A novel mode-splitting detection scheme in 43-Gb/s CS- and DCS-RZ signal transmission

Sophistication of the transmission format for 40-Gb/s/ch WDM networks is indispensable. In long-haul transmission applications, the selection of transmission format should be a principal issue. Recently, we have proposed several transmission formats including carrier-suppressed return-to-zero (CS-RZ) and duo-binary-carrier-suppressed (DCS-RZ), in so doing addressing the issue of superior performance versus fiber nonlinearity and spectral efficiency. The special spectrum structure of these formats enables a novel mode-splitting detection scheme. The scheme realizes a variety of applications in 40-Gb/s/ch transmission; including expansion of dispersion tolerance, automatic dispersion compensation, and BER improvement. We achieved 1.6 times. expansion of dispersion tolerance of 43-Gb/s DCS-RZ signals by introducing mode-splitting in the receiver. By applying the mode-splitting scheme for CS-RZ signals, we also demonstrated precise chromatic dispersion measurement with its sign detection without the need for any dithering operation and its application to automatic dispersion compensation at 43-Gb/s CS-RZ transmission.     

Compensation for chromatic dispersion and nonlinear effect in highdispersive coherent optical repeater transmission system

A design for a chromatic dispersion equalizer that provides 4.4 times higher efficiency in the dispersion compensation characteristics, compared with a conventional equalizer, is proposed. In addition, the amplitude response slope in the frequency domain is less than half of the conventional characteristic. This extends the compensation limit for chromatic dispersion up to 82500 ps/nm for a 2.5-Gb/s heterodyne system, which corresponds to a 4900-km normal dispersion fiber transmission system. A compensation method for modulational instability is also proposed. The method was confirmed by a 2.5-Gb/s continuous-phase frequency-shift-keying (CPFSK) 764-km normal dispersion fiber transmission experiment, with the abovementioned chromatic dispersion equalizer. Employing computer simulations, an over-1000-km normal dispersion fiber optical repeater transmission system with 2.5-Gb/s CPFSK heterodyne detection was shown to be feasible     

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.     

Dispersion Compensation Configuration Applying a Combination of EDC and Tunable-ODC for Extended $L$-Band WDM Transmission

We propose effective polarization-mode dispersion (PMD) and chromatic dispersion (CD) compensation configuration for practical use in the field, taking into consideration the system cost and the field condition such as the CD changes due to fiber temperature dependence or transmission route change, and rapidly fluctuate state of polarization of the signal lightwave. Our configuration combines electric dispersion compensators (EDCs) with fixed taps in each channel with a multichannel tunable optical dispersion compensator (T-ODC) that can simultaneously compensate all channels' accumulated CD. We demonstrate widely extended $L$-band 43-Gb/s-based wavelength-division-multiplexing transmission over 450 km using our dispersion compensation configuration, and obtain effectiveness that the PMD penalty is suppressed by 2 dB at a differential group delay of 33 ps by using the EDC and that the CD penalty is improved by about 2 dB at the accumulated CD change of $+{/}-$ 30 ps/nm by using T-ODC and EDC.      

Coherent Optical OFDM Transmission Up to 1 Tb/s per Channel

Coherent optical frequency-division multiplexing (CO-OFDM) is one of the promising pathways toward future ultrahigh capacity transparent optical networks. In this paper, numerical simulation is carried out to investigate the feasibility of 1 Tb/s per channel CO-OFDM transmission. We find that, for 1 Tb/s CO-OFDM signal, the performance difference between single channel and wavelength division multiplexing (WDM) transmission is small. The maximum Q is 13.8 and 13.2 dB respectively for single channel and WDM transmission. We also investigate the CO-OFDM performance on the upgrade of 10-Gb/s to 100-Gb/s based DWDM systems with 50-GHz channel spacing to 100-Gb/s systems. It is shown that due to the high spectral efficiency and resilience to dispersion, for 100-Gb/s CO-OFDM signals, only 1.3 dB Q penalty is observed for 10 GHz laser frequency detuning. A comparison of CO-OFDM system performance under different data rate of 10.7 Gb/s, 42.8 Gb/s, 107 Gb/s and 1.07 Tb/s with and without the impact of dispersion compensation fiber is also presented. We find that the optimum fiber launch power increases almost linearly with the increase of data rate. 7 dB optimum launch power difference is observed between 107 Gb/s and 1.07 Tb/s CO-OFDM systems.      

40-Gb/s WDM transmission with virtually imaged phased array (VIPA) variable dispersion compensators

We have demonstrated variable dispersion compensation by using a virtually imaged phased array (VIPA) to overcome the small dispersion tolerance in 40-Gb/s dense wavelength-division multiplexing (WDM) transmission systems. By utilizing the periodical characteristics of VIPA compensators, we performed simultaneous dispersion compensation in a 1.28-Tb/s (40-Gb/s/spl times/32 ch; C band) short-haul transmission and confirmed that only two VIPA compensators and one fixed dispersion-compensating fiber are required for a large transmission range of 80 km. This performance can greatly reduce the cost, size, and number of compensator menus in a 40-Gb/s WDM short-haul transmission system. In addition, we achieved 3.5-Tb/s (43-Gb/s/spl times/88 ch; C and L bands) transmission over a 600-km nonzero dispersion-shifted fiber by using VIPA compensators. Although channel-by-channel dispersion compensation is required due to the larger residual dispersion slope in long-haul transmission, the periodical characteristics of the VIPA compensators offer the advantage of considerably reducing the number of different modules required to cover the whole C (or L) band. An adequate optical signal-to-noise ratio, which was the same for all channels, was-obtained by using distributed Raman amplification, a gain equalizer, and a preemphasis technique. We achieved a Q-factor of more than 11.8 dB; (BER<10/sup -17/ with forward-error correction) for all 88 channels.     

Performance evaluation of prechirped RZ and CS-RZ formats inhigh-speed transmission systems with dispersion management

This paper describes the transmission performance of prechirped return-to-zero (RZ) and prechirped carrier-suppressed return-to-zero (CS-RZ) signals over a periodically dispersion-compensated transmission line. We analyze the transmission characteristics of both formats, taking account the transmitter configuration expected, in which pulse chirping is generated by using both a phase modulator and a linear dispersion compensating device. We also discuss the dependence of the transmission characteristics on phase modulation, pre- and postcompensating dispersion, and receiver optical and electrical filter widths. We show that, in single-channel transmission, phase modulation effectively reduces the intrachannel nonlinear interaction and improves the transmission performance. Next, we discuss the transmission characteristics of chirped RZ and chirped CS-RZ signals in dense wavelength division multiplexed (DWDM) signal transmission. In 100-GHz spaced 40-Gb/s-per-channel systems, it is shown that the phase modulation must be carefully optimized in order to minimize the linear crosstalk and waveform distortion induced by the intra- and interchannel nonlinear interaction in the transmission fiber     

Investigation into the temperature dependence of chromaticdispersion in optical fiber

The change in the chromatic dispersion of optical fiber with temperature is an important design parameter for 40-Gb/s systems. We derive an equation for the change in dispersion with a temperature that is more general than what has previously been published. We present experimental results for the change in fiber dispersion with temperature for six commercially available fiber types of interest for 40-Gb/s communication systems. In addition, we demonstrate that the empirical model developed by Ghosh et al in 1994 for the temperature-dependent index of refraction of SiO₂ can be used to accurately model the temperature dependence of the chromatic dispersion of a wide variety of optical fibers     

Study on the optimum Reed-Solomon-based FEC codes for 40-Gb/s-based ultralong-distance WDM transmission

The optimum redundancy for various Reed-Solomon (RS)-based forward-error correcting codes in 40-Gb/s-based ultralong-distance wavelength-division multiplexing (WDM) transmission based on erbium-doped fiber amplifier repeater and dispersion-flattened fiber span using A/sub eff/-enlarged single-mode fiber and slope-compensating disperion compensation fiber is numerically studied. In the case of single RS codes, a redundancy of approximately 7% was found to be the best choice and useful for the systems that are less than transoceanic distances. For transoceanic applications, the concatenated codes with a redundancy between 10% and 14% with four iterative decoding were found a better choice for transatlantic applications, and the product RS codes with a redundancy between 10% and 14% with four iterative decoding seem necessary for further distance expansion.     

40Gb/s DWDM系统不同码型传输性能的比较

采用Optisystem软件,对比分析了非归零码(NRZ)、归零码(RZ)、载波抑制归零码(CS-RZ)和载波抑制归零差分相移键控码(CSRZ-DPSK)四种码型在8×40Gb/s DWDM系统的传输性能。结果表明,CSRZ-DPSK码抗色度色散和PMD性能最优,CS-RZ码的OSNR容限最低。当入纤光功率适中、色散和色散斜率同时补偿时,CSRZ-DPSK码和CS-RZ码的最大传输距离超过2700km。     

PMD-induced transmission penalties in polarization-multiplexed transmission

In this paper, we investigate for the first time chromatic dispersion and nonlinearity tolerances in the presence of polarization-mode dispersion (PMD) for polarization-multiplexed (POLMUX) 2 /spl times/ 10-Gb/s nonreturn-to-zero (NRZ) transmission. In polarization-multiplexing, the interaction between fiber nonlinearity and PMD can lower the nonlinear tolerance beyond the tolerances evident when considering both transmission penalties separately; the combined penalties are significantly worse than in the case for non-POLMUX transmission. In this paper, we show, through simulations comparing POLMUX with non-POMUX transmission in the presence of nonlinearity, a reduction of about a factor of three in PMD tolerance. In addition, we show that the dispersion tolerance of POLMUX transmission is severely limited in the presence of PMD. For example, a 40-ps differential group delay (DGD) with worst case coupling of the polarization channels into the fiber lowers the dispersion tolerance, resulting in a 1-dB eye-opening penalty (EOP), from 1200 to 450 ps/nm. We conclude that the interaction between PMD, chromatic dispersion, and nonlinearity leads to the worst signal impairments in POLMUX transmission and increases the effort of using polarization-multiplexing as a modulation format.     

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.     

25-Gb/s optical NRZ transmission over 40 km of single-mode fiber at 1550 nm without dispersion compensation

We present a method for transmitting 25-Gb/s optical nonreturn-to-zero signals at a wavelength of 1550 nm over a 40-km single-mode fiber without any dispersion compensation methods. We propose optimized self-phase modulation by varying parameters of the fiber launching power and the extinction ratio of optical non-return to zero signals to overcome severe signal distortions by the chromatic dispersion effect. Using the optimization of the self-phase modulation effect, we were able to transmit 25-Gb/s optical nonreturn-to-zero signals over a 40-km single-mode fiber, which can be applicable to passive optical networks with a single wavelength channel and a high split ratio. We demonstrated that the self-phase modulation effect can be controlled by the extinction ratio and the fiber launching power.     

Performance Comparison of Duobinary Formats for 40-Gb/s and Mixed 10/40-Gb/s Long-Haul WDM Transmission on SSMF and LEAF Fibers

Duobinary formats are today considered as being one of the most promising cost-effective solutions for the deployment of 40-Gb/s technology on existing 10-Gb/s WDM long-haul transmission infrastructures. Various methods for generating duobinary formats have been developed in the past few years but to our knowledge their respective performances for 40-Gb/s WDM transmission have never been really compared. In this paper, we made an extensive numerical evaluation of the robustness of these different types of duobinary transmitter to accumulation of ASE noise, chromatic dispersion, PMD but also to single-channel and WDM 40-Gb/s transmission impairments on standard single-mode fiber. A numerical evaluation of the ability of duobinary format for mixed 10/40-Gb/s WDM long-haul transmission with 50-GHz channel spacing is also led, on both standard single-mode and LEAF fibers, and compared to DQPSK format. In order to clearly identify the limiting transmission effects on each of these two fiber types, the assessment of the performance of a 50-GHz spaced WDM 40-Gb/s long-haul transmission using either duobinary or DQPSK channels only is implemented at last.      

Combining DPSK and duobinary for the downstream in 40-Gb/s long-reach WDM-PONs

We propose and demonstrate combining differential phase-shift keying (DPSK) and duobinary transmission for the downstream in 40-Gb/s long-reach wavelength division multiplexed-passive optical networks (WDM-PONs) in order to provide robust transmission performance in the backhaul section and simple detection at the ONUs. DPSK is deployed in the trunk span as it provides stronger robustness to fiber nonlinearity. Duobinary is used in the access span where its higher chromatic dispersion tolerance relieves the need for dispersion compensation. All-optical multichannel modulation format conversion from DPSK to duobinary is realized in the local exchange in a single delay interferometer to reduce system cost. Single and multi-channel 80-km long-reach DPSK transmission and up to 5-km duobinary access transmission are experimentally demonstrated at 40 Gb/s. The proposed approach shows great potential for future high data rate optical access networks.     

Optimum fiber dispersion in high-speed TDM systems

Single-channel transmission at 40 Gb/s and above is investigated by numerical simulations with respect to optimal fiber dispersion. Since optimum dispersion depends on the bit rate nonzero dispersion shifted fiber is recommended for 40-Gb/s transmission and standard single-mode fiber for 160-Gb/s transmission     

Unrepeated 40-Gb/s RZ single-channel transmission at 1.55 μmusing various fiber types

We investigate experimentally and theoretically the effect of signal power and dispersion compensation scheme in unrepeated return-to-zero single-channel 40-Gb/s 150-km transmission using standard single-mode fiber (SMF), nonzero dispersion shifted fiber [true wave fiber (TWF)] and dispersion shifted fiber (DSF). It is shown, that standard SMF allows significantly higher fiber-input power than nonzero dispersion shifted fiber or dispersion shifted fiber and, therefore, offers larger transmission spans     

Applications of 40-Gb/s Chirp-Managed Laser in Access and Metro Networks

We investigate 40-Gb/s cost-efficient transmitter for access and metro networks. This 40-Gb/s transmitter comprises a standard directly modulated distributed-feedback (DFB) laser and a subsequent optical filter. Large dispersion tolerance of this transmitter is realized by chirp control through the phase correlation between adjacent bits for the destructive interference in order to erase the power of “0” bits while enhancing the extinction ratio. The chirp model of the DFB laser and the optimum parameters of the optical filter have been numerically analyzed. The chirp-managed 42.8-Gb/s transmission over 20-km standard single mode fiber (SSMF or SMF-28) without dispersion compensation and a centralized lightwave WDM-PON system are experimentally demonstrated. We have also realized the transmission over 100-m graded index plastic optical fiber (GI-POF). Moreover, the application in the metro network over 240-km SSMF or SMF-28 has also been investigated in this paper.      

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.     

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.