is that a burst-mode tunable directly modulated laser and burst-mode electronic dispersion compensation are demonstrated for 10 G upstream transmission instead of tunable external modulated lasers. The selection of the final NG-PON2 wavelength plan is first briefly reviewed. Then the key enabling technologies for our demonstrated TWDM-PON are analyzed and their technological choices, availability, and performances are further investigated. After illustrating the demonstrated system architecture and configuration, measurements and analysis are presented to prove the system feasibility and technical availability. In this demonstration, N1 and N2 optical distribution network (ODN) classes can be totally supported without amplifiers, whereas preamplification is needed to achieve E1 and E2 ODN classes. Both downstream and upstream optical parameters are summarized.

Dispersion Compensation for High-Speed and Long-Distance Transmission of CSRZ-DQPSK Optical Signal

AbstractThis paper compares the performances of 100 Gbit/s carrier-suppressed return-to-zero differential quadrature phase shift keying coded modulation signal through 3,600 km both in optical and photoelectric dispersion compensation schemes. Different dispersion compensation fiber methods are adopted in optical compensation while the photoelectric compensation is the combination of electronic dispersion compensation and optical compensation. It is shown that pre-compensation of DCFs and mixed (pre- and post-) compensation of DCFs are more excellent than the other two schemes in optical compensation, corresponding to mixed (pre- and post-) compensation of DCFs method, while pre-compensation of DCFs method is the best strategy in photoelectric compensation.

Demonstration of 10 Gbit/s Burst-Mode Transmission Using a Linear Burst-Mode Receiver and Burst-Mode Electronic Equalization [Invited

We report on the feasibility of using burst-mode electronic dispersion compensation (BM-EDC) combined with a linear burst-mode receiver (LBMRx) to transmit 10  Gbit/s bursts with a loud/soft ratio of up to 15 dB over a reach greater than 100 km. The experimental demonstration used a LBMRx fabricated using a 250 nm SiGe BiCMOS technology and a BM-EDC implemented by offline processing of sampled data. BM-EDC means that the EDC tap coefficients are adapted based on a training sequence embedded in the preamble at the start of each burst. BM-EDC can be used to increase the total and differential reach of passive optical networks limited by chromatic dispersion or improve link performance for other impairments, especially if these vary from burst to burst. The training sequence must be kept short in order to ensure high traffic efficiency (defined as the ratio of the effective number of transmitted data bits to the total number of transmitted bits). Here we show that, using gear-shifted least-mean-squares adaptation, the required number of training bits in the preamble can be as short as 250 bits.

Fiber optical parametric amplifiers in optical communication systems.

The prospects for using fiber optical parametric amplifiers (OPAs) in optical communication systems are reviewed. Phase-insensitive amplifiers (PIAs) and phase-sensitive amplifiers (PSAs) are considered. Low-penalty amplification at/or near 1 Tb/s has been achieved, for both wavelength- and time-division multiplexed formats. High-quality mid-span spectral inversion has been demonstrated at 0.64 Tb/s, avoiding electronic dispersion compensation. All-optical amplitude regeneration of amplitude-modulated signals has been performed, while PSAs have been used to demonstrate phase regeneration of phase-modulated signals. A PSA with 1.1-dB noise figure has been demonstrated, and preliminary wavelength-division multiplexing experiments have been performed with PSAs. 512 Gb/s have been transmitted over 6,000 km by periodic phase conjugation. Simulations indicate that PIAs could reach data rate x reach products in excess of 14,000 Tb/s × km in realistic wavelength-division multiplexed long-haul networks. Technical challenges remaining to be addressed in order for fiber OPAs to become useful for long-haul communication networks are discussed.

End-to-End Energy Modeling and Analysis of Long-Haul Coherent Transmission Systems

In this paper, we model and analyze the end-to-end energy consumption of 100-Gbps coherent long-haul transmission systems. In particular, we investigate the impact of forward error correction (FEC) on the end-to-end energy consumption. We compare the energy efficiency of commonly used modulation formats in 100-Gbps transmission, namely dual polarization-quadrature phase-shift-keying (DP-QPSK) and dual polarization-16-quadrature amplitude modulation (DP-16-QAM), for different transmission distance and input bit error rate. Our energy model includes consumption of transmitter, booster, link amplifier as well as receiver. Compared with previous digital signal processing models, we provide a very detailed model that not only includes all the significant functional blocks (such as timing and carrier recovery, chromatic and polarization mode dispersion compensation, and FEC), but also takes into account impact of the number of samples processed every clock cycle and of operations other than multiplications. We have found that receiver energy consumption dominates in transmission systems that use electronic dispersion compensation over long transmission distances. Our results show that for short transmission distances where hard-decision decoding is adequate for both modulation formats, DP-16-QAM is more energy efficient than DP-QPSK. However, as the transmission distance increases, the energy saving due to the low symbol rate of DP-16-QAM is offset by the energy consumption of soft-decision decoding. In this case, the two modulation formats have approximately similar energy consumption.

Architecture of a Single-Chip 50 Gb/s DP-QPSK/BPSK Transceiver With Electronic Dispersion Compensation for Coherent Optical Channels

The architecture of a single-chip dual-polarization QPSK/BPSK 50 Gigabits per second (Gb/s) DSP-based transceiver for coherent optical communications is presented. The receiver compensates the chromatic dispersion (CD) of more than 3,500 km of standard single-mode fiber using a frequency-domain equalizer. A time-domain four-dimensional MIMO transversal equalizer compensates up to 200 ps of differential group delay (DGD) and 8000 ps <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of second-order polarization-mode dispersion (SOPMD). Other key DSP functions of the receiver include carrier and timing recovery, automatic gain control, channel diagnostics, etc. A novel low-latency parallel-processing carrier recovery implementation which is robust in the presence of laser phase noise and frequency jitter is proposed. The chip integrates the transmitter, receiver, framer and host interface functions and features a 4-channel 25 Gs/s 6-bit ADC with a figure of merit (FOM) of 0.4 pJ/conversion. Each ADC channel is based on an 8-way interleaved flash architecture. The DSP uses a 16-way parallel processing architecture. Extensive measurement results are presented which confirm the design targets. Measured optical signal-to-noise ratio (OSNR) penalty when compensating 200 ps DGD and 8000 ps <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> is 0.1 dB, while OSNR penalty when compensating 55 ns/nm CD (corresponding to 3,500 km of standard single-mode fiber) is 0.5 dB.

Electronic dispersion compensation in a 50 Gb/s optically unamplified direct-detection receiver enabled by vestigial-sideband orthogonal frequency division multiplexing

We present a novel method for dispersion compensation based on vestigial-sideband transmission of an orthogonal frequency division multiplexed signal through standard signal-mode fiber with a direct-detection receiver. This technique requires simpler optical components and can withstand greater link attenuation and splitting ratios than similar methods previously studied, making the method ideal for optically unamplified receivers, such as those in passive optical networks. We present simulations as well as experimental measurements to demonstrate its practicality.

Performance Enhancement of 16 Channels Back Haul DWDM OADM Ring Network Using Electronic Dispersion Compensation

In this paper, electronic dispersion compensation (EDC) based on minimum mean square error optimization has been employed to improve the performance of 16 channels, gigabit capacity, back haul DWDM OADM ring network.. It is observed that EDC significantly reduce BER by e-33 and improved Q2 dB by 3 dB, thus resulting in improved eye opening and considerably reduced inter-symbol interference.

100 Gb s−1 coherent dense wavelength division multiplexing system reach extension beyond the limit of electronic dispersion compensation using optical dispersion management

We report numerical investigations of increasing system reach beyond the limit imposed by the state-of-the-art digital signal processing (typically 70 ns nm−1 or 4000 km of standard single mode fiber (SSMF)) by using partial optical dispersion compensation in wavelength division multiplexing 100 Gb s−1 dual polarization quadrature phase shift keying coherent systems. Our numerical model has been verified by the comparison of simulation results with the straight-line real-time transmission experiment. We find that for a legacy fiber-based (non-zero dispersion-shifted fiber) link the transmission distance can be extended to 7000 km with either hybrid spans consisting of SSMF and non-zero dispersion-shifted fiber, or by using partial dispersion compensation employing dispersion-compensating fiber (DCF)with a 1.5 and 0.6 dB optical signal-to-noise ratio (OSNR) margin respectively.

Reducing the complexity of perturbation based nonlinearity pre-compensation using symmetric EDC and pulse shaping

Perturbation based nonlinearity pre-compensation has been performed for a 128 Gbit/s single-carrier dual-polarization 16-ary quadrature-amplitude-modulation (DP 16-QAM) signal. Without any performance degradation, a complexity reduction factor of 6.8 has been demonstrated for a transmission distance of 3600 km by combining symmetric electronic dispersion compensation and root-raised-cosine pulse shaping with a roll-off factor of 0.1. Transmission over 4200 km of standard single-mode fiber with EDFA amplification was achieved for the 128 Gbit/s DP 16-QAM signals with a forward error correction (FEC) threshold of 2 × 10(-2).

Simulation and Comparative Analysis of SS-LMS &amp; RLS Algorithms for Electronic Dispersion Compensation

In this paper electronic feed forward equalization is performed to mitigate the link chromatic dispersion. The equalizer coefficients are computed by a decision-directed process based on the sign-sign least mean square and the recursive least square algorithm. Therefore, this paper evaluates the performance of these algorithms in chromatic dispersion compensation at bit rate of 10 Gb/s. This paper compares these two adaptation algorithms for receiver based on analogue electronic dispersion equalizers by simulation and experiment. This paper concluded that recursive least-square algorithm is computationally more complex than sign-sign least mean square algorithm since matrix inversion is required, but achieves faster convergence.

On nonlinearly-induced noise in single-channel optical links with digital backpropagation

In this paper, we investigate the performance limits of electronic chromatic dispersion compensation (EDC) and digital backpropagation (DBP) for a single-channel non-dispersion-managed fiber-optical link. A known analytical method to derive the performance of the system with EDC is extended to derive a first-order approximation for the performance of the system with DBP. In contrast to the cubic growth of the variance of the nonlinear noise-like interference, often called nonlinear noise, with input power for EDC, a quadratic growth is observed with DBP using this approximation. Finally, we provide numerical results to verify the accuracy of the proposed approach and compare it with existing analytical models.