We have demonstrated 240 channel, 10 Gbit/s WDM transmission over 7404 km using all Raman amplifier repeaters with a continuous signal bandwidth of 74 nm and dispersion-managed fiber with our proposed dispersion map for transmission systems based on distributed Raman amplifiers (DRA).

L-band amplifiers have high-order gain-wavelength variations that are dependent on their operating points. Complete compensation of this dependence was achieved by the concurrent use of our developed linear and second-order variable gain equalizers.

We proposed a gain-flattened amplification scheme using two types of Raman amplifiers with different pumping wavelength allocations. The average gain-deviation per amplifier without gain equalization was only 0.2 dB in a 39-nm bandwidth.

WDM transmission of 640Gbit/s (64 x 10Gbit/s) over 10,127km is demonstrated using an L-band erbium-doped fibre amplifier (EDFA). The L-band EDFAs have a total spectral bandwidth of 26.4nm on an ITU-T grid.

In an optical submarine cable transmission system, small size, low consumption power, and high reliability are required for inline repeaters. The structure of the inline repeater should be a simple single stage. The design of erbium doped fiber (EDF) itself is very important for the inline repeater to achieve broad bandwidth, high output power, and low noise figure. We designed and developed high alumina co-doped erbium doped fiber amplifiers (EDFAs) for long-haul, high-capacity WDM transmission systems. We investigated the trade-off relationship between the gain flatness and the output power to optimize the EDF length. We obtained high performance, including a slightly sloped gain flatness of +0.04 dB/nm at 1550 nm, a superior noise figure of 4.7dB, and a relatively large output power of +11.5 dBm for an EDF length of 5 m using a 1480-nm pumping laser diode. We applied gain-equalizers (GEQs) using Mach-Zehnder type filters with different FSRs to accurately compensate for the EDFAs' gain-wavelength characteristics. The main GEQs have free-spectral-ranges (FSRs) of 48-nm, which are about 2 times as long as the wavelength difference between a 1558-nm EDFA gain peak and a 1536-nm EDFA gain valley. Using a circulating loop with the above EDFAs and GEQs, we performed the broad wavelength bandwidth. The achieved signal wavelength bandwidth after 5,958-km transmission was 20nm. We successfully transmitted 700-Gbit/s (66 x 10.66-Gbit/s) WDM signals over 2,212 km. The combination of high alumina co-doped silica EDFA and large FSR GEQ is attractive for long-haul, high-capacity WDM transmission systems.

In long-haul wavelength-division-multiplexed (WDM) transmission systems, signals with shorter and longer wavelengths have self-phase modulation group-velocity-dispersion (SPM-GVD) penalty caused by to the dispersion slope even after the dispersion-compensation at the receiver has been optimized. As a countermeasure, we have already proposed both pre-compensation and post-compensation of chromatic dispersion at the transmitter and receiver for each channel. This method can decrease the channel variation of path-averaged chromatic dispersion along the transmission line, and it can improve the eye opening of the waveform after transmission. We investigated the optimized parameter of chromatic dispersion and chirping at the transmitter. The optimized pre-dispersion compensation parameter R was about 50%. The optimized chirping parameter ct was about 3 when the signal wavelength was less than the mean zero-dispersion wavelength. In a single-channel, 5.3-Gbit/s NRZ signal transmission experiment over a 4,760-km straight line, this method decreased SPM-GVD penalty. In a 32-channel, 5.3-Gbit/s WDM transmission experiment over 9,879 km using a circulating loop, this method improved Q-factors for the Ist and 32nd channels by more than 1.5 dB.

Large-capacity, long-haul wavelength-division-multiplexing (WDM) transm1ss1on systems require broad WDM signal bandwidth, which can be expanded with broadband erbium-doped fiber amplifier (EDFA),1 gain-equalizer (GEQ),2,3 and pre-emphasis at the transmitter.

To expand signal wavelength bandwidth in a long-haul, large-capacity WDM transmission system, we developed a high alumina codoped EDFA with broadband, high output power, and low noise figure using a 1480-nm pump laser. We applied gain-equalizers (GEQs) using Mach-Zehnder type optical filters with long free-spectral ranges to accurately compensate for the gain-wavelength characteristics of the EDFA. We investigated the signal wavelength bandwidth expanded by using the above EDFAs and GEQs. The achieved signal wavelength bandwidth after 10,000-km transmission was 18 nm. We successfully transmitted 170 Gbit/s (32 channel x 5.332 Gbit/s) WDM signals over 9,879 km and 700 Gbit/s (66 channel x 10.66 Gbit/s) WDM signals over 2,212 km.

We proposed polarisation dependent loss (PDL) induced noise reduction method using a band-rejection-filter in a long-haul large-capacity WDM transmission system with synchronous polarization scrambling. We demonstrated the effect in an 8 channel 5.332 Gbit/s WDM transmission experiment using this method

0.7Tbit/s WDM signals were successfully transmitted over 2212km using EDFA repeaters with pump reflectors, which improved EDFA output power and gain flatness. Our broadband EDFAs and accurate gain equalisation enabled a WDM bandwidth of 26nm.

To expand signal wavelength bandwidth in long-haul, large-capacity WDM transmission systems, we investigated gain-equalizers (GEQs) for Erbium doped fiber amplifiers (EDFAs). We applied GEQs using Mach-Zehnder type filters with two different free-spectral-ranges (FSRs) to accurately compensate For the EDFAs' gain-wavelength characteristics. The 1st GEQ with a longer FSR was the main GEQ to compensate for the overall gain-wavelength characteristics, and the 2nd GEQ with a shorter FSR was the secondary GEQ to compensate for the resultant gain undulation after the Ist GEQ. The 2nd GEQ had low maximum loss and long period of equalization-spacing compared to the Ist GEQ. We designed that the FSR for the 1st GEQ was twice the signal wavelength bandwidth, and the FSR for the 2nd GEQ was two thirds of the signal wavelength bandwidth. To compensate for the asymmetry in the EDFAs' gain-wavelength characteristics, we designed that the 2nd GEQ minimum-loss wavelength was shorter than the Ist GEQ maximum-loss wavelength. Using a circulating loop with a 21-EDFA chain, we confirmed the signal wavelength bandwidth expanded by the above GEQs. We also investigated the trade-off relationship between the signal wavelength bandwidth and the optical signal-to-noise ratio, as the parameter of the number of the 1st GEQ inserted in the EDFAs' chain. The achieved signal wavelength bandwidth after 10,000-km transmission was 12 nm. We successfully transmitted 170 Gbit/s (32 x 5.332 Gbit/s) WDM signals over 9,879 km employing high alumina codoped EDFAs and Mach-Zehnder type filters with long FSRs.

The authors have successfully demonstrated the transmission of RZ-modulated optical WDM signals at 170 Gbit/s over 9879 km, employing high alumina codoped EDFAs. A wide signal bandwidth of 15.5 nm was achieved using gain equalisation.

The authors demonstrate wavelength-division-multiplexing (WDM) transmission of 16 5.3 Gbit/s signals over 7931 km using a non-soliton return-to-zero (RZ) modulation format. In this experiment, a gain equalisation scheme is applied using two types of optical filters to accurately equalise the asymmetric gain profile of an EDFA chain, and a pre-compensation technique of group-velocity-dispersion (GVD) to reduce SPM-GVD penalties. These techniques made the WDM transmission of 16 channels possible without a serious channel imbalance in transmission performance.

This paper reviews several key technologies to realize a transoceanic wavelength-division-multiplexing (WDM) system with more than 100 Gb/s capacity. The key technologies include a novel gain equalization scheme, a broadband erbium-doped fiber amplifier, a chromatic dispersion compensation technique at a transmitter, and a RZ modulation format. Employing these new technologies, we successfully demonstrated a 32 channel 5.3 Gb/s (total capacity of 170 Gb/s) WDM signal transmission over 9879 km.

Eight 10 Gbit/s WDM signals were successfully transmitted over 2640 km using pre-and postcompensation of chromatic dispersion, unequal channel spacing, and a new method of gain equalization.

Summary form only given. In conclusion, four 5.332-Gbit/s optical WDM signals were successfully transmitted over 4760-km straight-line using pre and post-compensation of group velocity dispersion (GVD) for each channel and the reduction of four wave mixing (FWM) cross talk with high-speed polarization scrambling.

We describe 2.5 Gb/s 4 channel WDM transmission over 1060 km using 18 EDFAs. Gain bandwidth narrowing in concatenated EDFAs has been successfully suppressed using unsaturated EDFAs and a 1.53 mum ASE rejection filter.