Performance comparison of an 80-km-per-span EDFA system and a 160-km hut-skipped all-Raman system over standard single-mode fiber

In this paper, we present a comprehensive comparison of the performance of an 80-km-per-span erbium-doped fiber amplifier (EDFA) system and a hut-skipped (160-km-per-span) all-Raman system over standard single-mode fiber (SSMF) for the first time, using semianalytic models. The numerical results reveal that a hut-skipped all-Raman system (using one-order Raman pumping) can achieve comparable performance as the conventional 80-km-per-span EDFA system for a common 50-GHz-spaced 80 /spl times/ 10 Gb/s nonreturn-to-zero (NRZ) wavelength division multiplexing (WDM) system at typical fiber loss of 0.22 dB/km. For 100-GHz-spaced 40 /spl times/ 40 Gb/s carrier-suppressed return-to-zero (CS-RZ) WDM transmission, it was found that a hut-skipped all-Raman system can achieve even better performance than the current 80-km-per-span EDFA system. It was also found that the impact of pattern-dependent Raman crosstalk is more severe than interchannel cross-phase modulation (XPM) in a hut-skipped all-Raman system with 80 /spl times/ 10 Gb/s capacity.     

Field transmission of 8 /spl times/ 170 gb/s over high-loss SSMF link using third-order distributed Raman amplification

This paper reports on the field transmission of N/spl times/170-Gb/s over high-loss fiber links using third-order distributed Raman amplification (DRA) in a commercially operated network of Deutsche Telekom. It gives an overview of the key technologies applied for the realization of an 8 /spl times/ 170 Gb/s (1.28 Tb/s) dense wavelength division multiplexing (DWDM) system demonstrator and summarizes long-haul transmission experiments with terabit-per-second capacity over European fiber infrastructure. Third-order DRA enabled repeaterless transmission of 1 /spl times/ 170 Gb/s and 8 /spl times/ 170 Gb/s over links of 185- and 140-km field fiber, respectively. Including an additional 25 km of lumped standard single-mode fiber (SSMF) at the end of the span, a total loss of 61 and 44 dB, respectively, was bridged.     

Tunable dispersion compensation at 40-Gb/s using a multicavity etalon all-pass filter with NRZ, RZ, and CS-RZ modulation

We present a multichannel tunable dispersion compensator (TDC) based on multicavity all-pass etalons that is capable of operation at 40 Gb/s. The device has a tuning range of +200/-220 ps/nm with a group delay ripple < /spl plusmn/5 ps over a channel bandwidth of 80 GHz, an overall loss of < 5.2 dB, very low insertion loss ripple, and can operate on any channel on a 200-GHz grid over the C-band. In addition, we present system performance results at 40 Gb/s using NRZ, RZ, and CS-RZ modulation, compensating up to 45 km of nonzero dispersion shifted fiber (NZDSF). Our results show that this device introduces very little excess system penalty with signal frequency drifts of up to 20 GHz when operated near the center of its tuning range. For single channel experiments with fiber, the system penalty increase versus signal detuning is more significant, but can be reduced by dynamically optimizing the device dispersion during detuning. Finally, we demonstrate simultaneous compensation of 4 channels across the C-band over 25 km of NZDSF.     

10-Gb/s upgrade of bidirectional CWDM systems using electronic equalization and FEC

We discuss options for upgrading coarse wavelength-division multiplexed (CWDM) optical access links over standard single-mode fiber (SSMF) by increasing per-channel data rates from 2.5 to 10 Gb/s. We identify electronic equalization and forward error correction (FEC) as the enabling technologies to overcome the dispersion limit of SSMF. In addition, we show how FEC enhances the tolerance to in-band crosstalk, and paves the way toward fully bidirectional CWDM transmission. Due to the lack of CWDM sources rated for 10-Gb/s operation, we demonstrate full-spectrum (1310 to 1610 nm) 10-Gb/s CWDM transmission over standard-dispersion fiber using uncooled, directly modulated lasers specified for 2.5 Gb/s. All 16 CWDM channels could be transmitted over more than 40 km, yielding a capacity-times-distance product of 6.4 Tb/s/km. The longest transmission distance (80 km) was achieved at 1610 nm, equivalent to 1600 ps/nm of chromatic dispersion.     

10Gb/s和40Gb/s RZ-DPSK电预失真系统中非线性效应的研究

通过仿真研究了10和40Gb/s RZ-DPSK电预失真(EPD)系统中的自相位调制(SPM)和交叉相位调制(XPM)等非线性效应。EPD系统中的非线性效应比光色散补偿(ODC)中的大,但在不同比特率下非线性效应不同。对800km标准单模光纤(SSMF)传输的仿真的结果表明:单信道传输时受到SPM影响,比特率为10Gb/s的EPD系统的非线性阈值比ODC系统的小6dBm以上,而当比特率为40Gb/s时的EPD系统非线性阈值只比ODC系统小2dBm。波分复用(WDM)系统中受到SPM和XPM的影响,比特率为10Gb/s的EPD系统的非线性阈值比ODC系统的小6dBm,而比特率为40Gb/s时的EPD系统非线性阈值比ODC系统的小2dBm。研究结果表明,当比特率升高时,EPD系统的非线性效应减弱。     

色散平坦光纤中的高速率PM-16QAM信号传输研究

提出了一种高速率、偏振复用、正交幅度调制信号的色散平坦光纤传输系统,传输速率分别为160 Gbps和256 Gbps,调制格式为PM-16QAM。实验研究了色散平坦光纤链路系统的传输特性,并分别与非零色散位移光纤和标准单模光纤链路传输特性做了比较。实验结果表明,较低输入光功率情况下,PM-16QAM信号在160 Gbps传输50 km时,经色散平坦光纤传输后的误差矢量幅度EVM优于经非零色散位移光纤传输情况0.5%,比特误码率BER优于非零色散位移光纤传输情况两个数量级;色散平坦光纤链路能更好地衰减旁瓣噪声;256 Gbps传输50 km和75 km时,仅在色散平坦光纤链路传输后可以较好地解调出信号;传输距离越长,保持较好特性时输入光功率范围越小。对比160 Gbps和256 Gbps情况,高速率PM-16QAM信号在色散平坦光纤链路的传输特性优于非零色散位移光纤和标准单模光纤链路的传输特性,传输速率越高、传输距离越长效果越明显。     

Low insertion loss and low dispersion penalty InGaAsP quantum-well high-speed electroabsorption modulator for 40-Gb/s very-short-reach, long-reach, and long-haul applications

We present a metal-organic-chemical-vapor-deposition-grown low-optical-insertion-loss InGaAsP/InP multiple-quantum-well electroabsorption modulator (EAM), suitable for both nonreturn-to-zero (NRZ) and return-to-zero (RZ) applications. The EAM exhibits a dynamic (RF) extinction ratio of 11.5 dB at 1550 nm for 3 Vp-p drive under 40-Gb/s modulation. The optical insertion loss of the modulator in the on-state is -5.2 dB at 1550 nm. In addition, the EAM also exhibits a 3-dB small-signal response (S21) of greater than 38 GHz, allowing it to be used in both 40-Gb/s NRZ and 10-Gb/s RZ applications. The dispersion penalty at 40 Gb/s is measured to be 1.2 dB over /spl plusmn/40 ps/nm of chromatic dispersion. Finally, we demonstrate 40-Gb/s transmission performance over 85 km and 700 km.     

A dispersion flattened fiber front-haul transmission system with high bitrate signal at low input optical power

We propose a dispersion flattened fiber (DFF) front-haul transmission system with high bitrate, polarization multiplexing (PM) and quadrature amplitude modulation (QAM) signal at low input optical power. The modulation format of the system is PM-16QAM, and the bitrate is 256 Gbit/s. The transmission characteristics over DFF link system are experimentally studied, which are compared with those over non-zero dispersion shifted fiber (NZDSF) link and standard single mode fiber (SSMF) link. The experimental results show that the error vector magnitude (EVM) of 256 Gbit/s and PM-16QAM signal over 25 km DFF link is 0.75% better than that over 25 km NZDSF link at least, and the bit error rate (BER) and Q-factor are much better than those of NZDSF. Their EVM and BER are both decreased with the increase of input optical power, and the Q-factor is increased. Those characteristics over 25 km SSMF are the worst at the same case. The larger the dispersion is, the more the constellation points are deviated from their respective centers and the worse the constellation characteristics are. The greater the attenuation of the DFF is, the smaller the input power of the DFF is, the more the constellation points are deviated from their centers and the worse the constellation characteristics are. This study provides a new idea and experimental support for long span front-haul propagation in mobile communication.     

High-Speed PDM-RZ-8QAM DWDM Transmission (160 $times$ 114 Gb/s) Over 640 km of Standard Single-Mode Fiber

Based on the practicability issue, using the standard single-mode fiber (SSMF) in the transmission line is important for high-speed optical transmission. Here, we propose and experimentally demonstrate a 640-km SSMF-based high-speed dense wavelength-division-multiplexing (160times114 Gb/s) transmission system in 25-GHz channel spacing employing polarization-division-multiplexing return-to-zero (RZ) eight quadrature amplitude modulation format and digital coherent detection. The filtering effects for RZ and nonreturn-to-zero formats have also been probed in this investigation. For all 160 channels (1530-1560 nm, cover the whole C-band), the bit-error rate is smaller than 2times10^-3 without Raman amplification, optical dispersion compensation, and any special fiber in this straight-line slink.     

Repeaterless 10.7-Gb/s DPSK Transmission Over 304 km of SSMF Using a Coherent Receiver and Electronic Dispersion Compensation

Record repeaterless transmission of differential phase-shift keying (DPSK) at 10.7 Gb/s over 304 km of standard single-mode fiber (SSMF) is demonstrated using a coherent optical receiver and electronic dispersion compensation. This is the longest repeaterless 10-Gb/s transmission over SSMF in the absence of Raman amplifiers. The high receiver sensitivity and the high tolerance to nonlinearities of DPSK allow us to overcome a total link loss of 58 dB with a 3-dB system margin. Coherent detection enables linear electrical dispersion compensation and avoids the use of optical dispersion compensation.     

Performance Comparison of SSMF and UltraWave Fibers for Ultra-Long-Haul 40-Gb/s WDM Transmission

We experimentally compare the performance of standard single-mode fiber (SSMF) and UltraWave fiber (UWF) for ultra-long-haul (ULH) 40-Gb/s wavelength-division-multiplexing transmissions. We used the carrier-suppressed return-to-zero amplitude-shift-keying (CSRZ-ASK) and the carrier-suppressed return-to-zero differential-phase-shift-keying (CSRZ-DPSK) formats, which are particularly well-adapted to 40-Gb/s pulse-overlapped propagation. We demonstrate that transmission distance well beyond 2000 km can be reached on UWF with both the CSRZ-ASK and CSRZ-DPSK formats, or on SSMF with the CSRZ-DPSK format only, thus indicating that SSMF-based infrastructure of incumbent carriers can be upgraded at 40-Gb/s channel rates to ULH distances.     

Theoretical investigation of 8 /spl times/ 10-Gb/s WDM signal transmission performance based on gain-equalized SOAs using backward Raman pumping at DCF

We have theoretically investigated 8 /spl times/ 10-Gb/s wavelength-division multiplexing (WDM) signal transmission characteristics based on semiconductor optical amplifiers (SOAs) with equalized gain using discrete Raman amplification (DRA). Gain equalization and low noise figures have been obtained by adjusting the backward Raman pumping power and wavelength at a dispersion compensating fiber (DCF) for each span. Bit-error-rate characteristics were calculated for 8 /spl times/ 10-Gb/s WDM signal transmission over 6 /spl times/ 40-km single-mode fiber (SMF) + DCF links with gain-equalized SOAs using DRAs at DCF. Approximately a 2.5-dB improvement of the receiver sensitivity was achieved by using SOAs and DRAs with optimized Raman pumping. One can easily upgrade the transmission length of a link based on SOAs with an appropriate backward pump laser at each DCF.     

MLSE Equalizers for Frequency Discrimination Receiver of MSK Optical Transmission System

We propose maximum-likelihood sequence estimator (MLSE) equalizers based on either Viterbi algorithm or template matching temple matching (TM) for the equalization of impairments imposed on the minimum shift keying (MSK) modulation formats in long haul transmission without optical dispersion compensation. The TM-MLSE equalizer is proposed as a simplified alternative for the Viterbi-MLSE equalizer. It is verified that the Viterbi-MLSE equalizer can operate optimally when noise approaches a Gaussian distribution. Simulation results of the performances of the two MLSE equalizers for optical frequency discrimination receiver-based optical MSK systems are described. The transmission performance is evaluated in terms of: (1) the chromatic dispersion (CD) tolerance for both Viterbi-MLSE and TM-MLSE equalizers; (2) transmission distance limits of Viterbi-MLSE equalizers with various number of states; (3)the robustness to fiber polarization mode dispersion (PMD) of Viterbi-MLSE equalizers; and (4) performance improvements for Viterbi-MLSE equalizers when utilizing sampling schemes with two and four samples per bit over the conventional single sample per bit. With a small number of states (64 states), the non-compensating optical link can equivalently reach up to approximately 928 km SSMF for 10 Gb/s transmission or 58 km SSMF for 40 Gb/s. The performance of 16-state Viterbi-MLSE equalizers for optical frequency discrimination receiver (OFDR)-based optical MSK transmission systems for PMD mitigation is also numerically investigated. The performance of Viterbi-MLSE equalizers can be further improved by using the sampling schemes with multiple samples per bit compared to the conventional single sample bit. The equalizer also offers high robustness to fiber PMD impairment.     

40-Gb/s RZ transmission over a transoceanic distance in a dispersion managed standard fiber using a modified inline synchronous modulation method

This paper analyzes in detail numerically a 40-Gb/s return-to-zero (RZ) transmission system over a transoceanic distance in a strongly dispersion managed line composed of standard single-mode fiber (SMF) and dispersion compensation fiber (DCF). We derived a periodically steady-state pulse (a DM soliton) in a DM line. Since the pulse width of a steady-state pulse is too broad for a 40 Gb/s system, the conventional in-line synchronous modulation technique cannot greatly improve the transmission quality. However, we found that the modified inline synchronous modulation technique, which is reported as the black-box optical regenerator, can effectively extend the transmission distance even in such a strongly DM line. We discuss the mechanism of the modified synchronous modulation technique with respect to a steady-state pulse in a transmission line, and show that a 40-Gb/s RZ signal can be transmitted over 20 000 km.     

Alternative modulation formats in N×40 Gb/s WDM standardfiber RZ-transmission systems

A comparison of carrier-suppressed return-to-zero (CSRZ) and single sideband return-to-zero (SSB-RZ) formats is made in an attempt to find the optimum modulation format for high bit rate optical transmission systems. Our results show that CSRZ is superior to return-to-zero (RZ) and SSB-RZ with respect to signal degradation due to Kerr nonlinearities and chromatic dispersion in wavelength division multiplexing (WDM) as well as in single-channel 40-Gb/s systems over standard single-mode fibers (SSMF). It is shown that CSRZ enables a maximum spectral efficiency of approximately 0.7 (b/s)/Hz in a N×40 Gb/s WDM system with equally polarized channels. Furthermore, the CSRZ format in N×40 Gb/s WDM systems shows no further signal degradation compared to single-channel transmission     

Comparison between NRZ and RZ signal formats for in-line amplifiertransmission in the zero-dispersion regime

Nonreturn-to-zero (NRZ) and return-to-zero (RZ) signal formats are experimentally and numerically compared for single-channel long-distance transmission in an in-line amplifier system with dispersion management providing average zero dispersion and local nonzero dispersion at an interval equal to the in-line amplifier spacing. Among a 20-ps RZ signal, a 40-ps RZ signal, and an NRZ signal transmitted in 10 Gb/s straight-line experiments, the last signal achieves the longest transmission distance of 6000 km while the others are limited to 4400 km. Numerical simulations explain these results well and show that, along with linear amplified spontaneous emission (ASE) accumulation, signal waveform distortion due to the combined effect of higher order group-velocity dispersion (GVD) and self-phase modulation (SPM) dominates the performance. Nonlinear optical noise enhancement is not obvious because of the fiber dispersion arrangement. Signals with large pulse widths are less affected by the combined effect, while small-width signals yield superior initial signal-to-noise ratio (SNR) as determined by optical noise. A detailed simulation indicates that a pulse width of about 60 ps is optimum for long distance transmission under the fiber dispersion arranged in this paper     

Transparent ultra-long-haul DWDM networks with "broadcast-and-select" OADM/OXC architecture

We describe an experimental realization of ultra-long-haul (ULH) networks with dynamically reconfigurable transparent optical add-drop multiplexers (OADMs) and optical cross-connects (OXCs). A simple new approach to dispersion management in ULH dense-wavelength-division-multiplexing (DWDM) transparent optical networks is proposed and implemented, which enables excellent transmission performance while avoiding dispersion compensation on a connection-by-connection basis. We demonstrate "broadcast-and-select" node architectures that take full advantage of this method. Our implementation of signal leveling ensures minimum variations of path-averaged power among the wavelength-division-multiplexing (WDM) channels between the dynamic gain-equalizing nodes and results in uniform nonlinear and spontaneous-emission penalties across the WDM spectrum. We achieve 80/spl times/10.7-Gb/s DWDM networking over 4160 km (52 spans/spl times/80 km each) of all-Raman-amplified symmetric dispersion-managed fiber and 13 concatenated OADMs or 320/spl times/320 wavelength-port OXCs with 320-km node spacing. The WDM channels use 50-GHz grid in C band and the simple nonreturn-to-zero (NRZ) modulation format. The measured Q values exhibit more than a 1.8-dB margin over the forward-error correction threshold for 10/sup -15/ bit-error-rate operation. We compare these results with point-to-point transmission of 80/spl times/10-Gb/s NRZ WDM signals over 4160 km without OADM/OXC and provide detailed characterization of penalties due to optical signal-to-noise-ratio degradation, filter concatenation, and crosstalk.     

160×10Gbs C+L波段3040km无电再生光传输系统的研究与实现

大容量超长距离(ULH)传输是一种非常有应用前景的技术,本文介绍160×10GbsC+L波段3040km实际光纤的无电再生光传输系统的研究和实现.系统波道间隔为50GHz,波道速率10.7Gbs,发送采用CSRZ码,具有超强FEC功能,光信噪比大于15dB.国内首次成功在实际光纤传输3040km的C+L波段10Gbs信号,首次将C+L宽带喇曼光纤放大器应用于ULH系统,连续24小时无误码.取得的有实际意义的试验成果为我国的ULH系统的应用,提供了系统的性能、指标、参数、标准等实验依据.     

Analysis of 40 Gb/s TDM-transmission over embedded standard fiberemploying chirped fiber grating dispersion compensators

Nonreturn-to-zero (NRZ)- and return-to-zero (RZ)-transmission formats are investigated for 1.55 μm 40 Gb/s fiber grating dispersion compensated standard fiber transmission. The RZ-format is shown to give a twofold increase in transmission distance compared with the conventional NRZ-format. In addition, a larger power margin is obtained at the expense of a reduced dispersion tolerance. System guidelines are proposed relating the pulse width, equalizer spacing, input power and maximum transmission distance. The results are compared with prior theoretical works at 40 Gb/s using equalizer fiber and optical phase conjugation     

40Gb/s光纤通信系统中不同码型传输特性的实验研究

在高速光纤通信系统中码型的选择是决定系统传输质量和光谱效率的主要因素。码型的选择和信道速率、信道波长间隔、光放大器的选择、光放大器放置间隔、光纤的类型、色散管理策略等各种因素密切相关。分析了非归零码（NRZ）、归零码（RZ）和载波抑制归零码（CSRZ）码型的产生方式及特点。采用单信道和掺铒光纤放大器（EDFA）放大方式对三种码型进行了40Gb/s的100kmG.652光纤通信传输实验。比较了三种码型的系统传输持性、最佳入纤功率和不同入纤功率下的功率代价：载波抑制归零码最佳入纤功率为9dBm，功率代价小于非归零码和归零码。结果表明，在相同的色散补偿条件下，载波抑制归零码比归零码和非归零码有更优的非线性容忍度。