Long-haul Optical Transmission Research Articles

A novel construction algorithm of the LDPC code for high-speed long-haul optical transmission systems

According to the transmission characteristics of high-speed long-haul optical transmission system, the main construction method of Low-Density Parity-Check (LDPC) code for optical transmission system is presented and a novel construction algorithm of LDPC code is proposed, the theoretical analysis shows that the parity check matrix of the LDPC code constructed by the proposed construction algorithm has no four-girth phenomenon, this is also theoretically proved out. Both the novel LDPC(3969,3720) code with 6.69% redundancy and the novel LDPC(8281,7920) code with 4.56% redundancy for optical transmission systems are constructed by using the presented construction method and proposed construction algorithm. The simulation results show that the net coding gain (NCG) of the two novel LDPC codes at the eighteenth iteration for the BER of 10⿿12 are respectively 1.63dB and 1.49dB more than that of the RS(255,239) code in ITU-T G.975. Moreover, the decoding of the LDPC code in the hardware can parallel be implemented, so the decoding speed of the two novel LDPC codes are very rapid, the complexities of implementing the two novel LDPC codes, compared with the concatenated codes in ITU-T G.975.1, are relatively lower, furthermore, the hardware overhead and storage space can relatively be saved and the computation complexity can be reduced in implementing the hardware in the future. As a result, the two novel LDPC codes can better be suitable for high-speed long-haul optical transmission systems.

Optimized transmitter module for NRZ-duobinary in long-haul optical transmission link

In this work we present a comparative analysis of three different NRZ-duobinary transmitter modules made of either push–pull configuration based on dual arm MZIM or delay-and-add circuit based single arm MZIM or a duobinary filter followed by single arm MZIM in an ASE-noise-limited 10Gbps optical link. The performance of all three transmitter modules has been optimized for modulator chirp and extinction ratio. These optimized transmitter modules have been further investigated to observe which transmitter-generated pulse offers comparatively better tolerance to impairments induced by group velocity dispersion (GVD) and self phase modulation (SPM). Simulative analysis reports that delay-and-add circuit based single arm MZIM transmitter module outperforms the other two transmitter modules and hence can be treated as the optimized transmitter module for NRZ-duobinary in long-haul optical transmission link.

Nonbinary LDPC-Coded Mode-Multiplexed Coherent Optical OFDM 1.28-Tbit/s 16-QAM Signal Transmission Over 2000 km of Few-Mode Fibers With Mode-Dependent Loss

We demonstrate the possibility of nonbinary LDPC-coded mode-multiplexed coherent optical OFDM 1.28-Tbit/s 16-QAM signal transmission over 2000 km of few-mode fiber (FMF) with mode-dependent loss (MDL) by using an advanced mode-coupling compensation scheme. The performance of proposed coded-modulation scheme is evaluated for different number of spatial modes. The simulation results indicate that the MDL is the predominant effect in the long-haul optical transmission based on FMFs. Different pilot-aided OFDM based compensation methods are studied, and it has been found that minimum mean-square estimation with linear interpolation method is the most robust against mode coupling and MDL. We also show that the nonbinary LDPC-coded modulation provides about 1 dB improvement over binary LDPC-coded modulation (16 QAM OFDM and MDL of 25 dB). Finally, we study the degradation of increasing the number of modes and investigate the proposed scheme for different MDL values in both fourand eight-mode fibers.

Monolithic silicon-based 16-QAM modulator using two plasmonic phase shifters

We propose a compact silicon-based modulator for 16-point quadrature amplitude modulation (16-QAM) with a simple structure using two phase shifters. The phase shifters employ low-loss hybrid plasmon waveguide, consisting of a conductor-gap-dielectric structure filled with polymer. Combining the strong optical confinement ability of the plasmonic waveguide with the highly nonlinear characteristic of the polymer, the proposed 16-QAM modulator can achieve a compact footprint, high-speed operation, and low power consumption, potentially allowing for high-density on-chip integration and broadband long-haul optical transmission.

DFT-Precoded Coherent Optical OFDM With Hermitian Symmetry for Fiber Nonlinearity Mitigation

Coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems have inferior nonlinear performance due to their high peak to average power ratio (PAPR) characteristics. In order to mitigate fiber nonlinearities for the CO-OFDM systems, we propose a novel discrete Fourier transform (DFT)-precoded coherent optical OFDM combined with a Hermitian symmetry (DFT-precoded HS CO-OFDM) system, which is a combination of the DFT-spread OFDM and the Hermitian symmetry of the DFT. Furthermore, the proposed system can be easily implemented by using a fast Fourier transform (FFT) algorithm. Because the proposed system has a lower PAPR than the conventional CO-OFDM system, the DFT-precoded HS CO-OFDM system provides superior nonlinear tolerance. Moreover, the proposed system is superior to the conventional DFT-spread coherent optical OFDM (DFT-spread CO-OFDM) system in terms of maintaining low PAPR in optical fiber transmission. The low PAPR in the proposed scheme is suitable for long-haul optical transmission systems, compared with the conventional DFT-spread CO-OFDM. For the DFT-precoded HS OFDM system, we have developed a theoretical framework illustrating the principles of the proposed system. The numerical results show that the DFT-precoded HS CO-OFDM system outperforms the conventional CO-OFDM by 5.4% EVM performance after 1200-km transmission and the conventional DFT-spread CO-OFDM by 4.5% EVM performance after 2800-km transmission at a fiber launch power of ${-}2$ dBm.

Experimental demonstration of 108 Tb/s PDM CO-SCFDM transmission over 3170 km SSMF

Coherent optical single-carrier frequency-division-multiplexing (CO-SCFDM) is a promising candidate for future high-speed long-haul optical fiber transmission system. Being a modified form of coherent optical orthogonal frequency division multiplexing (CO-OFDM), the CO-SCFDM can inherit the advantages such as low computation complexity and high flexibility, while suffers less nonlinear impairment due to much lower peak-to-average power ratio (PAPR). In this paper, we experimentally demonstrate 1.08 Tb/s polarization-division multiplexing (PDM) CO-SCFDM transmission over 3170 km standard single-mode fiber (SSMF) with Erbium-doped fiber amplifier (EDFA) only. The back-to-back and nonlinear transmission performances for CO-OFDM and CO-SCFDM are also compared.

Long-haul transmission of 35-Gb/s all-optical OFDM signal without using tunable dispersion compensation and time gating

We propose that the optical OFDM technique using all optical discrete Fourier transform (DFT) has potential as a viable alternative for upgrading long-haul optical transmission systems towards 100-Gb/s. We demonstrate transmission of 35-Gb/s (7 x 5 Gb/s NRZ-OOK) all-optical OFDM signal over ~2000-km dispersion-managed span without using tunable dispersion compensation and time gating. We achieve bit error ratio of 1.2x10(-3) (7x10(-3)) for transmission over 1980-km (2310-km) all-EDFA amplified span consisting of standard single mode fiber (SSMF) and dispersion compensating fiber (DCF). We also study the nonlinear penalty impacting the all-optical OFDM transmission and discuss potential method for its mitigation.

Empirical modeling and simulation of phase noise in long-haul coherent optical transmission systems

An empirical phase noise channel model suitable for performance evaluation of high spectrally efficient modulations in 100G long-haul coherent optical transmission systems using polarization-division multiplexed and wavelength-division multiplexing channels is presented. The derivation of the model is worked out by exploiting the similarity between the power spectral density of the carrier extracted from the analysis of propagation measurements and the Lorentzian spectrum that is usually adopted to describe instabilities of semiconductor lasers. The proposed channel model is characterized by only two parameters: the linewidth of the carrier and the signal-to-noise ratio. We show that in the case of quadrature phase-shift keying transmission a good agreement exists between quantitative measures of performance extracted by processing experimental data and those obtained from simulations based on the use of the empirical model.

Optical orthogonal division multiplexing for long haul optical communications: A review of the first five years

Optical OFDM was proposed for dispersion compensation in long-haul optical communications systems in 2006 in two forms, one using direct-detection and the other using coherent detection. Since then there has been extensive innovation towards developing intermediate forms of optical OFDM that are more suited to specific applications. This review paper presents our view on the developments in optical OFDM for long-haul optical transmission applications. It covers the basic elements of radio OFDM before concentrating on direct detection optical OFDM and its development, followed by coherent optical OFDM. All-optical OFDM is then considered, together with optical methods of generating and separating the OFDM subcarriers. The paper then discusses the critical issue of nonlinear degradation due to the Kerr effect in optical fibers and reviews recent innovations to mitigate the effects of fiber nonlinearity. Finally some future research directions are discussed.

Performance Comparison of Long-Haul Direct Detection Optical Transmission Systems Adopting Dispersion Management with Pre-Compensation

This article reports a numerical investigation on the performance of return-to-zero intensity-modulated direct detection, return-to-zero differential phase shifting key, and return-to-zero differential quadrature phase shifting key systems operating in G.652 links adopting dispersion management. Also illustrated are the role and benefits of pre-compensation. For such an aim, the influence of the non-linear Kerr impairments on the in-phase and quadrature components of the signal are studied, along with the consequent degradations in terms of the Q-factor for the different modulation formats. Such an investigation is applied to evaluate the maximum propagation distances for 40- and 80-Gb/s capacities.

448-Gb/s Reduced-Guard-Interval CO-OFDM Transmission Over 2000 km of Ultra-Large-Area Fiber and Five 80-GHz-Grid ROADMs

We propose a novel coherent optical orthogonal frequency-division multiplexing (CO-OFDM) scheme with reduced guard interval (RGI) for high-speed high-spectral-efficiency long-haul optical transmission. In this scheme, fiber chromatic dispersion is compensated for within the receiver rather than being accommodated by the guard interval (GI) as in conventional CO-OFDM, thereby reducing the needed GI, especially when fiber dispersion is large. We demonstrate the generation of a 448-Gb/s RGI-CO-OFDM signal with 16-QAM subcarrier modulation through orthogonal band multiplexing. This signal occupies an optical bandwidth of 60 GHz, and is transmitted over 2000 km of ultra-large-area fiber (ULAF) with five passes through an 80-GHz-grid wavelength-selective switch. Banded digital coherent detection with two detection bands is used to receive this 448-Gb/s signal. Wavelength-division multiplexed transmission of three 80-GHz spaced 448-Gb/s RGI-CO-OFDM channels is also demonstrated, achieving a net system spectral efficiency of 5.2 b/s/Hz and a transmission distance of 1600 km of ULAF.

Analysis of RF-Pilot-Based Phase Noise Compensation for Coherent Optical OFDM Systems

In coherent optical long-haul transmission systems, orthogonal frequency-division multiplexing represents a promising modulation format. However, due to long symbol length, laser phase noise can be a major impairment. In this manuscript, the RF-pilot-based phase noise compensation scheme is analyzed and compared to conventional common-phase error compensation. It has been shown that the RF-pilot-based phase noise compensation scheme allows for a considerable increase in tolerable laser linewidth as compared to conventional common-phase error compensation at the cost of an increase in system complexity. For a 112-Gb/s transmission scheme, the tolerable linewidth is increased by a factor of ten as compared to common-phase error compensation.

Comparison of Transmission Performances for CO-SCFDE and CO-OFDM Systems

Single-carrier (SC) and multicarrier (MC) transmissions have emerged as two competitive technologies for long-haul coherent optical fiber transmission systems. In this letter, we compare chromatic dispersion (CD) and nonlinearity tolerances for coherent optical SC frequency-domain-equalization and SC orthogonal frequency-division-multiplexing systems. We establish the simulation systems employing the same structures of transmitter and receiver, the same structure of frame, and almost the same frequency-domain equalization method except the inverse fast Fourier transform processing. Both CD tolerance and nonlinear transmission performance in single-channel and wavelength-division-multiplexing scenarios are investigated. The comparison can reveal the difference of SC and MC transmissions.

SPM mitigation in 16-ary amplitude-and-differential-phase shift keying long-haul optical transmission systems

We report a self-phase-modulation (SPM) mitigation method in the electrical domain for 16-level amplitude-and-differential-phase-shift keying (16-ADPSK) signals. The method helps to increases the transmission distance of 60-Gbit/s/channel 16-ADPSK systems by around 1.5 times.

两类高速长距离非线性光传输系统的比较

两类高速长距离非线性光传输系统的比较

Simulative analysis of pre- and post-compensation using CRZ format in WDM optical transmission link

This paper reports the effects of pre- and post-compensation using CRZ modulation format in long-haul WDM optical transmission link using wavelengths in three bandwidths viz. 1537.4; 1550; 1562.6 nm at per channel bit rates of 10 Gbit/s. It has been investigated here that optimization of dispersion map results in improved management of nonlinear effects in long-haul light wave systems operating in the quasi-linear regime. In addition, pre- and post-dispersion compensation was applied at the transmitter and receiver depending on the signal wavelength, which resulted in improvement of performance metrics viz. Q 2 (dB), BER and OSNR over longer transmission distances. It is reported here that optimum values of Q 2 dB of 17.1 dB, BER of 8.4933e −015 and OSNR of 30.1 dB are obtained at 1550 nm at a transmission distance of 7360 km with pre- and post-compensation using CRZ modulation format.

Improving the Nonlinear Tolerance of Polarization-Division-Multiplexed CO-OFDM in Long-Haul Fiber Transmission

We present digital signal processing techniques and algorithms for improving the tolerance of polarization-division multiplexed (PDM) coherent optical orthogonal frequency-division multiplexing (CO-OFDM) to fiber nonlinear effects, in both single-channel and wavelength-division multiplexed (WDM) transmission. For single-channel transmission, we discuss a self-phase modulation (SPM) compensation method that jointly processes two polarization components of a PDM CO-OFDM signal. For WDM transmission, we describe a novel OFDM channel estimation scheme that reduces the cross-phase-modulation (XPM) penalty among the WDM channels. The nonlinear tolerance improvements enabled by these signal processing techniques are quantified through numerical simulations for both dispersion-unmanaged and dispersion-managed long-haul optical fiber transmission with 112-Gb/s PDM CO-OFDM wavelength channels.

Phase jitter in periodically dispersion-managed optical transmission systems

We investigate the phase jitter in long-haul optical transmission systems with periodic dispersion management and amplification. We compare different dispersion-managed soliton systems and a conventional soliton system having the same pulse width and path-averaged dispersion. Using the variational method, we derive the ordinary differential equations for the pulse parameters perturbed by amplifier noise and hence calculate the phase jitter. We verify the analytical results by numerically solving the nonlinear Schrödinger equation using split-step Fourier algorithm. The results suggest that the reduction of nonlinear phase noise in dispersion-managed soliton systems is possible compared to a conventional soliton system. It is also revealed that the phase noise is enhanced in stronger dispersion-managed systems. We also explore the phase noise effect in dispersion-managed quasi-linear systems and find that phase jitter is mitigated in highly dispersive fibers.

Unified analysis of weakly-nonlinear dispersion-managed optical transmission systems using a perturbative approach

Abstract We provide a unified theoretical framework based on a regular perturbation analysis, capable of both explaining most known results, and of deriving new ones, on system optimization in dispersion-managed long-haul terrestrial optical transmission systems with small-to-moderate nonlinearity. To cite this article: A. Bononi et al., C. R. Physique 9 (2008).

A Unified Design Framework for Single-Channel Dispersion-Managed Terrestrial Systems

This paper provides a unified framework to the design, performance optimization, and accurate numerical simulation of periodic, dispersion-managed (DM) single-channel long-haul optical transmission systems for nonsoliton on-off keying (OOK) modulation. The focus is on DM terrestrial systems, with identical spans composed of a long transmission fiber compensated at the span end by a linear dispersion compensating module, with pre- and postcompensation fibers at the beginning and end of the link. The framework is based on the dispersion-managed nonlinear Schrodinger equation (DM-NLSE). First, expressions of the DM-NLSE kernel are provided both in the frequency and the time domain, and a novel map strength parameter, appropriate for terrestrial systems, is introduced. It is then shown that the DM-NLSE contains all the basic information needed for system design, as summarized by three parameters: i) nonlinear phase, ii) in-line dispersion, and iii) map strength. Through a large-signal perturbative analysis of the DM-NLSE, the well-known linear relationship between the in-line dispersion and the optimal precompensation is derived, along with the large-signal step response of the DM link, from which the ghost pulses energy growth and a first estimation of the link memory are derived. The DM-NLSE is then linearized around the average signal field to get the amplitude/phase small-signal system matrix of the overall DM link, including pre- and postcompensation. By a singular-value decomposition of the small-signal DM link matrix, a novel expression of the memory of the optimized DM link is finally provided. Knowledge of such a memory is mandatory to run accurate numerical simulations and laboratory measurements with a sufficiently long pseudorandom bit sequence to avoid patterning effects.